Discussion of Canopy Versus Hard Connection Of Class II, Type A2 Biological Safety Cabinets
The topic of canopy versus hard connection of Class II, Type A2 Biological Safety Cabinet (BSC's) has long been a matter of discussion over the years. Safety professionals have interpreted the many revisions of both the NSF 49 standard and the CDC/NIH Biosafety in Microbiological and Biomedical Laboratories (BMBL) guidelines differently when exhausting type A2 BSC's. In addition, certifiers also added to the discussion. Prior to the 1992 NSF 49 standard, most certifiers didn’t have the resources to properly test canopy connections and thus would typically recommend hard connections that could utilize an exhaust duct measurement to assure the correct inflow velocity. Not until recently was the direct measurement of inflow velocity available as a tool ( 5 years after the 1992 NSF 49 standard took effect) did the certifiers have the means to properly test a canopy connection. Now all NSF listed BSC’s have published acceptance criteria allowing direct measurement of inflow velocity. A canopy connection can now be properly installed and tested assuring containment performance.
During the last NSF 49 standard review process for the 2002 revision. The joint committee of the NSF Standard 49 reviewed Annex E, "Recommendations for Installation". The topic of canopy versus hard connection was of primary concern due to the various past interpretations and the current use of direct measurement for inflow velocity, as discussed above. As we know, the installation of the BSC, room location, mechanical, and electrical interfaces has as much to do with the BSC containment performance as the BSC design itself.