7 
Lappi 
reproduce In Its new environment (risk: 1 In a million). Successful 
epidemic conditions would then require that the first Infected or- 
ganisms contact other hosts, that the bacteria leave the first host 
in infectious form, and grow and multiply once again. The aggregate 
risk (which the authors consider conservative) Is given as 1 In a 
-12 
trillion (1 x 10 ) . Let me review some actual experience which 
may help the reader decide what weight a reasonable person might 
wish to assign to this comforting figure. 
I will deal with only two probability estimates: the chances 
that an organism will escape a containment facility and Infect a 
human host. The two facilities which might be used for work with 
the potentially harmful organism are designated P3 and P4. A P3 
facility Is separated from areas open to the general public by 
controlled access corridors and air locks or locker rooms. Bio- 
logical safety cabinets are available within the building and 
environmental protection Insured by waste sterilization techniques. 
All surfaces are easily cleaned and the ventilation system provides 
a positive pressure which vents the air from within the building 
into a sterilizer or scrubber. All work Is conducted in bio- 
logical safety cabinets. A P4 facility has all of the above 
features plus "monolithic" walls, floors and ceilings; airlocks; 
clothing exchange and shower rooms; double-door autoclaves for 
sterilizing materials within the facility; and a blowaste treat- 
ment system to sterilize fluid effluents. 
Appendix K — 16 
