to harmonize levels of physical containment among the various 
countries promulgating guidelines. Many of the revisions were 
based on the outcome of a NIH/EMBO sponsored workshop on containment. 
Dr. Barkley indicated that three major categories had been 
developed. These included safer laboratory practices, such as employ- 
ment of standard microbiological techniques, containment equipment, 
and special laboratory design. With regard to containment equip- 
ment, the P2 level requires the use of biological safety cabinets 
in certain experiments, the P3 level requires biological safety cab- 
inets for all experiments, and the P4 level requires the use of glove 
boxes. Special laboratory design at the P3 level requires access 
control, directional air flow and surface treatment, and at the 
P4 level requires facility isolation, a change room, sealed surfaces 
and a secondary treatment systen. 
Dr. Barkley noted that the safety of the individual worker 
depends primarily on laboratory practice and the use of containment 
equipment while environmental protection depends upon all three 
elements. Current NIH designations for increasing levels of physical 
containment adhere closely to the equipment and special laboratory 
design criteria described by the NIH/EMBO workshop. Revisions in 
the Guidelines incorporate laboratory design recommendations and 
new mandatory requirements for safe biological practices. 
A number of comments were made both by members of the DAC and 
by the various public witnesses. Dr. Sinsheimer (DAC) pointed out 
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