What kinds of test devices are used?
Two groups of devices are more commonly used for short-term testing.
Passive devices do not need power to function. The group includes alpha track detectors, charcoal canisters, and charcoal liquid scintillation detectors. Some charcoal technologies are prone to interference by high humidity, so may not be appropriate for use in all buildings. They are sometimes available in drug, hardware, and other stores, the Internet, and through some laboratories. Electret ion chamber detectors, another type of short-term test device, are usually only available through laboratories. After being used, passive devices are returned to a laboratory for analysis.
Charcoal canisters for short-term use are sold through the National Radon Program Services website. These test kits are designed to be used for two or four days before being returned for analysis by the laboratory that provides it. A return mailer is provided with the kit.
Active devices require power to function. This group consists of different types of continuous monitors and continuous working level monitors. Some of the active monitors can provide data on the range of variation within the test period. Some are designed to detect and deter interference. However, they usually require operation by trained testers. These tests often cost more than passive testing.
Alpha track and electret ion chamber detectors are commonly used for long-term testing. Long-term test kits currently sold through the National Radon Program Services website are alpha-track detectors. They are designed to be used for three months to a year before being returned to the providing laboratory for analysis.
Technical information on use of various devices used to measure radon or radon decay products is found in the EPA publication, Indoor Radon and Radon Decay Product Measurement Device Protocols.
Continuous monitors are not available through the National Radon Program Services website at this time.
Why are short- and long-term tests used?
Radon levels within a building often change on a day-to-day basis. Highest indoor levels are often found during the heating season. Weather conditions, operation of furnaces and fireplaces, and opening/closing of windows and doors are among the factors that cause these patterns.
Short-term test kits are the quickest way to test. These kits should remain in the building from two to 90 days, depending on the device. Testing must be conducted for at least 48 hours. Some devices must be exposed for a longer time. Because radon levels tend to vary from day to day and season to season, a short-term test is less likely than a long-term test to tell you your year-round average radon level.
The EPA recommends that for homes, initial measurements be short-term tests placed in the lowest lived-in level. Short-term testing under closed-building conditions helps to ensure that residents quickly learn if a home contains very high levels of radon. If you are doing a short-term test, close your windows and outside doors and keep them closed as much as possible during the test. If testing for just 2 or 3 days, be sure to close your windows and outside doors at least 12 hours before beginning the test, too. You should not conduct short-term tests lasting just 2 or 3 days during unusually severe storms or periods of unusually high winds.
Because radon levels may fluctuate by as much as a factor of two or three, additional testing is sometimes recommended to better assess the average radon level. Though short-term tests are sometimes used, long-term tests are often recommended.
Long-term tests remain in your home for more than 90 days. A long-term test gives a reading that is more likely to reflect the building's year-round average radon level than a short-term test. Because of season variations in radon levels, the closer the long-term measurement is to 365 days, the more representative it will be of annual average radon levels.
If time permits (more than 90 days), long-term tests can be used to confirm initial short-term results between 4 pCi/L and 10 pCi/L. When long-term test results are 4 pCi/L or higher, the EPA recommends the problem be corrected.