Basic Documentation

Laboratory Ventilation Codes and Standards
Siemens Industry, Inc. 84
Topic Requirement(s) Commentary
Biological
Safety
Cabinets and
Classifications
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• Type B1 40% recirculation within the cabinet; 60% exhaust through a HEPA
filter; separate plenum configuration, must be exhausted to the outside
• Type B2 100% exhaust through a HEPA filter to the outside
• Class III Special applications; 100% exhaust through a HEPA filter to the
outside; researcher manipulates material within cabinet through physical
barriers (gloves)
A general rule of thumb should be that, if the cross draft or other disruptive room
airflow exceeds the velocity of the air curtain at the unit’s face, then problems do
exist. Drafts from open windows and doors are the most hazardous sources
because they can be far in excess of 200 fpm and accompanied by substantial
turbulence. Heating and air-conditioning vents perhaps pose the greatest threat to
the safety cabinet because they are much less obvious and therefore seldom
considered….. It is imperative then that all room airflow sources and patterns be
considered before laboratory installation of a safety cabinet.
Biological safety cabinets may require periodic decontamination before service and
filter replacement. During the decontamination procedure, the cabinet must be
isolated or sealed from the laboratory and the exhaust system. The responsible
safety officer should be consulted to determine the need for and placement of
isolation dampers to facilitate decontamination operations. If provisions for
decontamination are necessary, the ventilation system design should maintain
laboratory airflow and pressure during the decontamination procedure.
Class I Cabinets
The Class I cabinet is a partial containment device designed for research
operations with low and moderate risk etiologic agents. It does not provide
protection for materials used in the cabinet. Room airflows through a fixed opening
and prevents aerosols that may be generated in the cabinet enclosure from
escaping into the room. Depending on cabinet usage, air exhausted through the
cabinet may be HEPA filtered prior to being discharged into the exhaust system.
The fixed opening through which the researcher works is usually 8 in. high. To
provide adequate personnel protection, the air velocity through the fixed opening is
usually at least 75 fpm.
If approved by the appropriate safety officer, it is possible to modify the Class I
cabinet to contain chemical carcinogens by adding appropriate exhaust air
treatment and increasing the velocity through the opening to 100 fpm. Large pieces
of research equipment can be placed in the cabinet if adequate shielding is
provided.
The Class I cabinet is not appropriate for containing systems that are vulnerable to
airborne contamination because the air flowing into the cabinet is untreated. Also,
the Class I cabinet is not recommended for use with highly infectious agents
because an interruption of the inward airflow may allow aerosolized particles to
escape.
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