United States Environmental Protection Agency Office of Radiation Programs Washington, D.C. 20460 EPA 520/1-86-014-1 February 1987 Radiation £EPA Interim Protocols For Screening And Followup Radon And Radon Decay Product Measurements ------- 520/1-86-014 INTERIM PROTOCOLS FOR SCREENING AND FOLLOW-UP RADON AND RADON DECAY PRODUCT MEASUREMENTS U.S. Environmental Protection Agency Office of Radiation Programs January 1987 M. Ronca-Battista P. Magno P. Nyberg ------- CONTENTS Page Acknowledgements ii Summary iii 1. INTRODUCTION 1 2. SCREENING MEASUREMENTS 2 2.1 Screening Measurement Location 3 2.2 Interpretation of Screening Measurement Results . 5 3. FOLLOW-UP MEASUREMENTS 7 3.1 Follow-up Measurement Location 7 3.2 Interpretation of Follow-up Measurement Results . 10 4. EXAMPLES OF APPROPRIATE MEASUREMENT LOCATIONS 12 5. RECOMMENDED USES OF GRAB SAMPLING 13 6. CLOSED-HOUSE CONDITIONS 14 7. INSTRUMENT SELECTION 16 7.1 Continuous Radon Monitors (CRM) or Continuous Working Level Monitors (CWLM) 16 7.2 Alpha-Track Detectors 17 7.3 Charcoal Canisters 18 7.4 Radon Progeny Integrating Sampling Units 18 7.5 Grab Sampling 19 References 21 ------- ACKNOWLEDGEMENTS There are many generous individuals who have contributed substantially to this document during months of discussion and review. The authors wish to extend special thanks to Thomas Gerusky, Larry Lloyd, Eileen Hotte, Larainne Koehler, Bill Belanger, Dan Egan, and the Environmental Protection Agency's (EPA) Radon Action Program staff. Their efforts enabled the authors to better address the needs of homeowners. States, and other organizations performing radon measurements. 11 ------- SUMMARY This document presents guidance for making reproducible measurements of radon concentrations in residences, including recommendations for using the results to make well-informed decisions about the need for additional measurements or remedial action. The Environmental Protection Agency (EPA) recognizes that radon concentrations in homes may vary greatly over time (Ge83; He85; St79; F184; Wi86; Ny83). Furthermore, concentrations at different locations in the same house often vary by a factor of two or more (Geo84; Ke84; He85). Because of these temporal and spatial variations, the EPA does not know of a way to provide an accurate estimate of health risks or make a well-informed decision on the need for remedial action with a single measurement. What is necessary, therefore, is a logical system for making the fewest measurements possible, while ensuring that there are not serious underestimations of the concentrations. The EPA recommends a two-step measurement strategy for assessing radon levels in homes. The first step is a screening measurement, made to quickly and inexpensively determine whether a house has the potential for causing high exposures to its occupants. There are two possible outcomes from a screening measurement: (1) if the result is above the screening level, additional follow-up measurements are recommended as the second step to both estimate the health risk to the occupants and assess the urgency for remedial action; and (2) if the result is below the screening level, follow-up measurements are probably not needed. Screening measurements should be made under conditions that maximize the probability of finding elevated radon concentrations. Screening measurements should be made in the lowest livable area of the house (closest to the underlying soil) that the residents now use o_r could adapt for use as a living area. In many houses this will be a basement that could be converted to a den, playroom, or bedroom without major structural changes. Furthermore, screening measurements should be made under closed-house conditions when the doors and windows of the house are kept closed as much as practical and the use of ventilation systems mixing indoor and outdoor air is minimized. Both these conditions will help to ensure that short-term measurements are made during the time of highest and most stable radon concentration and will also increase the reproducibility of the measurements. If the screening measurement result is above 4 pCi/1 (0.02 WL), follow-up measurements are recommended. The EPA does not recommend taking any significant remedial action on the basis of a single screening measurement. Therefore, the appropriate response to an elevated screening result is additional measurements. 111 ------- Follow-up measurements should be made in at least two locations in the house, preferably on each of the different living levels, if there are more than one. The results from each location should be averaged to obtain an overall average result for the living areas of the home. The duration of the follow-up measurements depends on the magnitude of the screening measurement result. If the screening result is significantly elevated, then a short-term follow-up measurement should be made, which will minimize the additional exposure of the occupants. If the result is only moderately elevated, then a full-year schedule of follow-up measurements is recommended, with the expectation that the additional exposure of the occupants during that period will not significantly increase health risk. The recommended follow-up procedure is based on the screening result as follows: 1. If the screening measurement result is less than about 4 pCi/1 (or about 0.02 WL), follow-up measurements are probably not needed, as it is highly unlikely that radon levels in the living areas of the home would exceed 4 pCi/1 or 0.02 WL as an annual average. 2. If the result of the screening measurement is greater than about 4 pCi/1 (0.02 WL) but less than about 20 pCi/1 (0.1 WL), EPA recommends that the follow-up measurements consist of 12-month integrated measure- ments made in several areas of the house. The average annual concentration in the living space can be used to estimate health risks and to compare to guidance levels on the need for remedial action. This guidance is available in "A Citizen's Guide to Radon," published by EPA, the U.S. Department of Health and Human Services, and the Centers for Disease Control. This pamphlet can be obtained from the Government Printing Office by calling (202) 275-2091 and asking for document number 055-000-00258-4. 3. If the screening measurement result is greater than about 20 pCi/1 (0.1 WL), then EPA recommends that a short-term follow-up measurement over at least 24 hours be made in several living areas of the house under closed-house conditions. A short-term follow-up measurement will minimize additional significant exposure to the occupants while providing reproducible results that conservatively estimate the annual average concentration. IV ------- 1. INTRODUCTION This document supplements "Interim Radon and Radon Decay Product Measurement Protocols" (EPA 520/1-86-04) prepared by the Office of Radiation Programs of the Environmental Protection Agency (EPA) and published in February, 1986 (EPA86). That report provides guidance for measuring radon concentrations with continuous radon monitors (CRM), charcoal canisters, alpha-track detectors (ATD), and grab radon techniques; it also provides guidance for measuring radon decay product concen- trations with continuous working level monitors (CWLM), radon progeny integrating sampling units (RPISU), and grab radon decay product methods. The 1986 report includes a discussion of recommended quality control practices for each method. Copies of that protocols report, numbered EPA 520/1-86-04, can be obtained by contacting the Program Management Office (ANR-458), Office of Radiation Programs, Environmental Protection Agency, 401 M Street, S.W., Washington, D.C., 20460; your EPA regional office; or your State radiation control office. This report provides guidelines that are primarily intended to aid State radiation control programs, other organizations conducting measurements, and homeowners who want detailed information on measurements. They can be adopted as part of a State program as particular circumstances and resources allow or can be provided by States to homeowners and measurement firms as recommendations. The philosophy presented here serves as the basis for consistent radon measurements that produce accurate and reproducible results within a reasonable time and for a reasonable cost. Consistency is important, because decisions about the need for remedial action should be based on a common rationale and comparable measurements. In addition, consistency among measurement programs will help assure valid comparison of measurement results from different State or regional programs. These guidelines will be periodically evaluated and may be refined to reflect increasing knowledge and experience with indoor radon. ------- 2. SCREENING MEASUREMENTS Screening measurements may be conducted by homeowners wanting to make single measurements to quickly determine whether their homes contain high radon concentrations, and to decide whether and what type of additional measurements are needed. Another use of screening measurements is in multiple-home surveys designed to efficiently identify homes that contain high concentrations. Screening measurements should be inexpensive and simple, so that time or money is not wasted in houses that do not pose a health threat. However, the screening measurement alone usually will not provide enough information to decide on the need and timing of remedial action. Screening measurements should be made in the lowest livable area in the house that the residents now use or could adapt for use as a living area, which will be the basement in many houses. (The guidance presented here assumes the source of radon to be the underlying soil, rather than building materials or water. If other radon sources are suspected, additional types of measurements should be made.) Any screening measurement should be made during closed-house conditions (described on page 14) to ensure that information is obtained on the maximum concentrations to which the house occupants may potentially be exposed. Under these conditions, EPA believes that there is a low probability that a home with a low screening result could have a high long-term average concentration in the living area. There is a growing body of data indicating that basement concentrations tend to be a factor of two to three times higher (Ge83; Geo84; F184, Mo82) and are more reproducible, i.e., less variable over time (DOE86; DOE87), than concentrations in nonbasement rooms. Therefore, if the result of a screening measurement is very low, there is a high probability that the long-term average concentrations in the rooms currently used as living areas are even lower, and the homeowner can eliminate the need for further measurements with confidence. Screening measurements will minimize the number of false negatives, or homes that contain concentrations at which EPA recommends that remedial action be considered but which would not be identified as such because of a low measurement result. The outcome of a false positive screening measurement should be a follow-up measurement, which would reveal that the concentra- tions in the house are low. However, the outcome of a false negative is no further measurements, so that potentially high concentrations may never be identified. In the interests of reducing radon exposures, therefore, EPA believes that a significant fraction of false positives is preferable to a high rate of false negatives. Guidelines for the duration of screening measurements are summarized in Table 2-1. ------- 2.1 Screening Measurement Location The screening measurement should be made in the room or area in which the highest and most stable radon or radon decay product concentration is expected. The following criteria should be used to select this room: 1. The measurement should be made in a livable room on a level closest to the underlying soil, such as the basement. The room need not be currently lived in or frequently occupied but should be in a condition that would allow it to be easily converted to a bedroom, playroom, den, etc. Measurements may be made in unfinished basements, but usually not in a room that would require major structural changes (such as the installation of a floor) before it could be used as a living area. 2. The instrument should be placed in the room expected to have the lowest ventilation rate, such as an interior room with tight doors and few or no windows. 3. The measurements should not be made in a kitchen, because of the likelihood that an exhaust fan system and changes in small, airborne particles (caused by cooking) may affect the stability of working level measurements. In addition, measurements should not be made in a bathroom, because relatively little time is spent in a bathroom and high humidities may affect the sensitivity of some detectors. (If radon in water is expected to be a major contributor to the concentra- tion of airborne radon, diagnostic measurements may be made in the bathroom to determine the contribution from this source; however, such diagnostic measure- ments should not be used to estimate the resident's exposures.) These criteria are flexible, and sound judgment is required as to what space actually constitutes a room. Measurements should not be made in closets, cupboards, sumps, crawl spaces, or nooks within the foundation. ------- Table 2-1 Screening Measurements Made in Lowest Livable Area Under Closed-House Conditions Instrument Charcoal Canister Alpha Track Detector Radon Progeny Integrated Sampling Unit Continuous Working Level Monitor Continuous Radon Monitor Grab WL* Sampling Times 2 to 7 days 3 months (or less if laboratory uses adequate lower limit of detection) 100 hours minimum, 7 days preferred 6 hours minimum, 24 hours or longer preferred 6 hours minimum, 24 hours or longer preferred 5 minutes Grab Rn 5 minutes *Grab measurements, because of the short 5-minute sampling duration, have a relatively large uncertainty and are recommended only for the purposes described on page 13. ------- 2.2 Interpretation of Screening Measurement Results If the screening measurement result is less than about 4 pCi/1 or 0.02 WL, follow-up measurements are probably not needed. If the screening measurement was made in the lowest livable area under the closed-house conditions described on page 14, there is relatively little chance that the concen- trations in the general living areas on nonbasement floors of the house are greater than about 4 pCi/1 or 0.02 WL as an annual average. If the result of the screening measurement is between about 4 and 20 pCi/1 or between about 0.02 and 0.1 WL, the occupant should be aware that, while there is a concern about the long-term exposure to these radon concentrations, there will probably be no large increase in risk with an additional 12 months of exposure. Therefore, since guidance for action to reduce radon levels is usually expressed in terms of annual average concentrations, we recommend a 12-month measurement whenever possible. If the result of the screening measurement is between about 20 and 200 pCi/1, or between about 0.1 and 1 WL, a short-term follow-up measurement should be made within the next several months under closed-house conditions. Since the occupants may be exposed to elevated concentrations in their living areas, an annual average measurement alone is usually not recommended because the additional 12 months of exposure during the measurement could cause a significant increase in health risk. If the results are greater than about 200 pCi/1 or 1 WL, the State radiation control program or regional EPA office should be contacted for advice on a follow-up measurement and immediate reductions in concentrations. The recommended follow-up measurements are summarized in Table 2-1. ------- Table 2-1 Recommended Actions Based on Results of Screening Measurements Screening Measurement Result Greater than 1 WL or 200 pCi/1 Recommended Action Perform short-term follow-up measurements and consider short-term actions to reduce the radon levels as soon as possible Between 0.1 and 1 WL or Between 20 pCi/1 and 200 pCi/1 Between 0.02 and 0.1 WL or Between 4 pCi/1 and 20 pCi/1 Perform short-term follow-up measurements within several months Perform follow-up measurements over the next 12 months Less than 0.02 WL or 4 pCi/1 Relatively low probability of significant health risk from concentrations in general living areas of home; follow-up measure- ments are probably not needed, but may be made at the discretion of the resident ------- 3. FOLLOW-UP MEASUREMENTS The results of follow-up measurements will enable a homeowner to make a well-informed decision about possible health risks and the need for remedial action. As this decision often entails spending a significant amount of money, follow-up measurements should be reliable and reproducible estimators of the actual or maximum potential exposures of the occupants. These guidelines represent EPA's current thinking on the optimal method for obtaining these estimates. An individual homeowner or a State may be limited by available resources to making follow-up measurements in only one living area, rather than in two areas as outlined here. However, in those situations involving the investment of a large amount of money or whenever a good estimate of average concentrations in living areas is critical, all efforts should be made to perform follow-up measurements in more than one area of the house. If the result of the screening measurement is between about 4 and 20 pCi/1 or between about 0.02 to 0.1 WL, measure- ments to estimate the annual average concentrations should be made. The occupant should consider using a long-term measurement device, such as a 12-month alpha-track detector (ATD), to estimate the annual average concentrations in the living areas. An alternate, but less accurate, method for estimating an annual average is to use the average of four measurements made at 3-month intervals. The year-long measurement is more reliable for determining long-term exposure, because both short-term and seasonal variations will be incorporated into the annual estimate. All measure- ments made to estimate annual averages, whether 12-month integrated or a series of quarterly measurements, should be made under normal living conditions rather than closed house conditions. The results of the four measurements in each living area are then averaged to estimate the annual average. Guidelines for the duration of follow-up measurements are summarized in Table 3-1. 3.1 Follow-up Measurement Location The following criteria should be used to select the rooms in which follow-up measurements are made. 1. The measurements should be made in each level (floor) of the house that is frequently used as a living ^ area. Living areas include family rooms, living rooms, dens, playrooms, and bedrooms. ------- 2. The measurements should be made in the most frequently occupied room in each of the above levels. A bedroom may be a good choice, because most people generally spend more time in their bedrooms than in any other room in the house (Sz72; Ch74; Mo76). 3. If there are children in the house, it may be appropriate to measure the concentrations in their bedrooms or in other areas where they spend a lot of time, such as a playroom. There is some concern that children may be more sensitive to the effects of inhaled radon decay products. 4. The measurements should not be made in a kitchen, because of the likelihood that an exhaust fan system and changes in small, airborne particles (caused by cooking) may affect the stability of working level measurements. In addition, measurements should not be made in a bathroom, because relatively little time is spent in a bathroom, and high humidities may affect the sensitivity of some detectors. (If radon in water is expected to be a major contributor to the concentra- tion of airborne radon, diagnostic measurements may be made in the bathroom to determine the contribution from this source; however, such diagnostic measure- ments should not be used to estimate the resident's exposures.) ------- Table 3-1 Follow-up Measurements Made in General Living Areas Instrument If Screening Result is If Screening Result is Greater than 20 pCi/1 Less than 20 pCi/1 Alpha Track Detector 3-month measure- ments (may be less than 3 months if laboratory uses adequate lower limit of detection), made under closed-house (winter) conditions* 12-month measurements made under normal living conditions Charcoal Canister Measurements of 2 to 7 days made under closed-house conditions Four measurements made under normal living conditions every 3 months Radon Progeny 100-hour measure- Integrating ments, made under Sampling Unit closed-house conditions Four 100-hour measurements made under normal living conditions every 3 months Continuous 24-hour measure- Working Level ments, made under Monitor closed-house conditions Four 24-hour measurements made under normal living conditions every 3 months Continuous 24-hour measure- Radon Monitor ments, made under closed-house conditions Four 24-hour measurements made under normal living conditions every 3 months 'It the result of the screening measurement is greater than about 200 pCi/1, a short-term, follow-up measurement over days or weeks may be appropriate. ------- 3.2 Interpretation of Follow-up Measurement Results The purpose of the follow-up measurement is to estimate the long-term average radon or radon decay product concentra- tions in general living areas with sufficient confidence to allow an informed decision to be made about risk and the need for remedial action. It should be noted that if the results of the screening measurement was above 20 pCi/1 or 0.1 WL and short-term follow-up measurements were conducted under closed- house conditions, an over-estimation of the annual average concentration may result. However, the EPA recommends short- term follow-up measurements in these situations because an additional 12 months of exposure could cause a significant increase in health risk. The average of the follow-up measurements made in the two different living areas in the home are intended for comparison to guidance levels given- in terms of annual average concentra- tion. Such guidance levels are discussed in the "Citizen's Guide to Radon," published by the EPA Office of Radiation Programs and available through your EPA regional office or your State radiation control office. The following four paragraphs are excerpted from that document and summarize the EPA guidance for action based on the results of follow-up measurements. If the follow-up measurement results are about 1.0 WL or higher, or about 200 pCi/1 or higher, residents should be aware that exposures in this range are among the highest observed in homes and should undertake action to reduce levels as far below 1.0 WL (200 pCi/1) as possible. EPA recommends that action be taken within several weeks. If this is not possible, residents should determine, in consultation with appropriate State or local health or radiation protection officials, if temporary relocation is appropriate until the levels can be reduced. If the follow-up measurement results are about 0.1 to about 1.0 WL, or about 20 to about 200 pCi/1, residents should be aware that exposures in this range are considered greatly above average for residential structures, and should undertake action to reduce levels as far below 0.1 WL (20 pCi/1) as possible. EPA recommends that such action be taken within several months. If the follow-up measurement results are about 0.02 to about 0.1 WL, or about 4 pCi/1 to about 20 pCi/1, EPA advises that exposures in this range are considered above average for residential structures. Residents should undertake action to lower levels to about 0.02 WL (4 pCi/1) or below. EPA recommends that residents take action within a few years, sooner if levels are at the upper end of this range. 10 ------- If the follow-up measurement reults are about 0.02 WL or lower, or about 4 pCi/1 or lower, residents should be aware that exposures in this range are considered average or slightly above average for residential structures. Although exposures in this range do present some risk of lung cancer, reductions of levels this low may be difficult, and sometimes impossible, to achieve. Diagnostic measurements made to determine the source of radon influx into the house and to guide the choice of mitigation techniques are beyond the scope of this document. However, since a follow-up measurement should be made before the need for permanent mitigation is decided, a similar follow-up measurement conducted after the mitigation work is completed can be used as a benchmark to estimate the efficacy of the mitigation effort. 11 ------- 4. EXAMPLES OF APPROPRIATE MEASUREMENT LOCATIONS The following are examples of locations where screening and follow-up measurements should be made. 1. A split-level house is built over a garage on the lowest level and has a den and a bedroom built several feet higher than the garage, a kitchen on a middle level over the garage, and bedrooms on a level over the den several feet higher than the kitchen. The screening measurement should be made in the lowest bedroom on the floor next to the garage. The follow-up measurement should be the average of measurements made in that same lower bedroom and measurements made in one of the upper bedrooms. 2. A farm house has an uninhabitable dirt-floor cellar, a ground floor containing a kitchen and a living room, and an upper floor containing bedrooms. The screening measurement should be made in the ground floor living room, and the follow-up measurement should be the average of measurements made in the same living room and measurements made in one of the upper floor bedrooms. 3. A multi-story apartment building has a livable, finished basement used as a laundry room. The screening measurement should be made in the basement, and if the results warrant follow-up measurements, they should be made in the bedroom and living room of each apartment unit. If the source of radon is believed to be the underlying soil, only the apartment units on the lowest floors need to be tested. 4. A one-story, no basement, slab-on-grade house is tested for radon. The screening measurement should be made in a bedroom, and the follow-up measurement should consist of measurements made in a bedroom and the living room. 12 ------- 5. RECOMMENDED USES OF GRAB SAMPLING Short-term or grab sampling techniques can be used to measure concentrations of either radon gas or radon decay products in the air. Samples are usually acquired over a 5 or 10 minute sample period, which may be considered a virtually instantaneous measurement when compared with most other measurement techniques commonly used in homes. While an individual grab sample may be quite accurate in representing the concentration of radon or radon decay products at the moment of sampling, it is usually a poor indicator of the long-term average concentration because of the inherent variability of the radon concentration in homes. For this reason, grab sample results should be interpreted with caution. However, grab sampling methods have two distinct advantages over other measurement techniques. First, grab samples can produce results within a matter of minutes to hours, enabling one sampling team to test and produce results for several houses each day. Second, the conditions at the time of measurement are known to the sampler who must be present during the measurement and who can take note of unusual weather or other factors that may influence the result. If grab samples are to be used, it is important to remember that, unlike the other measurement techniques, the results are greatly influenced by conditions that existed in the home for 8 to 12 hours prior to the moment of measurement. The results of measurements made in a tightly closed home will differ significantly from the results of measurements made in the same home after it has been thoroughly ventilated. The results of integrated measurements of at least 24 hours in duration, however, are most influenced by conditions during the measurement period. It is therefore especially important when taking grab samples to make every effort to conform to the closed-house conditions for 12 hours before the measurement. Grab sampling has been particularly useful in situations in which homes located near sites of known high concentrations must be screened quickly. Grab samples are also very useful as diagnostic tools to trace the probable cause of elevated levels in a home, although that application is beyond the scope of this document. Grab techniques are not recommended for follow-up measurements, however, because of their poor correlation with long-term averages. Because of the high uncertainties associated with the short measurement duration, the results of a single grab sample should not be used as the sole estimate of average concentrations upon which a decision, such as the need for remedial action, is based. 13 ------- 6. CLOSED-HOUSE CONDITIONS Short-term measurements used for comparison to guidance levels should be made under closed-house conditions. (Short- term measurements are made over a shorter period of time than 12 months and are not part of a series of four measurements made over a year's time.) Closed-house conditions are necessary for short-term measurements to stabilize the radon and radon decay product concentrations and increase the reproducibility of a measurement. To the extent reasonable, windows and external doors should be kept closed (except during normal entry and exit). Normal entry and exit includes a brief opening and closing of a door, but an external door should not be left open for more than a few minutes. In addition, external-internal air exchange systems (other than a furnace) such as high-volume, whole-house attic and window fans should not be operating. For measurement periods of 3 days or less, these conditions should exist for 12 hours prior to beginning the measurement. It may be difficult to verify these conditions or to implement them for an extended period, but they should be adhered to as closely as possible. Closed-house conditions will generally exist as normal living conditions in northern areas of the country when the average daily temperature is low enough so that windows are kept closed. Depending on the area, this can be the period from late fall to early spring. In some houses, the most stable levels occur during late fall and early spring, when windows are kept closed but the home heating system (which causes some ventilation and circulation) is not used.§ If information about variations of indoor radon levels i'n a particular area is available, the information can be used to choose a measurement time when the radon concentrations are highest and most stable. We recommend that measurements in northern climates be made during the winter season for two major reasons. First, closed-house conditions exist as normal living conditions, so there is a fairly good assurance that the proper conditions will exist prior to and during the measurement period. Second, information on factors other than ventilation rates that influence indoor radon concentrations indicate that concentra- tions during the winter are generally higher than during the summer. It may be necessary, however, to make measurements in northern climates during the summer, when closed-house conditions are not the normal living conditions. It will then be necessary to establish some means for providing reasonable assurance that closed-house conditions exist prior to and during the measurements. 14 ------- Organizations performing measurements in southern areas that do not experience extended periods of cold weather should evaluate seasonal variations in living conditions and identify if there are times of the year when closed-house conditions normally exist. If such times can be identified, that is when measurements should be conducted. Air conditioning systems that recycle interior air can be operated during the closed- house conditions if radon measurements are being made. Home owners should be aware that any air circulation system can drastically alter the radon decay product concentration without significantly changing the radon concentration. Measurements lasting a few days or less should not be conducted if severe storms with high winds are predicted. Severe weather will affect the measurement results in the following ways. First, a high wind will increase the variability of radon concentration because of wind-induced differences in air pressure between the house interior and exterior. Second, rapid changes in barometric pressure increase the chance of a large difference in the interior and exterior air pressures, therefore changing the rate of radon influx. The rate of radon released from the ground is also affected. Weather predictions available on local news stations should be sufficient to determine if this criterion is satisfied. A measurement made over 12 months, whether it is an integrated measurement or a series of measurements, provides information about the average concentrations during an entire year, so the closed-house conditions do not have to be satisfied for annual average measurements. 15 ------- 7. INSTRUMENT SELECTION There are several different measurement systems that may be used to determine the radon or radon decay product concentra- tions in houses. In practice, the choice of a system is often dictated simply by availability -- if an adequate system is available, you use it. If alternative systems are available, then the cost or the duration of the measurement may become the deciding factor. EPA has developed measurement protocols for seven different systems (EPA86), and the Agency believes that any of these systems, when used in accordance with the guidance in that protocol document, can produce valid results. This does not mean that all such measurements will produce results with identical uncertainties, but rather that any of the listed systems is capable of producing adequate results for screening or follow-up purposes. Each system has its own advantages and disadvantages, however, and the user must exercise some judgment in selecting the system best suited to the individual situation. The following sections detail the characteristics of the seven systems, pointing out some of the advantages and disadvantages of each one. This summary is not exhaustive but is intended to guide the user in making an informed selection of a measurement system. 7.1 Continuous Radon Monitors (CRM) or Continuous Working Level Monitors CCWLM): These two types of measurement systems are similar in that they use an electronic detector to accumulate and store information related to the periodic (usually hourly) average concentration of radon gas or radon decay products. They are installed in the house, turned on or programmed for the desired operating time, and then left to operate for the programmed time. Advantages: o Relatively short measurement duration (minimum of 6 hours for screening, 24 hours for follow-up measurements). o Hourly results can track the variation of concentra- tions in the house. o Most models have small precision errors. o Results are available onsite. Disadvantages: o Costly (each unit may cost from $2500 to $10,000, depending on model). 16 ------- o Some models are heavy and awkward to move. o Requires extensive calibration in a radon calibration chamber. o Requires a trained operator. 7.2 Alpha-Track Detectors Alpha-track detectors consist of a small sheet of a special plastic material. The material is permanently marked when exposed to alpha particles, such as those emitted by the decay of radon or some of the short-lived radon decay products. The detectors are usually in a filtered container that serves to make the measurement specific for radon gas. They are installed in the home and left for periods of up to 1 year. At the end of that period, they must be returned to a laboratory for processing and analysis. Advantages: o Relatively low cost per detector. o Convenient to handle and install. o Unobtrusive when installed. o No special skills required for deployment. o Can be distributed by mail. o Completely passive, needs no external power. o Can measure the integrated average concentration over a 12-month period, which is the optimal measure of long-term concentration. Disadvantages: o Relatively long measurement period necessary (3 months recommended minimum for currently available detectors) o Large inherent variability (precision errors) particularly at low concentrations if the area of the detector that is counted is small. 17 ------- 7.3 Charcoal Canisters Charcoal canisters are small, flat containers filled with a measured amount of activated charcoal. The top is often perforated or screened to keep the charcoal from falling out, and the container is covered with an airtight seal when the canister is not being used for measurement. Some systems now use a filter bag to contain the charcoal. The canisters are usually obtained from a supplier and are typically left in place for 2 to 7 days, resealed, and returned to the supplier or analytical laboratory for evaluation. Analysis usually consists of counting the gamma radiation emission rate from the radon decay products resulting from the radon adsorbed on the charcoal. Advantages: o Low cost per canister. o Convenient to handle and install. o Unobtrusive when installed. o No special skills needed for deployment. o Can be distributed by mail. o Completely passive, needs no external power. o With proper analysis, can yield precise results. Disadvantages: o Some canister types are sensitive to temperature and humidity. o The charcoal adsorption technique is inherently limited to a few days of sampling, which makes a longer term measurement impossible with a single detector. 7.4 Radon Progeny Integrating Sampling Units (RPISU) The RPISU is a radon decay product measurement system consisting of a low flow-rate air pump that pulls air continuously through a detector assembly containing a thermoluminescent dosimeter (TLD). The unit is operated for periods of 100 hours or longer. At the end of that time the unit is removed, and the detector assembly is returned to the analytical laboratory. The analysis consists of measuring the light given off by the TLD during heating. 18 ------- Advantages: o Measures radon decay product concentration directly. o Relatively short measurement period. o The detector assembly (not the entire unit) can be sent by mail. o There is extensive experience in the use of RPISUs, and measurement errors are well established. Disadvantages: o The entire unit may be both heavy and awkward to move- o May be limited to location with a.c. power. o Significant capital cost per unit ($500-$3,000) and for the readout system ($5,000-$10,000). o Units must be installed and picked up by trained personnel. o Proper operation may be affected by high concentrations of airborne particulates, such as those caused by smoking. 7.5 Grab Sampling Grab sampling consists of taking a small sample of air from the home and analyzing the radon or radon decay product concen- tration it contained. The radon grab sample is collected in a special flask containing 100 to 2000 cubic centimeters of air. The radon decay product grab sample consists of particulates collected on a small filter. Both samples can be acquired simultaneously with some systems. The samples should be taken in accordance with guidelines in the protocols and evaluated according to standard procedures using an electronic scintillation counting system. Advantages: o Results are quickly obtained. p Equipment can be portable. o Can measure both radon and its decay products simultaneously. 19 ------- o Can acquire and evaluate several samples per day. o Conditions during the measurement are known to the sampler. Disadvantages: o Very short measurement period may not be representative of long-term average. o Requires a skilled operator. o Requires careful control of house conditions for 12 hours before the measurement. o System cost is $2,500 to $10,000. 20 ------- References Ch74 EPA86 DOES 6 DOE87 F184 Geo84 Go83 He85 Ke84 Chapin, F- Stuart Jr., 1974, "Human Activity Patterns in the City: Things People do in Time and Space," John Wiley and Sons, New York. U.S. Environmental Protection Agency, Ronca-Battista, M. , Magno, P., Windham, S., Sensintaffer, E., 1986, "Interim Indoor Radon and Radon Decay Product Measurement Protocols," Office of Radiation Programs, EPA 520/1-86-04. Department of Energy, George, J.L., Langner, Jr. , 1986, "Field Study of Indoor Average U.S. G.H.. Radon-daughter Estimation Methods," Technical Measurements Center, Grand Junctions Operations Office, GJ/TMC-26. U.S. Department of Energy, Karp, K.E., in preparation, "Comparison of Radon and Radon-daughter Grab Samples Obtained During the Winter and Summer," Technical Measurements Center, Grand Junctions Operations Office, GJ/TMC-29. Fleischer, R.L. Measurements , Turner, L.G., 1984, "Indoor Radon in the New York Capital District," Health Physics, Vol. 46, No. 5, pp. 999-1011. Ge83 Gesell, T.F., 1983, "Background Atomspheric Rn-222 Concentrations Outdoors and Physics, Vol. 45, No. 2, pp Indoors: A 289-302. Review," Health George, A.C., Duncan, M. , and Franklin, H. , 1984, "Measurements of Radon in Residential Buildings in Maryland and Pennsylvania," Radiation Protection Dosimetry, Vol. 7, No. 1, pp. 291-294. Goldsmith, W.A., Poston, J.W., Perdue P.T., and Gibson, M.O., 1983, "Radon-222 and Progeny Measurements in 'Typical' East Tennessee Residences," Health Physics, Vol. 45, No. 1, pp. 81-88. Hess, C.T., 1985, "Field and Laboratory Tests of Etched Track Detectors for Rn-222: Summer-vs-Winter Variations and Tightness Effects in Maine Houses," Health Physics, Vol. 49, No. 1, pp. 65-79. Keller, G., Folkerts, K.H., Muth, H., 1984, "Special Aspects of the Rn-222 and Daughter Product Concentrations in Dwellings and the Open Air," "--•-• — --«--• '' " ' Vol. 7, No. 1, Concentrations in Dwellings -..~ Radiation Protection Dosimetry, pp. 151-154. 21 ------- Mo76 Moeller, D.W., Underbill, D.W-, December 1976, "Final Report on Study of the Effects of Building Materials on Population Dose Equivalent", School of Public Health, Harvard University, Boston, Massachusetts. Mo82 Moschandreas, D.J., Rector, H.E., 1982, "Indoor Radon Concentrations," Environment International, Vol. 8, pp. 77-82. Ny83 Nyberg, P.C., Bernhardt, D.E., 1983, "Measurement of Time-Integrated Radon Concentrations in Residences," Health Physics, Vol. 45, No. 2, pp. 539-543. St79 Stranden, E., Berteig, L., Ugletveit, F., 1979, "A Study on Radon in Dwellings," Health Physics, Vol. 36, pp. 413-421. Sz72 Szalai, A., 1972, "The Use of Time: Daily Activities of Urban and Suburban Populations in Twelve Countries," Mouton, The Hague, Paris. Wi86 Wilkening, M., and Wicke, A., 1986, "Seasonal Variations of Indoor Rn at a Location in the Southwestern United States," Health Physics, Vol. 51, No. 4, pp. 427-436. 22 ------- |