User Manual
5
I. INTRODUCTION
Investigators and technicians concerned with microbiological safety have for many
years utilized specialized containment enclosures to limit their exposure to harmful
pathogens. In addition, it is recognized that exacting research, as well as routine
pathology, is often compromised by environmental contamination. The ENVIRCO
Class II Biohazard Cabinet is designed to limit the contamination exposure of both
the worker and the work when handling biohazard material.
The Class II enclosure is an open face cabinet with a high volume of air recirculated
through internal HEPA filters. Air is drawn into the open front of the cabinet and
exhausted through a HEPA filter. The controlled airflow direction and volume
balance provides protection for the worker, the work (sample) and against cross
contamination within the cabinet.
II. DEFINITIONS
Class II, Type A Cabinets (formerly designated Type 1):
1. Maintain a minimum calculated average inflow velocity of 75 fpm through the
work area access opening.
2. Have HEPA filtered downflow air from a common plenum (i.e. a plenum from
which a portion of the air is exhausted from the cabinet and the remainder
supplied to the work area).
3. May exhaust HEPA filtered air back into the laboratory.
4. May have positive pressure contaminated ducts and plenums.
Type A cabinets are suitable for work with low to moderate risk biological agents in
the absence of volatile toxic chemicals and volatile radionuclides.
Class II, Type B3 Cabinets:
1. Maintain a minimum (calculated or measured) average inflow velocity of 100 fpm
through the work access opening.
2. Have HEPA filtered downflow air that is a portion of the mixed downflow and
inflow air from a common exhaust plenum.
3. Discharge all exhaust air to the outdoor atmosphere after HEPA filtration.
4. Have all biologically contaminated ducts and plenums under negative pressure,
or surrounded by negative pressure ducts or plenums.
Type B3 cabinets are suitable for work with low to moderate risk biological agents
treated with minute quantities of toxic chemicals and trace quantities of radionuclides
that will not interfere with the work if recirculated back with the downflow air.