54 
In looking at these elements and trying to place the descriptions in 
our revised Guidelines against this matrix, we can see that the PI, P2, P3, 
and P4 primarily fall on a diagonal here, each step providing an increment 
in protection of the laboratory worker, and of the environment. 
It was the consensus at this meeting, interestingly enough, that this 
diagonal, which is now represented by our P2, P3, and P4, is the most commonly 
accepted increase in gradation of safety used in the area of handling patho- 
genic organisms. Indeed, the recommendations by the Center for Disease Con- 
trol for the handling of human pathogens follows very closely with this, in 
that their Class 2 agents are recommended for control at what we would call 
P2 , their Class 3 human pathogens would be incorporated under P3, and their 
Class 4 agents would be incorporated in P4 . 
The other concept that came from this meeting, however, was that each 
one of these combinations of primary and secondary containment might be 
appropriate for certain types of experiments — that one need not just take 
out four blocks, that they all have some value in the area of safety. I 
might point out, if we take an agent like foot-and-mouth disease, which is 
not known to be hazardous to man but could create extreme hazard to domes- 
tic livestock, that it is commonly handled in the United Kingdom under a com- 
bination of a maximum containment facility, because we need environmental pro- 
tection, but under minimum-level primary containment because of the lack of 
concern for harm to the worker. On the other hand, the World Health Organi- 
zation is recommending that for the handling of smallpox virus, which is 
nearly eradicated on our earth, that those laboratories that will be allowed 
to maintain stocks of smallpox will be handling it under conditions that 
would be represented by this box, where a maximum level of containment, of 
primary containment, a glove box system would be used within a containment 
laboratory and would not go to this high level. 
This — if we could term it flexibility, but probably more appropriately 
an effort to relate more closely the safety needs to the assessed potential 
risk of the experiment — could use this type of matrix; and indeed, in the 
revised Guidelines, we have made an effort to try to provide for an inter- 
change of different approaches for containment. You will note that one of 
the major changes in the Guidelines will allow for experiments that are 
assessed to require P4-level containment — the Guidelines will allow those 
experiments to be conducted under high-level primary containment within a 
maximum containment facility if a one-step increase in biological contain- 
ment is provided. So with that one-step increase in biological safety, it 
is assumed that the hazard to the worker would be less, and therefore it 
could be controlled at a lesser, primary containment, and the hazard to the 
environment would be less, so it could be maintained under less restriction 
for the environment. 
Similarly, for work that would be assessed that would require our 
basic P3 level of containment, if one were to use one higher step of bio- 
logical containment, the Guidelines will allow the use of medium-level 
primary containment within a containment facility. On the other hand, for 
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