Biological safety cabinets (BSCs) require different considerations than fume hoods. BSCs are constant-volume devices, depending on operational mode, and must be set and operated within close tolerances (NSF, 1992). For some cabinets this may represent an airflow tolerance of as little as 15 cfm. Typical air-balancing specifications usually call for an accuracy of +10% (AABC, 1989). Certifications of the BSC must be carefully understood to insure that they are appropriate for the facility. See the American Institute of Architect's "Biomedical Research Laboratory Facilities: Guidelines for Planning and Design" 1999, manual for comprehensive guidance. For these reasons, energy-efficiency opportunities are limited when a laboratory has BSCs required, as follows: [Biomedical Research…, 1999]
·BSC energy consumption is proportional to the required intake velocity of the "Class" and "Type" of the cabinet and the area of its opening. Therefore, the greatest energy efficiency can be achieved when the appropriate intake velocity and cabinet opening area are minimized with the choice of a BSC. Researchers and engineers should not choose BSCs that are more sophisticated than needed. [Crane, 1994]
·Not all BSCs are exhausted outside of the facility. Some BSCs can recirculate the air back into the laboratory in which they are located, saving energy by reducing heating and cooling energy rejected by the exhaust system.
·BSCs that are exhausted outside require constant air flow during their normal operational mode because they do not have a moveable sash. However, using a VAV system, which compensates for dynamic HEPA filter loading over time, will save energy In contrast to typical arrangements where the air flow is simply set to accommodate the HEPA filter's clogged state. The VAV system must carefully track and provide the flow level for BSCs, which have a narrower flow tolerance (+5% for BSCs) than fume hoods. The typical VAV has a +10% flow tolerance, according to many manufacturers' specifications, so the necessary control can be difficult to achieve. [Carroll, 1995; Ghidoni, 1994]
·Depending on class and type, a BSC has different modes of operation: a zero-flow mode during decontamination, an idle mode where only an internal fan is on, normal mode with internal and external fans on, and emergency mode for full speed exhaust fan operation. A laboratory that accommodates these different air flows with a VAV system will save energy.
Types of biological safety cabinets
