6 
II. DEFINITIONS 
In discussions about precautionary facilities desirable to minimize 
human risk accompanying research with recombinant DNA hybrid microorganisms, 
it is not uncommon to hear the Fort Detrick experience quoted as proof that 
infection of laboratory personnel cannot be prevented. It is true that good 
engineering design is not a completely adequate substitute for thoughtfully 
applied good technique, but the reverse also is true. Both are necessary. 
A typical public statement is as follows: "Even in the P4 conditions of 
the Army's biological warfare laboratories at Fort Detrick, there were 423 
cases of infection and three deaths over some 25 years" (I). 
Detailed analysis of the conditions under which those 423 infections were 
acquired does not support the statement, because P4 conditions, insofar as 
this requires biological safety cabinets or a gastight cabinet system with 
attached gloves, never was present in all the laboratories during the 25 
years' experience. P4 and P3 conditions are defined as follows (51): 
"P4 level (high) . Work areas are in a special facility of the type designed 
to contain highly infectious and hazardous microbiological agents. These 
areas are isolated by airlocks, a negative pressure environment, personnel 
clothing change and shower rooms, and treatment systems to inactivate or 
remove biohazardous agents contaminating exhaust air, liquid and solid wastes. 
All persons occupying these areas should wear protective laboratory clothing 
and shower at each exit from the facility. The handling of the biohazardous 
agents should be confined to biological safety cabinets in which the exhaust 
air is incinerated or passed through HEPA filters." 
[3773 
