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National Research Council (US) Committee on Prudent Practices in the Laboratory. Prudent Practices in the Laboratory: Handling and Management of Chemical Hazards: Updated Version. Washington (DC): National Academies Press (US); 2011.

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Prudent Practices in the Laboratory: Handling and Management of Chemical Hazards: Updated Version.

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6Working with Chemicals

6.A. INTRODUCTION

Prudent execution of experiments requires not only sound judgment and an accurate assessment of the risks involved in the laboratory, but also the selection of appropriate work practices to reduce risk and protect the health and safety of trained laboratory personnel as well as the public and the environment. Chapter 4 provides specific guidelines for evaluating the hazards and assessing the risks associated with laboratory chemicals, equipment, and operations. Chapter 5 demonstrates how to control those risks when managing the inventory of chemicals in the laboratory. The use of the protocols outlined in Chapter 4 in carefully planned experiments is the subject of this chapter.

This chapter presents general guidelines for laboratory work with hazardous chemicals rather than specific standard operating procedures for individual substances. Hundreds of thousands of chemicals are encountered in the research conducted in laboratories, and the specific health hazards associated with most of these compounds are generally not known. Also, laboratory work frequently generates new substances that have unknown properties and unknown toxicity. Consequently, the only prudent course is for laboratory personnel to conduct their work under conditions that minimize the risks from both known and unknown hazardous substances. The general work practices outlined in this chapter are designed to achieve this purpose.

Specifically, section 6.C provides guidelines that are the standard operating procedures where hazardous chemicals are stored or are in use. In section 6.D, additional special procedures for work with highly toxic substances are presented. How to determine when these additional procedures are necessary is discussed in detail in Chapter 4, section 4.C. Section 6.E gives detailed special procedures for work with substances that pose risks due to biohazards and radioactivity, section 6.F addresses flammability, and section 6.G, reactivity and explosivity. Special considerations for work with compressed gases are the subject of section 6.H. Section 6.I covers microwave ovens, and section 6.J describes working with nanoparticles.

Chapter 7 provides precautionary methods for handling laboratory equipment commonly used in conjunction with hazardous chemicals. Chapters 4, 6, and 7 should all be consulted before working with hazardous chemicals.

Four fundamental principles underlie all the work practices discussed in this chapter. Consideration of each should be encouraged before beginning work as part of the culture of safety within the laboratory.

  • Plan ahead. Determine the potential hazards associated with an experiment before beginning.
  • Minimize exposure to chemicals. Do not allow laboratory chemicals to come in contact with skin. Use laboratory chemical hoods and other ventilation devices to prevent exposure to airborne substances whenever possible.
  • Do not underestimate hazards or risks. Assume that any mixture of chemicals will be more toxic than its most toxic component. Treat all new compounds and substances of unknown toxicity as toxic substances. Consider how the chemicals will be processed and whether changing states or forms (e.g., fine particles vs. bulk material) will change the nature of the hazard.
  • Be prepared for accidents. Before beginning an experiment, know what specific action to take in the event of accidental release of any hazardous substance. Post telephone numbers to call in an emergency or accident in a prominent location. Know the location of all safety equipment and the nearest fire alarm and telephone, and know who to notify in the event of an emergency. Be prepared to provide basic emergency treatment. Keep your co-workers informed of your activities so they can respond appropriately.

Virtually every laboratory experiment generates some waste, which may include such items as used disposable labware, filter media and similar materials, aqueous solutions, and hazardous chemicals. (For more information about disposal of chemical waste, see Chapter 8.)

6.B. PRUDENT PLANNING

Before beginning any laboratory work, determine the hazards and risks associated with the experiment or activity and implement the necessary safety precautions. Ask yourself a hypothetical question before starting work: “What would happen if … ?” Consider the possible contingencies and make preparations to take appropriate emergency actions. For example, what would be the consequences of a loss of electrical power or water pressure? Within each laboratory, all personnel should know the location of emergency equipment and how to use it, be familiar with emergency procedures, and know how to obtain help in an emergency. Laboratories should have a standing operational plan that describes how reactions, chemicals, and other laboratory processes will be handled in the case of a natural disaster or in the event that the individual responsible for laboratory activities is unavailable indefinitely (i.e., in the case of illness or death). Included in the plan should be emergency procedures and actions to be taken in the event that laboratory personnel experience a sudden medical emergency while performing an experiment.

Pay attention to the potential safety implications of subtle changes to experimental procedures. Slight changes to commonly performed operations often present unrecognized hazards. Changing solvents, suppliers, reagent concentration, reaction scale, and materials of construction may bring unintended consequences.

Determine the physical and health hazards associated with chemicals before working with them. This determination may involve consulting literature references, laboratory chemical safety summaries (LCSSs), material safety data sheets (MSDSs), or other reference materials (see also Chapter 4, section 4.B) and may require discussions with the laboratory supervisor, safety personnel, and industrial hygienists. Check every step of the waste minimization and removal processes against federal, state, and local regulations. Before producing mixed chemical-radioactive-biological waste (see Chapter 8, section 8.C.1.3) consult your institution's or firm's environmental health and safety (EHS) personnel.

Many of the general practices applicable to working with hazardous chemicals are given elsewhere in this volume (see Chapter 2). (See Chapter 5, section 5.F for detailed instructions on the transport of chemicals and section 5.E on storage; Chapter 7 for information on use and maintenance of equipment and glassware; and Chapter 8 for information on disposal of chemicals.)

6.C. GENERAL PROCEDURES FOR WORKING WITH HAZARDOUS CHEMICALS

6.C.1. Personal Behavior

Demonstrating prudent behavior within the laboratory is a critical part of a culture of safety. This includes following basic safety rules and policies (see Chapter 2, section 2.C.1), being cognizant of the hazards within the laboratory (see Chapter 4), and exhibiting professionalism with co-workers. Maintaining an awareness of the work being performed in nearby hoods and on neighboring benches and any risks posed by that work is also important.

6.C.2. Minimizing Exposure to Hazardous Chemicals

Take precautions to avoid exposure by the principal routes, that is, contact with skin and eyes, inhalation, and ingestion (see Chapter 4, section 4.C, for a detailed discussion).

The preferred methods for reducing chemical exposure are, in order of preference,

  1. substitution of less hazardous materials or processes (see Chapter 5, section 5.B, Green Chemistry for Every Laboratory),
  2. engineering controls (Chapter 9),
  3. administrative controls (Chapter 2), and
  4. personal protective equipment (PPE)

See also the Occupational Safety and Health Administration's (OSHA) Safety and Health Management eTool, Hazard Prevention and Control module available at www.osha.gov Before beginning work, review all proposed laboratory procedures thoroughly to determine potential health and safety hazards. Refer to the MSDS for guidance on exposure limits, health hazards and routes of entry into the body, and chemical storage, handling, and disposal. Avoid underestimating risk when handling hazardous materials.

6.C.2.1. Engineering Controls

Engineering controls are measures that eliminate, isolate, or reduce exposure to chemical or physical hazards through the use of various devices. Examples include laboratory chemical hoods and other ventilation systems, shields, barricades, and interlocks. Engineering controls must always be considered as the first and primary line of defense to protect personnel and property. When possible, PPE is not to be used as a first line of protection. For instance, a personal respirator should not be used to prevent inhalation of vapors when a laboratory chemical hood (formerly called fume hoods) is available. (See Box 6.1 and Chapter 9 for more information about laboratory design and ventilation.)

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BOX 6.1

A Simple Qualitative Method to Verify Adequate Laboratory Chemical Hood Ventilation. 200 g (approximately 250 ml) of dry ice pellets (5 to 10-mm diam) Shallow bowl, approximately 3-L volume

6.C.2.2. Avoiding Eye Injury

Eye protection is required for all personnel and visitors in all locations where laboratory chemicals are stored or used, whether or not one is actually performing a chemical operation. Visitor eye protection should be made available at the entrances to all laboratories.

Researchers should assess the risks associated with an experiment and use the appropriate level of eye protection:

  • Safety glasses with side shields provide the minimum protection acceptable for regular use. They must meet the American National Standards Institute (ANSI) Z87.1-2003 Standard for Occupational and Educational Eye and Face Protection, which specifies minimum lens thickness and impact resistance requirements.
  • Chemical splash goggles are more appropriate than regular safety glasses to protect against hazards such as projectiles, as well as when working with glassware under reduced or elevated pressures (e.g., sealed tube reactions), when handling potentially explosive compounds (particularly during distillations), and when using glassware in high-temperature operations.
  • Chemical splash goggles or face shields should be worn when there is a risk of splashing hazardous materials or flying particles.
  • Because chemical splash goggles offer little protection to the face and neck, full-face shields should be worn in addition to safety glasses or goggles when conducting particularly hazardous laboratory operations (e.g., working with glassware under vacuum or handling potentially explosive compounds). In addition, glassblowing and the use of laser or ultraviolet light sources require special glasses or goggles.
  • Operations at risk of explosion or that present the possibility of projectiles must have engineering controls as a first line of protection. For instance, in addition to chemical splash goggles or full-face shields, these operations must be conducted behind blast shields, in rubber-coated or taped glassware.

Ordinary prescription glasses do not provide adequate protection against injury because they lack side shields and are not resistant to impact, but prescription safety glasses and chemical splash goggles are available.

Similarly, contact lenses offer no protection against eye injury and do not substitute for safety glasses and chemical splash goggles. They should not be worn where chemical vapors are present or a chemical splash or chemical dust is possible because contact lenses can be damaged under these conditions. If, however, an individual chooses to wear contact lenses in the laboratory, chemical splash goggles must be worn. Note that there has been a change in recommended guidance regarding the wearing of contact lenses since the previous edition. Many organizations, including the National Institute for Occupational Safety and Health (NIOSH) (HHS/CDC/NIOSH, 2005) and the American Chemical Society (Ramsey and Breazeale, 1998) have removed most restrictions on wearing contact lenses in the laboratory.

6.C.2.3. Avoiding Ingestion of Hazardous Chemicals

Eating, drinking, smoking, gum chewing, applying cosmetics, and taking medicine in laboratories where hazardous chemicals are used or stored should be strictly prohibited. Food, beverages, cups, and other drinking and eating utensils should not be stored in areas where hazardous chemicals are handled or stored. Glassware used for laboratory operations should never be used to prepare or consume food or beverages. Laboratory refrigerators, ice chests, cold rooms, and ovens should not be used for food storage or preparation. Laboratory water sources and deionized laboratory water should not be used as drinking water. Never wear gloves or laboratory coats outside the laboratory or into areas where food is stored and consumed, and always wash laboratory apparel separately from personal clothing.

Laboratory chemicals should never be tasted. A pipet bulb, aspirator, or mechanical device must be used to pipet chemicals or to start a siphon. To avoid accidental ingestion of hazardous chemicals, pipetting should never be done by mouth. Hands should be washed with soap and water immediately after working with any laboratory chemicals, even if gloves have been worn.

6.C.2.4. Avoiding Inhalation of Hazardous Chemicals

Only in certain controlled situations should any laboratory chemical be sniffed.1 In general, the practice is not encouraged. Toxic chemicals or compounds of unknown toxicity should never be deliberately sniffed. Conduct all procedures involving volatile toxic substances and operations involving solid or liquid toxic substances that may result in the generation of aerosols in a laboratory chemical hood. Air-purifying respirators are required for use with some chemicals if engineering controls cannot control exposure. Significant training, along with a medical evaluation and respirator fit, are necessary for the use of respirators. For further guidance on the use of respirators with specific chemicals refer to Chapter 7, section 7.F.2.4 of this book, the OSHA Respiratory Protection Standard (29 CFR § 1910.134), and ANSI Standard Z88.2-1992.

Laboratory chemical hoods should not be used for disposal of hazardous volatile materials by evaporation. Such materials should be treated as chemical waste and disposed of in appropriate containers according to institutional procedures and government regulations. (See Chapter 8 for information on waste handling.)

6.C.2.4.1. General Rules for Laboratory Chemical Hoods

Detailed information regarding laboratory ventilation can be found in Chapter 9. The information here is intended to provide a brief overview. These general rules should be followed when using laboratory chemical hoods:

  • Before using a laboratory chemical hood, learn how it operates. They vary in design and operation.
  • For work involving hazardous substances, use only hoods that have been evaluated for adequate face velocity and proper operation. They should be inspected regularly and the inspection certification displayed in a visible location.
  • Review the MSDS and the manufacturer's label before using a chemical in the laboratory or hood. Observe the permissible exposure limit, threshold limit value, the primary routes of exposure, and any special handling procedures described within the document. Confirm that the experimental methods and available engineering controls are capable of controlling personnel exposure to the hazardous chemicals being used.
  • Keep reactions and hazardous chemicals at least 6 in. (15 cm) behind the plane of the sash, farther if possible.
  • Never put your head inside an operating hood to check an experiment. The plane of the sash is the barrier between contaminated and uncontaminated air.
  • On hoods where sashes open vertically, work with the sash in the lowest possible position. Where sashes open horizontally, position one of the doors to act as a shield in the event of an accident. When the hood is not in use, the sash should be kept at the recommended position to maintain laboratory airflow.
  • Keep laboratory chemical hoods clean and clear; do not clutter with bottles or equipment. If there is a grill along the bottom slot or a baffle in the back, clean it regularly so it does not become clogged with papers and dirt. Allow only materials actively in use to remain in the hood. Following this rule provides optimal containment and reduces the risk of extraneous chemicals being involved in any fire or explosion. Support any equipment in hoods on racks or feet to provide airflow under the equipment.
  • Do not remove the airfoil, alter the position of inner baffles, block exterior grills, or make any other modifications without the approval of the appropriate staff.
  • Report suspected laboratory chemical hood malfunctions promptly to the appropriate office, and confirm that the problems are corrected.
  • If working in a glovebox, check the seals and pressures on the box before use.

Post the name of the individual responsible for the hood in a visible location. Clean hoods before maintenance personnel work on them.

(See Chapter 9, section 9.C, for more information on laboratory chemical hoods.)

6.C.2.5. Avoiding Injection of Hazardous Chemicals

Solutions of chemicals are often transferred in syringes, which for many uses are fitted with sharp needles. The risk of inadvertent injection is significant, and vigilance is required to avoid an injury. Use special care when handling solutions of chemicals in syringes with needles. When accompanied by a cap, syringe needles should be placed onto syringes with the cap in place and remain capped until use. Do not recap needles, especially when they have been in contact with chemicals. Remove the needle and discard it immediately after use in the appropriate sharps containers. Blunt-tip needles, including low-cost disposable types, are available from a number of commercial sources and should be used unless a sharp needle is specifically required to puncture rubber septa or for subcutaneous injection.

6.C.2.6. Minimizing Skin Contact

6.C.2.6.1. Gloves

The OSHA Personal Protective Equipment (PPE) Standard (29 CFR §§ 1910.132-1910.138) requires completion of a hazards assessment for each work area, including an evaluation of the hazards involved and selection of appropriate hand protection. Wear gloves whenever handling hazardous chemicals, sharp-edged objects, very hot or very cold materials, toxic chemicals, and substances of unknown toxicity. No single glove material provides effective protection for all uses. Before starting, carefully evaluate the type of protection required in order to select the appropriate glove. The discussion presented here is geared toward gloves that protect against chemical exposure. (For information about gloves that protect against other types of hazards, see Chapter 7, section 7.F.1.4.)

Select gloves carefully to ensure that they are impervious to the chemicals being used and are of correct thickness to allow reasonable dexterity while also ensuring adequate barrier protection. Choosing an improper glove can itself be a serious hazard in handling hazardous chemicals. If chemicals do penetrate glove material, they could be held in prolonged contact with the hand and cause more serious damage than in the absence of a proper glove. The degradation and permeation characteristics of the selected glove material must be appropriate for protection from the hazardous chemicals that are handled. Double gloves provide a multiple line of defense and are appropriate for many situations. Find a glove or combination of gloves that addresses all the hazards present. For example, operations involving a chemical hazard and sharp objects may require the combined use of a chemical-resistant (butyl, viton, or neoprene) glove and a cut-resistant (e.g., leather, Kevlar®) glove. Reusable gloves should be washed and inspected before and after each use. Be sure to wash your hands after wearing gloves and handling laboratory chemicals, to remove any skin contamination that might have occurred.

Gloves that might be contaminated with toxic materials should not be removed from the immediate area (usually a laboratory chemical hood) in which the chemicals are located. To prevent contamination of common surfaces that others might touch bare-handed, never wear gloves when handling common items such as doorknobs, handles, or switches on shared equipment, or outside the laboratory. Along the same lines, consider, before touching a surface while wearing gloves, whether it would be common for people to touch the surface with or without gloves and use appropriate precautions. For example, controls for hood nitrogen or water may be located outside the hood itself but may well be contaminated.

When working with chemicals in the laboratory, wear gloves of a material known to be resistant to permeation by the substances in use. Glove selection guides for a wide array of chemicals are available from most glove manufacturers and vendors. In general, nitrile gloves are suitable for incidental contact with chemicals. Both nitrile and latex gloves provide minimum protection from chlorinated solvents and should not be used with oxidizing or corrosive acids. Latex gloves protect against biological hazards but offer poor protection against acids, bases, and most organic solvents. In addition, latex is considered a sensitizer and triggers allergic reactions in some individuals. (For more information, see section 6.C.2.6.1.1.) Neoprene and rubber gloves with increased thickness are suggested for use with most caustic and acidic materials. Barrier creams and lotions can provide some skin protection but are never a substitute for gloves, protective clothing, or other protective equipment. Use these creams only to supplement the protection offered by PPE.

According to the National Ag Safety Database (www.nasdonline.org), a program supported by NIOSH and the Centers for Disease Control and Prevention, materials that are used in the manufacture of gloves designed to provide chemical resistance include the following:

  • Butyl is a synthetic rubber with good resistance to weathering and a wide variety of chemicals.
  • Natural rubber latex is a highly flexible and conforming material made from a liquid tapped from rubber plants. It is a known allergen. (See section 6.C.2.6.1.1 for more information.)
  • Neoprene is a synthetic rubber having chemical and wear-resistance properties superior to those of natural rubber.
  • Nitrile is a copolymer available in a wide range of acrylonitrile content; chemical resistance and stiffness increase with higher acrylonitrile content.
  • Polyethylene is a fairly chemical-resistant material used as a freestanding film or a fabric coating.
  • Poly(vinyl alcohol) is a water-soluble polymer that exhibits exceptional resistance to many organic solvents that rapidly permeate most rubbers.
  • Poly(vinyl chloride) is a stiff polymer that is made softer and more suitable for protective clothing applications by the addition of plasticizers.
  • Polyurethane is an abrasion-resistant rubber that is either coated into fabrics or formed into gloves or boots.
  • 4H®or Silvershield® is a registered trademark of North Hand Protection; it is highly chemical-resistant to many different class of chemicals.
  • Viton®, a registered trademark of DuPont, is a highly chemical-resistant but expensive synthetic elastomer.

When choosing an appropriate glove, consider the required thickness and length of the gloves as well as the material. Consult the glove manufacturer for chemical-specific glove recommendations and information about degradation and permeation times. Certain disposable gloves should not be reused. (For more information, see OSHA PPE Standard, 29 CFR § 1910.138, regarding hand protection.)

The following general guidelines apply to the selection and use of protective gloves:

  • Do not use a glove beyond its expiration date. Gloves degrade over time, even in an unopened box.
  • When not in use, store gloves in the laboratory but not close to volatile materials. To prevent chemical contamination of nonlaboratory areas by people coming to retrieve them, gloves must not be stored in offices or in break rooms or lunchrooms.
  • Inspect gloves for small holes, tears, and signs of degradation before use.
  • Replace gloves periodically because they degrade with use, depending on the frequency of use and their permeation and degradation characteristics relative to the substances handled.
  • Replace gloves immediately if they become contaminated or torn.
  • Replace gloves periodically, depending on the frequency of use. Regular inspection of their serviceability is important. If they cannot be cleaned, dispose of contaminated gloves according to institutional procedures.
  • Decontaminate or wash gloves appropriately before removing them. [Note: Some gloves, e.g., leather and poly(vinyl alcohol), are water permeable. Unless coated with a protective layer, poly(vinyl alcohol) gloves will degrade in the presence of water.]
  • Do not wear gloves outside the laboratory, to avoid contamination of surfaces used by unprotected individuals.
  • Gloves on a glovebox should be inspected with the same care as any other gloves used in the laboratory. Disposable gloves appropriate for the materials being handled within the glovebox should be used in addition to the gloves attached to the box. Protect glovebox gloves by removing all jewelry prior to use.
6.C.2.6.1.1. Latex Gloves

Although natural rubber latex gloves can be used as protective equipment to prevent transmission of infectious diseases and for skin protection against contact with some chemicals, they can also cause allergic reactions. In addition to causing skin contact allergic reactions to individuals wearing the gloves, they can also cause allergic reactions through inhalation of latex proteins that may be released into the air when the powders used to lubricate the interior of the glove are dispersed as gloves are removed. Thus the risk of exposure via inhalation presents a risk both to the wearer of latex gloves and to sensitized individuals who may be working nearby.

Latex exposure symptoms include skin rash, respiratory irritation, asthma, and, in rare cases, anaphylactic shock. The amount of exposure needed to sensitize an individual to natural rubber latex is not known, but when exposures are reduced, sensitization decreases. Individuals with known latex allergies should never wear latex gloves and may not be able to work in areas where latex gloves are used. Persons with known latex allergies should follow their organization's procedures to ensure that they are not exposed.

To help minimize the risk of exposure to latex allergens, NIOSH issued an alert, Preventing Allergic Reactions to Latex in the Workplace (HHS/CDC/NIOSH, 1997). NIOSH recommends the following to reduce exposure to latex:

  • Whenever possible, substitute another glove material.
  • If latex gloves are the best choice, use reduced-protein, powder-free gloves.
  • Wash hands with mild soap and water after removing latex gloves.
6.C.2.6.2. Clothing and Protective Apparel

Protective clothing should be used when there is significant potential for skin-contact exposure to chemicals. Protective clothing does not offer complete protection to the wearer and should not be used as a substitute for engineering controls. The protective characteristics of any protective clothing must be matched to the hazard. As with gloves, no single material that provides protection to all hazards is available. When multiple hazards are present, multiple layers of protective clothing may be required. Some types of PPE, such as aprons of reduced permeability and disposable laboratory coats, offer additional safeguards when working with toxic materials. (See also Chapter 7, section 7.F.1.1.)

Commercial lab coats are fabricated from a variety of materials, such as cotton, polyester, cotton-polyester blends, polyolefin, and polyaramid. Selection of the proper material to deal with the particular hazards present is critical. For example, although cotton is a good material for laboratory coats, it reacts rapidly with acids. Plastic or rubber aprons can provide good protection from corrosive liquids but can be inappropriate in the event of a fire. Because plastic aprons can also accumulate static electricity, they should not be used around flammable solvents, explosives sensitive to electrostatic discharge, or materials that can be ignited by static discharge. Because many synthetic fabrics are flammable and can adhere to the skin, they increase the severity of a burn and should not be worn if working with flammable materials or an open flame. When working with flammable materials or pyrophorics, use laboratory coats made from flame-resistant, nonpermeable materials (polyaramids). Disposable garments may be a good option if handling carcinogenic or other highly hazardous materials. However, these provide only limited protection from vapor or gas penetration. Take care to remove disposable garments without exposing any individual to toxic materials and dispose of as hazardous waste.

To prevent chemical exposure from spilled materials in the laboratory, wear shoes that cover the entire foot. Perforated shoes, open-toe and open-heel shoes, sandals, or clogs should not be permitted. Shoes should have stable soles that provide traction in slippery or wet environments to reduce the chance of falling. Socks should cover the ankles so as to protect against chemical splashes. High heels should not be worn in the laboratory.

Once they have been used, laboratory coats and other protective apparel may become contaminated. Therefore, they must be stored in the laboratory and not in offices or common areas. Institutions should provide a commercial laundry service for laboratory coats and uniforms; they should not be laundered at home.

6.C.3. Housekeeping

A definite correlation exists between orderliness and the level of safety in the laboratory. In addition, a disorderly laboratory can hinder or endanger emergency response personnel. The following housekeeping rules should be adhered to:

  • Never obstruct access to exits and emergency equipment such as fire extinguishers and safety showers. Comply with local fire codes for emergency exits, electrical panels, and minimum aisle width.
  • Store coats, bags, and other personal items in the proper area, not on the benchtops or in the aisles.
  • Do not use floors, stairways, and hallways as storage areas. Items stored in these areas can become hazards in the event of an emergency.
  • Keep drawers and cabinets closed when not in use, to avoid accidents.
  • Properly label (see Chapter 4, section 4.B.5) in permanent marker and store (see Chapter 5, section 5.E) all chemicals appropriately by compatibility.
  • Label transfer vessels2 with the full chemical name, manufacturer's name, hazard class, and any other special warnings.
  • Store chemical containers in order and neatly. Face labels outward for easy viewing. Containers themselves should be clean and free of dust. Containers and labels that have begun to degrade should be replaced, repackaged, or disposed of in the proper location. Do not store materials or chemicals on the floor because these may present trip and spill hazards.
  • Keep chemical containers closed when not in use.
  • Secure all compressed gas cylinders to walls or benches in accordance with the guidance provided in Chapter 5, section 5.E.6.
  • Secure all water, gas, air, and electrical connections in a safe manner.
  • Return all equipment and laboratory chemicals to their designated storage location at the end of the day.
  • To reduce the chance of accidentally knocking containers to the floor, keep bottles, beakers, flasks, and the like at least 2 in. from the edge of benchtops.
  • Keep work areas clean (including floors) and uncluttered. Wipe up all liquid and ice on the floor promptly. Accumulated dust, chromatography adsorbents, and other chemicals pose respiratory hazards. To avoid formation of aerosols, dry sweeping should not be used in the laboratory. Remove broken glass, spilled chemicals, and paper litter from benchtops and laboratory chemical hoods.
  • To avoid flooding, do not block the sink drains. Place rubber matting in the bottom of the sinks to prevent breakage of glassware and to avoid injuries.
  • Do not pile up dirty glassware in the laboratory. Wash glassware carefully. Remember that dirty water can mask glassware fragments. Handle and store laboratory glassware with care. Discard cracked or chipped glassware promptly.
  • Dispose of all waste chemicals properly and in accordance with organizational policies.
  • Dispose of broken glass and in a specially labeled container for broken glass. Treat broken glassware contaminated with a hazardous substance as a hazardous substance.
  • Dispose of sharps (e.g., needles and razor blades) in a specially labeled container for sharps. Treat sharps contaminated with a hazardous substance as hazardous substances.

Formal housekeeping and laboratory inspections should be conducted on a regular basis by the Chemical Hygiene Officer or a designee.

6.C.4. Transport of Chemicals

For more detailed information about transfer and transport of chemicals, see Chapter 5, section 5.F.

When transporting chemicals outside the laboratory or between stockrooms and laboratories, use only break-resistant secondary containment. Commercially available secondary containment is made of rubber, metal, or plastic, with carrying handle(s), and is large enough to hold the contents of the chemical containers in the event of breakage. Resealable plastic bags serve as adequate secondary containment for small samples.

When transporting cylinders of compressed gases, the cylinder must always be strapped in a cylinder cart and the valve protected with a cover cap. When cylinders must be transported between floors, passengers should not be in the elevator.

6.C.5. Storage of Chemicals

Avoid the accumulation of excess chemicals by acquiring the minimum quantities necessary for each procedure or research project. Properly label all chemical containers. Indicate any special hazards on the label. For certain classes of compounds (e.g., ethers as peroxide formers), write the date the container was opened on the label. For peroxide formers, write the test history and date of discard on the label as well.

Keep only small quantities (<1 L) of flammable liquids at workbenches. Larger quantities should be stored in approved storage cabinets. Store large containers (>1 L) below eye level on low shelves. Unless additional protection and secondary containment are provided, never store hazardous chemicals and waste on the floor. Be aware that fire codes dictate the total volume of flammable liquids, liquefied gases, and flammable compressed gases in a given work area. Ask your institution's EHS expert for the fire code's maximum flammable liquid and gas load for your laboratory, and ensure that your laboratory is in compliance with this code.

Refrigerators used for storage of significant quantities of flammable chemicals must be explosion-proof laboratory-safe units. Explosion-proof refrigerators are sold for this purpose and are labeled and hardwire installed. Such a refrigerator is mandatory for a renovated or new laboratory where flammable materials need refrigeration. Because of the expense of an explosion-proof refrigerator, a modified sparkproof refrigerator is sometimes found in older laboratories and laboratories using very small amounts of flammable materials. However, a modified sparkproof refrigerator cannot meet the standards of an explosion-proof refrigerator. Where they exist, a plan to phase out the sparkproof refrigerator is recommended.

Materials placed in refrigerators should be clearly labeled with water-resistant labels. Storage trays or secondary containment should be used to minimize the distribution of material in the event a container should leak or break. Retaining the shipping can for secondary containment is good practice. Regularly inspect storage trays, shipping cans, and secondary containment for primary container leaks and degradation. Laboratory refrigerators should have permanent labels warning against the storage of food and beverages for human consumption.

All chemicals should be stored with attention to incompatibilities so that if containers break in an accident, reactive materials do not mix and react violently.

(See Chapter 5, section 5.E, and Chapter 8, section 8.C.1.2, for more information.)

6.C.6. Use and Maintenance of Equipment and Glassware

Good equipment maintenance is essential for safe and efficient operations. Laboratory equipment should be regularly inspected, maintained, and serviced on schedules that are based on the manufacturer's recommendations, as well as the likelihood and hazards of equipment failure. Maintenance plans should ensure that any lockout procedures cannot be violated.

Carefully handle and store glassware to avoid damage. Discard or repair chipped or cracked items. Handle vacuum-jacketed glassware with extreme care to prevent implosions. Evacuated equipment such as Dewar flasks or vacuum desiccators should be taped, shielded, or coated. Only glassware designed for vacuum work should be used for that purpose.

Use tongs, a tweezer, or puncture-proof hand protection when picking up broken glass. Small pieces should be swept up with a brush into a dustpan. Glassblowing operations should not be attempted unless an area has been made safe for both fabrication and annealing. Protect your hands and body when performing forceful operations involving glassware. For instance, leather or Kevlar® gloves should be used when placing rubber tubing on glass hose connections. Cuts from forcing glass tubing into stoppers or plastic tubing are a common laboratory accident and are often serious. (See Vignette 6.1.) Constructing adaptors from glass tubing and rubber or cork stoppers is obsolete; instead, use fabricated, commercial adaptors made from plastic, metal, or other materials.

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Vignette 6.1

Finger laceration from broken tubing connector. A technician planned to replace the rubber vacuum tubing leading from a vacuum pump to a glass cold trap. While attempting to remove the old rubber tubing from the trap, the glass nipple broke and the broken (more...)

(See Chapter 7 for more discussion.)

6.C.7. Working with Scaled-Up Reactions

Special care and planning is necessary to ensure safe scaled-up work. Scale-up of reactions from those producing a few milligrams or grams to those producing more than 100 g of a product may magnify risks by several orders. Although the procedures and controls for large-scale laboratory reactions may be the same as those for smaller-scale procedures, significant differences may exist in heat transfer, stirring effects, times for dissolution, and the effects of concentration—all of which need to be considered. (See Vignette 6.2.) When planning large-scale work, practice requires consulting with experienced workers and considering all possible risks.

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Vignette 6.2

Runaway reaction during scale-up. A researcher scaled up the cycloaddition reaction of maleic anhydride with quadricyclane, a strained high-energy hydrocarbon. This reaction is reported in the literature and was also previously performed in the researcher's (more...)

Although one cannot always predict whether a scaled-up reaction has increased risk, hazards should be evaluated if the following conditions exist:

  • The starting material and intermediates contain functional groups that have a history of being explosive (e.g., N—N, N—O, N—halogen, O—O, and O—halogen bonds) or that could explode to give a large increase in pressure.
  • A reactant or product is unstable near the reaction or workup temperature. A preliminary test to determine the temperature and mode of decomposition consists of heating a small sample in a melting-point tube.
  • A reactant is capable of self-polymerization.
  • A reaction is delayed; that is, an induction period is required.
  • Gaseous byproducts are formed.
  • A reaction is exothermic. What can be done to provide, or regain, control of the reaction if it begins to run away?
  • A reaction requires a long reflux period. What will happen if solvent is lost owing to poor condenser cooling?
  • A reaction requires temperatures less than 0 °C. What will happen if the reaction warms to room temperature?
  • A reaction involves stirring a mixture of solid and liquid reagents. Will magnetic stirring be sufficient at large scale or will overhead mechanical stirring be required? What will happen if stirring efficiency is not maintained at large scale?

In addition, thermal phenomena that produce significant effects on a larger scale may not have been detected in smaller-scale reactions and therefore could be less obvious than toxic or environmental hazards. Thermal analytical techniques should be used to determine whether any process modifications are necessary.

Consider scaling up the process in multiple small steps, evaluating the above issues at each step. Be sure to review the literature and other sources to fully understand the reactive properties of the reactants and solvents, which may not have been evident at a smaller scale.

(See sections 6.D.1 and 6.G.1 and Chapter 5, section 5.B, for more information.)

6.C.8. Responsibility for Unattended Experiments and Working Alone

It is prudent practice to avoid working alone at the bench in a laboratory building. Individuals working in separate laboratories outside normal working hours should make arrangements to check on each other periodically, or ask security guards to check on them. Experiments known to be hazardous should not be undertaken by a person who is alone in a laboratory. Under unusually hazardous conditions, special rules, precautions, and alert systems may be necessary. (See also Chapter 2, section 2.C.2.)

Laboratory operations involving hazardous substances are sometimes carried out continuously or overnight with no one present. Although unattended operations should be avoided when possible, personnel are responsible for designing experiments to prevent the release of hazardous substances if utility services such as electricity cooling water, and flow of inert gas are interrupted.

For unattended operations, laboratory lights should be left on, and signs should be posted identifying the nature of the experiment and the hazardous substances in use. If appropriate, arrangements should be made for other workers to periodically inspect the operation. Information should be posted indicating how to contact the responsible individual in the event of an emergency.

(See also Chapter 4, section 4.A.)

6.C.9. Chemistry Demonstrations and Magic Shows

All planned demonstrations and chemistry magic shows that will be performed by chemistry personnel that are not a part of normal laboratory activities should be preapproved and authorized by the organization and should follow all institutional policies. Activity organizers should obtain safety advice from experts as necessary. Experienced chemists who are interested in participating in such activities and want to use the organization's chemicals and apparatus should submit an activity plan in advance of the event. This plan should include

  • location of the demonstration,
  • date of the event,
  • age of the intended audience,
  • number of persons who will attend the event,
  • degree of audience participation,
  • demonstrations that will be performed,
  • list of chemicals that will be transported to the demonstration site, and
  • PPE that will be worn and by whom.

All chemicals must be transported in accordance with U.S. Department of Transportation regulations, if applicable, and must be handled in a prudent manner, packaged appropriately, labeled properly, and transported back to the institution for disposal via the institution's chemical waste disposal system. Under no circumstances should any chemicals be left at the demonstration site or disposed of there. Prior to the planned event, organizers should ensure that, if an accident involving chemicals occurs in their personal vehicles, they will be covered under their private insurance policies.

[For more information about safety when performing chemistry demonstrations, see the American Chemical Society's NCW and Community Activity SAFETY GUIDELINES (available at http://portal.acs.org/).]

6.C.10. Responding to Accidents and Emergencies

6.C.10.1. General Preparation for Emergencies

Every laboratory should have a written emergency response plan that addresses injuries, spills, fires, accidents, and other possible emergencies and includes procedures for communication and response. All laboratory personnel should know what to do in an emergency. Laboratory work should not be undertaken without knowledge of the following points:

  • how to report a fire, injury, chemical spill, or other emergency and how to summon emergency response;
  • the location of emergency equipment such as safety showers and eyewash units;
  • the location of fire extinguishers and spill control equipment;
  • the locations of all available exits for evacuation from the laboratory; and
  • how police, fire, and other emergency personnel respond to laboratory emergencies, and the role of laboratory personnel in emergency response.

The above information should be available in descriptions of laboratory emergency procedures and in the institution's Chemical Hygiene Plan. Laboratory supervisors should ensure that all trained laboratory personnel are familiar with this information.

Trained laboratory personnel should know their level of expertise with respect to using fire extinguishers and emergency equipment, dealing with chemical spills, and handling injuries. They should not take actions outside the limits of their expertise but instead should rely on trained emergency personnel. A U.S. Environmental Protection Agency (EPA) regulation, Hazardous Waste Operations and Emergency Response (HAZWOPER), 29 CFR § 1910.120, specifies the training required for various response actions.

Names and contact information for individuals responsible for laboratory operations should be posted on the laboratory door.

6.C.10.2. Handling the Accidental Release of Hazardous Substances

Experiments should always be designed to minimize the possibility of an accidental release of hazardous substances. Laboratory personnel should use the minimum amount of hazardous material possible and perform the experiment so that, as much as possible, any spill is contained.

In the event of an incidental, laboratory-scale spill, follow these general guidelines, in order:

  1. Tend to any injured or contaminated personnel and, if necessary, request help (see section 6.C.10.4).
  2. If necessary, evacuate the area (see section 6.C.10.3).
  3. Notify other laboratory personnel of the accident.
  4. Take steps to confine and limit the spill if this can be done without risk of injury or contamination (see section 6.C.10.5).
  5. Clean up the spill using appropriate procedures, if this can be done without risk of injury and is allowed by institutional policy. (see section 6.C.10.6).
  6. Dispose of contaminated materials properly, according to the procedures described in Chapter 8, section 8.B.6.

(See Chapter 7, section 7.G for more information on emergency procedures.)

6.C.10.3. Notification of Personnel in the Area

Other nearby laboratory personnel should be alerted to the accident and the nature of the chemicals involved. If a highly toxic gas or volatile material is released, the laboratory should be evacuated and personnel posted at entrances to prevent others from inadvertently entering the contaminated area. In some cases (e.g., incidents involving the release of highly toxic substances and spills occurring in nonlaboratory areas), it may be appropriate to activate a fire alarm to alert personnel to evacuate the entire building. The proper emergency responders should be called. Follow your institution's policies for such situations.

6.C.10.4. Treatment of Injured and Contaminated Personnel

If an individual is injured or contaminated with a hazardous substance, tending to him or her generally takes priority over implementing the spill control measures outlined in section 6.C.10.5. Obtain medical attention for the individual as soon as possible by calling emergency personnel. Provide a copy of the appropriate MSDS to the emergency responders or attending physician, as needed. If you cannot assess the conditions of the environment well enough to be sure of your own safety, do not enter the area. Call emergency personnel and describe the situation as best you can.

Every laboratory should develop specific procedures for the highest-risk materials used in their laboratory. To identify these materials, consider past accidents, chemicals used in large volumes, and particularly hazardous chemicals. For example, laboratories in which hydrofluoric acid (HF) is used should establish special procedures for accidental exposures, and laboratory personnel should be trained in these emergency procedures. When specific procedures have not been established, the following steps provide general guidance.

For spills covering small areas of skin:

  1. Immediately flush with flowing water for no less than 15 minutes; remove any jewelry or clothing as necessary to facilitate clearing of any residual materials.
  2. If there is no visible burn, wash with warm water and soap.
  3. Check the MSDS to determine if special procedures are needed or if any delayed effects should be expected.
  4. Seek medical attention for even minor chemical burns.
  5. Do not use creams, lotions, or salves, unless specifically called for.

For spills on clothes:

  1. The emergency responder should wear appropriate PPE during emergency treatment to avoid exposure.
  2. Do not attempt to wipe the clothes.
  3. To avoid contamination of the victim's eyes, do not remove the victim's eye protection before emergency treatment.
  4. Quickly remove all contaminated clothing, shoes, and jewelry while using the safety shower. Seconds count; do not waste time or limit the showered body areas because of modesty. Take care not to spread the chemical on the skin or, especially, in the eyes.
  5. Cut off garments such as pullover shirts or sweaters to prevent spreading the contamination, especially to the eyes.
  6. Immediately flood the affected body area with water for at least 15 minutes. Resume if pain returns.
  7. Get medical attention as soon as possible. The affected person should be escorted and should not travel alone. Send a copy of the MSDS with the victim. If the institution's MSDS is digital, hardcopies of the relevant information should be provided to responders. If the MSDS is not immediately available, it is vitally important that the person in charge convey the name of the chemical involved to the responders. The responders can then arrange for an MSDS to be available at the hospital, if necessary.
  8. Discard contaminated clothes or have them laundered separately from other clothing.

For splashes into the eye:

  1. Immediately flush with tepid potable water from a gently flowing source for at least 15 minutes. Use an eyewash unit if one is available. If not, place the injured person on his or her back and pour water gently into the eyes for at least 15 minutes.
  2. Hold the individual's eyelids away from the eyeball, and instruct him or her to move the eye up and down and sideways to wash thoroughly behind the eyelids.
  3. Follow first aid by prompt treatment by medical personnel or an ophthalmologist who is acquainted with chemical injuries.
  4. Send a copy of the MSDS with the victim. If the institution's MSDS is digital, hardcopies of the relevant information should be provided to responders. If the MSDS is not immediately available, it is vitally important that the person in charge convey the name of the chemical involved to the responders. The responders can then arrange for an MSDS to be available at the hospital, if necessary.

For cuts:

  1. WARNING: Always wear gloves as a precaution when there is risk of contact with blood or other potentially infectious fluids to prevent the transmission of bloodborne pathogens. (See OSHA 29 CFR § 1910.1030 for more information.)
  2. If the injured person has experienced a minor cut, flush the wound with tepid running water to remove any possible chemical contaminants. If there is a cut on a gloved hand, remove the glove after thoroughly washing the affected area to avoid contamination of the cut with chemicals.
  3. Apply a bandage and advise the victim to report any signs of infection to a physician. If there is a possibility that the wound is contaminated by broken glass or chemicals, the victim should seek immediate medical attention.
  4. If the injured person has experienced a serious injury (if sutures will be necessary), call emergency personnel (911) and apply sterile gauze pads to the wound. If necessary, apply direct pressure to the wound to stop the bleeding.
  5. Apply additional pads if blood soaks through the first sterile pad. If bleeding continues, encourage the victim to lie down and elevate the wound area to a position above the heart. If you are unable to stop the bleeding, remain calm and carefully explain the situation to the emergency dispatcher (911). The dispatcher will advise you on further action.
  6. Send a copy of the MSDS with the victim. If the institution's MSDS is digital, hardcopies of the relevant information should be provided to responders. If the MSDS is not immediately available, it is vitally important that the person in charge convey the name of the chemical involved to the responders. The responders can then arrange for an MSDS to be available at the hospital, if necessary.

For ingestion:

  1. Call emergency personnel (911).
  2. Do not encourage vomiting except under the advice of a physician. Call the Poison Control Center (800-222-1222) immediately and consult the MSDS for the appropriate action.
  3. Save all chemical containers and a small amount of vomirus, if possible, for analysis.
  4. Stay with the victim until emergency medical assistance arrives.
  5. Send a copy of the MSDS with the victim. If the institution's MSDS is digital, hardcopies of the relevant information should be provided to responders. If the MSDS is not immediately available, it is vitally important that the person in charge convey the name of the chemical involved to the responders. The responders can then arrange for an MSDS to be available at the hospital, if necessary.

If the victim is unconscious:

  1. Call emergency personnel (911).
  2. If it is safe for you to enter the area, place the victim on his or her back and cover with a blanket. Do not attempt to remove the victim from the area unless there is immediate danger.
  3. Clear the area of any chemical spill or broken glassware.
  4. If the victim begins to vomit, turn the head so that the stomach contents are not aspirated into the lungs.
  5. Stay with the victim until emergency medical assistance arrives.
  6. If the incident involves a chemical exposure, send a copy of the MSDS with the victim. If the institution's MSDS is digital, hardcopies of the relevant information should be provided to responders. If the MSDS is not immediately available, it is vitally important that the person in charge convey the name of the chemical involved to the responders. The responders can then arrange for an MSDS to be available at the hospital, if necessary.

For convulsions:

  1. Call emergency personnel (911).
  2. If it is safe for you to enter the area, remove anything that might cause harm to the victim. Clear the area of any chemical spills or broken glassware.
  3. If the victim begins to vomit, turn the head so that the stomach contents are not aspirated into the lungs.
  4. Try to protect the victim from further danger with as little interference as possible. Do not attempt to restrain the victim.
  5. Stay with the victim until emergency medical assistance arrives.
  6. If the incident involves a chemical exposure, send a copy of the MSDS with the victim.

For burns from heat:

  1. Call emergency personnel (911).
  2. For first-degree burns, flush with copious amounts of tepid running water. Apply a moist dressing and bandage loosely.
  3. For second-degree (with open blisters) and third-degree burns, do not flush with water. Apply a dry dressing and bandage loosely. Immediately seek medical attention.
  4. Do not apply ointments or ice to the wound.

For cold burns:

  1. Call emergency personnel (911).
  2. Do not apply heat.
  3. If it is not in the area involved, loosen any clothing that may restrict circulation.
  4. Cryogenic liquids produce tissue damage similar to that associated with thermal burns and cause severe deep freezing with extensive destruction of tissue.
  5. Flush affected areas with large volumes of tepid water (41–46 °C [105–115 °F]) to reduce freezing.
  6. Cover the affected area with a sterile protective dressing or with clean sheets if the area is large, and protect the area from further injury.
  7. Seek medical attention.

6.C.10.5. Spill Containment

All personnel who work in a laboratory in which hazardous substances are used should be familiar with their institution's policy regarding spill control. For non-emergency3 spills, spill control kits may be available that are tailored to the potential risk associated with the materials being used in the laboratory. These kits are used to confine and limit the spill if such actions can be taken without risk of injury or contamination. An individual should be assigned to maintain the kit. Store spill kits near areas where spills may occur. Typical spill control kits include these items:

  • spill control pillows, which are commercially available and generally can be used for absorbing solvents, acids, and caustic alkalis, but not HF;
  • inert absorbents such as vermiculite, clay, sand, kitty litter, and Oil Dri, but not paper because it is not an inert material and should not be used to clean up oxidizing agents such as nitric acid;
  • neutralizing agents for acid spills such as sodium carbonate and sodium bicarbonate;
  • neutralizing agents for alkali spills such as sodium bisulfate and citric acid;
  • large plastic scoops and other equipment such as brooms, pails, bags, and dustpans; and
  • appropriate PPE, warnings, barricade tapes, and protection against slips or falls on the wet floor during and after cleanup.

In an emergency,4 follow institutional guidelines regarding spill containment.

6.C.10.6. Spill Cleanup

Specific procedures for cleaning up spills vary depending on the location of the accident, the amount and physical properties of the spilled material, the degree and type of toxicity, and the training of the personnel involved. Any cleanup should be performed while wearing appropriate PPE and in line with institutional guidance. General guidelines for handling several common incidental, non-emergency spills follow:

  • Materials of low flammability that are not volatile or that have low toxicity. This category of hazardous substances includes inorganic acids (e.g., sulfuric and nitric acid) and caustic bases (e.g., sodium and potassium hydroxide). For cleanup, appropriate PPE, including gloves, chemical splash goggles, and (if necessary) shoe coverings, should be worn. Absorption of the spilled material with an inert absorbent and appropriate disposal are recommended. The spilled chemicals can be neutralized with materials such as sodium bisulfate (for alkalis) and sodium carbonate or bicarbonate (for acids), absorbed on Floor-Dri or vermiculite, scooped up, and disposed of according to the procedures detailed in Chapter 8, section 8.B.6.
  • Flammable solvents. Fast action is crucial when a flammable solvent of relatively low toxicity is spilled. This category includes acetone, petroleum ether, pentane, hexane, diethyl ether, dimethoxyethane, and tetrahydrofuran. Other personnel in the laboratory should be alerted, all flames extinguished, and any spark-producing equipment turned off. In some cases the power to the laboratory should be shut off with the circuit breaker, but the ventilation system should be kept running. The spilled solvent should be soaked up with spill absorbent or spill pillows as quickly as possible. If this cannot be done quickly, evacuation should occur, and emergency personnel (911) should be called. Used absorbent and pillows should be sealed in containers and disposed of properly. Nonsparking tools should be used in cleanup.
  • Highly toxic substances. The cleanup of highly toxic substances should not be attempted alone. Emergency responders should be notified, and the appropriate EHS expert should be contacted to obtain assistance in evaluating the hazards involved. These professionals will know how to clean up the material and may perform the operation.
  • Debris management. Debris from the cleanup should be handled as hazardous waste if the spilled material falls into that category.

6.C.10.7. Handling Leaking Gas Cylinders

Leaking gas cylinders constitute serious hazards that may require an immediate evacuation of the area and a call to emergency responders. If a leak occurs, do not apply extreme tension to close a stuck valve. Wear appropriate PPE, which usually includes a self-contained breathing apparatus or an air-line respirator, when entering the area with the leak. (See also section 6.D.6.) The following guidelines cover leaks of various types of gases:

  • Flammable, inert, or oxidizing gases. If safe to do so, move the cylinder to an isolated area, away from combustible material if the gas is flammable or an oxidizing agent. Post signs that describe the hazards and state warnings. Take care when moving leaking cylinders of flammable gases so that accidental ignition does not occur. If feasible, move the leaking cylinder into a laboratory chemical hood until it is exhausted.
  • Corrosive gases. Corrosive gases may increase the size of the leak as they are released, and some corrosives are also oxidants, flammable, or toxic. Move the cylinder to an isolated well-ventilated area, and, if possible, use suitable means to direct the gas into an appropriate chemical neutralizer. If there is apt to be a reaction with the neutralizer that could lead to a suck-back into the valve (e.g., aqueous acid into an ammonia tank), place a trap in the line before starting neutralization. Post signs that describe the hazards and state warnings.
  • Toxic gases. The same procedure should be followed for toxic gases as for corrosive gases. Be sure to warn others of exposure risks. Move the cylinder to an isolated well-ventilated area. Direct the gas into an appropriate chemical neutralizer. Post signs that describe the hazards and state warnings.

Contact the supplier for specific information and guidance.

6.C.10.8. Handling Spills of Elemental Mercury

When spilled in a laboratory, mercury can become trapped beneath floor tiles, under cabinets, and even between walls. Even at very low levels, chronic mercury exposure can be a serious risk, especially in older laboratory facilities, where multiple historic spills may have occurred. Government and standard-setting organizations have established cleanup standards for laboratory spills. These stringent standards ensure the safety of trained laboratory personnel, students, and future occupants of the space.

A portable atomic absorption spectrophotometer with a sensitivity of at least 2 ng/m3 or other suitable instruments are used to find mercury residues and reservoirs that result from laboratory spills, and for the final clearance survey. Follow institutional procedures in cleaning up spills. General guidelines for handling incidental, non-emergency elemental mercury spills are as follows:

  • First, isolate the spill area. Keep people from walking through and spreading the contamination.
  • Wear protective gloves, booties, and a Tyvek® suit when necessary, while performing cleanup activities.
  • Collect the droplets on wet toweling, which consolidates the small droplets to larger pieces, or with a piece of adhesive tape. Do not use sulfur; the practice is ineffective and the resulting waste creates a disposal problem.
  • Consolidate large droplets by using a scraper or a piece of cardboard.
  • Use commercial mercury spill cleanup sponges and spill control kits.
  • Use specially designed mercury vacuum cleaners that have special collection traps and filters to prevent the emission of mercury vapors. A standard vacuum cleaner should never be used to pick up mercury.
  • Waste mercury should be treated as a hazardous waste. Place it in a thick-walled high-density polyethylene bottle and transfer it to a central depository for reclamation.
  • Decontaminate the exposed work surfaces and floors by using an appropriate decontamination kit.
  • Verify decontamination to the current standards by using a portable atomic absorption spectrophotometer or other suitable instrument as described above.

Prevent mercury spills by using supplies and equipment that do not contain mercury. (For information about reducing the use of mercury in laboratories, see Chapter 5, section 5.B.8.)

6.C.10.9. Responding to Fires

Fires are one of the most common types of laboratory accidents. All personnel should be familiar with the general guidelines below to prevent and minimize injury and damage from fires. Hands-on experience with common types of extinguishers and the proper choice of extinguisher should be part of basic laboratory training. (See also Chapter 7, section 7.F.2.)

Be prepared to respond to a fire:

  • Preparation is essential! Make sure all laboratory personnel know the locations of all fire extinguishers in the laboratory, what types of fires they can be used for, and how to operate them correctly. Also ensure that they know the location of the nearest fire-alarm pull station, telephone, emergency contact list, safety showers, and emergency blankets.
  • In case of fire, immediately notify emergency response personnel by activating the nearest fire alarm. After initial containment, it is also important to report all fires to appropriate personnel for possible follow-up action.
  • Even though a small fire that has just started can sometimes be extinguished with a laboratory fire extinguisher, attempt to put out such fires only if you are trained to use that type of extinguisher, confident that you can do it successfully and quickly, and from a position in which you are always between the fire and an exit to avoid being trapped. Do not attempt to extinguish fires of any size if the institution's policy prohibits this. A fire can spread and surround you in seconds. Toxic gases and smoke present additional hazards. When in doubt, evacuate immediately instead of attempting to extinguish the fire. Only attempt to extinguish fires of any size if the institution's policy allows.
  • Put out fires in small vessels by covering the vessel loosely. Never pick up a flask or container of burning material.
  • Extinguish small fires involving reactive metals and organometallic compounds (e.g., magnesium, sodium, potassium, and metal hydrides) with Met-L-X or Met-L-Kyl extinguishers or by covering with dry sand. Apply additional fire suppression techniques if solvents or combustibles become involved. Because these fires are very difficult to extinguish, sound the fire alarms before you attempt to put out the fire.
  • In the event of a more serious fire, evacuate the laboratory and activate the nearest fire alarm. When the fire department and emergency response team arrive, tell them what hazardous substances are in the laboratory.
  • If a person's clothing catches fire, douse him or her immediately in a safety shower. The drop-and-roll technique is also effective. Use fire blankets only as a last resort because they tend to hold in heat and to increase the severity of burns by creating a chimney-like effect. Remove contaminated clothing quickly. Wrap the injured person in a blanket to avoid shock, and get medical attention promptly.

6.D. WORKING WITH SUBSTANCES OF HIGH TOXICITY

Individuals who work with highly toxic chemicals, as identified in Chapter 4 (see section 4.C, Tables 4.1, 4.2, and 4.3), should be thoroughly familiar with the general guidelines for the safe handling of chemicals in laboratories (see section 6.C). They should also have acquired through training and experience the knowledge, skill, and discipline to carry out safe laboratory practices consistently. However, these guidelines alone are not sufficient when handling substances that are known to be highly toxic and chemicals that, when combined in an experimental reaction, may generate highly toxic substances or produce new substances with the potential for high toxicity. Additional precautions are needed to set up multiple lines of defense to minimize the risks posed by these substances. As discussed in section 6.B, preparations for handling highly toxic substances must include sound and thorough planning of the experiment, an understanding of the intrinsic hazards of the substances and the risks of exposure inherent in the planned processes, selection of additional precautions that may be necessary to minimize or eliminate these risks, and review of all emergency procedures to ensure appropriate response to unexpected spills and accidents. Each experiment must be evaluated individually because assessment of the level of risk depends on how the substance will be used. Therefore, a prudent planner does not rely solely on a list of highly toxic chemicals to determine the level of the risk; under certain conditions, chemicals not on these lists may react to form highly toxic substances.

In general, the guidelines in section 6.C reflect the minimum standards for handling hazardous substances and should become standard practice when handling highly toxic substances. For example, although working alone in laboratories should be avoided, it is essential that more than one person be present when highly toxic materials are handled. All people working in the area must be familiar with the hazards of the experiments being conducted and with the appropriate emergency response procedures.

Use engineering controls to minimize the possibility of exposure (see section 6.D.5). The use of appropriate PPE to safeguard the hands, forearms, and face from exposure to chemicals is essential in handling highly toxic materials. Cleanliness, order, and general good housekeeping practices create an intrinsically safer workplace. Compliance with safety rules should be maintained scrupulously in areas where highly toxic substances are handled. Source reduction is always a prudent practice, but in the case of highly toxic chemicals it may mean the difference between working with toxicologically dangerous amounts of materials and working with quantities that can be handled safely with routine practice. Emergency response planning and training are very important when working with highly toxic compounds. Additional hazards from these materials (e.g., flammability and high vapor pressures) can complicate the situation, making operational safety all the more important.

6.D.1. Planning

Careful planning should precede any experiment involving a highly toxic substance whenever the substance is to be used for the first time or whenever an experienced user carries out a new protocol that increases the risk of exposure substantially. Planning should include consultations with colleagues who have experience in handling the substance safely and in protocols of use. Experts in the institution's EHS program are a valuable source of information on the hazardous properties of chemicals and safe practice. They also need to be consulted for guidance regarding those chemicals that are regulated by federal, state, and local agencies or by institutional policy. Thoroughly review the wealth of information available in the MSDS, the literature, and toxicological and safety references.

When planning, always consider substituting less toxic substances for highly toxic ones. Also, be sure to use the smallest amount of material that is practicable for the conduct of the experiment. Other important factors to be considered in determining the need for additional safeguards are the likelihood of exposure inherent in the proposed experimental process, the toxicological and physical properties of the chemical substances being used, the concentrations and amounts involved, the duration of exposure, and known toxicological effects. Plan for careful management of the substances throughout their life cycle—from acquisition and storage through destruction or safe disposal. Document these plans, and review them with personnel doing the work, as well as others in the laboratory. Finally, include a method for receiving feedback that can be incorporated into policy revisions, allowing for continuous improvement of the procedures.

6.D.2. Experiment Protocols Involving Highly Toxic Chemicals

Before the experiment begins, prepare an experiment plan that describes the additional safeguards that will be used for all phases of the experiment from acquisition of the chemical to its final safe disposal. The amounts of materials used and the names of the people involved should be included in the written summary and recorded in the laboratory notebook.

The planning process may demonstrate that monitoring is necessary to ensure the safety of the experimenters. Such a determination is made when there is reason to believe that exposure levels for the substances planned to be used could exceed OSHA-established regulatory action levels, similar guidelines established by other authoritative organizations, or when the exposure level is uncertain.

People who conduct the work should know the signs and symptoms of acute and chronic exposure, including delayed effects. Arrange ready access to an occupational health physician, and consult with the physician to determine if health screening or medical surveillance is appropriate.

6.D.3. Designated Areas

Experimental procedures involving highly toxic chemicals, including their transfer from storage containers to reaction vessels, should be confined to a designated work area in the laboratory. This area, which may be a laboratory chemical hood or glovebox, a portion of a laboratory, or the entire laboratory module, should be recognized by everyone in the laboratory or institution as a place where special training, precautions, laboratory skill, and safety discipline are required.

Post signs conspicuously to indicate the designated areas. It may also be prudent to post any relevant LCSS outside the laboratory door. The designated area may be used for other purposes, as long as all laboratory personnel comply with training, safety, and security requirements, and they are familiar with the emergency response protocols of the institution.

In consultation with the institution's EHS experts, the laboratory supervisor should determine which procedures and highly toxic chemicals need to be confined to designated areas. The general guidelines (section 6.C) for handling hazardous chemicals in laboratories may be sufficient for procedures involving very low concentrations and small amounts of highly toxic chemicals, depending on the experiment, the reagents, and their toxicological and physical properties.

6.D.4. Access Control

Restrict access to laboratories where highly toxic chemicals are in use to personnel who are authorized for this laboratory work and trained in the special precautions that apply. Administrative procedures or even physical barriers may be required to prevent unauthorized personnel from entering these laboratories.

Keep laboratory doors closed and locked to limit access to unattended areas where highly toxic materials are stored or routinely handled. However, security measures must not prevent emergency exits from the laboratory. Be sure to make special arrangements for emergency response, including after normal work hours. Use locks to secure refrigerators, freezers, and other storage areas. Keep track of authorized personnel, and be sure to retrieve keys and change locks and access when these people no longer work in the area.

Keep a detailed inventory of highly toxic chemicals. The date, amount, location, and responsible individual should be recorded for all acquisitions, syntheses, access, use, transport, distribution to others, and disposal. Perform a physical inventory every year to verify active inventory records. A procedure should be in place to report security breaches, inventory discrepancies, losses, diversions, or suspected thefts.

When long-term experiments involving highly toxic compounds require unattended operations, securing the laboratory from access by untrained personnel is essential. These operations should also include failsafe backup options such as shutoff devices in case a reaction overheats or pressure builds up. Additionally equipment should include interlocks that shut down experiments by turning off devices such as heating baths or reagent pumps, or that close solenoid valves if cooling water stops flowing through an apparatus or if airflow through a laboratory chemical hood becomes restricted or stops. An interlock should be constructed in such a way that if a problem develops, it places the experiment in a safer mode and will not reset even if the hazardous condition is reversed. Protective devices should include alarms that indicate their activation. Security guards and untrained personnel should never be asked or allowed to check on the status of unattended experiments involving highly toxic materials. Warning signs on locked doors should list the trained laboratory personnel to be contacted in case an alarm sounds within the laboratory.

6.D.5. Special Precautions for Minimizing Exposure to Highly Toxic Chemicals

The practices listed below help establish the necessary precautions to enable laboratory work with highly toxic chemicals to be conducted safely:

  1. Conduct procedures involving highly toxic chemicals that can generate dust, vapors, or aerosols in a laboratory chemical hood, glovebox, or other suitable containment device. Check hoods for acceptable operation prior to conducting experiments with toxic chemicals. If experiments are to be ongoing over a significant period of time, the hood should be rechecked at least quarterly for proper operation and be equipped with flow-sensing devices that show at a glance or by an audible signal whether they are performing adequately. When toxic chemicals are used in a glovebox, it should be operated under negative pressure, and the gloves should be checked for integrity and appropriate composition before use. Consider if reactive or toxic effluents may be generated by the procedure. If so, scrubbing may be necessary. If dusts or aerosols are generated, consider using high-efficiency particulate air (HEPA) filters prior to discharge to the atmosphere. Hoods should not be used as waste disposal devices, particularly when toxic substances are involved. To offer maximum protection, they should be operated with sashes at their proper level whenever possible. Monitoring equipment might include both active and passive devices to sample laboratory working environments. The experimenter must ensure that the hood exhaust will not present a hazard to anyone outside the immediate laboratory environment. For instance, rooftop access may need to be eliminated during certain operations or, when rooftop access is required, work with highly toxic materials must not be allowed. (See Chapter 9, section 9.C, for detailed discussion on laboratory chemical hoods and environmental control.) When available, alarmed detection devices are another engineering control that should be used for highly toxic materials. Air dispersion modeling may be necessary to determine if exhaust ventilation will affect nearby air intakes or other sensitive receptors.
  2. Gloves must be worn when working with toxic liquids or solids to protect the hands and forearms. Select gloves carefully to ensure that they are impervious to the chemicals being used and are of correct thickness to allow reasonable dexterity while also ensuring adequate barrier protection. (See section 6.C.2.6.1 for more information on gloves.)
  3. Face and eye protection is necessary to prevent ingestion, inhalation, and skin absorption of toxic chemicals. Safety glasses with side shields are a minimum standard for all laboratory work. When using toxic substances that could generate vapors, aerosols, or dusts, additional levels of protection, including full-face shields and respirators, are appropriate, depending on the degree of hazard represented. Transparent explosion shields in hoods offer additional protection from splashes. Medical certification, training, and fit-testing are required if respirators are worn.
  4. Equipment used for the handling of highly toxic chemicals should be isolated from the general laboratory environment. Consider venting laboratory vacuum pumps used with these substances via high-efficiency scrubbers or an exhaust hood. Motor-driven vacuum pumps are recommended because they are easy to decontaminate (decontamination should be conducted in a designated hood).
  5. Always practice good laboratory hygiene where highly toxic chemicals are handled. After using toxic materials, trained laboratory personnel should wash their face, hands, neck, and arms. Equipment (including PPE such as gloves) that might be contaminated must never be removed from the environment reserved for handling toxic materials without complete decontamination. Choose laboratory equipment and glassware that are easy to clean and decontaminate. Work surfaces should also be easy to decontaminate or covered with appropriate protective material, which can be properly disposed of when the procedure is complete. Mixtures that contain toxic chemicals or substances of unknown toxicity must never be smelled or tasted.
  6. Carefully plan the transportation of very toxic chemicals. Handling these materials outside the specially designated laboratory area should be minimized. When these materials are transported, the transporter should wear the full complement of PPE appropriate to the chemicals and the type of shipping containers being transported. Samples should be carried in unbreakable secondary containment. (See Chapter 5 for more information about transporting laboratory chemicals.)

6.D.6. Preparing for Accidents with and Spills of Substances of High Toxicity

Be sure that emergency response procedures cover highly toxic substances. Spill control and appropriate emergency response kits should be nearby, and laboratory personnel should be trained in their proper use. These kits should be marked, contained, and sealed to avoid contamination and to be accessible in an emergency. Essential contents include spill control absorbents, impermeable surface covers (to prevent the spread of contamination while conducting emergency response), warning signs, emergency barriers, first-aid supplies, and antidotes. Before starting experiments, the kit contents should be validated. Safety showers, eyewash units, and fire extinguishers should be readily available nearby. Self-contained impermeable suits, a self-contained breathing apparatus, and cartridge respirators may also be appropriate for spill response preparedness, depending on the physical properties and toxicity of the materials being used (see section 6.C.2.4).

Experiments conducted with highly toxic chemicals should be carried out in work areas designed to contain accidental releases (see also section 6.D.3). Trays and other types of secondary containment should be used to contain inadvertent spills. Careful technique must be observed to minimize the potential for spills and releases.

Prior to work, all toxicity and emergency response information should be posted outside the immediate area to ensure accessibility in emergencies. All laboratory personnel who could potentially be exposed must be properly trained on the appropriate response in the event of an emergency. Conducting occasional emergency response drills is always a good idea. Such dry runs may involve medical personnel as well as emergency cleanup crews.

(See also sections 6.C.10.5 and 6.C.10.6.)

6.D.7. Storage and Waste Disposal

Use unbreakable secondary containment for the storage of highly toxic chemicals. If the materials are volatile (or could react with moisture or air to form volatile toxic compounds), containers should be in a ventilated storage area. All containers of highly toxic chemicals should be clearly labeled with chemical composition, known hazards, and warnings for handling. Chemicals that can combine to make highly toxic materials (e.g., acids and inorganic cyanides, which can generate hydrogen cyanide) should not be stored in the same secondary containment. A list of highly toxic compounds, their locations, and contingency plans for dealing with spills should be displayed prominently at any storage facility. Highly toxic chemicals that have a limited shelf life need to be tracked and monitored for deterioration in the storage facility. Those that require refrigeration should be stored in a ventilated refrigeration facility.

Procedures for disposal of highly toxic materials should be established before experiments begin, preferably before the chemicals are ordered. The procedures should address methods for decontamination of all laboratory equipment that comes into contact with highly toxic chemicals. Waste should be accumulated in clearly labeled impervious containers that are stored in unbreakable secondary containment. Volatile or reactive waste must always be covered to minimize release.

Follow procedures established by the institution's EHS experts for commercial waste disposal. Alternatively, consider the possibility of pretrearment of waste either before or during accumulation. In-laboratory destruction may be the safest and most effective way of dealing with waste, but regulatory requirements may affect this decision.

(For further information about disposal of hazardous waste, see Chapter 8. For information about regulatory requirements, see Chapter 11.)

6.D.8. Multihazardous Materials

Some highly toxic materials present additional hazards because of their flammability (see Chapter 4, section 4.D.1, and Chapter 6, section 6.F), volatility (see sections 6.F and 6.G.6), explosivity (see Chapter 4, section 4.D.3; see also section 6.G.4), or reactivity (see Chapter 4, section 4.D.2; see also section 6.G.2). These materials warrant special attention to ensure that risks are minimized and that plans to deal effectively with all potential hazards and emergency response are implemented. (Table 5.1 provides information regarding incompatible chemicals and substances requiring extreme caution.)

6.E. WORKING WITH BIOHAZARDOUS AND RADIOACTIVE MATERIALS

6.E.1. Biohazardous Materials

For even the most experienced laboratory personnel, careful review of the 2009 publication Biosafety in Microbiological and Biomedical Laboratories (BMBL; HHS/CDC/NIH, 2009) should be a prerequisite for beginning any laboratory activity involving a microorganism, whether naturally or synthetically derived. It defines four levels of control that are appropriate for safe laboratory work with microorganisms that present occupational and public health risks, ranging from no risk of disease for normal healthy adults to high risk of life-threatening disease. The BMBL provides guidance for handling specific agents and a tiered approach to control and containment for each biosafety level.

The four levels of control, referred to as biosafety levels (BSLs) 1 through 4, describe microbiological practices, safety equipment, and features of laboratory facilities for the corresponding level of risk associated with handling a particular agent. The designation of a BSL is influenced by several characteristics of the infectious agent, the most important of which are the severity of the disease, the mode and efficiency of transmission of the infectious agent, the availability of protective immunization or effective therapy, and the relative risk of exposure created by manipulations used in handling the agent. Novel synthetic agents should be handled at a higher BSL until the characteristics of the agent are better understood. Biological toxins are generally safely handled using BSL 2 practices and procedures with strict attention to sharps safety, PPE, and appropriate use of containment equipment. Certain agents and toxins designated as select agents under 42 CFR Part 73 have security requirements that must be met in addition to the biosafety requirements addressed through the application of BSL.

BSL 1 is the basic level of protection appropriate only for agents that are not known to cause disease in normal healthy adult humans.

BSL 2 is appropriate for handling a broad spectrum of moderate-risk agents that cause human disease by ingestion or through percutaneous or mucous membrane exposure. Hepatitis B virus, salmonellae, Toxoplasma spp., and human blood and body fluids are representative BSL 2 agents. Extreme precaution with needles or sharp instruments is emphasized at this level.

BSL 3 is appropriate for agents with potential for respiratory transmission, agents that may cause serious and potentially lethal infections, and agents that have a moderate risk to the outside community as well as the individual. Emphasis is placed on the control of aerosols by performing all manipulations within a biological safety cabinet or other containment equipment. At this level, the facility is at least two doors from general building traffic, has a dedicated exhaust fan designed to operate the facility under a negative pressure gradient, and usually is equipped with HEPA filters to purify the air before it is exhausted to the outside. Air from these laboratories cannot be recirculated to other areas of the building. These requirements are designed to control access to the laboratory and to minimize the release of infectious aerosols from the laboratory. The bacterium Mycobacterium tuberculosis is an example of an agent for which this higher level of control is appropriate.

Exotic agents that pose a high individual risk of life-threatening disease by the aerosol route and for which no treatment is available are restricted to high-containment laboratories that meet BSL 4 standards. These agents represent a higher risk to the community because of their higher morbidity and mortality rates. Protection for personnel in these laboratories includes physically sealed gloveboxes or fully enclosed barrier suits that supply breathing air.

Several authoritative reference works are available that provide excellent guidance for the safe handling of infectious microorganisms in the laboratory, including BMBL (HHS/CDC/NIH, 2009), the NIH Guidelines for Research Involving Recombinant DNA Molecules (NIH, 2011), and Biosafety in the Laboratory—Prudent Practices for the Handling and Disposal of Infectious Materials (NRC, 1989). Standard microbiological practices described in these references are consistent with the prudent practices used for the safe handling of chemicals. Biosafety in the Laboratory lists seven foundational work practices in biosafety:

  1. Do not eat, drink, or smoke in the laboratory. Do not store food in the laboratory. Keep your hands away from your face; avoid touching your eyes, nose, or mouth with gloved hands.
  2. Do not pipette liquids by mouth; use mechanical pipetting devices.
  3. Wear personal protective clothing in the laboratory (e.g., eye protection, laboratory coats, gloves, and face protection).
  4. Eliminate or work very carefully with sharp objects (such as needles, scalpels, Pasteur pipettes, and capillary tubes).
  5. Work carefully to minimize the potential for aerosol formation. Confine aerosols as close as possible to their source of generation (i.e., use a biosafety cabinet).
  6. Disinfect work surfaces and equipment after use.
  7. Wash your hands after removing protective clothing, after contact with contaminated materials, and before leaving the laboratory.

Other practices that are most helpful for preventing laboratory-acquired infections or intoxications are as follows:

  • Keep laboratory doors closed when experiments are in progress.
  • Use leakproof secondary containment to move or transfer cultures.
  • Deactivate, disinfect, or sterilize infectious waste before disposal.

6.E.2. Radioactive Materials

The receipt, possession, use, transfer, and disposal of most radioactive materials is strictly regulated by the U.S. Nuclear Regulatory Commission (USNRC) (see 10 CFR Part 20, Standards for Protection Against Radiation) and by state agencies who have agreements with the USNRC to regulate the users within their own states. Radioactive materials may only be used for purposes specifically described in licenses issued by these agencies. Individuals working with radioactive materials need to be aware of the restrictions and requirements of these licenses. Consult your institution's radiation safety officer or other designated EHS expert for training, policies, and procedures specific to uses at your institution. Prudent practices for working with radioactive materials are similar to those needed to reduce the risk of exposure to toxic chemicals (section 6.C has similar information) and to biohazards:

  • Know the characteristics of the radioisotopes that are being used, including half-life, type and energy of emitted radiation, potential for and routes of exposure, and annual exposure limit. Know how to detect contamination.
  • Protect against exposure to airborne and ingestible radioactive materials.
  • Never eat, drink, smoke, handle contact lenses, apply cosmetics, or take or apply medicine in the laboratory. Keep food, drinks, cosmetics, and tobacco products out of the laboratory entirely to avoid contamination.
  • Do not pipet by mouth.
  • Provide for safe disposal of waste radionuclides and their solutions.
  • Use PPE (e.g., eye protection, gloves, protective clothing, respirators) to minimize exposures.
  • Use shielding and gloveboxes to minimize exposure.
  • If possible, use equipment that can be operated remotely.
  • Plan experiments to minimize exposure by reducing the time, using shielding, increasing your distance from the radiation, and paying attention to monitoring and decontamination.
  • Keep an accurate inventory of radioisotopes.
  • Record all receipts, transfers, and disposals of radioisotopes.
  • Record surveys.
  • Check personnel and the work area each day that radioisotopes are used.
  • Plan procedures to use the smallest amount of radioisotope possible.
  • Minimize radioactive waste.
  • Check waste materials for contamination before discarding.
  • Place only materials with known or suspected radioactive contamination in appropriate radioactive waste containers.
  • Do not generate multihazardous waste (combinations of radioactive, biological, and chemical waste) without first consulting with the designated radiation and chemical safety officers.

(See Chapter 8 for more information on waste and disposal.)

6.F. WORKING WITH FLAMMABLE CHEMICALS

Flammable and combustible materials are a common laboratory hazard. Always consider the risk of fire when planning laboratory operations.

To prepare for fire, become familiar with your institution's response and evacuation procedures. Some institutions have a policy that forbids attempts to control or extinguish a fire. Laboratory personnel need to be trained in the necessary steps to take in case of a fire, including knowing the locations of fire alarms, pull stations, fire extinguishers, safety showers, and other emergency equipment (see section 6.C.10, above). Exit routes should be reviewed. Fire extinguishers in the immediate vicinity of an experiment should be appropriate to the particular fire hazards. Fires can be exacerbated by use of an inappropriate extinguisher. Post telephone numbers to call in an emergency or accident in a prominent location.

(Refer to section 6.F and Chapter 7, section 7.F.2, for further information.)

To minimize the risk of fire, all laboratory personnel should know the properties of chemicals they are handling as well as have a basic understanding of how these properties might be affected by the variety of conditions found in the laboratory. As stated in section 6.B, MSDSs or other sources of information should be consulted for information such as vapor pressure, flash point, and explosive limit in air. The use of flammable substances is common, and their properties are also discussed in Chapter 4, section 4.D.

For a fire to start, an ignition source, a fuel, and an oxidizer must be present. Eliminating ignition sources is difficult and takes careful planning, but avoiding the combined presence of fuel and an oxidizer is possible. Keep fuel sources in closed vessels. Control, contain, and minimize the amount of fuels and oxidizers. Containers with large openings (e.g., beakers, baths, vats) should not be used with highly flammable liquids or with liquids above their flash point. Although all flammable substances should be handled prudently, the extreme flammability of some materials requires additional precautions. Consider using inert gases to blanket or purge vessels containing flammable liquids.

Plan to both prevent and respond to a flammable liquid spill, especially one that occurs during a laboratory operation. Place distillation apparatuses and heated reaction flasks in secondary containment to prevent the spread of flammable liquid in the event of breakage. For example, secondary containment can be a large tray in which the apparatus stands. This precaution is particularly important for distillations and similar operations where the breakage of the still pot would result in the release of large quantities of flammable liquid, which may be at its boiling point.

Eliminate ignition sources from areas where flammable substances are handled. Open flames, such as Bunsen burners and matches, are obvious ignition sources. Gas burners should not be used as a source of heat in any laboratory where flammable substances are used. Less obvious ignition sources include gas-fired space heating or water-heating equipment and electrical equipment, such as stirring devices, motors, relays, and switches, which can all produce sparks that will ignite flammable vapors. Nonsparking, explosion-proof devices should be used. Alternatively, actions can be taken to minimize the potential contact of flammable vapors with ignition sources and air by ensuring that vessels containing flammables are closed and maintained under a blanket of inert gas. In situations where large volumes of flammable liquids are stored or in use, fire codes may legally mandate the use of nonsparking, explosion-proof equipment and electrical fixtures.

Even low-level sources of ignition, such as hot plates, static discharge from clothing, steam lines or other hot surfaces, provide a sufficiently energetic ignition source for the most flammable substances in general laboratory use, such as diethyl ether and carbon disulfide (see Chapter 4, section 4.D.1.3 and Vignette 6.3). Flammable substances that require low-temperature storage should be stored only in refrigerators designed for that purpose. Ordinary refrigerators are a hazard because of the presence of potential ignition sources, such as switches, relays, and, possibly, sparking fan motors, and should never be used for storing flammable chemicals. When transferring flammable liquids in metal containers, sparks from accumulated static charge must be avoided by grounding.

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Vignette 6.3

Solvent fire. A researcher placed a 1,000-mL beaker containing 60 g of a reagent on a magnetic stirrer located in the chemical fume hood. Carbon disulfide, 500 mL, was added from a second 1,000-mL beaker with stirring. During the solvent addition, the (more...)

Laboratory fires are also caused by hot plates, oil baths, and heating mantles that can melt and combust plastic materials (e.g., vials, containers, tubing). Dry and concentrated residues can ignite when overheated in stills, ovens, dryers, and other heating devices. Do not operate this equipment unattended. When purchasing these devices, choose those models with automatic high-temperature shutoffs. (See section 7.C.5 for more information about the hazards posed by heating devices.)

Fire hazards posed by water-reactive substances such as alkali metals and metal hydrides, by pyrophoric substances such as metal alkyls, by strong oxidizers such as perchloric acid, and by flammable gases such as acetylene require procedures beyond the standard prudent practices for handling chemicals described here (see sections 6.C and 6.D) and should be researched in LCSSs or other references before work begins. In addition, emergency response plans must address these substances and their special hazards.

6.F.1. Flammable Materials

The basic precautions for safe handling of flammable materials include the following:

  • As much as possible minimize or eliminate the combined presence of flammable material and oxidizer (air). Cap bottles and vessels not in use. Use inert gas blankets when possible.
  • Handle flammable substances only in areas free of ignition sources. In addition to open flames, ignition sources include electrical equipment (especially motors), static electricity, and, for some materials (e.g., carbon disulfide), hot surfaces. Check the work area for flames or ignition sources before using a flammable substance. Before igniting a flame, check for the presence of other flammable substances.
  • Never heat flammable substances with an open flame. Preferred heat sources include steam baths, water baths, oil and wax baths, salt and sand baths, heating mantles, and hot-air or nitrogen baths.
  • Provide ventilation until the vapors are dilute enough to no longer be flammable. This is one of the most effective ways to prevent the formation of flammable gaseous mixtures. Use appropriate and safe exhaust whenever appreciable quantities of flammable substances are transferred from one container to another, allowed to stand in open containers, heated in open containers, or handled in any other way. In using dilution techniques, make certain that equipment (e.g., fans) is explosion-proof and that sparking items are located outside the airstream.
  • Use only refrigeration equipment certified for storage of flammable materials.
  • Use the smallest quantities of flammable substances compatible with the need, and, especially when the flammable liquid must be stored in glass, purchase the smallest useful size bottle.

6.F.2. Flammable Liquids

Flammable liquids burn only when their vapor is mixed with air in the appropriate concentration. Therefore, such liquids should always be handled so as to minimize the creation of flammable vapor concentrations. Dilution of flammable vapors by ventilation is an important means of avoiding flammable concentrations. Containers of liquids should be kept closed except during transfer of contents. Transfers should be carried out only in laboratory chemical hoods or in other areas where ventilation is sufficient to avoid a buildup of flammable vapor concentrations. Spillage or breakage of vessels or containers of flammable liquids or sudden eruptions from nucleation of heated liquid can result in a sudden release of flammable vapor.

Metal lines and vessels discharging flammable liquids should be properly grounded to disperse static electricity. For instance, when transferring flammable liquids in metal equipment, static-generated sparks can be eliminated by proper grounding with ground straps. Development of static electricity is related closely to the level of humidity and may become a problem on cold dry winter days. When nonmetallic containers (especially plastic) are used, contact with the grounding device should be made directly to the liquid rather than to the container. In the rare circumstance that static electricity cannot be avoided, all processes should be carried out as slowly as possible to give the accumulated charge time to disperse or should be handled in an inert atmosphere.

Note that vapors of many flammable liquids are heavier than air and capable of traveling considerable distances along the floor. This possibility should be recognized, and special note should be taken of ignition sources at a lower level than that at which the substance is being used. Close attention should be given to nearby potential sources of ignition.

6.F.3. Flammable Gases

Leakage or escape of flammable gases can produce an explosive atmosphere in the laboratory. Acetylene, hydrogen, ammonia, hydrogen sulfide, propane, and carbon monoxide are especially hazardous. Acetylene, methane, and hydrogen have a wide range of concentrations at which they are flammable (flammability limits),5 which adds greatly to their potential fire and explosion hazard. Installation of flash arresters on hydrogen cylinders is recommended. Prior to introduction of a flammable gas into a reaction vessel, the equipment should be purged by evacuation or with an inert gas. The flush cycle should be repeated three times to reduce residual oxygen to approximately 1%.

(See section 6.H for specific precautions on the use of compressed gases.)

6.F.4. Catalyst Ignition of Flammable Materials

Palladium or platinum on carbon, platinum oxide, Raney nickel, and other hydrogenation catalysts should be filtered carefully from hydrogenation reaction mixtures. The recovered catalyst is usually saturated with hydrogen, is highly reactive, and, thus, inflames spontaneously on exposure to air. Especially for large-scale reactions, the filter cake should not be allowed to become dry. The funnel containing the still-moist catalyst filter cake should be put into a water bath immediately after completion of the filtration. Use of a purge gas (nitrogen or argon) is strongly recommended for hydrogenation procedures so that the catalyst can be filtered and handled under an inert atmosphere.

6.G. WORKING WITH HIGHLY REACTIVE OR EXPLOSIVE CHEMICALS

An explosion occurs when a material undergoes a rapid reaction that results in a violent release of energy. Such reactions can happen spontaneously or be initiated and can produce pressures, gases, and fumes that are hazardous. Highly reactive and explosive materials used in the laboratory require appropriate procedures. In this section, techniques for identifying and handling potentially explosive materials are discussed.

6.G.1. Overview

Light, mechanical shock, heat, and certain catalysts can be initiators of explosive reactions. Hydrogen and chlorine react explosively in the presence of light. Examples of shock-sensitive materials include many acetylides, azides, organic nitrates, nitro compounds, azo compounds, perchlorates, and peroxides. Acids, bases, and other substances may catalyze explosive polymerizations. The catalytic effect of metallic contamination leads to explosive situations. Many metal ions catalyze the violent decomposition of hydrogen peroxide.

Whenever possible, use a safer alternative. For example, perchlorate used as a counteranion to crystallize salts can often be replaced with safer alternatives such as fluorophosphate or fluoroborate.

Many highly reactive chemicals polymerize vigorously, decompose, condense, or become self-reactive. The improper handling of these materials may result in a runaway reaction that could become violent. Careful planning is essential to avoid serious accidents. When highly reactive materials are in use, emergency equipment should be at hand. The apparatus should be assembled in such a way that if the reaction begins to run away, immediate removal of any heat source, cooling of the reaction vessel, cessation of reagent addition, and closing of laboratory chemical hood sashes are possible. Restrict access to the area until the reaction is under control, and consider remote operating controls. A heavy transparent plastic explosion shield should be in place to provide extra protection in addition to the laboratory chemical hood window.

Highly reactive chemicals lead to reactions with rates that increase rapidly as the temperature increases. If the heat evolved is not dissipated, the reaction rate increases until an explosion results. Such an event must be prevented, particularly when scaling up experiments. Sufficient cooling and surface for heat exchange should be provided to allow control of the reaction. It is also important to consider the impact of solution concentration, especially when a reaction is being attempted or scaled up the first time. Use of too highly concentrated reagents has led to runaway conditions and to explosions. Particular care must also be given to the rate of reagent addition versus its rate of consumption, especially if the reaction is subject to an induction period. A chemical reaction with an induction period has a reaction rate that is slow initially but accelerates over time.

Large-scale reactions with organometallic reagents and reactions that produce flammables as products or are carried out in flammable solvents require special attention. Active metals, such as sodium, lithium, potassium, calcium, and finely divided magnesium are serious fire and explosion risks because of their reactivity with water, alcohols, and other compounds or solutions containing acidic hydrogens. These materials require special storage, handling, and disposal procedures. Where active metals are present, Class D fire extinguishers that use special extinguishing materials such as a plasticized graphite-based powder or a sodium chloride-based powder (Met-L-X) are required.

Some chemicals decompose when heated. Slow decomposition may not be noticeable on a small scale, but on a large scale with inadequate heat transfer, or if the evolved heat and gases are confined, an explosive situation may develop. The heat-initiated decomposition of some substances, such as certain peroxides, is almost instantaneous. In particular, reactions that are subject to an induction period can be dangerous because there is no initial indication of a risk, but after induction, a violent process can result.

Oxidizing agents may react violently when they come in contact with reducing materials, trace metals, and sometimes ordinary combustibles. These compounds include the halogens, oxyhalogens, peroxyhalogens, permanganates, nitrates, chromates, and persulfates, as well as peroxides (see also section 6.G.3). Even though inorganic peroxides are generally considered to be stable, they may generate organic peroxides and hydroperoxides in contact with organic compounds, react violently with water (alkali metal peroxides), or form superoxides and ozonides (alkali metal peroxides). Perchloric acid and nitric acid are powerful oxidizing agents with organic compounds and other reducing agents. Perchlorate salts can be explosive and should be treated as potentially hazardous compounds. Dusts—suspensions of oxidizable particles (e.g., magnesium powder, zinc dust, carbon powder, or flowers of sulfur) in the air—constitute a powerful explosive mixture.

Scale-up reactions create difficulties in dissipation of heat that are not evident on a smaller scale. Evaluation of observed or suspected exothermicity can be achieved by differential thermal analysis to identify exothermicity in open reaction systems; differential scanning calorimetry using a specially designed sealable metal crucible, to identify exothermicity in closed reaction systems; or syringe injection calorimetry and reactive systems screening tool calorimetry to determine heats of reaction on a microscale and small scale. [For an expanded discussion of identifying process hazards using thermal analytical techniques, see Tuma (1991).] When it becomes apparent that exothermicity exists at a low temperature or a large exothermicity occurs that might present a hazard, large-scale calorimetry determination of exothermic onset temperatures and drop weight testing are advisable. In situations where formal operational hazard evaluation or reliable data from any other source suggest a hazard, review or modification of the scale-up conditions by an experienced group is recommended to avoid the possibility that an individual might overlook a hazard or the most appropriate procedural changes. Finally, to verify the proper use of equipment and safeguards, it is recommended that researchers calculate the adiabaric temperature and pressure change for the reaction at a fixed volume to estimate the heat and pressure that may be generated.

Any sample of a highly reactive material may be dangerous. The greatest risk is due to the remarkably high rate of a detonation reaction rather than the total energy released. A high-order explosion of even milligram quantities can drive small fragments of glass or other matter deep into the body. It is important to use minimum amounts of hazardous materials with adequate shielding and personal protection.

Not all explosions result from chemical reactions. A dangerous physically caused explosion occurs if a hot liquid is brought into sudden contact with a lower-boiling-point one. The instantaneous vaporization of the lower-boiling-point substance can be hazardous to personnel and destructive to equipment. The presence or inadvertent addition of water to the hot fluid of a heating bath is an example of such a hazard. Explosions can also occur when warming a cryogenic material in a closed container or overpressurizing glassware with nitrogen (N2) or argon when the regulator is incorrectly set. Violent physical explosions have also occurred when a collection of very hot particles is suddenly dumped into water. For this reason, dry sand should be used to catch particles during laboratory thermite reaction demonstrations.

6.G.2. Reactive or Explosive Compounds

Occasionally, it is necessary to handle materials that are known to be explosive or that may contain explosive impurities such as peroxides. Because mechanical shock, elevated temperature, or chemical action might result in explosion with forces that release large volumes of gases, heat, and often toxic vapors, they must be treated with special care.

The proper handling of highly energetic substances without injury demands attention to the most minute details. The unusual nature of work involving such substances requires special safety measures and handling techniques that must be understood thoroughly and followed by all persons involved. The practices listed in this section are a guide for use in any laboratory operation that might involve explosive materials.

Work with explosive (or potentially explosive) materials generally requires the use of special protective apparel (e.g., face shields, gloves, and laboratory coats) and protective devices such as explosion shields, barriers, or even enclosed barricades or an isolated room with a blowout roof or window (see Chapter 7, sections 7.F.1 and 7.F.2).

Before work with a potentially explosive material is begun, the experiment should be discussed with a supervisor or an experienced co-worker, and the relevant literature consulted (see Chapter 4, sections 4.B.2, 4.B.5, and 4.B.6). A risk assessment should be carried out.

Various state and federal regulations cover the transportation, storage, and use of explosives. Along with EHS and transportation experts, these regulations should be consulted before explosives (and related dangerous materials) are used or generated in the laboratory. Explosive materials should be brought into the laboratory only as required and in the smallest quantities adequate for the experiment (see Chapter 5, section 5.B). Insofar as possible, direct handling should be minimized. Explosives should be segregated from other materials that could create a serious risk to life or property should an accident occur.

6.G.2.1. Protective Devices

Barriers such as shields, barricades, and guards should be used to protect personnel and equipment from injury or damage from a possible explosion or fire. The barrier should completely surround the hazardous area. On benches and laboratory chemical hoods, a 0.25-in.-thick acrylic sliding shield, which is screwed together in addition to being glued, can effectively protect trained laboratory personnel from glass fragments resulting from a laboratory-scale explosion. The shield should be in place whenever hazardous reactions are in progress or whenever hazardous materials are being stored temporarily. However, such shielding is not effective against metal shrapnel. The hood sash provides a safety shield only against chemical splashes or sprays, fires, and minor explosions. If more than one hazardous reaction is carried out, the reactions should be shielded from each other and separated as far as possible.

Dryboxes should be fitted with safety glass windows overlaid with 0.25-in.-thick acrylic when potentially explosive materials capable of explosion in an inert atmosphere are to be handled. This protection is adequate against most internal 5-g explosions. Protective gloves should be worn over the rubber drybox gloves to provide additional protection. Other safety devices that allow remote manipulation should be used with the gloves. Explosions of high-energy chemicals from static sparks can be a considerable problem in dryboxes, and so adequate grounding is essential, and an antistatic gun or antistatic ionizer is recommended.

Armored laboratory chemical hoods or barricades made with thick (1.0 in.) poly(vinyl butyral) resin shielding and heavy metal walls give complete protection against explosions less than the acceptable 20-g limit. They are designed to contain a 100-g explosion, but an arbitrary 20-g limit is usually set because of the noise level in the event of an explosion. Such chemical hoods should be equipped with mechanical hands that enable the operator to manipulate equipment and handle adduct containers remotely. A sign should be posted, for example,

CAUTION: NO ONE MAY ENTER AN ARMORED LABORATORY CHEMICAL HOOD FOR ANY REASON DURING THE COURSE OF A HAZARDOUS OPERATION.

Miscellaneous protective devices such as both long- and short-handled tongs for holding or manipulating hazardous items at a safe distance and remote control equipment (e.g., mechanical arms, stopcock turners, labjack turners, remote cable controllers, and closed-circuit television monitors) should be available as required to prevent exposure of any part of the body to injury.

6.G.2.2. Personal Protective Apparel

When explosive materials are handled, the following items of personal protective apparel are needed:

  • Safety glasses that have solid side shields or chemical splash goggles must be worn by all personnel, including visitors, in the laboratory.
  • Full-length shields that fully protect the face and throat must be worn whenever trained laboratory personnel are in a hazardous or exposed position. Special care is required when operating or manipulating synthesis systems that may contain explosives (e.g., diazomethane), when bench shields are moved aside, and when handling or transporting such systems. In view of the special hazard to life that results from severing the jugular vein, extra shielding around the throat is recommended.
  • Heavy leather gloves must be worn if it is necessary to reach behind a shielded area while a hazardous experiment is in progress or when handling reactive compounds or gaseous reactants. Proper planning of experiments should minimize the need for such activities.
  • Laboratory coats should be worn at all times. The coat should be made of flame-resistant material and should be quickly removable. A coat can help reduce minor injuries from flying glass as well as the possibility of injury from an explosive flash.

6.G.2.3. Evaluating Potentially Reactive Materials

Potentially reactive materials must be evaluated for their possible explosive characteristics by consulting the literature and considering their molecular structures. The presence of functional groups or compounds listed in Chapter 4, sections 4.D.2 and 4.D.3 and section 6.G.6 indicates a possible explosion hazard. Urben (2007) notes three methods for determining the sensitivity of very explosive compounds. The first is a commonly used drop test that measures sound levels, which as the editor notes, is “not entirely satisfactory.” The second is an electrostatic test, and the third uses friction generated by grinding two porcelain surfaces together under load. See Dou et al. (1999) for more information. Highly reactive chemicals should be segregated from materials that might interact with them to create a risk of explosion. They should not be used past their expiration date.

6.G.2.4. Determining Reaction Quantities

When a possibly hazardous reaction is attempted, small quantities of reactants should be used. When handling highly reactive chemicals, use the smallest quantities needed for the experiment. In conventional explosives laboratories, no more than 0.1 g of product should be prepared in a single run. During the actual reaction period, no more than 0.5 g of reactants should be present in the reaction vessel: The diluent, the substrate, and the energetic reactant must all be considered when determining the total explosive power of the reaction mixture. Special formal risk assessments should be established to examine operational and safety problems involved in scaling up a reaction in which an explosive substance is used or could be generated.

6.G.2.5. Conducting Reaction Operations

The most common heating devices are heating tapes and mantles and sand, water, steam, wax, silicone oil, and air (or nitrogen) baths. They should be used in such a way that if an explosion were to occur the heating medium would be contained. Heating baths should consist of nonflammable materials. All controls for heating and stirring equipment should be operable from outside the shielded area. (See Chapter 7, section 7.C.5, for further information.)

Vacuum pumps should carry tags indicating the date of the most recent oil change. Oil should be changed once a month, or sooner if it is known that the oil has been unintentionally exposed to reactive gases. All pumps should be either vented into a hood or trapped. Vent lines may be Tygon, rubber, or copper. If Tygon or rubber lines are used, they should be supported so that they do not sag and cause a trap for condensed liquids. (See Chapter 7, section 7.C.2, for details.)

When potentially explosive materials are being handled, the area should be posted with a sign such as

WARNING: VACATE THE AREA AT THE FIRST INDICATION OF [the indicator for the specific case] AND STAY OUT.

CALL [responsible person] AT [phone number].

When condensing explosive gases, the temperature of the bath and the effect on the reactant gas of the condensing material selected must be determined experimentally (see Chapter 7, section 7.D). Very small quantities should be used because explosions may occur. A taped and shielded Dewar flask should always be used when condensing reactants. Maximum quantity limits should be observed. A dry-ice solvent bath is not recommended for reactive gases; liquid nitrogen is recommended. (See also Chapter 4, section 4.D.3.1.)

6.G.3. Organic Peroxides

Organic peroxides are a special class of compounds with unusually low stability that makes them among the most hazardous substances commonly handled in laboratories, especially as initiators for free-radical reactions. Although they are low-power explosives, they are hazardous because of their extreme sensitivity to shock, sparks, and other forms of accidental detonation. Many peroxides that are used routinely in laboratories are far more sensitive to shock than most primary explosives (e.g., TNT), although many have been stabilized by the addition of compounds that inhibit reaction. Nevertheless, even low rates of decomposition may automatically accelerate and cause a violent explosion, especially in bulk quantities of peroxides (e.g., benzoyl peroxide). These compounds are sensitive to heat, friction, impact, and light, as well as to strong oxidizing and reducing agents. All organic peroxides are highly flammable, and fires involving bulk quantities of peroxides should be approached with extreme caution.

Precautions for handling peroxides include the following:

  • Limit the quantity of peroxide to the minimum amount required. Do not return unused peroxide to the container.
  • Clean up all spills immediately. Solutions of peroxides can be absorbed on vermiculite or other absorbing material and disposed of harmlessly according to institutional procedures.
  • Reduce the sensitivity of most peroxides to shock and heat by dilution with inert solvents, such as aliphatic hydrocarbons. However, do not use aromatics (such as toluene), which are known to induce the decomposition of diacyl peroxides.
  • Do not use solutions of peroxides in volatile solvents under conditions in which the solvent might vaporize because this will increase the peroxide concentration in the solution.
  • Do not use metal spatulas to handle peroxides because contamination by metals can lead to explosive decomposition. Magnetic stirring bars can unintentionally introduce iron, which can initiate an explosive reaction of peroxides. Ceramic, Teflon, or wooden spatulas and stirring blades may be used if it is known that the material is not shock sensitive.
  • Do not permit open flames and other sources of heat near peroxides. It is important to label areas that contain peroxides so that this hazard is evident.
  • Avoid friction, grinding, and all forms of impact near peroxides, especially solid peroxides. Glass containers that have screw-cap lids or glass stoppers should not be used. Polyethylene bottles that have screw-cap lids may be used.
  • To minimize the rate of decomposition, store peroxides at the lowest possible temperature consistent with their solubility or freezing point. Do not store liquid peroxides or solutions at or lower than the temperature at which the peroxide freezes or precipitates because peroxides in these forms are extremely sensitive to shock and heat.

6.G.3.1. Peroxidizable Compounds

Certain common laboratory chemicals form peroxides on exposure to oxygen in air. Over time, some chemicals continue to build peroxides to potentially dangerous levels, whereas others accumulate a relatively low equilibrium concentration of peroxide, which becomes dangerous only after being concentrated by evaporation or distillation. The peroxide becomes concentrated because it is less volatile than the parent chemical.

Excluding oxygen by storing potential peroxide formers under an inert atmosphere (N2 or argon) greatly increases their safe storage lifetime. Purchasing the chemical stored under nitrogen in septum-capped bottles is also possible. In some cases, stabilizers or inhibitors (free-radical scavengers that terminate the chain reaction) are added to the liquid to extend its storage lifetime. Because distillation of the stabilized liquid removes the stabilizer, the distillate must be stored with care and monitored for peroxide formation. Furthermore, high-performance liquid chromatography-grade solvents generally contain no stabilizer, and the same considerations apply to their handling.

  • If a container of Class B and C peroxidizables (see Chapter 4, Table 4.8 and section 4.D.3.2) is past its expiration date, and there is a risk that peroxides may be present, open it with caution and dispose of it according to institutional procedures (see section 6.G.3.3). If a container of a Class A peroxidizable is past its expiration date, or if the presence of peroxides is suspected or proven, do not attempt to open the container. Because of their explosivity, these compounds can be deadly when peroxidized, and the act of unscrewing a cap or dropping a bottle can be enough to trigger an explosion. Such containers should only be handled by experts. Contact your organization's safety personnel for assistance.
  • Test for the presence of peroxides if there is a reasonable likelihood of their presence and the expiration date has not passed (see section 6.G.3.2).

6.G.3.2. Peroxide Detection Tests

Warning: Do not test Class A peroxidizables suspected of or known to contain peroxides. Contact your safety coordinator.

The following tests detect most (but not all) peroxy compounds, including all hydroperoxides:

  • Peroxide test strips, which turn to an indicative color in the presence of peroxides, are available commercially. Note that these strips must be air dried until the solvent evaporates and exposed to moisture for proper indication and quantification.
  • Add 1 to 3 mL of the liquid to be tested to an equal volume of acetic acid, add a few drops of 5% aqueous potassium iodide solution, and shake. The appearance of a yellow to brown color indicates the presence of peroxides. Alternatively, addition of 1 mL of a freshly prepared 10% solution of potassium iodide to 10 mL of an organic liquid in a 25-mL glass cylinder produces a yellow color if peroxides are present.
  • Add 0.5 mL of the liquid to be tested to a mixture of 1 mL of 10% aqueous potassium iodide solution and 0.5 mL of dilute hydrochloric acid to which has been added a few drops of starch solution just prior to the test. The appearance of a blue or blue-black color within 1 minute indicates the presence of peroxides.

None of these tests should be applied to materials (such as metallic potassium) that may be contaminated with inorganic peroxides.

6.G.3.3. Disposal of Peroxides

Check with state and federal environmental agencies before attempting to treat any chemical for the purpose of disposal without a permit. Pure peroxides should never be disposed of directly but must be diluted before disposal. Small quantities (≤25 g) of peroxides are generally disposed of by dilution with water to a concentration of 2% or less, after which the solution is transferred to a polyethylene bottle containing an aqueous solution of a reducing agent, such as ferrous sulfate or sodium bisulfite. The material can then be handled as a waste chemical; however, it must not be mixed with other chemicals for disposal. Spilled peroxides should be absorbed on vermiculite or other absorbent as quickly as possible. The vermiculite–peroxide mixture can be burned directly or may be stirred with a suitable solvent to form a slurry that can be handled according to institutional procedures. Organic peroxides should never be flushed down the drain.

Large quantities (>25 g) of peroxides require special handling and should only be disposed of by an expert or a bomb squad. Each case should be considered separately, and handling, storage, and disposal procedures should be determined by the physical and chemical properties of the particular peroxide [see also Hamstead (1964)].

Peroxidized solvents such as tetrahydrofuran (THF), diethyl ether, and 1,4-dioxane may be disposed of in the same manner as the nonautoxidized solvent. Care should be taken to ensure that the peroxidized solvent is not allowed to evaporate and thus concentrate the peroxide during handling and transport.

(Also see Chapter 4, section 4.D.3.2.)

6.G.4. Explosive Gases and Liquefied Gases

Rapid evaporation of liquefied gases may present a serious hazard. Liquid oxygen, in particular, may introduce extreme risk due to the combined hazard of rapid overpressurization or volume expansion and the high concentration of a potent oxidizer. Liquefied air is almost as dangerous as liquid oxygen because the nitrogen boils away, leaving an increasing concentration of oxygen. Other cryogenic liquids, such as nitrogen and helium, if they have been open to air, may have absorbed and condensed enough atmospheric oxygen to be very hazardous. When a liquefied gas is used in a closed system, pressure may build up, so that adequate venting is required. Relief devices are required to prevent this dangerous buildup of pressure. If the liquid or vapor is flammable (e.g., hydrogen), explosive concentrations in air may develop. Because flammability, toxicity, and pressure buildup may become serious when gases are exposed to heat, gases should be stored only in specifically designed and designated areas (see Chapter 9, section 9.C.3.7).

6.G.5. Hydrogenation Reactions

Hydrogenation reactions pose additional risks because they are often carried out under pressure with a reactive catalyst. Hydrogenarions conducted at atmospheric pressure at some point require the use of a pressurized cylinder unless the hydrogen is generated chemically (e.g., NaBH4) as needed. Take all precautions for the gas cylinders and flammable gases, plus the additional precautions for reactions at pressures greater than 1 atm. The following precautions are applicable:

  • Choose a pressure vessel appropriate for the experiment, such as an autoclave or pressure bottle. For example, most preparative hydrogenarions of substances such as alkenes are carried out safely in a commercial hydrogenation apparatus using a heterogeneous catalyst (e.g., platinum and palladium) under moderate (<80 psi H2) pressure.
  • Review the operating procedures for the apparatus, and inspect the container before each experiment. Glass reaction vessels with scratches or chips are at risk to break under pressure; impaired vessels should not be used.
  • Never fill the vessel to capacity with the solution; filling it half full (or less) is much safer.
  • Remove as much oxygen from the solution as possible before adding hydrogen. This is one of the most important precautions to be taken with any reaction involving hydrogen. Failure to do this could result in an explosive oxygen-hydrogen (O2–H2) mixture. Normally, the oxygen in the vessel is removed by pressurizing the vessel with inert gas (N2 or argon), followed by venting the gas. If available, a vacuum can be applied to the solution. Repeat this procedure of filling with inert gas and venting several times before hydrogen or other high-pressure gas is introduced.
  • Stay well below the rated safe-pressure limit of the bottle or autoclave; a margin of safety is needed if heat or gas is generated. A limit of 75% of the rating in a high-pressure autoclave is advisable. If this limit is exceeded accidentally, replace the rupture disk on completion of the experiment.
  • Monitor the pressure of the high-pressure device periodically as the heating proceeds, to avoid excessive pressure.
  • Purge the system of hydrogen by repeated rinsing with inert gas at the end of an experiment to avoid producing hydrogen-oxygen mixtures in the presence of the catalyst during workup. Handle catalyst that has been used in a reaction with special care because it can be a source of spontaneous ignition on contact with air.

(Also see section 6.C.)

6.G.6. Materials Requiring Special Attention Because of Toxicity, Reactivity, Explosivity, or Chemical Incompatibility

The following list is not intended to be all-inclusive. Further guidance on reactive and explosive materials should be sought from pertinent sections of this book (see Chapter 4, sections 4.D.2 and 4.D.3) and other sources of information (note sources included in Chapter 4, section 4.B.6).

Acetylenic compounds, both organic and inorganic (especially heavy metal salts), can be explosive and shock sensitive. At pressures of 2 atm or greater and moderate temperature, acetylene (C2H2) has been reported to decompose explosively, even in the absence of air. Because of these dangers, acetylene must be handled in acetone solution and never stored alone in a cylinder.

Alkyllithium compounds are highly reactive and pyrophoric. Violent reactions may occur on exposure to water, carbon dioxide, and other materials. Alkyllithium compounds are highly corrosive to the skin and eyes. tert-Butyllithium solutions are the most pyrophoric and may ignite spontaneously on exposure to air. Contact with water or moist materials can lead to fires and explosions. These compounds should be stored and handled under an inert atmosphere in areas that are free from ignition sources. Detailed information about handling of organolithium compounds is provided by Schwindeman et al. (2002).

Aluminum chloride (AlCl3) should be considered a potentially dangerous material. If moisture is present, sufficient decomposition may form hydrogen chloride (HCl) and build up considerable pressure. If a bottle is to be opened after long storage, it should first be completely enclosed in a heavy towel.

Ammonia and amines. Ammonia (NH3) reacts with iodine to give nitrogen triiodide, which explodes on touch. Ammonia reacts with hypochlorites (bleach) to give chlorine. Mixtures of ammonia and organic halides sometimes react violently when heated under pressure. Ammonia is combustible. Inhalation of concentrated fumes can be fatal. Ammonia and amines can react with heavy metal salts to produce explosive fulminates.

Azides, both organic and inorganic, and some azo compounds can be heat and shock sensitive. Azides such as sodium azide can displace halide from chlorinated hydrocarbons such as dichloromethane to form highly explosive organic polyazides; this substitution reaction is facilitated in solvents such as dimethyl sulfoxide.

Boron halides are powerful Lewis acids and hydrolyze to strong protonic acids.

Carbon disulfide (CS2) is both very toxic and very flammable; mixed with air, its vapors can be ignited by a steam bath or pipe, a hot plate, or a lightbulb.

Chlorine (Cl2) is highly toxic and may react violently with hydrogen (H2) or with hydrocarbons when exposed to sunlight.

Diazomethane (CH2N2) and related diazo compounds should be treated with extreme caution. They are very toxic, and the pure gases and liquids explode readily even from contact with sharp edges of glass. Solutions in ether are safer from this standpoint. An ether solution of diazomethane is rendered harmless by dropwise addition of acetic acid.

Diethyl and other ethers, including tetrahydrofuran and 1,4-dioxane and particularly the branched-chain type of ethers, may contain peroxides that have developed from air autoxidation. Concentration of these peroxides during distillation may lead to explosion. Ferrous salts or sodium bisulfite can be used to decompose these peroxides, and passage over basic active alumina can remove most of the peroxidic material. In general, however, dispose of old samples of ethers if they test positive test for peroxide.

Diisopropyl ether is a notoriously dangerous, Class A (see Chapter 4, Table 4.8 and section 4.D.3.2) peroxide former. The peroxide is not completely soluble in the mother liquor. Peroxide concentrations from autoxidation may form saturated solutions that then crystallize the peroxide as it is being formed. There are numerous reports of old bottles of diisopropyl ether being found with large masses of crystals settled at the bottom of the bottle. These crystals are extremely shock sensitive, even while wetted with the diisopropyl ether supernatant. Mild shock (e.g., bottle breakage, removing the bottle cap) is sufficient to result in explosion. This ether should not be stored in the laboratory. Only the amount required for a particular experiment or process should be purchased; any leftover material should be disposed of immediately.

Dimethyl sulfoxide (DMSO), (CH3)2SO, decomposes violently on contact with a wide variety of active halogen compounds, such as acyl chlorides. Explosions from contact with active metal hydrides have been reported. DMSO does penetrate and carry dissolved substances through the skin membrane.

Dry benzoyl peroxide (C6H5CO2)2 is easily ignited and sensitive to shock. It decomposes spontaneously at temperatures greater than 50 °C. It is reported to be desensitized by addition of 20% water.

Dry ice should not be kept in a container that is not designed to withstand pressure. Containers of other substances stored over dry ice for extended periods generally absorb carbon dioxide (CO2) unless they have been carefully sealed. When such containers are removed from storage and allowed to come rapidly to room temperature, the CO2 may develop sufficient pressure to burst the container with explosive violence. On removal of such containers from storage, the stopper should be loosened or the container itself should be wrapped in towels and kept behind a shield. Dry ice can produce serious burns, as is also true for all types of dry-ice cooling baths.

Drying agents, such as Ascarite® (sodium hydroxide-coated silica), should not be mixed with phosphorus pentoxide (P2Os) because the mixture may explode if it is warmed with a trace of water. Because the cobalt salts used as moisture indicators in some drying agents may be extracted by some organic solvents, the use of these drying agents should be restricted to drying gases.

Dusts that are suspensions of oxidizable particles (e.g., magnesium powder, zinc dust, carbon powder, and flowers of sulfur) in the air can constitute powerful explosive mixtures. These materials should be used with adequate ventilation and should not be exposed to ignition sources. When finely divided, some solids, including zirconium, titanium, Raney nickel, lead (such as prepared by pyrolysis of lead tartrate), and catalysts (such as activated carbon containing active metals and hydrogen), can combust spontaneously if allowed to dry while exposed to air and should be handled wet.

Ethylene oxide (C2H4O) has been known to explode when heated in a closed vessel. Experiments using ethylene oxide under pressure should be carried out behind suitable barricades.

Fluorine (F2) is an extremely toxic reactive oxidizing gas with extremely low permissible exposure levels. Only trained personnel should be authorized to work with fluorine. (See Vignette 6.4.) Anyone planning to work with fluorine must be knowledgeable of proper first-aid treatment and have the necessary supplies on hand before beginning.

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Vignette 6.4

Fluorine inhalation. A graduate student was filling the chamber of an excimer laser with fluorine gas. The gas was connected to the laser with copper tubing. Over the course of 1 hour, the student noticed the chamber was not filling even though the gas (more...)

Halogenated compounds, such as chloroform (CHCl3), carbon tetrachloride (CCl4), and other halogenated solvents, should not be dried with sodium, potassium, or other active metals; violent explosions usually result. Many halogenated compounds are toxic. Oxidized halogen compounds—chlorates, chlorites, bromates, and iodates—and the corresponding peroxy compounds may be explosive at high temperatures.

Hydrogen fluoride and hydrogen fluoride generators. Anhydrous HF or hydrogen fluoride is a colorless liquid that boils at 19.5 °C. It has a pungent irritating odor, and a time-weighted average exposure of 3 ppm for routine work. Aqueous HF is a colorless very corrosive liquid that fumes at concentrations greater than 48%. It attacks glass, concrete, and some metals, especially cast iron and alloys containing silica as well as organic materials such as leather, natural rubber, wood, and human tissue. Although HF is nonflammable, its corrosive action on metals can result in the formation of hydrogen in containers and piping, creating a fire and explosion hazard. HF should be stored in tightly closed polyethylene containers. HF attacks glass and therefore should never be stored in a glass container. Containers of HF may be hazardous when empty because they retain product residues. HF and related materials (e.g., NaF, SF4, acyl fluorides) capable of generating HF upon exposure to acids, water, or moisture are of major concern because of their potential for causing serious burns.

HF causes severe injury via skin and eye contact, inhalation, and ingestion. It is very aggressive physiologically because the fluoride ion readily penetrates the skin and may cause decalcification of the bones and systemic toxicity, including pulmonary edema, cardiac arrhythmia and death. Burns from HF may not be painful or visible for several hours and even moderate exposure to concentrated HF can result in fatality. Unlike other acids which are rapidly neutralized, this process may continue for days if left untreated.

Strong HF acid concentrations (over 50%), particularly anhydrous HF, cause immediate, severe, burning pain and a whitish discoloration of the skin that usually proceeds to blister formation. In contrast to the immediate effects of concentrated HF, the onset of effects of contact with more dilute solutions or their vapors may be delayed. Skin contact with acid concentrations in the 20% to 50% range may not produce clinical signs or symptoms for 1 to 8 hours. With concentrations less than 20%, the latent period may be up to 24 hours. The usual initial signs of a dilute solution HF burn are redness, swelling, and blistering, accompanied by severe throbbing pain. Burns larger than 25 in.2 (160 cm2) may result in serious systemic toxicity.

When exposed to air, concentrated solutions and anhydrous HF produce pungent fumes which are especially dangerous. Acute symptoms of inhalation of HF include coughing, choking, chest tightness, chills, fever, and cyanosis (blue lips and skin). All individuals suspected of having inhaled HF should seek medical attention and observation for pulmonary effects. This includes any individuals with HF exposure to the head, chest, or neck areas. HF exposures require immediate and specialized first aid and medical treatment.

For skin exposure:

  1. Immediately start rinsing under safety shower or other water source and flush affected area thoroughly with large amounts of water, removing contaminated clothing while rinsing. Speed and thoroughness in washing off the acid is of primary importance.
  2. Call for emergency response.
  3. While wearing neoprene or butyl rubber gloves to avoid a secondary HF burn, massage 2.5% (w/w) calcium gluconate gel onto the affected area after 5 minutes of flushing with water. If calcium gluconate gel is unavailable, continue flushing the exposed areas with water until medical assistance arrives.
  4. Send a copy of the MSDS with the victim.

For eye exposure:

  1. Immediately flush the eyes, holding eyelids open, for at least 15 minutes with large amounts of gently flowing water, preferably using an eyewash station.
  2. Do not apply calcium gluconate gel directly onto the eye.
  3. Seek medical attention.
  4. Send a copy of the MSDS with the victim.

For inhalation:

  1. Immediately move to fresh air.
  2. Call emergency responders.
  3. Send a copy of the MSDS with the victim.

For ingestion:

  1. Ingestion of HF is a life-threatening emergency. Seek immediate medical attention.
  2. Drink large amounts of water or milk as quickly as possible to dilute the acid.
  3. Do not induce vomiting. Do not ingest emetics or baking soda. Never give anything by mouth to an unconscious person.
  4. If medical attention must be delayed and the materials are available, drink several ounces of milk of magnesia or other antacids.
  5. Send a copy of the MSDS with the victim.

Laboratory personnel should be trained in first-aid procedures for HF exposure before beginning work. Calcium gluconate gel (2.5% w/w) must be readily accessible in work areas where any potential HF exposure exists. Check the expiration date of your supply of commercially obtained calcium gluconate gel and reorder as needed to ensure a supply of fresh stock. Note that homemade calcium gluconate gel has a shelf life of approximately 4 months.

There are a number of ways to prevent HF exposure:

  • Only use HF when necessary. Consider substitution of a less hazardous substance whenever possible.
  • Establish written standard operating procedures for work with HF.
  • Ensure that all workers in a lab where HF is used are informed about the hazards and first-aid procedures involved.
  • Only use HF in a chemical hood.
  • Depending on the concentration used, workers should wear butyl rubber, neoprene, 4H® or Silvershield® gloves. Protective lab coats or aprons are also recommended.
  • At a minimum, workers should wear chemical splash goggles when working with HF. A face shield is also recommended when there is a significant splash hazard.

Hydrogen peroxide (H2O2) stronger than 3% can be dangerous; in contact with skin, it causes severe burns. Thirty percent H2O2 may decompose violently if contaminated with iron, copper, chromium, or other metals or their salts. Stirring bars may inadvertently bring metal into a reaction and should be used with caution.

Liquid nitrogen–cooled traps open to the atmosphere condense liquid air rapidly. When the coolant is removed, an explosive pressure buildup occurs, usually with enough force to shatter glass equipment if the system has been closed. Hence, only sealed or evacuated equipment should be so cooled. Vacuum traps must not be left under static vacuum; liquid nitrogen in Dewar flasks must be removed from these traps when the vacuum pumps are turned off.

Lithium aluminum hydride (LiAlH4) should not be used as a drying agent for solvents that are hygroscopic and may contain high concentrations of water, such as methyl ethers and tetrahydrofuran; fires from reaction with damp ethers are often observed. Predrying these solvents with a less efficient drying agent, followed by LiAlH4 treatment is recommended. The reaction of LiAlH4 with carbon dioxide has reportedly generated explosive products. Carbon dioxide or bicarbonate extinguishers should not be used for LiAlH4 fires; instead, such fires should be smothered with sand or some other inert substance.

Nitric acid is a strong acid, very corrosive, and decomposes to produce nitrogen oxides. The fumes are very irritating, and inhalation may cause pulmonary edema. Nitric acid is also a powerful oxidant and reacts violently, sometimes explosively reducing agents (e.g., organic compounds) with liberation of toxic nitrogen oxides. Contact with organic matter must be avoided. Extreme caution must be taken when cleaning glassware contaminated with organic solvents or material with nitric acid. Toxic fumes of NOx are generated and explosion may occur.

Nitrate, nitro, and nitroso compounds may be explosive, especially if more than one of these groups is present in the molecule. Alcohols and polyols may form highly explosive nitrate esters (e.g., nitroglycerine) from reaction with nitric acid.

Organometallics may be hazardous because some organometallic compounds burn vigorously on contact with air or moisture. For example, solutions of tert-butyllithium ignite some organic solvents on exposure to air. The pertinent information should be obtained for a specific compound.

Oxygen tanks should be handled with care because serious explosions have resulted from contact between oil and high-pressure oxygen. Oil or grease should not be used on connections to an O2 cylinder or gas line carrying O2.

Ozone (O3) is a highly reactive toxic gas. It is formed by the action of ultraviolet light on oxygen (air), and therefore certain ultraviolet sources may require venting to the exhaust hood. Ozonides can be explosive.

Palladium (Pd) or platinum (Pt) on carbon, platinum oxide, Raney nickel, and other catalysts presents the danger of explosion if additional catalyst is added to a flask in which an air-flammable vapor mixture or hydrogen is present. The use of flammable filter paper should be avoided.

Perchlorates should be avoided whenever possible. Perchlorate salts of organic, organometallic, and inorganic cations are potentially explosive and may detonate by heat or shock. Whenever possible, perchlorate should be replaced with safer anions such as fluoroborate, fluorophosphates, and trifluoromethanesulfonate (triflate).

Perchlorates should not be used as drying agents if there is a possibility of contact with organic compounds or of proximity to a dehydrating acid strong enough to concentrate the perchloric acid (HClO4) (e.g., in a drying train that has a bubble counter containing sulfuric acid). Safer drying agents should be used.

Seventy percent HClO4 boils safely at approximately 200 °C, but contact of the boiling undiluted acid or the hot vapor with organic matter, or even easily oxidized inorganic matter, leads to serious explosions. Oxidizable substances must never be allowed to contact HClO4. This includes wooden benchtops or laboratory chemical hood enclosures, which may become highly flammable after absorbing HClO4 liquid or vapors. Beaker tongs, rather than rubber gloves, should be used when handling fuming HClO4. Perchloric acid evaporations should be carried out in a chemical hood that has a good draft.

The hood and ventilator ducts should be washed with water frequently (weekly; but see also Chapter 9, section 9.C.2.10.5) to avoid danger of spontaneous combustion or explosion if this acid is in common use. Special HClO4 hoods are available from many manufacturers. Disassembly of such chemical hoods must be preceded by washing the ventilation system to remove deposited perchlorates.

Permanganates are explosive when treated with sulfuric acid. If both compounds are used in an absorption train, an empty trap should be placed between them and monitored for entrapment.

Peroxides (inorganic) should be handled carefully. When mixed with combustible materials, barium, sodium, and potassium peroxides form explosives that ignite easily.

Phenol is a corrosive and moderately toxic substance that affects the central nervous system and can cause damage to the liver and kidneys. Phenol-formaldehyde reactions are used in creation of phenolic resins, and can be highly exothermic. These reactions have been implicated in a number of plant-scale accidents when runaway reactions caused a sudden rise in pressure and rupturing of pressure disks or vessels (Urben and Bretherick, 1999). Care should be taken if performing such reactions in the laboratory.

Phenol is readily absorbed through the skin and can cause severe burns to the skin and eyes. Phenol is irritating to the skin, but has a local anesthetic effect, so that no pain may be felt on initial contact. A whitening of the area of contact generally occurs and severe burns may develop hours after exposure. Exposure to phenol vapor can cause severe irritation of the eyes, nose, throat, and respiratory tract. In the event of skin exposure to phenol, do not immediately rinse the site with water. Instead, treat the site with low-molecular-weight poly(ethylene glycol) (PEG) such as PEG 300 or PEG 400. This will safely deactivate phenol. Irrigate the site with PEG for at least 15 minutes or until there is no detectable odor of phenol.

Phosphorus (P) (red and white) forms explosive mixtures with oxidizing agents. White phosphorus should be stored underwater because it ignites spontaneously in air. The reaction of phosphorus with aqueous hydroxides gives phosphine, which is toxic and also may either ignite spontaneously or explode in air.

Phosphorus trichloride (PCl3) reacts with water to form phosphorous acid with HCl evolution; the phosphorous acid decomposes on heating to form phosphine, which may either ignite spontaneously or explode. Care should be taken in opening containers of PCl3, and samples that have been exposed to moisture should not be heated without adequate shielding to protect the operator.

Piranha solution is a mixture of concentrated sulfuric acid and 30% hydrogen peroxide. It is a powerful oxidant and strong acid used to remove organic residues from various surfaces. Many instances of explosions have been reported with this solution upon contact with reducing agents, especially organics. The solution slowly evolves oxygen, and therefore containers must be vented at all times.

Potassium (K) is much more reactive than sodium; it ignites quickly on exposure to humid air, and therefore should be handled under the surface of a hydrocarbon solvent such as mineral oil or toluene (see Sodium, below). Potassium can form a crust of the superoxide (KO2) or the hydrated hydroxide (KOH·H2O) on contact with air. If this happens, the act of cutting a surface crust off the metal or of melting the encrusted metal can cause a severe explosion due to oxidation of the organic oil or solvent by superoxide, or from reaction of the potassium with water liberated from the hydrated hydroxide (Yarnell, 2002).

Residues from vacuum distillations have been known to explode when the still was vented suddenly to the air before the residue was cool. To avoid such explosions, vent the still pot with nitrogen, cool it before venting, or restore pressure slowly. Sudden venting may produce a shock wave that explodes sensitive materials.

Sodium (Na) should be stored in a closed container under kerosene, toluene, or mineral oil. Scraps of sodium or potassium should be destroyed by reaction with n-butyl alcohol. Contact with water should be avoided because sodium reacts violently with water to form hydrogen (H2) with evolution of sufficient heat to cause ignition. Carbon dioxide, bicarbonate, and carbon tetrachloride fire extinguishers should not be used on alkali metal fires. Metals such as sodium become more reactive as the surface area of the particles increases. Prudence dictates using the largest particle size consistent with the task at hand. For example, use of sodium balls or cubes is preferable to use of sodium sand for drying solvents.

Sodium amide (NaNH2) can undergo oxidation on exposure to air to give sodium nitrite in a mixture that is unstable and may explode.

Sulfuric acid (H2SO4) should be avoided, if possible, as a drying agent in desiccators. If it must be used, glass beads should be placed in it to help prevent splashing when the desiccator is moved. To dilute H2SO4, the acid should be added slowly to cold water. Addition of water to the denser H2SO4 can cause localized surface boiling and spattering on the operator.

tert-Butyllithium. See Alkyllithium compounds, above.

Trichloroethylene (Cl2CCHCl) reacts under a variety of conditions with potassium or sodium hydroxide to form dichloroacetylene, which ignites spontaneously in air and explodes readily even at dry-ice temperatures. The compound itself is highly toxic, and suitable precautions should be taken when it is used.

6.G.7. Chemical Hazards of Incompatible Chemicals

For each chemical, follow specific storage recommendations in MSDSs and other references with respect to containment and compatibility. Keep incompatibles separate during transport, storage, use, and disposal (see Chapter 4, section 4.D; Chapter 5; and section 6.C). Contact could result in a serious explosion or the formation of substances that are highly toxic or flammable. Store oxidizers, reducing agents, and fuels separately to prevent contact in the event of an accident. Some reagents pose a risk on contact with the atmosphere.

6.H. WORKING WITH COMPRESSED GASES

6.H.1. Chemical Hazards of Compressed Gases

Compressed gases expose laboratory personnel to both chemical and physical hazards. If the gas is flammable, flash points lower than room temperature, compounded by rapid diffusion throughout the laboratory, present the danger of fire or explosion. Additional hazards arise from the reactivity and toxicity of the gas. Asphyxiation can be caused by high concentrations of even inert gases such as nitrogen. An additional risk of simple asphyxiants is head injury from falls due to rapid loss of oxygen to the brain. Death can also occur if oxygen levels remain too low to sustain life. Finally, the large amount of potential energy resulting from the compression of the gas makes a highly compressed gas cylinder a potential rocket or fragmentation bomb.

Monitoring for leaks and proper labeling are essential for the prudent use of compressed gases. If relatively small amounts are needed, consider on-site chemical gas generation as an alternative to compressed gas. Reduce risks by monitoring compressed gas inventories and disposing of or returning gases for which there is no immediate need. The equipment required for the safe use of compressed gases is discussed in Chapter 7, section 7.D.

6.H.2. Specific Chemical Hazards of Select Gases

Workers are advised to consult LCSSs and MSDSs for specific gases. Certain hazardous substances that may be supplied as compressed gases are listed below:

Boron trifluoride and boron trichloride (BF3 and BCl3, respectively) react with water to give HF and HCl, respectively. Their fumes are corrosive, toxic, and irritating to the eyes and mucous membranes.

Chlorine trifluoride (ClF3) in liquid form is corrosive and very toxic. It is a potential source of explosion and causes deep penetrating burns on contact with the body. The effect may be delayed and progressive, as in the case of burns caused by hydrogen fluoride.

Chlorine trifluoride reacts vigorously with water and most oxidizable substances at room temperature, frequently with immediate ignition. It reacts with most metals and metal oxides at elevated temperatures. In addition, it reacts with silicon-containing compounds and thus can support the continued combustion of glass, asbestos, and other such materials. Chlorine trifluoride forms explosive mixtures with water vapor, ammonia, hydrogen, and most organic vapors. The substance resembles elemental fluorine in many of its chemical properties and handling procedures, which include precautionary steps to prevent accidents.

Hydrogen selenide (H2Se) is a colorless gas with an offensive odor. It is a dangerous fire and explosion risk and reacts violently with oxidizing materials. Hydrogen selenide is an irritant to eyes, mucous membranes, and the pulmonary system. Acute exposures can cause symptoms such as pulmonary edema, severe bronchitis, and bronchial pneumonia. Symptoms also include gastrointestinal distress, dizziness, increased fatigue, and a metallic taste in the mouth.

Hydrogen sulfide (H2S) is a highly toxic and flammable gas. Although it has a characteristic odor of rotten eggs, it fatigues the sense of smell. This could result in failure to notice the seriousness of the situation before health becomes at risk and is problematic for rescuers who think danger has passed when the odor disappears.

Methyl chloride (CH3Cl) has a slight, not unpleasant, odor that is not irritating and may pass unnoticed unless a warning agent has been added. Exposure to excessive concentrations is indicated by symptoms similar to those of alcohol intoxication, that is, drowsiness, mental confusion, nausea, and possibly vomiting. Methyl chloride may, under certain conditions, react with aluminum or magnesium to form materials that ignite or fume spontaneously with air, and contact with these metals should be avoided.

Phosphine (PH3) is a spontaneously flammable and explosive poisonous colorless gas with the foul odor of decaying fish. The liquid can cause frostbite. Phosphine is a dangerous fire hazard and ignites in the presence of air and oxidizers. It reacts with water, acids, and halogens. If heated, it forms hydrogen phosphides, which are explosive and toxic. There may be a delay between exposure and the appearance of symptoms.

Silane (SiH4) is a pyrophoric colorless gas that ignites spontaneously in air. It is incompatible with water, bases, oxidizers, and halogens. The gas has a choking repulsive odor.

Silyl halides are toxic colorless gases with a pungent odor. They are corrosive irritants to the skin, eyes, and mucous membranes. When silyl halides are heated, toxic fumes can be emitted.

6.I. WORKING WITH MICROWAVE OVENS

Do not use domestic microwave ovens for laboratory work. Metal-based or volatile, flammable, and explosive compounds pose a significant hazard when used in a domestic microwave oven. Domestic microwave ovens do not provide mechanisms for monitoring temperature and pressure and contain no safeguards against explosion. Instead, use an industrial grade instrument (equipped with explosion-proof chambers, exhaust lines, and temperature and pressure monitors) suitable for such experiments.

Although industrial ovens may reduce the risk of such hazards, significant caution is required in their use. In general, the use of closed vessels should be avoided. Any reactions conducted in a microwave oven should be regarded with the same caution as those conducted with highly reactive and explosive chemicals. Reactions should use the smallest scale possible to determine the potential for explosions and fires (refer to sections 6.F and 6.G). Precautions should be taken for proper ventilation and potential explosion. (See Chapter 7, section 7.C.5.7 for more information about the use of microwave ovens in laboratories.)

6.J. WORKING WITH NANOPARTICLES

6.J.1. Controls for Research and Development Laboratory Operations That Utilize or Synthesize Nanomaterials

Nanoparticles are dispersible particles between 1 and 100 nm in size that may or may not exhibit a size-related intensive property. The U.S. Department of Energy (DOE, 2008,2009) states that engineered nanomaterials are intentionally created (in contrast with natural or incidentally formed) and engineered to be between 1 and 100 nm. This definition excludes biomolecules (proteins, nucleic acids, and carbohydrates).

Nanoparticles and nanomaterials have different reactivities and interactions with biological systems than bulk materials, and understanding and exploiting these differences is an active area of research. However, these differences also mean that the risks and hazards associated with exposure to engineered nanomaterials are not well known. At the time this book was written, NIOSH had only defined occupational exposure limits for one nanomaterial, titanium dioxide. Until material-specific guidance can be issued, NIOSH, DOE, the British Standards Institute, and others have issued general guidelines for management of engineered nanomaterials. The procedures outlined here are based on those guidelines, which were developed from accepted chemical hygiene protocols for handling compounds of unknown toxicity.

Because this is an area of ongoing research, consult trusted sources to ensure that the methods described here are not obsolete, and check for any applicable material-specific guidance. Sources include

  • Approaches to Safe Nanotechnology: Managing the Health and Safety Concerns Associated with Engineered Nanomaterials (HHS/CDC/NIOSH, 2009a), and the NIOSH nanotechnology topic Web page, www.cdc.gov/niosh;
  • Nanoscale Science Research Centers: Approach to Nanomaterial ES&H (DOE, 2008);
  • ASTM E 2535-07: Standard Guide for Handling Unbound Engineered Nanoscale Particles in Occupational Settings (ASTM International, 2007b);
  • the National Nanotechnology Initiative, www.nano.gov; and
  • the United Kingdom's Health and Safety Executive Web site, at www.hse.gov.uk.

6.J.1.1. Nanomaterial Work Planning and Hazard Assessment

Before beginning any work with or intended to produce nanomaterials, perform a safety assessment for the laboratory. Involve the organization's EHS personnel in the process, and consult subject-matter experts as needed. The assessment should

  • include a well-defined description of the work;
  • identify the state of the nanomaterials at each stage of the work (i.e., dry and dispersible, in a slurry or solution, affixed to a matrix, or embedded in a solid);
  • identify recognized and suspected hazards and uncertainties, both biological and physical, at each stage;
  • specify hazard controls including

    engineering controls,

    identification of appropriate PPE,

    training plans for laboratory personnel,

    emergency procedures, including spill or release response,

    experimental design elements to minimize risk of exposure, and

    any other administrative controls;

  • evaluate the potential for generating new nanomaterial-bearing waste streams and define waste management protocols for these streams; and
  • consider the potential for reactions involving nanomaterials or other incompatible materials already captured in exhaust air filters.

When developing controls for the nanomaterials, consider, but do not unquestioningly rely on, chemical hazard information for bulk or raw materials and any new information specific to the material at the scale being used. When evaluating the hazards and uncertainties for the materials, consider the recognized and foreseeable hazards of the precursor materials and intermediates as well as those of the resulting nanomaterials. Note that the higher reactivity of many nanoscale materials suggests that they should be treated as potential sources of ignition, accelerants, and fuel that could result in fire or explosion.

The risk of exposure may continue after laboratory work has been completed if, for example, a laboratory chemical hood was used to house a reaction. Before removing, remodeling, servicing, maintaining, or repairing laboratory equipment and exhaust systems, evaluate the potential for trained laboratory personnel's (including laboratory and maintenance workers) exposure to nanomaterials and escape of the materials into the environment.

6.J.1.2. A Graded Approach to Determining Appropriate Nanomaterial Controls

When performing the assessment described above, follow a graded approach in specifying controls. For example, from the perspective of managing the health of laboratory personnel, easily dispersed dry nanomaterials pose the greatest health hazard because of the risk of inhalation, and operations involving these nanomaterials deserve more attention and more stringent controls than those where the nanomaterials are embedded in solid or suspended in liquid matrixes. The list below and Figure 6.1 describe the graded risk posed by the state of the material. Preference should be given to handling materials in the lower risk forms (top of the list).

Arrow and accompanying text showing grades of increasing risk associated with exposure to nanomaterials, going from lower risk (fewer controls required) for nanomaterials embedded in a matrix to higher risk (more controls required) for dry, dispersible nanomaterials.

FIGURE 6.1

U.S. Department of Energy graded exposure risk for nanomaterials. This figure assumes no disruptive force (e.g., sonication, grinding, burning) is applied to the matrix. SOURCE: Adapted from Karn (2008)

  1. solid materials with embedded nanostructures,
  2. solid nanomaterials with nanostructures fixed to the material's surface,
  3. nanoparticles suspended in liquids, and
  4. dry dispersible (engineered) nanoparticles, nanoparticle agglomerates, or nanoparticle aggregates.

Be sure to consider all routes of possible exposure to nanomaterials including inhalation, ingestion, injection, and dermal contact (including eye and mucous membranes). Avoid handling nanomaterials in the open air in a free-particle state. Whenever possible, handle and store dispersible nanomaterials, whether suspended in liquids or in a dry particle form, in closed (tightly sealed) containers. Unless cutting or grinding occurs, nanomaterials that are not in a free form (encapsulated in a solid or a nanocomposite) typically will not require engineering controls. If a synthesis is being performed to create nanomaterials, it is not enough to only consider the final material in the risk assessment. Consider the hazardous properties of the precursor materials as well as those of the resulting nanomaterial product.

6.J.1.3. Engineering Controls for Nanomaterials Research

6.J.1.3.1. Work Area Design

When evaluating the work area, consider the need for additional engineering or procedural controls to ensure trained laboratory personnel are protected in areas where engineered nanoparticles will be handled. Additional controls to ensure that engineered nanoparricles are not brought out of the work area on clothing or other surfaces may be advisable. Examples of possible additional controls include installing step-off pads to trap dust, creating a buffer area around the work zone, and ensuring the availability of decontamination facilities (possibly for daily use) for laboratory personnel.

6.J.1.3.2. Ventilation Preferences

To minimize laboratory personnel exposure, conduct any work that could generate engineered nanoparticles in an enclosure that operates at a negative pressure differential compared to the laboratory personnel breathing zone. Examples of such enclosures include gloveboxes, glovebags, and laboratory benchtop or floor-mounted chemical hoods. Do not use horizontal laminar-flow hoods (clean benches) that direct a flow of HEPA-filtered air into the user's face for operations involving engineered nanomaterials. If the air reactivity of precursor materials may make it unsafe to perform a synthesis in a negative-pressure glovebox, a positive-pressure box may be used if it has passed a helium leak test. If a process (or subset of a process) cannot be enclosed, use other engineering systems to control fugitive emissions of nanomaterials or hazardous precursors that might be released. For example, use a local exhaust system such as a snorkel hood. Laboratory ventilation and exhaust systems should be chosen on the basis of what is known about nanoparticle motion in air. (For more information about ventilation options, see Chapter 9, section 9.E.5.)

Do not exhaust unfiltered effluent (air) that has been demonstrated or strongly suspected to contain engineered nanoparticles to the laboratory. Whenever practical, filter it or otherwise clean (scrub) it before releasing it to the outdoors. Although HEPA filtration appears to effectively remove nanoparticles from air, the filters must be held in well-designed housings. A poorly seated filter can allow nanomaterials to escape through the gaps. If it is not practicable to contain the nanoparticles with such a system, conduct and document the results of a hazard analysis before using alternative hazard controls.

Exhaust the effluent from the ventilated enclosure outside the building whenever feasible. Filters, scrubbers, or bubblers used to treat unreacted precursors appropriately may also be effective in reducing nanomaterial emissions. If using portable benchtop HEPA-filtered units, exhaust them through ventilation systems that carry the effluent outside the building whenever possible.

If it is not feasible to duct HEPA-filtered treated exhaust air outside the building, follow the guidance in ANSI Z9.7-2007, American National Standard for Recirculation of Air from Industrial Process Exhaust Systems, and conduct a hazard assessment to identify appropriate engineering controls. Examples of such controls include periodic air monitoring and an accurate warning or signal capable of initiating corrective action or process shutdown before nanoparticles are exhausted or reenter the work area. If using a Type II biological safety cabinet for work with nanomaterials, consider exhausting directly to the exterior (hard ducted) or through a thimble connection over the cabinet's exhaust.

All exhaust systems should be maintained and tested as specified by the manufacturer. Before beginning any maintenance, however, evaluate equipment for contamination and chemical incompatibilities.

6.J.1.3.3. Clothing and PPE

Minimal data exist regarding the efficacy of PPE against exposure to nanoparticles. However, until further information is available, it is prudent to follow standard chemical hygiene practices. Conduct a hazard evaluation to determine PPE appropriate for the level of hazard according to the requirements set forth in 29 CFR § 1910.132. Protective clothing that would typically be required for a wet-chemistry laboratory would be appropriate and could include but is not limited to

  • closed-toed shoes made of a low-permeability material (disposable over-the-shoe booties may be necessary to prevent tracking nanomaterials from the laboratory);
  • long pants without cuffs;
  • long-sleeved shirt;
  • gauntlet-type gloves or nitrile gloves with extended sleeves; and
  • laboratory coats.

Wear polymer (e.g., nitrile rubber) gloves when handling engineered nanomaterials and particulates in liquids. Choose gloves only after considering the resistance of the glove to chemical attack by both the nanomaterial and, if suspended in liquids, the liquid.

  • Recognize that exposure to nanomaterials is not known to have good warning properties, and change gloves routinely to minimize potential exposure hazards. Alternatively, double glove.
  • Keep contaminated gloves in a plastic bag or other sealed container until disposed of.
  • Dispose of contaminated gloves in accordance with organizational requirements.
  • Wash hands and forearms after wearing gloves.
  • Follow any additional institutional rules regarding nanoparticles, such as proper waste disposal.

Wear eye protection, for example, spectacle-type safety glasses with side shields (meeting basic impact resistance of ANSI Z87.1-2003), face shields, chemical splash goggles, or other safety eyewear appropriate to the type and level of hazard. Do not consider face shields or safety glasses to provide sufficient protection against unbound dry materials that could become airborne.

Contact the organization's EHS professionals for an evaluation of airborne exposures to engineered nanomaterials. If respirators are to be used for protection against engineered nanoparticles, NIOSH-certified respirators should provide the expected levels of protection if properly selected and fit-tested as part of a complete respiratory protection program. Refer to the NIOSH publications Approaches to Safe Nanotechnology (HHS/CDC/NIOSH, 2009a) and Respirator Selection Logic (Bollinger, 2004) for guidance on choosing appropriate air-purifying particulate respirators. These documents are available online at www.cdc.gov/ niosh. If employees are required to wear respirators, consideration must be given to the OSHA regulation 29 CFR § 1910.134.

Keep potentially contaminated clothing and PPE in the laboratory or change-out area to prevent engineered nanoparticles from being transported into common areas.

Clean and dispose of all potentially contaminated clothing and PPE in accordance with the laboratory procedures.

6.J.1.3.4. Monitoring and Characterization

The NIOSH publication Approaches to Safe Nanotechnology (HHS/CDC/NIOSH, 2009a) describes an emission assessment technique that can be used for identification of sources and releases of engineered nanomaterials. The technique includes determining the particle number concentration using direct-reading, handheld particle counters at potential emission sources and comparing those data to background particle number concentrations. If elevated concentrations of suspected nanoparticles are detected at potential emission sources, relative to the background particle number concentrations, then a pair of filter-based, source-specific air samples are collected with one sample analyzed by transmission electron microscopy or scanning electron microscopy-for particle identification and characterization, and the other used for determining the elemental mass concentration.

If resources allow, a more comprehensive and quantitative approach using additional aerosol sampling equipment (such as impactors or diffusion charges) may be performed.

6.J.1.3.5. Housekeeping

Practice good housekeeping in laboratories where nanomaterials are handled. Follow a graded approach paying attention where dispersible nanomaterials are handled. Insofar as practicable, maintain all working surfaces (i.e., benches, glassware, apparatus, laboratory chemical hoods, support equipment) free of engineered nanoparticle contamination and otherwise limit laboratory personnel exposure to engineered nanoparticles and associated hazards. In areas where engineered nanoparticles might settle, perform precautionary cleaning, for example, by wiping horizontal surfaces with a moistened disposable wipe, no less frequently than at the end of each shift or day.

Before selecting a cleaning method, consider the potential for complications due to the physical and chemical properties of the engineered nanoparticles, particularly in the case of larger spills. Complications could include reactions with cleaning materials and other materials in the locations where the waste will be held. Such locations include vacuum cleaner filters and canisters.

Clean up dry engineered nanomaterials using

  • Wet wiping.
  • A dedicated approved HEPA vacuum with verified filtration effectiveness. (Note: Consider possible pyrophoric hazards associated with vacuuming up nanoparticles.) If using the vacuum for multiple types of nanomaterials, keep a log of the materials captured and check for chemical incompatibilities prior to use.
  • Other facility-approved methods that do not involve an energetic cleaning method. Avoid dry sweeping or the use of compressed air, to prevent suspension of particles into the air.

Note that vacuum brushes may generate electrostatic charges that could make cleaning of charged particles difficult. Consider using vacuum cleaners with electrostatic-charge-neutralization features (such as those used for cleaning copier and printer toners.) Again, be sure that the vacuum is exhausted through a properly fitted and maintained HEPA filter.

Clean up spills of liquids containing nanomaterials using absorbent materials. If the size of the spill is large, place absorbent pads at all points of egress from the room to reduce tracking the spill into the other parts of the building. Use plastic sheeting to reduce ventilation in the area of a liquid spill to reduce the chance that it will dry prior to cleanup. As noted above, dry nanomaterials pose a greater hazard than those suspended in liquid.

Dispose of used cleaning materials and wastes in accordance with the laboratory's hazardous waste procedures.

6.J.1.3.6. Work Practices

Evaluate hazards and implement work practices to control potential contamination and exposure hazards, if engineered nanoparticle powders must be handled without the use of exhaust ventilation (i.e., laboratory chemical hood, local exhaust) or enclosures (i.e., glovebox). Take reasonable precautions to minimize the likelihood of skin contact with engineered nanoparticles or nanoparticle-containing materials likely to release nanoparticles (nanostructures). Transfer engineered nanomaterial samples between workstations such as laboratory chemical hoods, gloveboxes, furnaces in closed labeled containers (e.g., marked zip-lock bags). Handle nanomaterial-bearing waste according to the laboratory's hazardous chemical waste guidelines.

6.J.1.3.7. Marking, Labeling, and Signage

Post signs indicating hazards, PPE requirements, and administrative control requirements at entry points into designated areas where dispersible engineered nanoparticles are handled. A designated area may be an entire laboratory, an area of a laboratory, or a containment device such as a laboratory chemical hood or glovebox. Clearly label storage containers to indicate that the contents are in engineered nanoparticulate form (e.g., nanoscale zinc oxide particles, or other identifier instead of simply zinc oxide).

When engineered nanoparticles are being moved outside a laboratory, use leakproof double containment. For example, use compatible double zip-lock bags or “Tupperware-type” containers, or proper shipping containers. Include label text that indicates that the particulates might be unusually reactive and vary in toxic potential, quantitatively and qualitatively, from normal size forms of the same material. (See Chapter 5, section 5.F.2, for more information about transport and shipping of nanomaterials.)

6.J.1.3.8. Disposal of Nanomaterial-Bearing Waste Streams

Do not put material containing nanomaterials down the drain or in the regular trash. Contact the organization's EHS personnel to assist in determining the appropriate waste disposal method. Using the guidelines provided by EPA (see Chapter 8), identify whether the material should be considered hazardous or nonhazardous. Remember that nanomaterials often have different reactivities than the bulk material, and while bulk material properties can be used as a guide, do not rely upon them to determine the properties of the nanomaterials. If the sample is in liquid, be sure to consider the hazards of the liquid as well as the nanoparticles.

As general guidance, DOE recommends collecting items that come in contact with nanomaterials, such as PPE, wipes, and the like in a sealable plastic bag or other sealable container under appropriate ventilation controls. When it is full, place the bag in a second sealable container before disposal. Label the waste container as containing nanomaterials, and note any particular hazards on the label. Notify the organization's hazardous waste handler that nanomaterials are in the waste stream.

6.J.1.3.9. Personnel Competency

Laboratory and support personnel who risk potential exposure to engineered nanoparticles should be given training on the risks of exposure and on safe handling procedures. Do not assume that laboratory personnel or visiting researchers are aware of the health and safety concerns posed by nanomaterials. At a minimum, provide personnel conducting hands-on work with an awareness-level orientation that will alert them to concerns (potential hazards) and to the laboratory's policies concerning prudent material handling.

Training should cover requirements and recommendations for

  • employing engineered controls,
  • using PPE,
  • handling potentially contaminated laboratory garments and protective clothing,
  • cleaning of potentially contaminated surfaces,
  • disposal of spilled nanoparticles, and
  • use of respirators, if applicable.

Footnotes

1

In a controlled instructional setting, students may be told to sniff the contents of a container. In such cases, the chemical being sniffed should be screened ahead of time to ensure that it is safe to do so. If instructed to sniff a chemical, gently waft the vapors toward your nose using a folded sheet of paper. Do not directly inhale the vapors.

2

Transfer vessels may also be known as “secondary containers.” The term “transfer vessel” is used here to avoid confusion with secondary containment, which is a tray, bucket, or other container used to control spills from a primary container in the event of breakage.

3

A non-emergency response is appropriate in the case of an incidental release of hazardous substances where the substance can be absorbed, neutralized, or otherwise controlled at the time of release by personnel in the immediate area or by maintenance personnel.

4

An emergency is a situation that poses an immediate threat to personal safety and health, the environment, or property that cannot be controlled and corrected safely and easily by individuals at the scene.

5

Acetylene, lower flammability limit (LFL) = 2.5%, upper flammability limit (UFL) = 82%; methane, LFL = 5%, UFL = 15%; hydrogen, LFL = 4%, UFL = 75% (NFPA, 2004).

Copyright © 2011, National Academy of Sciences.
Bookshelf ID: NBK55872

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