Northwestern Office for Research


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 process.

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 unit.

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