APPENDIX E 
dissemination of potentially hazardous organisms from the laboratory 
situation, and as setting up barriers between the I aboratory worker and 
the organisms. Two of these approaches involve the limitation of the actual 
physical escape of the organisms, and are referred to as physical containment. 
The first such approach is the set of standard microbiological practices, 
that have been developed over a period of many years, and are widely used for 
handling pathogenic organisms both in research and clinical I aborator i es . 
In the hands of well trained personnel, these procedures have proven to De 
effective in safeguarding both the worker and the environment from the spread 
of pathogenic agents. The second approach to physical containment involves 
the use of special kinds of equipment and facilities I) to limit spread of 
aerosols, 2) for decontamination and containment of I aboratory air and wastes, a 
3) limitation of access to I aborator i es . As with the standard microbiological 
techniques the type of equipment and facilities are not new, but have been 
developed and used previously for containment of known pathogenic organisms. 
The guidelines go into some detail concerning the practices and facilities 
required for physical containment: four levels of physical containment are 
specified. They are termed PI, P2, P3 and P4 in the document, in the order of 
increasing levels of containment. PI, the lowest level, consists of the use of 
the standard microbiological practices mentioned before. The P2 and the next 
higher level P3, each require special procedures and facilities (including 
vertical laminar flow biological safety cabinets and laboratories maintained 
at lower air pressure than the surrounding building) designed to limit to 
increasing extents any possible accidental escape of potentially hazardous 
organisms. Finally, P4 , the maximum level of containment requires sophisticated 
Appendix E — 5 
