Because many chemicals require a unique protocol for sampling and analysis, a chemical contamination assessment usually requires that the potential contaminants be well-defined. A field sampling plan should describe how wipe tests will be taken, the wetting solvent used, the protocol for grid sampling (or other sampling scheme), necessary analytical sensitivity, and the methodology that will be used to evaluate the results.
9.I.2 Removal, Cleaning, and Decontamination
The second step in decommissioning is to remove all hazards from the space. Be sure that all chemicals, radioactive materials, and biologicals have been removed from use and storage areas, including refrigerators and freezers. Movable equipment should be appropriately cleaned and/or disinfected, and removed from the lab.
Residual perchloric acid and mercury contamination are common concerns for laboratory decommissioning. If perchloric acid was used outside of a hood designed for that purpose, hoods and ductwork can become contaminated with explosive metal perchlorates. (See section 9.C.2.10.5 for information about the hazards of perchloric acid in laboratory hoods and ventilation.)
Mercury is used in most laboratories, and mercury spills are common. Unless it is certain that no mercury was used, laboratory decommissioning should include testing of floors, sinks, cupboards, and molding around furniture and walls. Be sure to check and clean sink p-traps. Visual inspection alone is inadequate as historic spills may reach beneath floor tiles and furniture, and behind walls. As described in the ANSI Laboratory Decommissioning Standard, modern mercury testing utilizes a portable atomic absorption spectrophotometer with a sensitivity of 2 ng/m3. Decommissioning clearance levels consider the U.S. Agency for Toxic Substances and Disease Registry’s Minimal Risk Level (MRL) of 200 ng/m3 for non-occupationally exposed individuals. Chapter 6, section 6.C.10.8, includes information on dealing with mercury contamination. Additional mercury testing may be necessary as furniture, floors, walls, and plumbing are removed during renovation.
After hazardous materials and movable equipment have been removed, areas known to be contaminated (e.g., stained floors and cupboards) should be cleaned appropriately, or destructively removed and disposed of. Chemical decontamination can be done using appropriate surfactant soaps, solvents, neutralizing agents, or other cleaners.
Unless is it known that no biological materials were used in the space, the furniture, equipment, and other surfaces should be cleaned with an appropriate disinfectant. Sophisticated biological decontamination technologies are available for areas where high-risk pathogens have been used.
As a precautionary measure, it is a standard practice to remove dusts and other settled particulates via a thorough final wet-cleaning of floors, vertical surfaces and furniture using commercial cleaning products.
Final tests or survey results can be used to verify decontamination. In some cases regulatory authorities allow permanent marking of a porous floor or wall where a radioactive material or chemical has penetrated deeply, and destructive removal is impractical prior to the building’s demolition. When removal, decontamination, and cleaning meet planned decommissioning standards, a final area clearance statement can be issued, and renovation, demolition, or the new occupancy can commence.