This portion of the audit check list is primarily directed at chemical fume hoods and gas cabinets, which are necessary to prevent worker exposures to hazardous chemicals. Most other containment devices are addressed in the Laboratory and Engineering Controls section. A chemical fume hood is required when working with volatile, hazardous chemicals. A fume hood is unique from other types of ventilation devices, such as biosafety cabinets and clean benches.
- A biosafety cabinet is designed to create a sterile environment by passing air that circulates in the cabinet through a HEPA filter. Exhaust from the cabinet is also HEPA filtered. Various classes of cabinets exist and are distinguished based on the amount of air that is re-circulated in the cabinet and the manner in which the cabinet is exhausted. Most Biosafety Cabinets exhaust HEPA-filtered air back into the laboratory. While HEPA filters will trap microbiological agents, they will not trap chemical vapors. Air leaving the cabinet and exhausting back into the laboratory will not have infectious particles, but chemical vapors existing the cabinet will be dumped back into the laboratory. In addition, chemical contaminants in the cabinet can concentrate within the cabinet as most cabinets are designed to recirculate about 70% of the air. This is one reason why natural gas burners should not be used in a cabinet. In the event of a leak, the gas can build up to explosive levels in the cabinet. This has been known to happen at several institutions. Use of chemicals or natural gas burners in a biosafety cabinet is typically cited only in Biosafety Surveys.
- A clean bench is also designed to create a sterile environment by passing air through a HEPA filter. But, unlike a biosafety cabinet, only air entering the cabinet is HEPA-filtered. Air typically enters the back of the cabinet and blows out toward the front of the cabinet. Anything in the cabinet will be blown toward the operator. A clean bench is intended for product protection, not people protection. Again, it will not provide any protection from chemical vapors.
The images show a typical fume hood, biosafety cabinet, and clean bench.