Biocontainment Security,Isolation and Containment,Biocontainment

Question: Which type of pass-thru BSC should be used to enter small animals into a facility — re-circulating or 100% exhausted? It seems that to be safe, a B2 unit might be a good choice but because there are two openings on the hood (even though they are interlocked) the air requirements are astronomical. Does a re-circulating BSC provide the right amount of protection for the animals and the personnel? Is it true that some of the chemicals used to wipe down the animal boxes can deteriorate HEPA filters in the recirc units, and if so, does it require the filters be changed all that much more often than usual?

Response: A Class II Type A2 Biological Safety Cabinet (30% exhaust/70% re-circulation) is the cabinet of choice for use as a pass-thru device into an animal facility. This cabinet will provide the user and animals with Class II safety from a standpoint of both personnel and product protection.

The access opening across either side of the cabinet should be a minimum of 12 inches to facilitate the movement of standard mouse cages through the opening. A variety of window configurations are available; hinged, sliding, interlocked, etc. Key is the fact that the air barrier across the 12-inch access is 105 FPM (feet per minute), something you get when the cabinet is designed and specified as a Class II Type A2 device.

A six foot Class II Type A2 BSC will typically require 1320 CFM of exhaust at 0.1’ w.g. of static pressure, when fitted with hinged windows and 12-inch access openings on both sides. By comparison a six foot Class II Type B2 BSC (100% Total Exhaust) would require 1976 CFM of exhaust at 2.5” w.g. of static pressure. The author of the question has very accurately noted that the difference in exhaust requirements between an A2 and B2 is in fact astronomical!

Since a Type B2 BSC also provides an air barrier of 105 FPM like the Type A2, there is nothing gained in terms of either sterility for the animal or personnel protection of the technician from a standpoint of allergens or other airborne particulates.