Share thisChlorine dioxide gas is now approved for the decontamination of biological safety cabinets under Annex G of NSF/ANSI 49.
Formaldehyde had been the only fully accepted process for biological safety cabinet (BSC) decontamination by NSF International under their NSF/ANSI 49 standard until recently. When formaldehyde was approved in 1983, chlorine dioxide gas and vaporized hydrogen peroxide were still in their beginning stages as decontaminating agents. Since formaldehyde’s approval, no other method has been approved until now. Chlorine dioxide gas has now been named as an appropriate method for the decontamination of BSCs. Although formaldehyde is easily circulated within the cabinet, has fairly good penetrability, and has the proper sporicidal activity, there were enough disadvantages to warrant the search for a new method. As such, in 2005 NSF International established a task group to design and implement a protocol to validate the use of chlorine dioxide gas, and to revise the NSF/ANSI 49 standard for BSCs.
Reason for Change
With formaldehyde, a residue is typically left following a decontamination, which can be neutralized from easily accessible areas using an ammonia solution. However the residue is much harder to remove from hard to reach places, such as blowers, HEPA filters, and plenums. The ammonia solution can also leave a residue if too much is used, making a residual wipe down necessary as well. Formaldehyde is also considered to be a carcinogen in much of the world. This makes its use and residual levels a concern to those involved with the decontamination of BSCs and those working inside of them also.
Chlorine dioxide gas was selected for testing due to its penetrative properties as a gas similar to formaldehyde. It can be easily distributed throughout the cabinet and through HEPA filters, decontaminating them as well because of its good penetrability. Chlorine dioxide gas also has the proper sporicidal activity, giving it all of the benefits that formaldehyde had, however, it does not share formaldehyde’s downside of residues left in the cabinet, or its carcinogenicity. NSF International recommends a six hour gas exposure when using formaldehyde, which does not include time necessary for aeration or cleaning up residues left in the cabinet. A complete decontamination cycle of a BSC using chlorine dioxide gas can be performed in 90 minutes from start to finish.
Methods and Testing
The task group decided that, like formaldehyde, it was not necessary to validate the effectiveness of chlorine dioxide gas in each model and size of BSC because chlorine dioxide gas is a non-condensing gas at room temperature. It was deemed sufficient for validation to test it on at least two different makes of Class II type A1 and A2 bench and console models, B1 and B2 biological safety cabinets. Three successful decontamination runs on each cabinet needed to be performed to validate the process. This accounts for a total of eight individual BSCs needing to be tested successfully for validation.