Class II cabinets

Biological safety cabinets (BSCs) used in the United States are divided into three classes 1,11, and III. Class II cabinets are further divided into four types A, Bl, B2, and B3." In other countries, other categorization schemes are sometimes used, but usually follow the same general operating conditions. This division is quite unlike the rest of the local ventilation chapter, but since these descriptions are used whenever BSCs are used, it is practical to describe them here. 

Class I BSCs are, from the functional view, similar to a fume cupboard (Section 10.2.3). Class II cabinets are used for product and worker protection. Class III cabinets are used for work with very dangerous microbiological or radioactive agents and provide maximum protection to the environment and the worker. The class and type of BSC used is dependent on the demands for worker and product protection. 

Class II BSC. The Class II BSC (Fig. 9) provides product, personnel, and environmental protection, and is the most common BSC employed in pharmaceutical manufacturing and pharmacy-compounding operations. The Class II BSC has several subclassifications, based upon cabinet ventilation design (Table 1). The Class II BSC (Fig. 8), the most widely used by hospital and home-care pharmacies, features a front access opening with carefully maintained inward airflow for replacement of air exhausted from the cabinet, a HEPA-filtered vertical laminar flow airstream within the entire work area, and HEPA-filtered exhaust air. The vertical laminar flow airstream and front access opening are common to all Class II cabinets, although LAF velocities and patterns, HEPA filter sizes and position, ventilation rates, and cabinet exhaust methods vary considerably in different designs (Fig. 7). 

BSC class II cabinets protect personnel, the environment, products, and specimens. These cabinets contain an open front and an inward airflow of 75-100 fpm to protect the operator. The laminar air that comes in contact with the product is first HEPA filtered to protect the product from contamination. The exhaust air then goes through a second HEPA filter to protect the environment. Use class II cabinets with products requiring biosafety levels 1, 2, or 3 containment. 

Beside using a Class HI cabinet, one can achieve Class III standards another way. Workers wear one-piece, positive pressure, fiill-body protective suits containing a life-support system. They work inside Class I or Class II cabinets. In this case, the work area must have an airlock with airtight doors. Workers must pass through a chemical shower to decontaminate the suit before leaving the work area. Exhaust from the suit must pass through a two-stage HEPA filter. 

Prepare Cell Factoiy in a Class II cabinet by removing packaging and fixing the provided air filter and tube coimector to the two open adaptor caps. 

Monitor the growth daily by removing a small sample through the side-arm in a Class II cabinet and carrying out a cell count and visual inspection for ceU morphology and lack of microbial contamination. 

A Class II biological safety cabinet provides protection for both the worker and the sample or product, making it suitable as a sterile compartment for cell culture. This type of cabinet is the most versatile and most common, with face velocities similar to those of Class I. There are four types of Class II cabinets, the main features of which are discussed below. Note that there are additional differences among the types in Class II (types Al, A2, Bl and B2), primarily concerning the geometry of the air flows and placement of HEPA filters. 

Class II Type A models recirculate 70 percent of the air flowing through the cabinet, and 30 percent is exhausted into the room. Because a majority of the air in the cabinet is recirculated, the Qass II Type A cabinet must not be used with explosive, flammable, or toxic substances, including radioactive or carcinogenic chemicals. Table 9.1 lists some of the performance characteristics of the four types of Class II cabinets. 

Class II cabinets, like Class I units, depend on an air barrier for their operation. Therefore, maintaining the integrity of the air barrier at the work face of the unit is essential for both operator and product protection. The same considerations apply to the placement of both Class I and II cabinets. They should be installed out of traffic areas, away from air supply and exhaust registers, and doors. They must not be positioned opposite each other on both sides of an aisle. The exhaust grille of Class II Type A units, which exhaust into the room, must not be blocked or restricted. Nothing should be placed on the tops of these devices. 

It has not been easy to determine the factors required to assure maximum performance efficiency of the Class II biological safety cabinet. In its Standard 49 (326) the National Sanitation Foundation (NSF, an industrial organization that sets standards for the performance of cabinets) has attempted to define efficiency and performance for these cabinets. Unfortunately, many factors influence efficiency and performance after the cabinet is removed from the ideal situations that prevail in the factory or in the NSF testing laboratory. All Class II cabinets are manufactured to meet the standards set by NSF 49. At a minimum the average airflow velocity cannot deviate by more than 5 linear feet per minute (Ifpm) from the established set point for a particular cabinet model. However, in practice, the airflow velocities may vary significantly more than this. These variations result from some of the following factors that are external to the design and operation of the cabinet ... 

Class I-III Cabinets Containment cabinets used for various requirements. In a high-risk area, a Class III cabinet would be used. Class I and II cabinets are used in low-risk areas. 

Laminar flow biological safety cabinet, class II. 

In general, four types of cabinets are used for work with research quantities of chemical carcinogens. These are the conventional fume hood a Class I biological safety cabinet a Class II (Type B) biological safety cabinet and a Class III closed glove box system (8). 

The facility must be designed to control access. Signs should designate restricted areas. Clothing requirements for entry should be identified. There should be directional air control with adequate ventilation rates. Primary containment equipment such as chemical fume hoods, a Class I or Class II (Type B) biological safety cabinet, or a glove box system should be available for use with known or suspect chemical carcinogens or other toxic substances. 

Place the tumor material in a 10 cm Petri dish and cover with medium. This should be carried out in a class II biological safety cabinet. 

Regular maintenance of biological (microbiological) safety cabinets is essential. National standards, for example, British Standard BS 5726 1992, have been set for their construction, installation and operation. The inward face air velocities of Class I and II cabinets must provide an operator protection factor of at least 1 x 105 (for every 100,000 particles released at the working aperture, no more than one should escape into the laboratory). Also, HEPA fdters must have a mini-... 

The first step of the extrachon procedure, i.e., the denaturation of the sample with the lysis buffer, should be performed in a class II biosafety cabinet. The remainder of the procedure can be carried out on the bench, because the lysis buffer completely inactivates HIV. 

NFPA 30, 4.5.S.3 4.4.5 In an office occupancy, not more than ten gallons (37.8 liters) of Class I and Class II liquids (see definition) combined shall be kept in a single fire area (see definition) outside of a storage cabinet or an inside liquid storage area, unless the liquids are in safety cans (see definition). 

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