Radon is a naturally occurring radioactive gas. Odourless and colourless, it originates from the decay of uranium in rock.
Radon decays to form radioactive particles in the air. In open spaces these particles dissipate harmlessly. In buildings and enclosed spaces, however, radioactive radon particles accumulate to form higher concentrations.
When inhaled into the lungs, these particles give a radioactive dose which may, over time, damage cells in the lungs, leading to lung cancer.
The Radiological Protection Institute of Ireland (RPII) estimates that a 70-year (lifetime) exposure to radon levels of 200 becquerels per cubic metre carries a 1-in-50 risk of contracting a fatal lung cancer. A becquerel is a unit of radioactivity corresponding to one radioactive disintegration per second.
How great is the risk of developing lung cancer from radon gas? This depends on the level of radon, how long the person is exposed for and also whether someone is a smoker or not.
Apart from itself being the single biggest cause of lung cancer, smoking enhances the likelihood of a cancer developing from other causes.
Asbestos exposure causes a rare form of lung cancer.
In the same way that smokers are at a greater risk from radon exposure, the likelihood of developing an asbestos-related cancer is similarly enhanced.
In July 2003 the RPII discovered a home close to Castleisland, Co Kerry, with radon levels of 49,000 Bq/m3.
At 250 times the cut-off level of 200 Bq/m3, a massive exposure such as this over a period of years puts the occupants at a high risk of developing lung cancer.
Although children are known to be at greater risk than adults from certain types of radiation exposure, it is not known whether exposure to radon represents a greater threat to them compared with adults exposed to similar levels of radon-related radioactivity.
Radon exposure may also occur in an occupational setting. It is recommended that workers' exposure be kept below a level of 400 Bq/m3, averaged over a three-month period.
The RPII has the power to direct an employer to measure radon levels in the workplace.