6.1.1 Selecting a biological safety cabinet for a TB laboratory

The two types of BSCs described below are best suited for use in moderate-risk laboratories and in high-risk laboratories (TB-containment laboratories).

Class I

This type of BSC provides personal and environmental protection but does not offer product protection. This lack of product protection may contribute to increased contamination rates, especially when preparing and inoculating liquid cultures (see Figure 1).

Class II

A Class II BSC offers personal, environmental and product protection, and, in type A2 models all biologically contaminated ducts are under negative pressure or are surrounded by negative pressure ducts (see Figure 2). (This is the PREFERRED type of BSC.)

• Class II type A1 BSCs are not a good choice because the ducts may become contaminated, and plenums have positive pressure relative to the room

• Class II type B1 and type B2 BSCs must be hard-ducted to the outside; this means that the building’s exhaust system must precisely match the airflow requirements specified by the manufacturer for both volume and static pressure. Certification, operation and maintenance of these types are therefore more difficult, so these BSCs are not recommended for any new TB laboratory facilities.

BSCs should be equipped with HEPA filters that meet applicable international standards (for example, European norm standards EN12469 or United States NSF/ANSI Standard 49 – 2008).²⁰ ²¹

For all newly procured BSCs, Class II type A2 cabinets with a moveable sash are recommended.

A BSC should be selected primarily according to the type of protection needed: product protection or protection for personnel against the risk of infection. Selecting the correct type of BSC, installing it, using it properly, and annually certifying its operation are complex processes. It is highly recommended that these processes are performed by well trained and experienced professionals familiar with all aspects of BSCs.

BSCs should be connected to an uninterrupted power supply to ensure that staff have adequate time to complete a procedure in the event of a power outage.

Biosafety cabinets must undergo certification at the time of installation, whenever they are moved, and following any repairs or filter changes; they also require regular (annual)maintenance to ensure proper functioning. Delaying maintenance or using under-qualified personnel to conduct maintenance can put laboratory workers at risk. (See section 6.1.5.)

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