Negative air pressure is maintained in the labs, and the air leaving them is filtered.
"It was literally hell up there because of that negative air system," Mr. Little said.
Although no safeguards are absolute, negative air filters attempt to insure that no particles accidentally escape from the lab.
Plum Island employs negative air pressure, sealed laboratories and rigorous shower and cleaning routines to keep biological agents from escaping.
It may sound suspiciously close to snake oil, but the newest promising therapy for SAD is negative air ionization.
Those areas, which hold dangerous pathogens, feature filtered air, sealed doors and negative air pressure, which prevent germs from leaking out.
They have built "negative air pressure" rooms that germs cannot escape, bought body suits and respirators and installed backup computer systems.
The letter writer is correct, Mr. Varsalona said, that this negative air pressure can create a hazard during a fire because smoke can be drawn into apartments.
Mr. Carroll writes that was long enough for viruses in freezers to thaw and for negative air pressure designed to keep air inside the building to fall off to nothing even as forced-air seals on lab doors went flat.
Steps to isolate contaminants would include the use of air pumps to create negative air pressure within the enclosed areas; installing barriers at windows, doors, elevator shafts and stairways; and cleaning surfaces with high-efficiency particulate air-filter vacuums.
Inside a room with negative air pressure, researchers retrieve blood samples from an incubator and place them in a laminar flow hood, which draws up a stream of air.
