Decontamination of Biological Safety Cabinets (BSC)
Decontamination of the work surfaces in BSCs and other containment equipment is required:
- after a particular work project using infectious materials is completed
- before any maintenance work is undertaken on a cabinet
- prior to certification or performance tests
- before HEPA filter replacement
- prior to relocation of the unit to another laboratory
- after a major spill of biohazardous agent.
The decontamination procedure should be conducted in accordance with the method recommended by the National Institutes of
Health (NIH). The suggested process involves placing paraformaldehyde flakes in an electric frying pan inside the cabinet. Heating of the flakes
depolymerizes them, with the concomitant generation of formaldehyde gas. The formaldehyde then serves to disinfect the interior of the unit.
Due to the potential for exposure to formaldehyde, an OSHA-classified carcinogen, decontamination should always be performed
by a trained person. BSC users are strongly urged to hire a contractor to perform this function. Please contact Dr. Andrea Hall in ORS for assistance in identifying a qualified company to conduct the decontamination. Contractors experienced in this method are much
less likely to run afoul of the stringent OSHA Formaldehyde Standard (29 CFR 1910.1048) than are lab workers who attempt
this process on an infrequent basis.
The expertise of a contractor is important not only from the safety standpoint but also in avoiding the pitfalls of incorrect
decontamination technique. If an excess of paraformaldehyde is used, a white polymer residue can be produced on the cabinet walls. This
residue may interfere with future research projects. Therefore, precise calculation of the amount of paraformaldehyde needed is
imperative. Furthermore, the temperature and humidity inside the unit must be carefully regulated to ensure maximum efficiency of the
Although the actual decontamination work is to be completed by a contractor, there are responsibilities which must be
met by the lab supervisor. Building occupants who may be impacted by these activities must be protected against accidental exposure. And,
while the contractor's employees are on Northwestern property, their safety is our concern.
We ask that, in light of the risk of exposure, the lab supervisor oversee the preparation for the decontamination project.
Ask yourself whether the contractor follows appropriate safety practices. For instance, are signs posted at the door to the laboratory indicating
that decontamination is in progress and entry is limited? A warning sign should also be displayed at the face of the BSC to prevent someone from
opening it during the procedure.
The exhaust fan for the BSC must be turned off before gas is released. If the BSC is exhausted into the room and not into an exhaust
duct leading to the outside, a flex hose should be attached (and sealed with tape) to the cabinet exhaust port and extended to a nearby hood.
All cracks and seams of the cabinet should be taped to make it air-tight. The paraformaldehyde should not be heated until
the cabinet has been inspected for leak sites. Once the electric pan and any extension cords have been set up, the face of the cabinet must be
insulated with a sheet of polyethylene. Remember that with the exhaust shut down, a positive pressure will be created in the cabinet and the
gas will want to escape into the room.The contractor charged with performing the decontamination should don appropriate personal protective
equipment such as safety glasses, face shield or goggles and a respirator with cartridges specific for formaldehyde exposure. A body coverall
with a hood for the head should be worn. Air monitoring for formaldehyde during the procedure is advisable to identify leaks of gas from the