Office of Air and Radiation
EPA 402-R-93-003, June 1993PROTOCOLS FOR RADON AND RADON DECAY
PRODUCT MEASUREMENTS IN HOMESSection 2: DISCUSSION OF GUIDELINES PRESENTED IN CITIZEN'S GUIDE TO RADON
2.1 Introduction and Summary 2.2 Measurement Location 2.3 Initial Measurements 2.4 Follow-Up Measurements The Citizen's Guide to Radon (EPA 402-K-92-001; U.S. EPA 1992a) presents a measurement strategy for assessing radon levels in homes for the purpose of determining the need for remedial action. This measurement strategy is intended to reduce the risk to public health from exposure to radon in air in homes. The strategy begins with an initial measurement made to determine whether a home may contain radon concentrations sufficient to cause high exposures to its occupants.
EPA recommends that initial measurements be short-term tests placed in the lowest lived-in level of the home, and performed under closed-building conditions. An initial short-term test ensures that residents are informed quickly should a home contain very high levels of radon. Short-term tests are conducted for two days to 90 days. Closed-building conditions (Section 2.3.2) should be initiated at least 12 hours prior to testing for measurements lasting less than four days, and are recommended prior to tests lasting up to a week.
If the short-term measurement result is equal to or greater than 4 picocuries per liter (pCi/L), or 0.02 working levels (WL), a follow-up measurement is recommended. Follow-up measurements are conducted to confirm that radon levels are high enough to warrant mitigation. If the result of the initial measurement is below 4 pCi/L, or 0.02 WL, a follow-up test is not necessary. However, since radon levels change over time, the homeowner may want to test again sometime in the future, especially if living patterns change and a lower level of the house becomes occupied or used regularly.
There are two types of follow-up measurements that may be conducted, and the choice depends, in part, on the results of the initial test. An initial measurement result of 10 pCi/L (or 0.05 WL) or greater should be followed by a second short-term test under closed-building conditions. If the result of the initial measurement is between 4 pCi/L (or 0.02 WL) and 10 pCi/L (or 0.05 WL), the follow-up test may be made with either a short-term or a long-term method. Long-term tests are conducted for longer than 90 days, and give a better estimate of the year-round average radon level. The closer the long-term measurement is to 365 days, the more representative it will be of annual average radon levels. On the other hand, short-term tests yield results more quickly and can be used to make mitigation decisions. If the long-term follow-up test result is 4 pCi/L, or 0.02 WL, or higher, EPA recommends remedial action. If the average of the initial and second short-term results is equal to or greater than 4 pCi/L, or 0.02 WL, radon mitigation is recommended. These recommendations are summarized in Exhibit 2-1.
In certain instances, such as may occur when measurements are performed in different seasons or under different weather conditions, the initial and follow-up tests may vary by a considerable amount. Radon levels can vary significantly between seasons, so different values are to be expected. The average of the two short-term test results can be used to determine the need for remedial action.
The testing strategy policies presented here allow homeowners to decide on the need for mitigation with a high level of confidence that their decision is correct (EPA 400-R-92-011; U.S. EPA 1992g).
Short-term or long-term measurements should be made in the lowest lived-in level of the house. The following criteria should be used to select the location of the detectors within a room on this level:
- The measurements should be made in the lowest level which contains a room that is used regularly. Test areas include family rooms, living rooms, dens, playrooms, and bedrooms. A bedroom on the lower level may be a good choice, because most people generally spend more time in their bedrooms than in any other room in the house (Chapin 1974, Moeller and Underhill 1976, Szalai 1972). If there are children in the home, it may be appropriate to measure the radon concentration in their bedrooms or in other areas where they spend a lot of time, such as a playroom, that are situated in the lowest levels of the home.
- In general, measurements should not be made in kitchens, laundry rooms, or bathrooms. 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 WL measurements. Measurements should not be made in a bathroom because relatively little time is spent in a bathroom, because high humidities may affect the sensitivity of some detectors, and because of the likelihood that use of a fan may temporarily alter radon or decay product levels.
Although radon in water may be a contributor to the concentration of airborne radon, radon in air should be measured before any diagnostic radon-in-water measurements are made. (Diagnostic measurements may be made in the bathroom; however, such diagnostic measurements should not be used to determine the need for mitigation.)
- 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 heat, such as on appliances, near fireplaces or in direct sunlight, and areas of high humidity should be avoided.
- Because some detectors are sensitive to increased air motion, fans should not be operated in the test area. Forced air heating or cooling systems should not have the fan operating continuously unless it is a permanent setting.
- The measurement location should not be within 90 centimeters (three feet) of the doors and windows or other potential openings to the outdoors. If there are no doors or windows to the outdoors, the measurement should not be within 30 centimeters (one foot) of the exterior wall of the building.
- The detector should be at least 50 centimeters (20 inches) from the floor, and at least 10 centimeters (four inches) from other objects. For those detectors that may be suspended, an optimal height is in the general breathing zone, such as two to 2.5 meters (about six to eight feet) from the floor.
Sound judgement is required as to what space actually constitutes a room. Measurements made in closets, cupboards, sumps, crawl spaces, or nooks within the foundation should not be used as a representative measurement.2.3.1 Rationale
EPA recommends that a homeowner assessing the need for mitigation should first make a short-term test. Short-term measurements can be simple, produce results quickly, and allow the public to make decisions about radon reduction that are cost-effective and protective of human health.
The duration of short-term measurements can range from 48 hours to 90 days, depending upon the method used.
2.3.2 Closed – Building Conditions
Short-term measurements lasting between two and 90 days should be made under closed-building conditions. Closed-building conditions are necessary for short-term measurements in order to stabilize the radon and radon decay product concentrations and increase the reproducibility of the measurement. Windows on all levels and external doors should be kept closed (except during normal entry and exit) during the measurement period. Normal entry and exit include a brief opening and closing of a door, but--to the extent possible--external doors 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 and window fans should not be operating. However, attic fans intended to control attic and not whole building temperature or humidity should continue to operate. Combustion or make-up air supplies must not be closed.
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 lasting up to a week in duration. Normal operation of permanently installed energy recovery ventilators (also known as heat recovery ventilators or air-to-air heat exchangers may also continue during closed-building conditions. In houses where permanent radon mitigation systems have been installed, these systems should be functioning during the measurement period.
Closed-building 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 geographical area, this can be the period from late fall to early spring. In some houses, the most stable radon levels occur during late fall and early spring, when windows are kept closed but the house heating system (which causes some ventilation and circulation) is not used. Available information about variations of indoor radon levels in a particular area can be used to choose a measurement time when the radon concentrations are most stable.
It may be necessary, however, to make measurements during mild weather, when closed-building conditions are not the normal living conditions. It will then be necessary to establish some more rigorous means to ensure that closed-building conditions exist prior to and during the measurements.
Those 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-building conditions normally exist. Ideally, measurements should be conducted during those times. The closed-building conditions must be verified and maintained more rigorously when they are not the normal living conditions. Air conditioning systems that recycle interior air can be operated during the closed-building conditions when radon measurements are being made. However, homeowners should be aware that any air circulation system can alter the radon decay product concentration without significantly changing the radon concentration.
Short-term tests lasting just two or three days should not be conducted during unusually severe storms or periods of unusually high winds. Severe weather will affect the measurement results in several ways. First, a high wind will increase the variability of radon concentration because of wind-induced differences in air pressure between the building interior and exterior. Second, rapid changes in barometric pressure increase the chance of a large difference in the interior and exterior air pressures, consequently changing the rate of radon influx. Weather predictions available on local news stations can provide sufficient information to determine if these conditions are likely. While unusual variations between radon measurements may be due to weather or other effects, the measurement system should be checked for possible problems.
2.3.3 Interpretation of Initial Measurement Results
If the initial measurement result is less than 4 pCi/L, or 0.02 WL, follow-up measurements are probably not needed. There is a relatively low probability that mitigation is warranted if the result is less than 4 pCi/L or 0.02 WL (EPA 400-R-92-011; U.S. EPA 1992g). Even if the measurement result is less than 4 pCi/L, or 0.02 WL, however, a homeowner may want to test again sometime in the future. If the occupants' living patterns change or renovations are made to the house and they begin using a lower level (such as a basement) as a living area, a new test should be conducted on that level.
The average year-round indoor radon level is estimated to be about 1.3 pCi/L, and about 0.4 pCi/L of radon is normally found in outside air. The U.S. Congress has set a long-term goal that indoor radon levels be no more than outdoor levels. There is some risk from radon levels below 4 pCi/L, and EPA recommends that the homeowner consider reducing the radon level if the average of the first and second short-term measurements or if a long-term follow-up measurment is between 2 and 4 pCi/L (0.01 and 0.02 WL). While it is not yet technologically achievable for all homes to have their radon levels reduced to outdoor levels, the radon levels in some homes today can be reduced to 2 pCi/L or below.
If the result of the short-term measurement is equal to or greater than 4 pCi/L, or 0.02 WL, the occupant should conduct a follow-up measurement using a short-term or long-term test, as described in Section 2.4.
2.4.1 Rationale
The purpose of a follow-up measurement is to provide the homeowner with enough information to make an informed decision on whether to mitigate to reduce radon levels. The follow-up measurement, whether it is short-term or long-term, provides an additional piece of information to confirm that radon levels are high enough to warrant mitigation. There are two major reasons why a second measurement is necessary. First and most important, radon levels fluctuate over time (see Section 1), and a second short-term measurement, when averaged with the first test result, will provide a more representative value for the average radon level during the period of the test. If a long-term follow-up measurement is conducted, that result should provide an even more representative value for the long-term average radon concentration. The second reason for making a follow-up measurement prior to mitigation is that there is a small chance of laboratory or technician error in all measurements, including radon measurements, and a second test will serve as a check on the first.
A follow-up test is necessary regardless of the initial test result. Homes tested using the protocol in this section should not be mitigated on the basis of a single short-term test.
2.4.2 Short-Term and Long-Term Follow-Up Testing
Follow-up testing should be conducted in the same location as the first measurement (see Section 2.2).
A follow-up test can be conducted with either a short-term or long-term measurement device. Long-term tests (> 90 days) will produce a reading that is more likely to represent the home's year-round average radon level than a short-term test. However, if the initial test result is high (for example, greater than about 10 pCi/L, or 0.05 WL) or if results are needed quickly, EPA recommends a second short-term test. This will allow the homeowners to obtain information necessary to decide quickly on the need for mitigation. If the result of the initial measurement is not severely elevated (between 4 pCi/L and 10 pCi/L or between 0.02 WL and 0.05 WL), then either a short-term or long-term test can be taken.
If the long-term follow-up test result is 4 pCi/L, or 0.02 WL, or higher, then EPA recommends remedial action. Likewise, if the average of the initial and second short-term results is equal to or greater than 4 pCi/L, or 0.02 WL, radon mitigation is recommended. These recommendations are summarized in Exhibit 2-1.
As with the initial short-term test, the second short-term test should be conducted under closed-building conditions (Section 2.3.2). These conditions, however, are not necessary for long-term tests (those lasting longer than 90 days).
Table of Contents || Section One || Section Three || Section Four || Appendices || Glossary || References
http://www.epa.gov/iaq/radon/pubs/homprot3.html
Created: July 30, 1999
