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Radon is a colorless, odorless, radioactive gas produced by the radioactive decay of radium-226, an element found in varying concentrations in many soils and bedrock.

Figure 1 shows the series of elements that begin with uranium-238 and eventually decay to lead-210. Of all the elements and isotopes in the decay chain, radon is the only gas. Because radon is a gas,it can easily move through small spaces between particles of soil and thus enter a building. Radon can enter a building as a component of the soil gas and reach levels many times higher than outdoor levels.
While many of the isotopes in the uranium-238 decay series exist for a long time before they decay, radon has a half life of only 3.8 days. Radon decay products have even shorter half-lives than radon and decay within an hour to relatively stable lead-210.At each level of this decay process,energy is released in the form of radiation.This radiation constitutes the health hazard to humans. When radon and radon decay products are present in the air, some will be inhaled. Because the decay products are not gases, they will stick to lung tissue or larger airborne particles that later lodge in the lungs. The radiation released by the decay of these isotopes can damage lung tissue and can increase one’s risk of developing lung cancer.The health risk depends on how long and at what levels a person is exposed to radon decay products. Radon and radon decay products cause thousands of deaths per year in the world.
Like other environmental pollutants,there is some uncertainty about the magnitude of radon health risks. However, we know more about radon risks than the risks from most other cancer-causing substances. This is because estimates of radon risks are based on the studies of cancer in humans (underground miners). Additional studies of more typical populations are underway. Smoking combined with exposure to elevated levels of radon is an especially serious health risk. Children have been reported to have greater risk than adults of certain types of cancer from radiation, but there are currently no conclusive data on whether children are at greater risk than adults from radon.

Radon levels are usually measured in picocuries per liter of air (pCi/L). Currently, it is recommended that indoor radon levels be reduced to less than 4 pCi/L. But the lower the radon level, the lower the health risk: therefore, radon levels should be reduced to as close to ambient levels as feasible (0.4 pCi/L).

Architects and engineers should consider the health risks of radon prior to constructing new buildings or renovating existing buildings in radon-prone areas. Including radon prevention techniques during building design and construction will reduce the chance that a building will have a radon problem and also reduce the cost of reducing radon levels, if needed.


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