Continuous Air Monitors

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

Precautions. The intricacies and procedures of sample analysis are beyond the scope of this manual.

However, a few general precautions are important to mention. The naturally occurring radionuclides, radon

and thoron and their decay products, are present in all atmospheres in widely varying concentrations. These

radionuclides are typically present in higher concentrations than the isotopes of interest, and tend to

interfere with radiometric analysis, unless the short-lived progeny are given time to decay after sample

collection. Radon progeny, which are much more abundant than thoron progeny in most areas, decay with

an effective half-life of about 30 minutes and a counting delay of 3 hours may be adequate. Thoron progeny

decay with an effective half- life of 10.6 hours, and where they exist in significant concentrations, a

counting delay of several days is advisable. The presence of either radionuclide on a filter can be detected

by recounting two or three times at intervals of a few hours.

The sensitivity of any counting method depends primarily on the background count rate of the

counting instrument; estimates of low radionuclide concentrations can be seriously in error if the counting

background is not accurately known. Even in stable instruments for which the background count may be

quite constant, a daily check is advisable because of the possibility of contamination from sample material.

Background counts should be made with a blank filter in place because some filter media contain trace

Counting instruments also require periodic standardization. Standard sources used for this purpose

should match the samples both in size and energy.

The active (upstream) sides of filters collected in clean atmospheres can be difficult to identify. Some

convention should be followed by sampling personnel to ensure that the proper sides of filters will be

counted. This may consist of marking one side of the filter or placing the filter in the sample holder

consistently with the exposed side toward the identifying number or label on the holder.

4.1.7 Continuous Air Monitors

The combination of an air sampler and an activity counter into a single device for automatic

operation and alarm control constitutes a CAM.

4.1.8 Monitoring Strategies and Protocols

Designing an air-sampling program for the work place is a complex task because each facility has

unique design and operational characteristics. It is important that the radiologic al control personnel who

coordinate the sampling program have a thorough understanding of basic facility operations, especially

with respect to the potential each operation has for generating airborne material. In addition, these

personnel should be familiar with the working habits of potentially-exposed workers. The success of most

sampling programs depends on the ability of radiological control personnel to accurately assess worker

exposure risk and properly select workers for personal air sampling. This can only be accomplished by

well-trained, observant safety personnel.

The following questions should be considered for an airborne activity hazard evaluation:

a. Where are the potential aerosol generation and release locations in the work-site, and what is the

magnitude of potential exposures associated with each?

b. How effective or failure-prone are the physical and procedural barriers that protect the worker

from airborne radioactive material generated at these locations?

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