What Is Radon?

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Radon can accumulate in the lower levels of your house.

Radon is a radioactive chemical element, part of a group known as the noble gases. More importantly, radon is a gas that poses notable health risks when present in your home. It is important to know if your home contains radon, and at what levels, so that you can take the steps necessary to correct the problem.

The Chemistry of Radon

Noble gases are characterized as being non-reactive and inert. Non-reactivity means that radon does not ordinarily form multi-atom molecules and thus, as a single atom, it remains small and more able to penetrate common materials such plastic sheeting, paints, concrete block, gypsum board and most insulation. Of the noble gases, radon is the heaviest and it's nine times denser than air. That density means radon will accumulate most intensely in the lower levels of a residence, principally in basements and crawl spaces.

Because it's a gas, radon is readily breathed and, because it's odorless and colorless, the only way to detect its presence is to test for it. It's essential to know whether radon is present in your home and in what concentration because radon, especially at high concentrations, is carcinogenic and the second leading cause of lung cancer after smoking. The U.S. Surgeon General's office has estimated that radon exposure results in 21,000 lung cancer deaths per year. Radon is especially lethal to smokers, who account for about 85 percent of those 21,000 deaths.

The product of the radioactive decay of natural uranium in rock, soil, and water, radon has a half-life of 3.8 days. As it decays, radon emits alpha radiation—the same radiation emitted by radioactive elements such as plutonium. By-products of radon's rapid decay are short-lived and known as radon progeny or radon daughters. These radon daughters are also radioactive and, because they are not gases, can attach themselves to dust and other particles that may also be breathed. As the decay process continues, the radon daughters release radiation until stable, non-radioactive isotopes of lead result.

Radon occurs in all 50 states. The red areas have the highest concentrations.

Radon Is Everywhere

Because radon is so ubiquitous, the question is seldom one of whether radon is present but rather in what concentration it's found. Especially common in igneous rocks, uranium can be detected in soils throughout the U.S. As uranium's radiation dissipates, radon is constantly released. In the outdoors, radon doesn't represent a hazard, because natural air flow keeps radon at inconsequential levels and allows it to disperse harmlessly. Only when radon is allowed to accumulate undisturbed does it become dangerous.

Testing Radon Levels

There are two basic methods of testing for radon: passive testing and active testing. Passive testing uses a radon collection device such as a charcoal canister or an alpha-track detector. These collection devices are positioned undisturbed for a prescribed amount of time and then sent to a lab for analysis. Passive testing can be performed by a homeowner, but it's not considered precise. Use it preliminarily to signal whether there may be a problem that calls for more precise testing.

Home test kits come in a number of forms and are simple to use.

Active radon testing devices are powered units that measure and record radon levels in the air over a set period—the longer the period, the more accurate the reading. Active radon testing equipment is normally utilized only by home inspectors and air quality specialists. If you need documentation of your home's radon levels, these professionals are additionally qualified to certify their results.

Radon may also be present in drinking water, especially if you get your water from a private well. Testing water for radon requires sending a sample to a testing laboratory. If the results prove positive, the radon level can be mitigated through the addition of an aeration system or through the use of charcoal filters.

Radon Remediation

The remediation techniques for radon in residential areas usually employ two basic strategies. First, the inflow of radon must be addressed as thoroughly as possible. Because radon is a gas, and a penetrative one at that, and because radon originates in the soil, the first step is to seal any cracks or gaps or defects that provide points of entry. Careful attention to those serves to minimize the radon influx.

Next, action needs to be taken to vent the radon harmlessly outside and to improve the overall air circulation. Removing radon before it enters the living space may be achieved by inserting a vent pipe equipped with an in-line fan through the concrete floor and into the soil. Within the living space, removal of concentrated radon usually entails drawing air from near the floor where the heavier radon gas has accumulated and allowing fresh air to replace it.

Recognition of the danger posed by high levels of radon gas has risen in the public consciousness in the past decade or so. If you have built or bought or sold a home during that time, the topic has been almost unavoidable. If you have been in your home longer than that, it is possible that the question of radon levels has never come up. Consider testing to see if your home has a radon problem.


A former agency art director then freelance designer, illustrator and copywriter, Bill has written for the medical, technical, industrial, food and agricultural industries. With over 35 years experience in the area of home improvement. He has produced books on multiple subjects for Home Depot, The Handyman Club of America, Hometime, Black & Decker and Popular Mechanics.

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