Understanding Class II Biological Safety Cabinets
As indicated in the previous section selecting a Class II Biological Safety Cabinet must take into consideration a considerable number of factors which include, among others, the work being done within the cabinet, the facility requirements based on biosafety levels, the location of the cabinet within the laboratory itself, the installation requirements of the cabinet, and the exhaust/supply system(s) to both the laboratory and the cabinet, whether or not the cabinet is to be vented.
All of NuAire’s Class II Biological Safety Cabinets, regardless of type (i.e. Types: A2, B1, or B2) provide the same level of product and personnel protection from a biological point of view. The National Sanitation Foundation’s Listing Program for compliance to NSF Std. No. 49* has subjected each type to the exactly the same testing procedures and exactly the same pass/fail criteria for all Class II cabinets.
What then is the difference between the types of biological safety cabinets that affect selection?
It is the amount of air that is recirculated within the cabinet.
- Type A2 cabinets recirculate 70%
- Type B1 recirculate less than 50%
- Type B2 cabinets recirculate 0% (total exhaust)
Therefore, if it is determined that a process or procedure must be contained in a Class II biological safety cabinet (based on biosafety levels or cleanliness requirements), the selection of the cabinet, in our opinion, is based solely on the quantity and the flammability of volatiles used in the process/procedure within the cabinet. For all Class II cabinets, EXCEPT the NU-435 Total Exhaust Biological Safety Fume Hood, NuAire places a bright red warning label on the face of the cabinet concerning the use of flammables, as follows:
DO NOT USE FLAMMABLE, TOXIC OR EXPLOSIVE SUBSTANCES IN THIS CABINET
NuAire recognizes, however, that some procedures demand the use of volatiles. Studies to determine the dilution within the Class II cabinet of highly volatile liquids, were conducted by the NSF Advisory Committee in the early eighties. Those studies indicated that the total quantity of volatiles designated as flammable which are used in a type A2 cabinet be limited to 25 ml or less. For Type B1 cabinets slightly more is permitted, if the work is carried out in the dedicated exhaust portion (i.e. rear) of the work surface. For the Type B2 total exhaust cabinet, one may think that being total exhaust, there are no restrictions! Wrong. Quantities of volatiles must be limited due to the potential of electrical spark ignition within the cabinet’s work zone. Only the NU-435 has been evaluated and is UL Classified without any use restrictions.
Once again, if you need additional information and/or copies of relative information or links to on-line guidelines please see the reference materials section or call us at the number below, or e-mail us.
*NOTE:
NuAire is not qualified to provide proper guidance for selecting, recommending laboratory biosafety levels, selection of engineering controls, or facility requirements.
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