Pardon the attempt at humor on a serious topic. The fact is, many people only think about radon when buying or selling a house. But the radioactive gas poses a danger 24-7 and all year long. Are you protecting yourself and your family?

In case you haven't heard, radon causes an estimated 20,000 lung cancer deaths in the United States every year. Only smoking causes more lung cancer, and the risk from radon is far greater for people who smoke or used to smoke.

Radon is present in the soil and the air worldwide. The threat arises when radon builds up inside a house and the occupants breathe the invisible gas over long periods.

U.S. health and environmental authorities have recommended for two decades that every home be tested for radon. Because radon concentrations in the home can change, authorities recommend that homes be re-tested every two years -- even homes with radon mitigation systems installed.

What will the test cost you? As little as $20 if you do it yourself with kits available online and in home centers; more -- $110 to $140 -- if you hire a state-certified radon tester to conduct the test with more sophisticated equipment.

Either approach will give you a good idea of whether your home has elevated levels of radon. If you do the test yourself, be sure that the kit is EPA-approved and that you follow the kit's instructions for preparing your home and handling, placing and shipping the test device to a lab.

Here are health and environmental agencies' guidelines on when to test:

• When buying a home. If the seller can't provide documentation of a recent test, testing is recommended. [Radon is measured in "picocuries per liter" (pCi/l), and the agencies recommend that a house be fixed if the number is 4.0 pCi/l or higher.]

• If it has been more than two years since the last test on your home.

• If you have a radon mitigation system that has not been tested recently. These systems can fail, and conditions in the home or below it may have changed since the system was installed.

• If you plan to increase the time spent in low-lying areas of the home, such as adding a family room, office or bedroom in a basement.

• If you are making structural changes that could allow more radon to enter. Radon seeps in through cracks and openings between the ground and the floor and walls of the home.

Beware of the many myths about radon.

Elevated levels of radon have been found in new homes and old, tight homes and drafty. Homes with or without basements can have a radon problem, and homes side by side can have far different radon concentrations. Elevated levels of radon can be found in any neighborhood.

Radon levels can almost always be reduced if yours is one of the estimated 1 in 7 homes with a radon problem.

But the only way to know is to test. Then test again.

©2007 Good Move Home Inspections, Abington, PA. [http://www.goodmoveinspections.com]. Reuse or reproduction freely permitted if copyright information is included.