49 
The principal item of containment equipment is the biological safety 
cabinet. This is an open-front cabinet, with an inward airflow from the 
laboratory room of at least 75 linear feet per minute. The cabinet serves 
primarily to protect the operator from aerosols that may be created 
by the activities performed within the cabinet; it also serves to prevent 
the release ©f airborne contaminants to the environment. The air which 
is exhausted from these cabinets is either filtered by high-efficiency 
particulate air filters or incinerated. The high -efficiency particulate 
air filter is capable of removing more than 99. 997 percent of all 
microorganisms that may be in the cabinet exhaust air. 
A laboratory suitable for experiments involving recombinant DNA 
molecules requiring physical containment at the P2 level (see Figure V-2) 
is identical in construction and design to the Pi laboratory. Access to 
the P2 laboratory is limited when experiments requiring P2 -level physical 
containment are being conducted. 
Figure V-2 
Physical containment procedures required for P2 -level work are 
generally applied as safeguards in the conduct of research with 
organisms that cause most bacterial and viral diseases of man. For 
example, these safeguards are recommended by the Center for Disease 
Control for the containment of bacteria that cause anthrax, diphtheria, 
pneumonia, gonorrhea, salmonellosis, strep throat, syphilis, and 
cholera. They are also recommended to contain viruses that cause 
influenza, measles, mumps, and polio. 
