Share thisBiological safety cabinets (BSCs) are given surface decontamination as part of their routine use to prevent against contamination. They are also given a more thorough decontamination when they are serviced, to ensure that no contaminants exit the BSC when the cabinet is opened up for maintenance or repair. Methods for decontamination vary depending on the type of decontamination that is necessary. One thing to always remember is to use each agent according to its label, to ensure that proper concentration and contact time is used in order to obtain adequate decontamination.
One of the biggest drawbacks in the surface decontamination of BSCs is that many agents are incompatible with stainless steel, and either pit or rust the surfaces. Typical agents include bleach, liquid chlorine dioxide, hydrogen peroxide, and peracetic acid. This incompatibility is often due to the agent’s pH level, as many are highly acidic. The acidity can usually be attributed to the nature of the agent or the byproducts of the agent’s generation method. This is the case with some (but not all) of the common liquid chlorine dioxide solutions, as common generation methods include the mixture of an acid and a base resulting in chlorine dioxide, an acidic solution, and sodium chlorite byproducts.
mixture of base + water + activator = acidified sodium chlorite + chlorous acid + chlorine dioxide
The liquid chlorine dioxide itself will not oxidize or pit stainless steel, but its byproducts may. An easy way to avoid this issue is to use agents, including chlorine dioxide solutions, that are pH neutral (pH level of 7), or those that are closer to neutral. Another possible solution is to rinse the BSC with tap water after your decontaminating agent has been applied for the correct contact time.
When decontaminating the entire BSC including the HEPA filter, National Sanitation Foundation (NSF) protocols must be followed. NSF has two methods approved for the decontamination of BSCs, formaldehyde gas and chlorine dioxide gas. Formaldehyde is not an oxidizer and has good material compatibility. Formaldehyde, as well as its neutralizing agents may leave residues that require removal. Chlorine dioxide gas has no acidic byproducts as do some liquid solutions, this leaves just the pure chlorine dioxide gas contacting the contents of the space. Chlorine dioxide gas does not leave a residue, so there is no worry of residual contact causing a negative effect on materials and components within the area being decontaminated.With a comparatively low oxidation/reduction potential, using chlorine dioxide gas generated in this fashion is one of the best methods of decontamination available when concerned with material compatibility.
Table 1 shows several biocidal agents and their oxidation/reduction potentials. Oxidation/reduction potential is a measure of the tendency of a chemical species to gain electrons and oxidize other chemical species. A higher oxidation/reduction potential means that the species is more likely to gain electrons and is a stronger oxidizer. This gives a numerical value as to how corrosive the agent is.
Kevin Lorcheim is an Engineer for ClorDiSys Solutions, Inc. (908) 236-4100; www.clordisys.com.