The following description is from the "Medical aspects of chemical and biological warfare" published in 1997 by Office of The Surgeon General, Department of the Army, United States of America Fig. 19-3. Members of the Aeromedical Isolation Team (AIT) prepare to transfer a patient from a stretcher isolator into the Biosafety Level 4 (BL-4) isolation suite at the U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, Maryland. The interior of the isolator is maintained at a pressure negative to the external environment by a high-efficiency particulate air (HEPA) filtered blower. The isolator can be attached directly to a transfer port, visible on the external wall of the building, to allow movement of the patient into the suite without exposing the environment to the patient. Team members are seen wearing protective suits and positive-pressure, HEPA-filtered Racal hoods (manufactured by Racal Health & Safety, Inc, Frederick, Md). Photograph: Public Affairs Office, Fort Detrick, Frederick, Md.