Class III cabinets

BS 5726 requires there to be an airflow of 0.75 m/s into the cabinet when gauntlets are detached and at least 3 m /min through the inlet filter when the gauntlets are attached. In addition the dimensions of the inlet and exhaust filters should be such as to achieve a minimum negative pressure of 200 Pa within the cabinet under operating conditions. 

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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 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. 

Glove boxes (including Class III cabinets) may be necessary for most toxic operations or where aerosols are involved. Glove boxes permit the use of inert or otherwise controlled atmospheres. They shield the operator during use, require less ventilation than fume hoods, and don t cease to protect when house power is lost, though they may lose their negative pressure. 

Biological materials to be removed from the Class III cabinet or from the Biosafety/Laboratory Containment Level 4 laboratory in a viable or intact state are transferred to a nonbreakable primary container and then enclosed in a nonbreakable, sealed secondary container. This is removed from the facility through a disinfectant dunk tank, fumigation chamber or an airlock designed for this purpose. 

The effective operation of safety cabinets relies on the use of High Efficiency Particulate Air (HEPA) filters to remove micro-organisms from exhaust air and, for Class III cabinets, inlet air also. It is essential that HEPA filters be mounted such that air cannot bypass the filter. This means that the filter must be mounted directly against the cabinet wall and not remotely along an air duct, unless that duct forms an integral and unbroken component of the cabinet itself. 

Small unit volumes of effluent (up to 50 litres) can be treated in a steam autoclave, provided that adequate measures are taken to transfer the material in a safe and contained manner to the autoclave chamber. A Class III cabinet line or contained suite in which the work is performed, and to which the autoclave chamber has direct access provides excellent containment security, but is not conducive to the processing of more than a few litres at a time. Transport of liquid in a leak-proof secondary container permits larger volumes to be handled, but consideration must be given to the logistical problems associated with the transport, especially if the autoclave is situated in a relatively remote location, or is inside another suite. If the autoclave has one door only, procedures must be adopted to ensure that contaminated and safe materials are not mixed. Double door autoclaves permit the uni-directional flow of waste out of the facility, and in the UK are recommended or mandatory for the higher categories of containment. " ... 

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