52 
themselves in the containment of potentially hazardous materials has been 
addressed by giving that one particular section. And the important area of 
containment equipment has also been addressed as a particular area. 
The laboratory practices area is actually a statement of good micro- 
biological practices that has been used in the past in dealing with human 
pathogens. It has been adopted for the purposes of these Guidelines. We 
have spent more attention, however, in the revised Guidelines on descrip- 
tions of containment equipment and facility design. I wanted to emphasize 
the containment equipment because this is the means by which the laboratory 
worker implements practices to provide a more positive containment of 
research materials within the laboratory setting. 
The Guidelines define basically four levels of primary containment 
which I will refer to as minimum, medium, high and maximum. The minimum 
level does not rely on containment equipment other than those which comple- 
ment actual practice, like pipetting aids. But these are operations that 
are generally conducted on the open bench. 
At the medium level, which is used at our P2 containment level, we 
rely on the selective use of biological safety cabinets. These are cabi- 
nets that are designed for procedures that are known to create excessive 
aerosols. The cabinets are used, therefore, to prevent inhalation expo- 
sures to the laboratory worker in the conduct of those procedures. 
At the high level of primary containment (P3), one uses biological 
safety cabinets for all procedures that involve the transfer of biological 
materials. This provides further protection against inhalation exposures, 
and reduces the environment in which the materials are actually handled. 
The highest level of primary containment is required under our P4 
level. This is where all materials must be confined to glove-box systems 
that provide physical isolation of the agent--phys ical separation of the 
agent and the laboratory worker. 
In the area of special laboratory design, we refer to three basic 
types of laboratories. These laboratory types were described in a report 
by NIH and the European Molecular Biology Organization at a meeting that 
was held in London in March of this year. It was a meeting in which phys- 
ical containment experts from a number of European countries and the U.S. 
were convened to assess the elements of physical containment. The purpose 
of this meeting was not to define safeguards for the handling of recombi- 
nant DNA molecules, but was for the purpose of defining elements of phys- 
ical containment that would be appropriate for the handling of hazardous 
microbiological materials. I will refer to them as basic containment and 
maximum containment, but you can see by my notes that the descriptions of 
a basic laboratory are ones that would fall within our PI and P2 catego- 
ries, and these facilities do not call for any special safeguards in their 
design. When we get to a containment type laboratory at the P3 level, our 
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