ROCKET EMISSIONS

The Air Force needs to evaluate risks to human health from rocket emissions at two locations: Vandenberg Air Force Base (VAFB), Western Range, and the Cape Canaveral Air Station (CCAS), Eastern Range. The intercontinental ballistic missile (ICBM) test program (including the Minuteman III and Peacekeeper) and the polar orbit space launches are carried out at Vandenberg; the equatorial and low inclination launches and shuttle-mission support occur at Cape Canaveral. The rockets and missiles launched at both ranges are powered by motors using specified solid or liquid propellants or both. The potentially toxic emissions resulting from these propellants are HCl, NO₂, HNO ₃, hydrazines, and lesser amounts of other substances.

HCl is emitted from rockets using solid-propellant motors, usually the first stage of a launch vehicle, and the nitrogen-based compounds are emitted from rockets using liquid propellants, a first or later stage of a launch vehicle. Solid-propellant motors burn a hydrocarbon fuel with ammonium perchlorate as the oxidizer. The resulting rocket emissions at ground level include other combustion products (e.g., CO, CO₂, N_2, H₂, and H₂O) as well as HCl, but the Air Force has considered HCl to be the most hazardous. Liquid-propellant motors often use Aerozine-50 (50:50 blend of hydrazine and unsymmetrical dimethyl hydrazine) as the fuel and N₂O₄ as the oxidizer. For normal launches, nitrogen oxide emissions at ground level are negligible. However, in the case of an accident during fuel transfer or a catastrophic abort near the ground, large quantities of N₂O₄ can be released. In the atmosphere, some of the N₂O₄ is rapidly converted to NO₂. The Air Force speculates that NO₂ rapidly converts further to HNO₃ (T. Clapp, U.S. Air Force Space Command, personal commun., February 25,1997).

Aerozine-50 also can be released from rockets using liquid propellants in catastrophic aborts (or during transfer operations); however, the Air Force did not ask the subcommittee to review the toxicity of hydrazines for this report. COT recently reviewed the toxicity of hydrazine for the National Aeronautics and Space Administration (NASA) (NRC 1996).

The Air Force has measured and estimated rocket-emission exposure concentrations and durations in the event of normal and catastrophic launches. Projected exposure concentrations and durations during a normal Titan IV launch and a catastrophic abort at Vandenberg are listed below (D. Dargitz, U.S. Air Force 30th Space Wing; L. Philipson, ACTA Inc.; and T. Clapp, U.S. Air Force Space Command; personal commun., March 14, 1997):

A. Normal launch

Peak HCl concentration reaches ≈30 parts per million (ppm) out to 3 kilometers (km) downwind

Range of passage times

≥10 ppm, ≈2 min (7 km)

≥5 ppm, ≈3 min (15 km)

≥2 ppm, ≈4 min (15 km)

B. Catastrophic launch abort

1. Peak HCl concentration reaches ≈90 ppm out to 4 km for an abort 20 sec after takeoff

Range of passage times

≥10 ppm, ≈10 min (5 km)

≥5 ppm, ≈12 min (36 km)

≥2 ppm, ≈16 min (36 km)

2. Peak NO₂ concentration reaches ≈50 ppm out to 7 km

Range of passage times

≥10 ppm, ≈3 min (8 km)

≥4 ppm, ≈4 min (27 km)

Similar short passage times are expected for the ground clouds emanating from the other types of vehicles (e.g., Delta and Atlas rockets, Minuteman and Peacekeeper missiles, and the space shuttle) launched at the Eastern and Western Ranges.

DEFINITIONS OF TIER LIMITS

As noted in Chapter 1, the Air Force initially developed acceptable human exposure levels for the rocket-emission toxicants for military and civilian populations called tier limits. The toxicity information supporting the tier limits influenced the selection of exposure concentrations associated with 1% and 99% incidence of effect in sensitive and normal populations included in LATRA ERFs, as noted in Table 2-1. Derivation of the tier limit values is described below.

The Air Force adopted a three-tiered concept to delineate acceptable exposure concentrations and durations for the public (tier 1), government and contractor personnel on the ranges (tier 2), and operational personnel directly involved with the launch (tier 3). The concept is similar to the three-tier system proposed for the emergency response planning guidelines (ERPGs) of EPA (1987; see box) and comparable to a system proposed by the California Environmental Protection Agency to meet the requirements of the California air toxics ''hot spots" law (Cal EPA 1995).

The Air Force defines the tier 1 exposure limit (the outermost tier) as the airborne exposure concentration that poses no hazard to the general population but might affect certain sensitive individuals (e.g., individuals with asthma or emphysema and people with certain other lung diseases; U.S. Air Force 1997).¹ If tier 1 concentrations are exceeded beyond the base, the Air Force notifies public officials.

The Air Force defines the tier 2 exposure limit (the middle tier) as the airborne exposure concentration that might cause short-term symptoms that most individuals could endure without experiencing or developing irreversible or other serious health effects or symptoms that could impair their ability to take protective action. For personnel in areas with a tier 2 concentration, the Air Force recommends seeking shelter and evacuation (Killan 1994). If tier 2 concentrations are predicted to overlay unprotected population centers (e.g., a single house, building, or facility or, in the case of residential or commercial areas, a small area encompassing houses, stores, etc.) on-or off-base, the Air Force wing safety office recommends a launch hold to the wing commander.

The Air Force defines the tier 3 exposure limit (the innermost tier surrounding the launch pad) as an airborne exposure concentration that can be immediately dangerous to life and health (IDLH). Tier 3 exposure concentrations are based on the NIOSH IDLH (1994) values (U.S. Air Force 1997). Areas within tier 3 concentrations warrant immediate isolation and evacuation actions to prevent exposure (Poitrast 1993; Killan 1994).

Definitions of IDLH and other short-term exposure limits established by various groups and referred to in this report are provided in Appendix B.

In 1994, the Air Force Space Command Surgeon General established the Rocket Emissions Working Group (REWG) to review and provide recommendations for the three-tier limits for HCl and N₂O₄ (NO₂). REWG consisted of personnel from the Air Force Armstrong Laboratory, the U.S. Environmental Protection Agency (EPA), the Lawrence Livermore Laboratory, ACTA, Inc., and others. The Air Force has changed some of the tier limit values on the basis of recommendations from REWG; REWG-recommended tier limits for rocket-emission toxicants are listed in Table A-1.

TABLE A-1

REWG Recommendations for Air Force Tier Exposure Limits for Rocket-Emission Toxicants.

The Rocket Exhaust Effluent Diffusion Model (REEDM) output is used to identify the locations encompassed by a ground plume concentration exceeding each tier limit, and actions and decisions on whether to launch are made on the basis of the tier-concentration contours relative to the populations defined for each tier (Poitrast 1993).²

COMPARISON OF REWG TIER RECOMMENDATIONS AND LATRA ERFS

The Air Force used REWG's recommended tier limits to adjust the toxicity values initially used to quantify the LATRA-ERFs (see Philipson et al. 1996). REWG tier 1 recommendations, chosen to protect the more sensitive members of the general population, correspond to the 1% effect level (or lower) for adverse effects in sensitive populations in LATRA. The definition of REWG tier 2 corresponds less directly to the LATRA-ERF structure, but was used to set the 1% incidence levels of the LATRA-ERFs for normal individuals. REWG considered that the individuals most likely to be exposed to tier 2 concentrations would be the on-base community of military personnel, workers involved in base operations, and their dependents living on base. Although those individuals usually represent a younger and healthier portion of the general population, they might still contain some percentage of sensitive responders. The tier 2 exposure limit might cause some workers to seek medical attention. At one time, tier 3 limits were considered for setting the 99% effect level for ERFs for serious effects in sensitive individuals, but a 5-fold multiple of the 1% effect concentration was selected instead (see Chapter 2).

REFERENCES

• Cal EPA (California Environmental Protection Agency). 1995. Technical Support Document for the Determination of Acute Toxicity Exposure Levels for Airborne Toxicants. Draft for Public Comment. Office of Environmental Health Hazard Assessment, Sacramento, Calif. January.
• EPA (U.S. Environmental Protection Agency). 1987. Technical Guidance for Hazards Analysis: Emergency Planning for Extremely Hazardous Substances. Prepared in cooperation with the Federal Emergency Management Agency, Washington, D.C., and U.S. Department of Transportation, Washington, D.C. U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, Washington, D.C. Available from NTIS, Springfield, Va., Doc. No. PB93-206910.
• Killan, G.A. 1994. Memorandum from HQ AFSPC/SECE to meeting attendees. Toxic Risk Analysis Models and Exposure Limits Meeting Minutes. U.S. Air Force Space Command.
• NIOSH (National Institute for Occupational Safety and Health). 1994. Documentation for Immediately Dangerous to Life or Health Concentrations (IDLHs). U.S. Department of Health and Human Services, National Institute for Occupational Safety and Health, Division of Standards Development and Technology Transfer, Cincinnati, Ohio. Available from NTIS, Springfield, Va., Doc. No. PB94-195047.
• NRC (National Research Council). 1986. Criteria and Methods for Preparing Emergency Exposure Guidance Level (EEGL), Short-Term Public Emergency Guidance Level (SPEGL), and Continuous Exposure Guidance Level (CEGL) Documents. Washington, D.C.: National Academy Press.
• NRC (National Research Council). 1996. Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, Vol. 2. Washington, D.C., National Academy Press.
• Organization Resources Counselors. 1987. Memorandum to ORC Occupational Safety and Health Group from Darrell K. Mattheis and Rebecca L. Daiss, update on Emergency Response Planning Guidelines (ERPG) Task Force. Organization Resources Counselors, Washington, D.C. July 20, 1987.
• Philipson, L.L., J.M. Hudson, and A.M. See. 1996. Exposure-response functions in Air Force toxic risk modeling. Toxicology 111:239-249. [PubMed: 8711740]
• Poitrast, B.J. 1993. Memorandum to HQ AFSPACECOM/SGPB 30 MEDGP/SGPB. Consultative letter, AL-CL-1993-0058, Evaluation of Three-Tier Exposure Philosophy and Tier Limits, Vandenberg AFB Calif. Department of the Air Force, Armstrong Laboratory (AFMC), Brooks Air Force Base, Tex. March. U.S. Air Force 30th Space Wing. 1997. Toxic Hazard Assessments. 30th Space Wing Instruction 91-106. 30th Space Wing, Air Force Space Command Range Safety Office, Vandenberg Air Force Base, Calif.
• U.S. Air Force 45th Space Wing. 1998. Toxic Hazard Control, Daily and Launch Operations. 45th Space Wing Range Safety Operations Requirement No. 19, 24 March 1998. Patrick Air Force Base, Fla.

Footnotes

1

There are differences between the Eastern and Western Range interpretations of the tier limits; the definitions provided here were developed by the Western Range. (For the Eastern Range tier limits, see Toxic Hazard Control, Daily and Launch Operations (U.S. Air Force 45th Space Wing, 1998)). Although the types of effects in sensitive individuals were not defined in the documentation provided to the subcommittee, the subcommittee assumes that the effects would be as described for ERPG-1.

2

REEDM and LATRA are used somewhat differently at the Eastern and Western Ranges. VAFB operates LATRA, which contains a subset of REEDM, as the single toxic-risk-analysis model used as a basis for go/no-go recommendations to the wing commander. At CCAS, REEDM is used in a stand-alone configuration for go/ no-go recommendations; LATRA is operated before the launch to help determine the levels of risk to which off-base population centers can be exposed (D. Dargitz, U.S. Air Force 30th Space Wing, personal commun., March 14, 1997).