Acknowledgments 

The author would like to acknowledge and thank the following people for their kind and thoughtful advice: Mr. Greg Budd, of the U.S. EPA Las Vegas facility (Radiation and Indoor Environment National Laboratory); Mr. Samuel W. Poppell, Jr. of the U.S. EPA Montgomery facility (NAREL); Mr. Dave Gray, also at the U.S. EPA in Montgomery and who has a wealth of information concerning the technical aspects of measuring radon and radon decay products; Dr. Phillip H. Jenkins of Bowser-Morner, Inc. in Dayton Ohio, who is certainly one of the leading experts on the operation of radon chambers.

Disclaimers

1. Although this document was written with a great deal of technical advice from the above-mentioned experts, any errors or omissions contained herein are solely the responsibility of the author and are not to be a reflection upon anyone else.

2. This document is a final version of, and replaces the Interim Chamber Protocols of September 1998. Anyone using this document shall verify that it has not been superseded by an updated version by calling Mr. Larry Marcum, J.D., at NEHA at 303-756-9090, ext. 303.

3. This document contains technical terms and procedures which will require an extensive knowledge of radon and radon decay product measurement procedures to understand and implement. However, it is not a training manual. It is, therefore not intended to teach someone how to set up, operate or maintain a radon or radon decay product chamber. 

September 1, 1999

James F. Burkhart, Ph. D.
Professor of Physics,
Director, WRRTC
University of Colorado
Colorado Springs, CO 80918

Background

Since the mid 1980’s, the U.S. EPA has been using its radon chambers at the National Air and Radiation Environmental Laboratory in Montgomery, Alabama, and its radon chambers at the Radiation and Indoor Environment National Laboratory in Las Vegas, Nevada, to conduct performance testing on the so-called "Primary Laboratories" (more recently named "Analytical Service Providers").

As part of this performance test, the laboratory sent one (or more) of its radon and/or radon decay product measurement devices to the radon chambers upon the request of the U.S. EPA Radon Proficiency Program coordinator. At the chambers, the device was exposed to a well-regulated radon or radon decay product concentration, the exact value of which was kept blind from the laboratory participant. After completion of the exposure, the device was returned to the laboratory for analysis (in some cases, the device was read on-site at the chamber by the laboratory operator who accompanied the device to Montgomery or Las Vegas).

The radon or radon decay product value calculated by the laboratory was then compared to the known chamber value. Participants passed the performance test if all of their devices read within 25% of the chamber values (with some accommodations for retesting if certain criteria were met).

However, the U.S. EPA discontinued its involvement in the Radon Proficiency Program (RPP) as of September 30, 1998. This means that the chambers in Las Vegas or in Montgomery are no longer available for these performance tests. Any organization which intends to set up an alternative program to replace the U.S. EPA’s RPP will necessarily have to find a different way to approve the radon and radon decay product measurement devices used by laboratories and measurement professionals with analytical capabilities. In particular, private chambers will need to be used for the performance tests in lieu of the EPA chambers.

The National Environmental Health Association has been awarded the pilot program designed to consider alternatives to the EPA’s RPP. As part of the implementation of the pilot program, NEHA intends to use private chambers to continue the performance test procedures formerly done by the U.S. EPA chambers in Las Vegas and Montgomery.

Purpose of this Document

This document is intended to be a set of guidelines which will be used to approve radon/radon decay product chambers wishing to become certified by NEHA to conduct the NEHA performance tests on testing devices from laboratories and measurement providers with analytical capabilities who wish to be NEHA certified as such.

It is intended that the guidelines in this document set minimal standards, which are sufficient to ensure that chambers that are certified under its rubric will produce a product of high quality and have the confidence of the radon industry. On the other hand, these standards allow for many existing (and future) chambers to enter the NEHA program, thereby fostering competition, with the usual market implications.

What This Document Is Not

This document is not intended to set guidelines for radon/radon decay product chambers that are used exclusively for calibration of radon or radon decay product measurement devices. The reasons for this are two-fold.

1. Historically, the EPA’s RPP program did not require the approval of such calibration chambers; hence, NEHA would not find it a priority to establish criteria for chambers for which the EPA itself had not established criteria.

2. The ultimate test of the accuracy of a measurement device is the performance test. In other words, even though regular calibration of a measuring device may be required, it is only upon passing the performance test that a laboratory will be certified by NEHA. Therefore, it is the performance test aspect of the radon/radon decay product chambers that is of most concern to NEHA presently.

This document is not intended to replace existing draft or completed criteria for the certification of radon/radon decay product chambers. Various documents exist and they should be used by NEHA’s technical committees in the future, but these documents (for example, the IEC 45B/203/CDV "STAR" protocol, "Design Criteria and Performance Characteristics of Radon Chambers" by Andreas George and Nancy Bredhoff, and "Manual for the Radon Chamber Qualification (RCQ) Proficiency Program" by Jon A. Broadway) were not used, in whole or in part, in the writing of this interim protocol.

The chamber must provide NEHA evidence that it complies with all applicable Federal, State and local regulations concerning the ownership of radioactive materials and the discharging of radon gas into the environment. A worker safety document must be provided if it is required by any of the above agencies.

1.2 Quality Assurance/Quality Control Plan and SOP

The chamber must provide NEHA a Quality Assurance/Quality Control Plan which details the way in which the chamber routinely checks its own performance, the types of control charts or statistics it employs, and the mechanisms that are in place in the event that control charts or statistics indicate that corrective measures need to be taken. A list of the people and their responsibilities is also required.

The chamber must provide NEHA a standard operating plan (SOP) detailing its normal operating procedures. Any updates that the chamber makes to its SOP shall be forwarded to NEHA in a timely fashion.

The radon source must be a shielded commercial radium source from which the radon is bled off in a controlled fashion. In no case may the radon source be soil gas because of the inherent difficulties with soil gas (it is difficult to control and has widely varying amounts of thoron (radon 220)).

Although a few radon chambers are large enough to walk inside, smaller chambers have proven reliable as long as the number and type of devices being spiked is commensurate with the volume of radon available for spiking. A minimum size of 50 cubic feet, however, is strongly recommended because of the propensity for large radon fluctuations when devices are put into or taken out of the chamber, and the very real possibility of some depletion of the radon inside the chamber because of passive diffusion or forced convection of radon from the chamber and into the device being spiked. There is no maximum size limit to the chamber volume although very large chambers shall have, as part of their quality control plan, a method of verifying that the radon concentrations (at any one time) are homogeneous throughout the chamber volume.

1.4 Environmental Controls

1.4.1 The chamber must be able to be controlled in such a way as to allow the change in radon concentration in a controlled manner. The radon concentration must be able to be set as low as 4.0 pCi/L and as high as 30 pCi/L to allow for a variety of exposures. It is preferred, but not necessary, that the chamber be able to be set as high as one hundred pCi/L to allow for relatively rapid exposure of long term devices.

1.4.2 Once the radon concentration is set to a particular value, there shall be sufficient control of the radon source and/or chamber parameters to be able to maintain the new radon level consistently (defined as meaning that the coefficient of variation of the hourly measurements must be 10%, or less) over the exposure period for the particular device being tested.

1.4.3 The temperature of the chamber must be able to be maintained at room temperature (68 degrees to 72 degrees Fahrenheit) over the entire exposure period for the particular device being tested. The temperature of the chamber must be monitored continuously with an hourly recording device. It is preferred, but not necessary, that the temperature of the chamber be controlled in such a manner as to allow a change in temperature when desired.

1.4.4 The humidity of the chamber must be constantly monitored and recorded at least hourly. It is necessary that the chamber be able to maintain humidity conditions that reflect realistic (real-world) parameters. It is preferred, but not necessary, that the humidity inside the chamber be controlled in such a way as to allow the humidity to be varied at will and maintained at any new level set for the duration of an exposure period (dependent upon the device being tested).

1.4.5 It is preferred, but not necessary, that the barometric pressure within the chamber be monitored and recorded at least daily. This information may be useful for correcting calculations involving measurement devices that are sensitive to atmospheric pressure.

1.4.6 The radon in the chamber must be monitored continuously with a continuous radon monitor which has a precision which is as good, or better, than the precision of the device which is being exposed within the chamber at the time. The continuous monitor must be able to provide hourly readings at the minimum.

1.4.6.1 Periodic grab samples must be taken to normalize or verify the continuous monitor’s readings. It is preferred, but not required, that at least one grab be taken daily with the results compared to the continuous monitor’s output for the equivalent time period. If the radon chamber is being maintained at a constant value over a long time period, then one grab sample taken once a week is sufficient as long as the chamber value is not varied during that week. However, during an actual performance test (in other words, while (a) test device(s) is (are) inside the chamber) no less than two simultaneous grabs shall be taken during the exposure period of the device(s).

1.4.6.2 The scintillation or Lucas cells used for the grab samples shall have a minimum volume of 125 ml in order to ensure a large enough radon sample is taken to allow for reasonable statistics during later calculations.

1.5.1 Regardless of any in-house calibrations or standards (NIST traceable or otherwise) employed by the chamber to ascertain chamber values, all chambers shall have an intercomparison with an EPA chamber at least annually. It is the results of this intercomparison which will be used by NEHA to ascertain the viability of the chamber, as described below.

1.5.2 At this time, it is expected that at least one chamber at the Radiation and Indoor Environment National Laboratory at Las Vegas will be available for the purposes of the intercomparisons. Any costs involved will have to be borne by those private chambers using the Las Vegas facility.

1.5.2.1 To conduct the actual intercomparison, four scintillation or Lucas cells (with a minimum volume of 125 ml) will be sent simultaneously to the EPA chamber. Accompanying the cells will be a complete set of instructions on how to conduct the sampling. Also, any tubing, pumps, valves, etc., must be supplied by the private radon chamber.

1.5.2.1.1 For these protocols, the only devices allowed to be used for inter comparison purposes will be scintillation or Lucas cells as described above. Passive devices (such as charcoal devices, electret ion chambers and alpha-track detectors) do not have sufficient precision for this purpose. Some continuous radon monitors do have sufficient precision to be used as inter-comparison devices, but the decision on which monitors could be used requires lengthy discussions by industry groups and the technical board of NEHA, which have not yet occurred.

1.5.2.2 The four cells will be exposed as simultaneously as possible to an identical radon concentration in the EPA chamber. The cells will be returned to the private chamber as quickly as possible and the EPA chamber will inform NEHA of the chamber concentration, including its standard deviation.

1.5.2.3 The private chamber will read the four cells and report the average and the standard deviation to the group at NEHA which will be assigned the responsibility of comparing this average value to the EPA chamber value. A private chamber will have passed the inter comparison if the average of the four cells is within 10% of the EPA chamber value and no individual cell is more than +/- 25% from the EPA chamber value. By EPA chamber value it is meant the radon concentration, plus and minus 2 standard deviations, in pCi/L, as determined by the EPA using whatever methodology for spiking the cells and for determining the concentrations they feel are appropriate.

For example, if the EPA reports a chamber value of 10 pCi/L, with a 2 sigma of 1 pCi/L, then the private chamber must report an average radon value of no more than 25% above 11 pCi/L and no lower than 25% below 9 pCi/L, where the 11 pCi/L is the average EPA chamber value plus 2 sigma and the 9 pCi/L is the average EPA chamber value minus 2 sigma.

1.6 Business Practices

1.6.1 Because of the potential conflict of interest, a company or individual which runs a private radon chamber shall not performance test any lab or device associated with that company. For example, a laboratory which sells charcoal canisters and also runs a radon chamber shall not use the radon chamber, even if it is certified by NEHA as a performance testing chamber, to performance test its own charcoal canisters. This does not preclude, of course, the chamber from running performance tests on test devices marketed by other companies or from using its chamber to calibrate its own devices.

1.6.2 Companies or individuals that run private radon chambers (which are certified by NEHA as performance testing chambers) and also manufacture, market or sell radon measurement devices, or have any financial interest in radon measurement devices, shall notify potential performance test customers (laboratories and/or measurement professionals with analytical capabilities) of the types of devices which the company manufactures, markets or sells or has a financial interest in. In this way, the potential customer (laboratory and/or measurement professionals with analytical capabilities) can decide whether it wishes to have its device performance tested by a possible business competitor.

1.6.3 As long as the EPA action level remains at 4.0 pCi/L, it is expected that NEHA certified radon chambers will maintain radon concentrations of 4.0 pCi/l or higher during performance tests. Except for performance tests of grab devices, the minimum exposure time for the performance testing of all devices will be 48 hours. The minimum exposure (in pCi days/L) for a specific device is found by multiplying 4.0 pCi/L times the minimum number of days the device can be deployed (as determined from the advertising or manufacturer’s brochure accompanying the device). For example, for a device which is advertised as having a 91 day minimum exposure time, the minimum exposure in the chamber will be 4.0 pCi/L multiplied by 91 days, or 364 pCi days/L. However, in no case will the exposure time be less than 48 hours, regardless of the radon concentration used.

1.6.4 Minimal educational and/or training standards must be set by the NEHA board for a chamber designer and for a chamber operator. In the interim, it is necessary that the designer and operator have at least the training equivalent to that of a two day Radon Measurement Operator course as offered by the National Radon Training Centers.

The chamber must provide NEHA evidence that it complies with all applicable Federal, State and local regulations concerning the ownership of radioactive materials and the discharging of radon gas into the environment. A worker safety document must be provided if it is required by any of the above agencies. This document can be combined with the document required in section 1.1 if the chamber wishes to be certified in both radon and radon decay products.

2.2 Quality Assurance/Quality Control Plan and SOP

The chamber must provide NEHA a Quality Assurance/Quality Control Plan which details the way in which the chamber routinely checks its own performance, the types of control charts or statistics it employs, and the mechanisms that are in place in the event that control charts or statistics indicate corrective measures need to be taken. A list of the people and their responsibilities is also required. This document can be combined with the document required in section 1.2 if the chamber wishes to be certified in both radon and radon decay products.

The chamber must provide NEHA a standard operating plan (SOP) detailing its normal operating procedures. Any updates that the chamber makes to its SOP shall be forwarded to NEHA in a timely fashion.

The radon decay product source will be a shielded commercial radium source from which the radon is bled off in a controlled fashion. In no case may the radon source be soil gas because of the inherent difficulties with soil gas (it is difficult to control and has widely varying amounts of thoron (radon 220)). 

Because of the propensity for radon decay products to plate out on the interior chamber walls, a minimum chamber volume of 125 cubic feet is required.

2.4 Environmental Controls

2.4.1 The chamber must be able to be controlled in such a way as to allow the change in radon decay product concentration in a controlled manner. A particle generator is required. The particle generator must have some method of being controlled so that the secular equilibrium of the chamber can be set and maintained.

2.4.2 Once the radon decay product concentration is set to a particular value, there shall be sufficient control of the radon and particle source and/or chamber parameters to be able to maintain the new radon decay product concentration at a constant value (defined as meaning that the coefficient of variation of the hourly measurements must be 10% or less) over the exposure period for the particular device being tested.

2.4.3 It must be possible to maintain the temperature of the chamber at room temperature (68 degrees to 72 degrees Fahrenheit) over the entire exposure period for the particular device being tested. The temperature of the chamber must be monitored continuously with an hourly recording device. It is preferred, but not necessary, that the temperature of the chamber be controlled in such a manner as to allow a change in temperature when desired.

2.4.4 The humidity of the chamber must be constantly monitored and recorded at least hourly. It is necessary that the chamber be able to maintain humidity conditions that reflect realistic (real-world) parameters. It is preferred, but not necessary, that the humidity inside the chamber be controlled in such a way as to allow the humidity to be varied at will and maintained at any new level set for the duration of an exposure period (dependent upon the device being tested).

2.4.5 It is preferred, but not necessary, that the barometric pressure within the chamber be monitored and recorded at least daily.

2.4.6 The radon decay product concentration in the chamber must be monitored continuously with a continuous working level monitor which has a precision comparable to the precision of the device which is being exposed within the chamber at the time. The continuous monitor must be able to provide hourly readings at the minimum.

2.4.6.1 Periodic grab samples must be taken to normalize or verify the continuous monitor’s readings. It is required, that at least one grab sample be taken daily with the results compared to the continuous monitor’s output for the equivalent time period.

2.4.6.2 The grab samples shall be taken with a minimum flow rate of 10 L/minute and a minimum filter size of 1" diameter. The flow rate needs to be measured accurately. The minimum sampling time for the grab sample is five minutes. Various counting regimes are allowed.

2.4.6.3 In order to calculate the counting efficiency of the detector used to analyze the grab sample, some kind of alpha-emitting standard using the same geometry as the filter is required.

2.5.1 Regardless of any in-house calibrations or standards (NIST traceable or otherwise) employed by the chamber to ascertain chamber values, all chambers shall have an intercomparison with an EPA chamber at least annually. It is the results of this intercomparison that will be used by NEHA to ascertain the viability of the chamber, as described below.

2.5.2 At this time, it is expected that at least one chamber at the Radiation and Indoor Environment National Laboratory at Las Vegas will be available for the purposes of the intercomparisons. Any costs involved will have to be borne by the private chambers using the Las Vegas facility.

2.5.2.1 To conduct the actual intercomparison, the chamber operator must take the radon decay product (RDP) grab sampling equipment to the EPA chamber and do the intercomparison in person. The same minimum characteristics which described an appropriate grab device in sections 2.4.6.2 and 2.4.6.3 apply.

2.5.2.2 Intercomparisons using RDP grabs require that four grabs are taken one after the other, while the target chamber (the EPA chamber) varies the working level concentration. Specifically, two RDP samples (grabs) are taken at one chamber value and two RDP samples (grabs) are taken at a second value. The EPA chamber will then inform NEHA of the two chamber concentrations, including their standard deviations.

2.5.2.3 The private chamber will analyze the four samples and report the four individual results to the group at NEHA which will be assigned the responsibility of comparing these four values to the two EPA chamber results. A private chamber will have passed the intercomparison if (a) the average of each pair of samples is within 10% of the corresponding target chamber value and (b) no individual sample is more than 25% from the corresponding chamber value. By EPA chamber value it is meant the radon decay product concentration, plus and minus 2 standard deviations, in WL, as determined by the EPA using whatever methodology for producing the radon decay products and for determining the concentrations they feel are appropriate.

Note: the NEHA RPP Technical committees may want to consider averaging the performance ratios (called "Bias factors") as discussed in the U.S. EPA’s "Manual for the Radon Chamber Qualification (RCQ) Proficiency Program", pages 3-17and 3-18, as an alternative to the passing indicators discussed above.

2.6 Business Practices

2.6.1 Because of the potential conflict of interest, a company or an individual which runs a private radon decay product chamber shall not performance test any lab or device associated with that company. For example, a laboratory which sells continuous working level monitors and also runs a performance testing radon decay product chamber shall not use the chamber, even if it is certified by NEHA as a performance testing chamber, to performance test its own continuous working level monitor. This does not preclude, of course, the chamber from running performance tests on test devices manufactured by other companies or from using its chamber to calibrate its own equipment.

2.6.2 Companies which run private radon decay product chambers (which are certified by NEHA as performance testing chambers) and also manufacture, market or sell radon decay product measurement devices or have any financial interest in the selling or marketing of such devices, shall notify potential performance test customers (laboratories and/or measurement professionals with analytical capabilities) of the types of devices which the company manufactures, markets or sells or has a financial interest in. In this way, the potential customer (laboratory and/or measurement professional with analytical capabilities) can decide if it wishes to have its device performance tested by a possible business competitor.

2.6.3 As long as the EPA action level remains at 4.0 pCi/L, it is expected that NEHA certified radon decay product chambers will maintain radon decay product concentrations of .02 WL or higher during performance tests. Except for performance tests of grab devices, the minimum exposure time for the performance testing of all devices will be 48 hours.