Chemical Health & Safety

July/August 1996

Chemical Health & Safety, 1996, 3(4), 34-39.
Copyright © 1996 by the American Chemical Society.

Appendixes

Appendix 1. Decommissioning radiation laboratories
The goal of the decommissioning process is to ensure that intermediate (movers, construction workers) and future users of the laboratory are not exposed to unacceptable levels of radiation or radioactive contamination. The following guidelines for laboratory surveys, recommendations on radiation survey instruments, and Nuclear Regulatory Commission (NRC) "Acceptable Surface Contamination Levels" (5) may be used in the preparation of radiation laboratories for release for unrestricted use.

Facility characterization: Document and history review

  1. Obtain a description of the types and locations of experiments performed using radioactive material.
  2. Obtain a list of the specific radionuclides used and the amounts stored or used in the laboratory.
  3. Obtain information about use of ventilation system for volatile radioactive materials and the sanitary sewerage systems for the disposal of low-level radioactive waste.
  4. Obtain information about the history of radiation survey results. Also include any information about incidents or spills that resulted in facility contamination.
This information should be readily available from the facility radiation safety officer. Interviews with the laboratory occupants may also provide valuable information.

Radiation surveys
Radiation surveys must be done to determine the extent of exposure rate and surface activity.

Exposure rate: Ambient radiation levels

  1. Determine background radiation levels in µR per hour. Chose an on-site building of similar construction that has no history of use of radioactive materials.
  2. Measure exposure rate levels at 1 m from floor and lower wall surfaces. The measurements may be averaged over a 10-m2 area (the approximate size of a small office).
  3. Maximum exposure rate should not exceed two times the guideline values, above background.
  4. Guideline values are determined by federal or state licensing agencies.

Surface activity: Fixed radiation contamination

  1. Survey all surfaces and equipment for fixed contamination, including benchtops, drawers, floor, hood base, hood walls, ductwork, sink basins, and sink drain traps.
  2. Contaminated areas should be cleaned to the best extent possible.
  3. Results should be averaged over a 100-cm2 area and should not exceed guideline values.
  4. Do not cover contaminated areas with paints, cement, or other forms of covering to reduce contamination levels to guideline levels.

Surface activity: Removable radioactivity contamination levels

  1. Grid the laboratory into approximately 1-m2 sections.
  2. Do swipe tests for removable contamination by rubbing a 1-2-in. filter disc over approximately 100 cm2 of area to be tested.
  3. Analyze swipe tests for the radionuclides of interest and compare results with guideline values.
  4. Decontaminate any areas of removable contamination above the guideline values. It is advisable to decontaminate removable contamination to background levels if possible with a reasonable effort.

Note: It is important to thoroughly survey the inside of hoods and ductwork if volatile radioactive materials were handled. Likewise, it is important to thoroughly survey sink basin and sink drain traps for contamination. Some laboratories contain individual waste neutralization "chip" tanks at each sink drain. The inside of these tanks or the calcium carbonate chips may be a source of radioactive contamination and should be tested.

A detailed map showing location of testing and a description of how the tests were performed should be kept with the results of the surveys.

Instrumentation
The following are examples of instruments that may be used in laboratory decommissioning efforts.

Exposure rate

  1. Pressurized ion chamber with sensitivity to 1 µR/h
  2. Geiger Mueller (GM) end window with sensitivity to 50 µR/h

Fixed contamination

  1. GM pancake detector for beta/gamma emitters with a sensitivity of 1000-2000 dpm/100 cm2
  2. Scintillation detector (NaI) for gamma emitters with sensitivity of 1000-2000 dpm/100 cm2
  3. Proportional counter for beta/gamma emitters with sensitivity of 500-2000 dpm/cm2 dependent on detector area

Removable contamination

  1. Liquid scintillation counting of swipe tests with sensitivity to 50 dpm/100 cm2
  2. Gas flow proportional to counting of swipes with sensitivity to 10 dpm/100 cm2

Note: Some radioactive materials, in particular the naturally occurring radioactive materials such as uranium and thorium, do not require the user to be licensed or permitted for use. Many chemistry, biology, and materials science laboratories use these materials routinely without the knowledge of the radiation safety office. It is important to identify if a laboratory uses forms of these radionuclides before they become mixed with other chemical wastes.

Appendix 2. Decontamination protocols Class 1 and 2 biological agents

  1. Select a disinfectant appropriate for the agent(s) in use. For example, although a quaternary ammonium compound would be adequate for E. coli, it would not be effective for Mycobacterium tuberculosis, for which one would want a phenolic-based disinfectant.
  2. Identify areas that need to be disinfected. These include benchtops, surfaces of equipment, and other potentially contaminated places (hoods, waterbaths, centrifuges, etc.).
  3. Wear personnel protective equipment (long-sleeve lab coat and gloves). You want a barrier between yourself and the disinfectant chemical(s).
  4. If the disinfectant in use does not contain a surfactant, wash the areas to be decontaminated with soap (detergent) and water first to remove oily dirt that may prevent the disinfectant from contacting and killing the microorganisms.
  5. Pour the disinfectant on the areas to be decontaminated or onto toweling. Rub the areas and repeat. Let a film of disinfectant remain on the surface to air dry. If using a phenolic-based compound, follow up with a water rinse to remove the residual phenolic (if desired). For this procedure to be effective, the disinfectant must contact the organism and be in contact for a sufficient time to kill.

Class 3 biological agents

  1. If proper Biosafety Level 3 procedures were rigorously adhered to, contamination should be limited to the BSC. However, because of the inherent risk of a class 3 agent, it is advisable to decontaminate the whole laboratory before moving equipment.
  2. Remove or seal all cultures gas-tight.
  3. Have an outside contractor, your environmental health and safety personnel, or other qualified personnel perform a gaseous decontamination of the entire laboratory space by using formaldehyde gas, vaporized hydrogen peroxide, ozone, or chlorine dioxide.

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References

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