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Ann Emerg Med. 2004 Dec;44(6):628-34.

Use of a portable forced air system to convert existing hospital space into a mass casualty isolation area.

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  • 1Department of Emergency Medicine, Christiana Care Health System, Newark, DE 19718, USA.



Patients with communicable diseases may require respiratory isolation to reduce the chance of transmission to health care workers and the public. This project was conducted to determine whether negative-pressure isolation for multiple patients can be achieved quickly and effectively using general hospital space not previously dedicated to respiratory isolation.


The physical therapy gymnasium was the area designated to test the ability to create a negative-pressure isolation environment in a large space. The conversion was planned in advance of an unscheduled drill to convert the space. Four high-efficiency particulate air (HEPA) filtered forced air machines were used to generate negative pressure. The units were vented to the outside air by a 25-foot length of 10-inch-diameter reusable duct. We evaluated the time needed for equipment setup and room conversion and noted any subjective difficulty with either setup or operation of the equipment. We measured the ability of the equipment to generate a negative air pressure relative to adjacent areas and determined the noise levels created during the use of different combinations of machines at various power settings.


After drill activation and the request for equipment setup, 1 hour was required to convert the physical therapy gymnasium into an operational negative-pressure environment. The room pressure readings "high" power ranged from -1.5 to -13 Pa (-0.006 to -0.052 inches of water), and noise levels ranged from 70 to 76 dB. Calculated air changes per hour using 1, 2, 3, or 4 units running simultaneously at "high" power were 4.1, 8.2, 12.3, and 16.4, respectively. Using 4 units at once running at "low" power setting yielded 8.2 air changes per hour and generated a room pressure reading of -8.0 Pa, or -0.032 inches of water.


Portable HEPA filtered forced air units are an effective means of creating large patient care areas with the negative-pressure environment required for respiratory isolation. This design results in a significantly lower-cost alternative compared with construction of individual rooms or units with similar capability and can be retrofitted to existing space. This type of unit would allow treatment of many more patients than current hospital capability would permit and would be an important asset in meeting the needs created by bioterrorism or a naturally occurring epidemic.

[PubMed - indexed for MEDLINE]
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