It is formed by the natural breakdown of radium, which is itself a decay product of uranium. Invisible and odorless, radon is a health hazard when it accumulates to high levels inside homes or other structures. And it is deadly. Indoor radon exposure is estimated to be the second leading cause of lung cancer deaths each year in the United States. Radon problems have been identified in every state.
Radon can be a problem in schools and work places, too.
Radium, which releases radon, is common in the earth's crust. Soils and rocks containing high levels of uranium, such as granite, phosphate, shale and pitchblende are natural sources of radon. High levels of radon in the soil are primarily responsible for radon problems. The radon gas percolates up through porous soils under the home or building and enters through gaps and cracks in the foundation or in the insulation and through pipes, sumps, drains, walls or other openings. Water is another possible pathway for bringing radon into the home.