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principal safeguards Chat are addressed in the standards relate to the 
access control of the laboratory, the manner in which the laboratory is 
separated from areas open to uncontrolled flow of personnel, requires the 
use of air balancing techniques to provide directional air flow of air that 
is used to ventilate these spaces, and it requires the treatment of sur- 
faces within the laboratory that make them more easily cleanable, so that 
they can be conditioned in a manner that would allow for space decontamina- 
tion in the event of some adverse accident or spill. 
The maximum containment laboratory, which we refer to as P4 , involves 
an isolated facility that requires access through change room facilities. 
It also has an air balance requirement for directional air flow. It requires 
sealed surfaces for space decontamination, and it also requires a battery of 
secondary treatment systems for the treatment of exhaust air, the treatment of 
liquid waste, and the treatment of solid waste that is to be removed from 
these facilities. 
At the conference in London that I referred to, which was designed in 
an effort to bring about more harmonization in the physical containment 
guidelines, the elements of secondary containment, special laboratory design, 
and the elements of primary containment, the equipment, were greatly debated. 
A concept from that meeting evolved which we would term a physical containment 
matrix where we have the elements of a laboratory, which I have across the 
top--the basic containment and maximum conta inment--and the elements of 
primary containment, or that provided by containment equipment, on the far 
lef t . 
This matrix addresses the question of the use of these elements for 
the protection of laboratory workers who are handling potentially hazardous 
materials. I would like to emphasize that it was the consensus of this 
group that the facility itself contributed very little to the safety of the 
laboratory worker. That depended primarily on laboratory practices and the 
use of containment equiment. So one can see that the maximum level of 
protection which is provided by the darkest red color is basically equiva- 
lent and is based on the primary equipment, the laboratory containment 
equipment, and is basically independent of the design of the laboratory 
itself. 
When we look at this matrix, however, from the standpoint of protec- 
tion of people outside the laboratory or the protection of the environment, 
we see that there is a dependence on the use of primary containment mea- 
sures, equipment, as well as special laboratory design, and in this case 
our increase in protection for the environment follows a diagonal, the 
greatest protection being at our deepest green color. So environmental 
protection is dependent on all three elements of physical containment — 
laboratory practices, the special laboratory design, and the containment 
equipment . 
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