Radon Testing and Measurement

How testing devices measure radon
Radon is measured by detecting the radiation it emits when it decays. Radioactive decay produces three types of particles: Alpha, Beta and Gamma. All of the commonly used radon detectors, except charcoal canisters, count Alpha particles. Charcoal canisters count Gamma ray pulses.

With Alpha track devices the method being used is one radioactive pulse, one molecule. Count the pulses and you count the molecules and compute the amount or radon in the area being tested. This is done with a device that has a very fine diffusion screen on the top of that will allow the radon molecules inside, while keeping out the larger particles. When the radon decays, the alpha particles pock a small piece of plastic. This plastic is scanned with a microscope to count the number to decays that have taken place in the time that the test was placed.

Radon measurement utilizes radiation measurement not chemical analysis; therefore, they are not affected by natural gas leaks, paint fumes or carbon monoxide.

Short-term testing
A short-term test utilizes devices such as E-PERMs, Continuous Radon Monitors and charcoal canisters. The test period is a minimum is 48 hours and a maximum of 90 days. The short-term test is designed for real estate transactions and must be done under the below conditions.

Before a short-term test is placed, the house should be kept closed except for normal entry and exit and the HVAC system operated normally. This allows the home to reach dynamic equilibrium and to stabilize the radon entry to a normal level. A house will reach equilibrium usually within 12 hours.

During the test, closed house conditions must be maintained. All windows must remain closed and doors closed except for normal entry and exit. The fireplace should not be used unless it is a primary heat source. Excessive use of devices that vent air from the house could increase the radon entry rate above that which is normally created by the houses ‘stack effect.’

The test should be placed in the lowest livable level, not necessarily the one being used by the current occupants. (The future occupants may choose to utilize the home differently.) An unfinished basement should be considered livable. Crawlspaces and dug out basement with exposed earth are not considered livable spaces.

The short-term test is actually measuring the houses propensity to draw radon from the soil, not the actual radon level in the home (i.e., average yearly level). Studies have shown that there is a 90% certainty that measured short-term test levels are +/- 25% from the true yearly average radon level.

The EPA recommends reducing levels of radon in houses where radon concentrations exceed the EPA radon action level of 4 picocuries per liter. A second test by electronic means is recommended if the first results exceed the threshold level of 4.0 before committing funds to remediation.

Long-term testing
A long-term test uses devices such as Alpha track detectors. Long-term tests last between thee months to a year and are placed in the lowest lived in level of the structure. This measurement is affected by the lifestyle of the occupants and provides a measure of actual exposure to radon. This test is best for homeowners who can test for a full year to average their exposure over all four seasons.

We recommend that all homeowners test their homes with long term testing devices at least once every two years.

Does weather affect test results?
In general, typical weather conditions have little measurable effect on the radon level in a house. Only when the weather is severe to alter the stack effect of the home, will there be any change.

For short-term tests of less than four days, high winds should be avoided (defined as sustained winds over 30 MPH, not brief gusts). Short-term tests should not be placed during severe storms. The National Weather Service defines a severe storm as a storm that generates winds of 58 MPH and/or ¾ inch diameter hail and that may produce tornados – not necessarily in that order. If the weather during the test meets either of these criteria, a retest may be recommended.

If you have a question about the weather that arose during a test, consult a radon testing professional.