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Radon-222 is an invisible, odorless, radioactive soil gas. EPA has determined it to be a Group 1 carcinogen, which means that it causes cancer in humans. The Surgeon General has warned that it is the second leading cause of cancer in the United States and that tobacco smoking significantly increases the risk.

EPA recommends that every home involved in a real estate transaction be tested for radon. The test is to be done at the lowest livable level – usually the basement. By livable, EPA means an area of the home that could conceivably be converted to living space. This does not include crawl spaces.

Exposure is a function of two factors – concentration and time. Testing determines concentration. Lifestyle determines time.

Average outdoor concentration is estimated to be about 0.4 pCi/l (pico Curies per liter) of air.

Average indoor concentration is estimated to be about 1.3 pCi/l.

EPA action level is 4.0 pCi/l. This means that EPA has recommended that houses that have concentrations of 4.0 or greater be mitigated.

The nuclear physics part: The nuclei of radioactive elements emit particles. Each event in which a particle is emitted is called a decay. Every time a decay takes place, a new element is formed. The result then is a chain of elements beginning with uranium 238 and ending with lead 206, which is a stable element. Each element in this decay chain is a solid except for radon 222. Radon and two of its progeny, polonium 214 and polonium 218 are especially dangerous because they emit alpha particles. We measure radioactivity in Curies. A Curie is a rate of radioactive decay. A pico Curie (pCi) is a trillionth of a Curie.

The mobility part: Because radon is a gas, it has the ability to move readily in nature. Because soil gases are typically at a higher pressure than the atmosphere and gases move in nature from areas of high pressure to areas of low pressure, there is a tendency for radon gas to move from the ground into the atmosphere. There is a natural tendency for air currents to move upward through a house. We refer to this as the stack effect. The stack effect places lower levels of the house under negative pressure which tends to draw air into the house through cracks and openings in basement floors and foundations.

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