Class 2 safety cabinet venting methods

A class 2 biohazard cabinet combines the product protection features of a laminar flow hood, with the user and environment protection features of a class 1 safety cabinet. This is a achieved by a combination of laminar air flow and HEPA (high efficiency particulate air ) filters. However, the way in which this is done varies depending on the type of cabinet installed.

A class 2 biohazard cabinet is an essential item of safety equipment when handling infectious or sensitizing material, with the advantage that, unlike a class 1 cabinet, the supply air entering the cabinet is HEPA-filtered as well as the contaminated (exhaust air) leaving it. This minimises the risk of cross-contamination, maintains product sterility and ensures integrity of results.

Both classes of biohazard cabinet are available as recirculating or exhaust models. Often, the two are combined, with part of the air filtered and vented to the outside and the rest filtered and reused. To simplify matters, class 2 biohazard cabinets are standardised into four subtypes in the US, depending on their venting and laminar flow rates. With type A1 and A2 cabinets, HEPA-filtered air can be recirculated to the laboratory, or discharged to the building exhaust via a canopy or “thimble” fitting. With class 2 B1 and B2 cabinets, the exhaust must have a hard connection and be vented directly to the outdoors. Although all four subtypes are used in the UK, a simpler standardisation system, employing standards BS EN 12469 and BS 5726:1992, is in use. Among other things, these state that double HEPA filters must be installed on recirculating models.

If the work requires the use of volatile, toxic chemicals or radionuclides, it is important to remember that class 2 safety cabinet HEPA-filters will not filter these out and can, in fact be damaged by them. Therefore such chemicals should be used in minimum quantities, with all the exhaust air vented to the outside. Filters will also need renewing on a frequent basis.

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