7 
"P3 level (moderate) . In addition to the P2 procedures, this level requires 
the following: (i) Operations with potentially hazardous organisms that 
require P3 containment should be carried out in a laboratory that is 
separated from areas where less than P3 containment is practiced. The 
ventilation system shall be balanced to provide for an inflow of supply air 
from the adjacent corridor into the laboratory through the access doorway. 
This supply airflow shall be in excess of 50 cubic feet per minute. The 
general exhaust air from these laboratories should be discharged outdoors 
and dispersed to the atmosphere to prevent reentry into the building. If 
recirculated, the air must be decontaminated. Appropriate biohazard signs 
should be posted at access points to the laboratory, and only persons 
specifically authorized by the principal investigator should enter when 
these signs are posted. Normally, authorized persons should be limited to 
those who work in the laboratory, (ii) Properly installed biological safety 
cabinets, meeting appropriate NIH performance standards, should be used for 
all transfer operations and for all procedures likely to produce aerosols. 
Operations that produce large amounts of aerosols, such as blending, soni- 
cation, vortex mixing, and vigorous agitation, should be avoided where 
possible. Where necessary, they must be carried out in enclosed systems 
that are not opened until adequate time has been allowed for aerosols to 
settle, (iii) Gloves should be worn during the handling of biohazardous 
materials, (iv) Vacuum lines should be protected by filters. 
P3 level research can be conducted in laboratories where the room airflow 
and general exhaust air conditions described above cannot be achieved, 
provided that this work is contained in closed systems which are maintained 
under a negative pressure of at least 0.25 inches water gauge. Operations 
including centrifugation, fractionation, sonication, etc., which involve the 
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