What exactly is an E-PERM®? How is it different from an electret?

An E-PERM® (which stands for electret passive environmental radon/radiation monitor) is an electret ion chamber. This means that an E-PERM® is comprised of two components: (1) an electret, and (2) a special chamber that will allow ionization to occur. Although electrets are an important component of an E-PERM®, they cannot measure radon by themselves. As soon as an electret is paired with an ionization chamber, the resulting configuration is known as an E-PERM®, which is also synonymous with an electret ion chamber.

How do Electret Ion Chambers measure radon?

Electret Ion Chambers are comprised of both an electret and an ionization chamber. The ionization chamber is constructed of electrically-conductive plastic, with a volume and shape that has been very accurately characterized. Because the ionization chamber is conductive, it displays strong anti-static properties (that prevents an electrical charge from accumulating on the chamber's exterior and interior surfaces). It also functions as a makeshift Faraday cage, which offers some protection against stray electromagnetic fields.

The second component of an Electret Ion Chamber -- the electret -- consists of a positively charged Teflon® disk, which is housed in an electrically-conductive plastic holder. When the electret is loaded into an ionization chamber, an Electret Ion Chamber (known as an E-PERM®) is created. As radon and its daughters decay inside the ionization chamber, they release alpha and beta particles; the alpha particle is like a tiny atomic cannonball, and the beta particles are the subatomic equivalent of bullets. As these particles fly through the ionization chamber, they strike other molecules in the air. Whenever this happens, an effect called ionization occurs -- and the resulting air molecule is left with either a positive or negative charge.

These negatively charged ions are attracted to the positively charged electret surface, and a reduction in voltage occurs. The radon concentration of a given environment is a direct function of the reduction in voltage over a known time period.

What is a Short-Term E-Perm® Radon Test ?

Electret Ion Chambers are used for short-term radon tests (-10 days). Short-term radon tests can be useful to get a preliminary idea of radon levels present in a home, or to provide short-term confirmation of the efficacy of a new radon mitigation system. Health Canada recommends following up the results of any short-term radon test with a long-term measurement to make informed decisions about mitigation. Only a long-term test should be used to determine the average level of radon gas exposure within a residence.

When conducting a short-term radon test, it is necessary to establish closed-house conditions to allow the radon levels to stabilize. When a radon measurement is less than 4 days in duration, closed-house conditions are to be established for the 12 hours immediately prior to starting the test and maintained for the duration of the test. If a radon test is 4 days or more in length, closed-house conditions are to be set up at the time of the start of the test and should be maintained for the duration of the test. If closed-house conditions are not established prior to the start of a short-term radon test, the results are considered invalid.

Closed-house conditions include:

• Windows should stay closed at all times
• External doors opened only for entry and exit
• Attached garage doors should be opened only for entry and exit
• Fireplaces should not be operated during the test, unless it’s a primary heat source
• Clothes dryer, range hood, and bathroom fan operation should be limited to the minimum necessary