Contamination control is a primary emphasis of the radiation safety program at the NIH. Prudent contamination control involves careful planning, process containment, protective coverings, personal protective equipment, and avoidance of spills. However, contamination monitoring is the most important element of a contamination control program. There are three fundamental types of radiation monitoring conducted at the NIH.
Routine Contamination monitoring at the NIH is recorded and documented on a variety of contamination surveys as needed
A daily contamination survey is required each day after any work with unsealed forms of radioactive material. Daily contamination surveys are not required on days when work with RAM was not performed.
Hand-held contamination metering should cover the hands, lab coat, work area, floor adjacent to the work area, shoes (top and bottom), waste storage area and potentially contaminated equipment. The daily survey does not have to be documented.
A portable survey meter is acceptable as long as the sensitivity of the instrument allows for efficient detection of the radionuclides used.
When using a hand-held contamination meter, a count rate of more than two times the background typically indicates the presence of contamination.
*For low-energy beta emitters, a smear survey is required (with an appropriate counting technique). Portable survey meters are not appropriate, due to their extremely low efficiency.
Monthly Surveys
A thorough contamination survey of the entire lab module is required to be performed once each calendar month. How lab modules are determined can be found in the supplement for the survey form NIH 88-12.
A minimum of ten smear sample locations must be collected, including at least two smears on the floor. Smear locations should include areas and items that have a higher potential for contamination. Locations should be varied from month to month. Some suggested areas to swipe for contamination are:
- Work areas, lab benches, and desks
- Sinks
- Lab equipment used with radioactive materials
- Refrigerators and freezers
- Incubators
- Floor adjacent to work areas and near hallway entrances
- Door handles
Smears should be counted by an appropriate counting technique (LSC or gamma counter).
Any contamination identified on a monthly survey must be decontaminated and re-surveyed to satisfy the ALARA policy and demonstrate compliance with the removable contamination limits for restricted areas.
Monthly surveys must be documented on a Form NIH 88-12 , with:
- A diagram of the laboratory
- What nuclides were used during the month
- Locations of smears
- Description of contamination identified during the survey
- Description of re-survey results
A copy of the completed survey form must be submitted to DRS, along with a copy of the counter printout. A copy of the survey must also be kept on file in the lab's Radiation Safety Records, and retained for a minimum of three years (for inspection by DRS or contract personnel and NRC inspectors).
If radioactive materials are not used for the month, monthly surveys indicating radioactive materials were not used must be submitted electronically via the DRS Authorized User Portal, however smears are not required. Access to the Authorized User Portal is available through this link - http://drsportal.ors.od.nih.gov
For complete instructions on filling out the monthly survey form please click: NIH 88-12
Monthly Survey Service
Monthly surveys may be contracted out to Clym Environmental Services (Clym), DRS's regulatory compliance support contractor.
The cost per lab module is $47 per month and may be paid by CAN, credit card, or purchase order.
To make arrangements for this service or for more information, contact Clym at 301-435-7953, 888-289-2324 or beth@clymenvironmental.com.
Comprehensive (Contractor) Surveys
In addition to daily and monthly surveys, DRS maintains a staff of contract technicians who perform routine comprehensive surveys of all posted laboratories. The frequency is determined by DRS, and varies for each lab (semiannual, quarterly, bimonthly, monthly, or weekly).
Like daily and monthly surveys, comprehensive surveys are designed to monitor for contamination. However, these surveys also include the measurement of radiation levels, inspection of lab records, and evaluation of general compliance with the NIH Radiation Safety Program.
Results of a comprehensive survey are reported to DRS on a Radiation Survey Report [contractor survey form], including any items of noncompliance. The Area Health Physicist reviews each comprehensive survey and determined an appropriate course of action.
A copy of each Radiation Survey Report is also furnished to the Authorized User of the lab, along with a set of Radiation Safety Survey Information Sheets to describe the survey results and suggest corrective actions.
Surveying for Removable Contamination
Removable contamination is defined as the radioactivity that can be transferred from a surface by rubbing with moderate pressure. The level of removable contamination is a primary focus of contamination control at NIH.
The smear (or wipe/swipe test) is the universal method of assessing removable contamination, and the required method for monitoring certain radionuclides.
A small cloth, filter paper, or fiberglass disk is used to "wipe" a sample of removable contamination. Fiberglass disks are preferable for low-energy beta emitters, since they dissolve or become transparent in liquid scintillation fluid.
A smear should cover a minimum surface area of 100 cm⊃; (approximately equal to a square measuring 4" by 4"). Smears should be dry, and taken using moderate pressure.
Smears must be separated to avoid cross contamination. Smear packets make this easy, and are commonly available at the NIH Self Service Stores.
If counting results are reported in counts per minute (cpm), they must be converted to decays per minute (dpm) using the counting efficiency:
The maximum allowable limits for removable contamination are as follows:
| 2,200 dpm/100 cm⊃; beta/gamma and 220 dpm/100 cm⊃; alpha |
220 dpm/100 cm⊃; beta/gamma and 22 dpm/100 cm⊃; alpha |
Data should be maintained regarding the date and location of each smear. For monthly surveys, the smears should be documented on the survey form (NIH 88-12).
If smears demonstrate that there is no removable contamination, but a survey meter indicates a count rate of greater than 1000 cpm, contact your Area Health Physicist for further instructions. Don't waste your time scrubbing when you can't remove anymore contamination. The Area Health Physicist can apply regulatory limits for fixed contamination and advise you accordingly.
Counting Methods
Smears to assess beta contamination must be analyzed with a liquid scintillation counter (LSC). Smears to assess gamma contamination should be analyzed with a gamma counter.
An LSC may be used to assess gamma contamination, but close attention must be given to the efficiency of the counter for the radionuclide in question.
The manufacturer or qualified service representative should calibrate counters on an annual basis. This calibration determines the counting efficiency for common radionuclides used at NIH, which must be used to convert between cpm and dpm.
When possible, liquid scintillation samples should be dark adapted before analysis to reduce the effect of chemiluminescence. This can be accomplished by simply leaving the rack in the counter (with the cover closed) for 30 minutes or more.
Additionally, a blank vial should be counted as a background and a known standard should be counted as well. For good counting statistics, samples should be counted for at least one minute.