Testing Your Home

  Radon is a colorless, odorless and tasteless gas that is unreactive chemically. It can only be detected with instruments that measure its radioactivity. Fortunately, there are a variety of devices available for measuring radon concentrations. Because radon concentrations can vary seasonally, it would be best to measure radon over the longest period of time possible. Ideally, this would be one full year because this allows you to determine the annual average radon concentration in your home. However, the longer you wait for the measurement to be completed, the greater your exposure risk. A short-term test can give you valuable information on which to make a remediation decision if you cannot wait for a long-term test.


The least expensive measuring devices, under $25, are also the easiest to use. There are generally two types most commonly available to homeowners: Charcoal Canisters, and Alpha-Track Detectors. Both are referred to as "passive" devices because they have no mechanical or electrical parts. They can be purchased in many hardware and home supply stores. Each device comes with easy to follow instructions and a mailing envelope to send it back to the laboratory. The laboratory will report the results to you. Sometimes the price of the test kit does not include the cost of the analysis. Read the package wrapping before you buy so you will know what you are paying for. Only those that have that have the phrase "meets EPA requirements" or "EPA listed" should be used. For a list of certified laboratories that provide detection kits, go to the List of Radon Professionals.

Short-term tests (Charcoal Canisters):

Charcoal canisters and similar charcoal-containing devices are used for short-term tests lasting a minimum of 48 hours and up to 7 days. They contain a quantity of granular activated carbon that absorbs the radon gas entering the canister from the surrounding air. At the end of the test period, the canister is sealed and returned to the manufacturer for analysis, who then reports the results to the buyer. 

Long-term tests (Alpha-Track Detectors):

Alpha-track detectors are long-term passive test devices that operate on a very different principle. Inside there is a piece of film that records the impacts (tracks) of alpha particles produced by the decay of radon and its decay by-product, polonium. Depending on the design of the detector, it may be set out for anywhere from 2 weeks to an entire year. At the end of the test period, the detector is returned to the manufacturer who counts the alpha tracks on the film, computes the radon concentration, and reports the results to the buyer.  
Electrostatic Radon Monitor:

A device known as the Electret Passive Environmental Radon Monitor (E-PERM) is used by many professional radon testers to obtain fast results on radon concentration. 

E-PERM is a passive integrating radon detection system consisting of a charged teflon disk (electret), an open-faced ionization chamber, a voltage reader, and a data logger. After placing the electret in the chamber, an electrostatic field is established. Radon gas diffuses passively into the chamber. The alpha particles emitted from the decay of radon ionize the air molecules. These ions are attracted to the charged surface of the electret, thus reducing the initial charge of the electret. The initial and the final voltages are measured using the voltage reader. The rate of change of the charge is proportional to the concentration of radon in the test area.


Professional radon testers will frequently perform tests using an "active" device, such as an electronic Continuous Radon Monitor. For the test to be valid, the device must be used according to the US EPA protocol, which includes the requirement that it operate for a minimum of 48 hours, and record measurements hourly or more frequently. Radon mitigators may use devices that make radon measurements over shorter periods. However, these measurements are for diagnostic purposes only; for example, to assist the radon mitigators in determining whether a foundation opening is an entry point for radon. Such measurements are not valid tests for whole-house radon concentrations and should not be used to make mitigation decisions.

Occasionally the radon tester may also use an instrument called a "Working Level Monitor." "Working level" is an alternative measure of radon concentration that is often used in occupational settings, such as in underground mines. Instead of measuring radon concentration directly, the working level measures the amount of radon decay products, which are an indirect measure of radon concentration. For a typical house, a 0.02 working level (WL) measurement corresponds to about 4.0 pCi/l of radon. This conversion between measurement units assumes that only half of the radon decay products are available for breathing because the rest have plated out on the walls, ceiling and furniture. The plate-out occurs because the radon decay-product particles are positively charged and are therefore attracted to surfaces of the opposite charge.

For more information on measurement of radon concentration, Click here

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