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Answer to Question #7605 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Surveys and Measurements (SM)

The following question was answered by an expert in the appropriate field:


This question is related to work with naturally occurring radioactive material (NORM) in the oil and gas industry. Generally, surveys to identify equipment that is contaminated (e.g., as required by environmental laws) require gamma measurements using the Ludlum Type 3 meter with the 44-2 probe. The other measurement we do for loose or fixed-surface contamination is when a vessel is opened or equipment is serviced. We use the 44-9 probe for that. My question is: for health and safety purposes, how can we use the value from the 44-9 readings to institute measures to protect employees against alpha and beta radiation, and what is a level of concern? There aren't any specific health and safety regulations for this and, generally, if the counts per minute (cpm) on the 44-9 is above 200 or 300, we have the employees wear half-face P100 respirators, Tyvek®, and goggles. The biggest question is: is this enough for respiratory protection against alpha/beta? We typically see ranges of background at about 2,000 or 3,000 cpm, but we have had a few cases where we had 600,000 cpm without any gamma readings. We don't know what that comes from (we think lead-210 [210Pb] or polonium), but we worry that a P100 filter might not be enough. Still, the contaminated work is not dusty so there isn't a lot of opportunity to breathe in material.  

Do you have advice on proper estimation of personal protective equipment use for employees using the 44-9? Is a P100 respirator adequate for high levels on the 44-9 without a dusty environment?


The decision as to whether to require the use of respiratory protection and the associated decision as to what type of respirator is necessary depends on the identity of the radionuclide(s) involved, the amount of radioactivity present in/on media accessible to workers, and the potential that accessible radioactivity will become airborne, thus representing a possible inhalation threat. Usually such decisions are made by persons in authority who have sufficient supporting information to make such decisions.

The use of respiratory protection in a formal program requires considerable preparation and testing to show that the respiratory protection is adequate for the job at hand and that the workers have been trained in its proper use and have participated in a respirator-fitting program. The respiratory protection program must be written up and should contain information necessary in making decisions about use of particular protective devices. See the OSHA regulations 29 CFR 1910.134 for specific requirements and recommendations. The state in which you are located will also have regulations that affect your operations, and the U.S. Nuclear Regulatory Commission and others may also be involved in regulatory aspects of importance to you.

The P-100 respirator that you refer to is a simple, low-cost, filtering half-mask that is adequate for protection against relatively low levels of some radioactive particulates. The highest protection factor associated with such a device is about a factor of 10. The maximum protection factor offered by a somewhat more sophisticated full-face mask (still with negative pressure) with particulate filter is about 50 (e.g., see 10 CFR 20 App. A, Protection Factors for Respirators). If a mask with particulate filter is used in which positive air pressure is maintained within the mask, the protection factor may be up to 1,000.

In order to assess the need for respiratory protection, your facility personnel should be conducting an air-sampling program that allows you to evaluate the airborne concentrations of radionuclides of interest when certain operations are ongoing. This is really the only effective way to obtain enough information to make the required judgments about whether respiratory protection is required and, if so, the type of respirator that is appropriate.

When you make measurements of exposed contamination with a particular probe, such as the thin-window Ludlum Model 44-9 pancake Geiger-Muller (GM) detector, you obtain a reading that is indicative of possible alpha- and beta-emitting radionuclides; gamma radiation is also detectable, but with a much lower efficiency than particulate radiations. A high reading, such as the 600,000 cpm that you note, appears as possibly indicative of relatively high levels of NORM surface contamination, but this in itself is not sufficient to be able to make a specific recommendation as to whether a particular type of respirator is necessary and/or adequate. You must know the identities of the radionuclides contributing to the observed count and must know whether the ongoing operation is such that it might produce airborne concentrations of such contaminants at concentrations of concern. There are situations in which the greatest release of activity into the air might occur when a closed system is being opened up. In such an event it is important to be taking an air sample during the time that the system is being opened as well as after, when other operations are ongoing. The measurement of the surface activity alone after the system has been opened might be informative but not adequate to tell you whether any significant airborne activity was created during the opening process.

I would like to be able to provide more quantitative information by which you could judge the significance of instrument readings, but I believe you must have more information in order to allow such estimations. Since you are dealing with NORM, I expect that you have a pretty good handle on the identities of likely radionuclides that appear in certain situations in which you are making measurements. It is important to know the relative amounts of different radonuclides that might be present and to know whether the operations being conducted are likely to generate particulate aerosols at concentrations of concern. Such information is best obtained through more quantitative measurements, especially in the context of an air-sampling program carried out as operations are taking place. Representative air samples can generally be obtained using high-efficiency, glass-fiber filter papers with suitable air pumps, preferably pumps that can draw tens of liters per minute through the filter in order to obtain adequate samples within reasonably short sampling times. You would have to arrange to analyze the filters to obtain quantitative estimations of the radionuclides present. I hope you are able to obtain the air concentration measurements that will assist you in making appropriate decisions about the use of respiratory protection.

George Chabot, PhD, CHP

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