Biological Safety Cabinets

Biological safety cabinets (BSC) provide primary containment for working with infectious agents, or as noted above, are also useful for working with microisolation cages. The CDC-NIH publication "Biosafety in Microbiological and Biomedical Laboratories"21 includes a detailed description of the various types of BSCs along with installation requirements.

There are three classes of biosafety cabinets: Class I, II, and III. Class I and II BSCs have inward airflow at velocities of 75 to 100 linear ft per min through an open front. Exhaust air from the cabinet passes through HEPA filters before being discharged into the room or into the laboratory exhaust system. Class II BSCs have the additional benefit of protecting objects in the cabinet from extraneous microbial contamination. Class I and II BSCs are suitable for working with up to BSL-3 infectious agents. Class III BSC cabinets provide the highest degree of personnel and environmental protection from infectious aerosols, as well as protection from extraneous microbiological contaminants for the materials in the

Figure 8.31 A rigid stainless steel isolator that was specially adapted to perform hysterectomies for rederivation of animals. The isolator is divided into two parts, one in which the hysterectomy is performed and one where the pups are resuscitated. The two parts are separated with a dip tank containing a disinfectant.

Figure 8.31 A rigid stainless steel isolator that was specially adapted to perform hysterectomies for rederivation of animals. The isolator is divided into two parts, one in which the hysterectomy is performed and one where the pups are resuscitated. The two parts are separated with a dip tank containing a disinfectant.

cabinet. They essentially are a totally enclosed, gas tight, ventilated cabinet. All operations in the cabinet are performed through attached rubber sleeves with surgical-type gloves. Supply air is HEPA filtered, and exhaust air is filtered through two HEPA filters. Class III BSCs are suitable for working with infectious agents classified at the highest biosafety level, BSL-4.

Class II BSCs, which are the type most commonly used in research animal facilities, come in two types, A and B. Type A is suitable for containing particulate hazardous agents only and may be exhausted into the room through HEPA filters or to the outside via a thimble connection to the building exhaust ductwork. Class II Type A BSCs, as noted previously in this chapter, are often used as rodent cage change cabinets. Class II Type B BSCs are suitable for containing infectious agents, volatile chemicals, and radionuclides. They have a face velocity of 100 linear ft per min and are hard-ducted to the exhaust system. Class II Type B BSCs are further subdivided into types B1, B2, and B3 depending on multiple features, including the degree of air recirculated within the cabinet versus that discarded, i.e., B1, 70% recirculation; B2, 30% recirculation; and B3, 0% recirculation, 100% exhausted. Of course, the higher the percent exhausted, the greater the control of volatile hazards.

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