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Radon (Rn)

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Indoor Radon and Radon Decay Product Measurement Device Protocols

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

Section 1: General Considerations

Please Note:

EPA closed its National Radon Proficiency Program (RPP) in 1998.  The information in this document which refers to companies, individuals or test devices that "meet EPA's requirements", or "EPA Certified...",  or refers to EPA's old RPP designations "RMP or RCP" is no longer applicable.  Please check our "How to ... page for more information on how to find a qualified radon service professional near you.

1.1 Introduction and Background
1.2 General Guidance on Measurement Strategy, Measurement Conditions, Device Location Selection, and Documentation
1.3 Quality Assurance

1.1 Introduction and Background

The risk of lung cancer due to exposure to radon and its decay products is of concern to State and Federal health officials. There is increased awareness that indoor radon concentrations may pose a significant health threat, and that there are areas in the country where some indoor levels are such that even short-term exposures can cause a significant increase in risk. It is extremely important that homes and other buildings be tested to determine if elevated radon levels are present indoors. However, in the process, the collection of unreliable or misleading data must be avoided.

There are many Federal, State, university, and private organizations now performing measurements or planning measurement programs. It is important for these different groups to follow consistent procedures to assure accurate and reproducible measurements, and to enable valid intercomparison of measurement results from different studies.

The objective of this document is to provide information, recommendations, and technological guidance for anyone providing measurement services using 15 radon and radon decay product measurement methods. The EPA has evaluated these techniques and found them to be satisfactory. However, the Agency has not conducted large-scale field tests using the unfiltered track detection technique, and an interim protocol has been prepared with the assistance of researchers who have field experience with this method. As the EPA and others acquire more experience with this interim technique, the guidelines may be revised.

These Protocols provide method-specific technological guidance that can be used as the basis for standard operating procedures. In keeping with good laboratory practices, each radon measurement company should develop its own detailed instrument-specific procedures that incorporate recommendations found in this and other radon-related EPA protocol and guidance documents. Mere duplication of sections of this report will not constitute an adequate standard operating procedure.

The recommendations contained in this report are similar to those being developed by industry and other groups (e.g., the American Society of Testing and Materials [ASTM 1991] and the American Association of Radon Scientists and Technologists [AARST 1991a]). This report is a guidance document; however, one condition of participation in EPA's former National Radon Proficiency Program (RPP) was conformance with these protocols.

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Table of Contents

Section 1

Section 2

Section 3

Appendixes

See also: Protocols for Radon and Radon Decay Product Measurements in Homes (available in PDF) (PDF, 47 pp., 674 K)

1.2 General Guidance on Measurement Strategy, Measurement Conditions, Device Location Selection, and Documentation

1.2.1 Measurement Strategy

The choice of measurement strategy depends upon the purpose of the radon measurement and the type of building where the measurement is made, such as a home, school or workplace. EPA's recommendations for measuring radon in various situations are outlined in documents such as the second edition of "A Citizen's Guide to Radon", the EPA "Home Buyer's and Seller's Guide to Radon", the "Protocols for Radon and Radon Decay Product Measurements in Homes" (U.S. EPA 1992c), and in "Radon Measurements in Schools" (EPA Document #402-R-92-014, revised July 1993). The following discussion on measurement conditions, device location selection, and documentation apply to measurements made in all types of buildings.

1.2.2 Measurement Conditions

The following conditions should exist prior to and during a measurement period to standardize the measurement conditions as much as possible. This list may be applied to each of the measurement methods discussed in Sections 2 and 3. However, there may also be method-specific conditions that are mentioned in the applicable protocol.

Short-term measurements lasting 90 days or less should be made under closed-building conditions. To the extent reasonable, all windows, outside vents, and external doors should be closed (except for normal entrance and exit) for 12 hours prior to and during the measurement period. Normal entrance and exit includes opening and closing a door, but an external door should not be left open for more than a few minutes. These conditions are expected to exist as normal living conditions during the winter in northern climates. For this reason, short-term measurements should be made during winter periods whenever possible.

In addition to maintaining closed-building conditions during the measurement, closed-building conditions for 12 hours prior to the initiation of the measurement are a required condition for measurements lasting less than four days, and are recommended prior to measurements of up to a week in duration.

Internal-external air exchange systems (other than a furnace) such as high-volume attic and window fans should not be operating during measurements and for at least 12 hours before measurements are initiated. Air conditioning systems that recycle interior air may be operating. Normal operation of permanently installed air-to-air heat exchangers may also continue during closed-building conditions.

In buildings where permanent radon mitigation systems have been installed, these systems should be functioning during the measurement period.

Short-term tests lasting just two or three days should not be conducted if severe storms with high winds (e.g., > 30 mph) or rapidly changing barometric pressure are predicted during the measurement period. Weather predictions available on local news stations can provide sufficient information to determine if these conditions are likely.

In southern climates, or when measurements must be made during a warm season, the closed-building conditions are satisfied by meeting the criteria listed above. The closed-building conditions must be verified and maintained more rigorously, however, when they are not the normal living conditions.

1.2.3 Measurement Device Location Selection

The following criteria should be applied to select the location of the detector within a room. For further guidance on selecting an appropriate area in a building in which to place the measurement device, the reader should refer to the relevant documents mentioned in section 1.2.1. The following list may be applied to each of the measurement methods discussed in Sections 2 and 3. However, there may be method-specific location criteria that will be mentioned in the applicable protocol.

A position should be selected where the detector will not be disturbed during the measurement period and where there is adequate room for the device.

The measurement should not be made near drafts caused by heating, ventilating and air conditioning vents, doors, fans, and windows. Locations near excessive heat, such as fireplaces or in direct sunlight, and areas of high humidity should be avoided.

The measurement location should not be within 90 centimeters (3 feet) of windows or other potential openings in the exterior wall. If there are no potential openings (e.g., windows) in the exterior wall, then the measurement location should not be within 30 centimeters (1 foot) of the exterior walls of the building.

The detector should be at least 50 centimeters (20 inches) from the floor, and at least 10 centimeters (4 inches) from other objects. For those detectors that may be suspended, an optimal height for placement is in the general breathing zone, such as 2 to 2.5 meters (about 6 to 8 feet) from the floor.

In general, measurements should not be made in kitchens, laundry rooms, closets, or bathrooms.

1.2.4 Documentation

The operator of the measurement device must record enough information about the measurement in a permanent log so that data interpretation and comparison can be made.

The results of radon decay product measurements should be reported in Working Levels (WL). If the WL value is converted to a radon concentration which is also reported to a homeowner, it should be stated that this approximate conversion is based on a 50 percent equilibrium ratio. In addition, the report should indicate that this ratio is typical of the home environment, but any indoor environment (especially in schools and workplaces) may have a different and varying relationship between radon and decay products.

The following list may be applied to each of the measurement methods discussed in Sections 2 and 3. However, there may be method-specific documentation requirements that will be mentioned in the applicable protocol.

  • The start and stop times and dates of the measurement;
  • Whether the standardized measurement conditions, as discussed in Section 1.2.2, are satisfied;
  • The exact location of the device, on a diagram of the room and building if possible;
  • Other easily obtained information that may be useful, such as the type of building and heating system, the existence of a crawl space or basement, the occupants' smoking habits, and the operation of humidifiers, air filters, electrostatic precipitators, and clothes dryers;
  • The serial number and manufacturer of the detector, along with the code number or description which uniquely identifies customer, building, room, and sampling position; and
  • The condition (open or closed) of any crawl space vents.

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1.3 Quality Assurance

The objective of quality assurance is to ensure that data are scientifically sound and of known precision and accuracy. This section discusses the four general categories of quality control measurements; specific guidance is provided for each method in the relevant section.

Anyone providing measurement services using radon and radon decay product measurement devices should establish and maintain quality assurance programs. These programs should include written procedures for attaining quality assurance objectives and a system for recording and monitoring the results of the quality assurance measurements described below. The EPA offers general guidance on preparing quality assurance plans (U.S. EPA 1980); a draft standard prepared by a radon industry group is also available (AARST 1991b). The quality assurance program should include the maintenance of control charts and related statistical data, as described by Goldin (Goldin 1984) and by the EPA (U.S. EPA 1984).

1.3.1 Calibration Measurements

Calibration measurements are samples collected or measurements made in a known radon environment, such as a calibration chamber. Detectors requiring analysis, such as charcoal canisters, alpha track detectors, electret ion chambers, and radon progeny integrating samplers, are exposed in a calibration chamber and then analyzed. Instruments providing immediate results, such as continuous working level and radon monitors, should be operated in a chamber to establish individual instrument calibration factors.

Calibration measurements must be conducted to determine and verify the conversion factors used to derive the concentration results. These factors are determined normally for a range of concentrations and exposure times, and for a range of other exposure and/or analysis conditions pertinent to the particular device. Determination of these calibration factors is a necessary part of the laboratory analysis, and is the responsibility of the analysis laboratory. These calibration measurement procedures, including the frequency of tests and the number of devices to be tested, should be specified in the quality assurance program maintained by manufacturers and analysis laboratories.

Known exposure measurements or spiked samples consist of detectors that have been exposed to known concentrations in a radon calibration chamber. These detectors are labeled and submitted to the laboratory in the same manner as ordinary samples to preclude special processing. The results of these measurements are used to monitor the accuracy of the entire measurement system. Suppliers and analysis laboratories should provide for the blind introduction of spiked samples into their measurement processes and the monitoring of the results in their quality assurance programs. Providers of passive measurement devices should conduct spiked measurements at a rate of three per 100 measurements, with a minimum of three per year and a maximum required of six per month. Providers of measurements with active devices are required to recalibrate their instruments at least once every 12 months. Participation in EPA's former National Radon Proficiency Program (RPP) did not satisfy the need for annual calibration, as this Program was a performance test, not a calibration procedure.

1.3.2 Background Measurements

Background measurements are required both for continuous monitors and for passive detectors requiring laboratory analysis. Users of continuous monitors must perform sufficient instrument background measurements to establish a reliable instrument background and to act as a check on instrument operation.

Passive detectors requiring laboratory analysis require one type of background measurement made in the laboratory and another in the field. Suppliers and analysis laboratories should measure routinely the background of a statistically significant number of unexposed detectors from each batch or lot to establish the laboratory background for the batch and the entire measurement system. This laboratory blank value is subtracted routinely (by the laboratory) from the field sample results reported to the user, and should be made available to the users for quality assurance purposes. In addition to these background measurements, the organization performing the measurements should calculate the lower limit of detection (LLD) for its measurement system (Altshuler and Pasternack 1963, ANSI 1989, U.S. DOE 1990). This LLD is based on the detector and analysis system's background and can restrict the ability of some measurement systems to measure low concentrations.

Providers of passive detectors should employ field controls (called blanks) equal to approximately five percent of the detectors that are deployed, or 25 each month, whichever is smaller. These controls should be set aside from each detector shipment, kept sealed and in a low radon environment, labeled in the same manner as the field samples to preclude special processing, and returned to the analysis laboratory along with each shipment. These field blanks measure the background exposure that may accumulate during shipment and storage, and the results should be monitored and recorded. The recommended action to be taken if the concentrations measured by one or more of the field blanks is significantly greater than the LLD is dependent upon the type of detector and is discussed in the section for each method.

1.3.3 Duplicate (Collocated) Measurements

Duplicate measurements provide a check on the quality of the measurement result, and allow the user to make an estimate of the relative precision. Large precision errors may be caused by detector manufacture or improper data transcription or handling by suppliers, laboratories, or technicians performing placements. Precision error can be an important component of the overall error, so it is important that all users monitor precision.

Duplicate measurements should be side-by-side measurements made in at least 10 percent of the total number of measurement locations, or 50 each month, whichever is smaller. The locations selected for duplication should be distributed systematically throughout the entire population of samples. Groups selling measurements to homeowners can do this by providing two measurements, instead of one, to a random selection of purchasers, with the measurements made side-by-side. As with spiked samples introduced into the system as blind measurements, the precision of duplicate measurements should be monitored and recorded in the quality assurance records. The analysis of data from duplicates should follow the methodology described by Goldin in section 5.3 of his report and plotted on range control charts (Goldin 1984, U.S. EPA 1984). If the precision estimated by the user is not within the precision expected of the measurement method, the problem should be reported to the analysis laboratory and the cause investigated.

1.3.4 Routine Instrument Performance Checks

Proper functioning of analysis equipment and operator usage require that the equipment and measurement system be subject to routine checks. Regular monitoring of equipment and operators is vital to ensure consistently accurate results. Performance checks of analysis equipment includes the frequent use of an instrument check source. In addition, important components of the device (such as a pump, battery, or electronics) should be checked regularly and the results noted in a log. Each user should develop methods for regularly monitoring (preferably daily) their measurement system, and for recording and reviewing results.

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