47 
For permissible experiments the Guidelines describe (1) safeguards 
that protect the laboratory worker, the general public, and the environ- 
ment, (2) the criteria for assessing the possible dangers from exper- 
iments involving recombinant DNA molecules, (3) the criteria for 
matching the assessed possible dangers of individual experiments with 
the appropriate safeguards, and (4) the roles and responsibilities of 
principal investigators, their institutions, and NIH for ensuring the 
implementation of the requirements specified in the Guidelines. The 
emphasis on protection of laboratory workers from infection reflects 
that those are the persons at the greatest risk of infection and are 
therefore the most likely route of escape of possibly hazardous agents 
from the laboratory. 
The physical safeguards have been grouped into four levels pro- 
viding increasing capability for containment. The four levels 
approximate those recommended by the Center for Disease Control 
for controlling known infectious agents that have been determined to 
be of 0) no or minimal, (2) ordinary, (3) special, or (4) extreme 
hazard to man and other living things. These correspond to the terms 
minimal, low, moderate, and high risk, respectively, as used in the 
NIH Guidelines. The safeguards include usual and special micro- 
biological safety practices, primary physical barriers that isolate the 
experiment from the laboratory worker, and facility installations that 
either eliminate or markedly reduce the potential for accidental dis- 
semination of recombinant DNA molecules into the environment. The 
four levels, designated PI to P4, provide increasing protection against 
contact with or accidental release of microorganisms containing recom- 
binant DNA molecules. 
B. Physical Containment Requirements 
The safeguards in the Guidelines require the use of procedures 
and physical containment systems to protect laboratory workers and 
the environment from exposure to potentially harmful organisms. 
The requirements include procedures and equipment in which work 
is to be done and special laboratory room and building features, as well 
as appropriate training of workers. The systems are grouped into four 
levels of containment --Pi, P2, P3, and P4--each providing a level 
of protection greater than the one preceding it. The level of contain- 
ment that must be provided by a laboratory in which an experiment 
is to be done is based on an assessment of the degree of hazard involved. 
The following description of the physical containment levels is 
presented to outline these requirements. A complete description may 
be found in the Guidelines (Appendix D). Please note that Appendix D 
to the Guidelines (see Appendix D to this EIS) provides detailed sup- 
plementary information on physical containment. Among many other 
items are specifics on care and use of laboratory animals, require- 
ments for an insect and rodent control program at all containment 
levels, and guidance on decontamination and disposal of liquid and 
solid waste. 
