The Health & Safety Executive acknowledges that approximately 2000 people in the UK die from lung cancer linked to radon exposure each year. It is a clear odourless radioactive gas that escapes naturally from the rock beneath the earth’s surface. In some regions the concentration is worse than others but, like all forms of ionising radiation, can be deadly.  Although geological maps provide some guide to the riskier areas of the UK, because of the nature of the gas high levels of radon can occur in many other parts of the UK. The Government has set guideline maximum levels that radon concentration should be inside buildings. These are referred to as Action Levels, as they are the point at which it is advised (or required, in the case of commercial buildings) that action is taken to lower the concentration. In domestic properties, the current Action Level is 200 Bq/m3 [Becquerels per cubic metre] and in commercial properties the current Action Level is 400 Bq/m3. The average background radon concentration outside is 4 bq/m3 and the average radon level inside buildings is 20Bq/m3. To put these levels into perspective, the estimated annual radiation dose that someone would receive from spending 8 hours per day in a building with 400 Bq/m3 is equivalent to undergoing approximately 225 chest x-rays. Put another way, the damage to the lungs from spending 8 hours in radon levels of 400 Bq/m3 is estimated as equivalent to smoking over 10 cigarettes during the same time period. Radon gas seeps into enclosed spaces such as houses and other buildings where it collects. It can build up to high concentrations, depending upon the local geology, atmospheric conditions and ventilation in different structures. Radon itself also decays to form short-lived radioactive particles, which remain suspended in air. When such radioactive particles are inhaled into the lungs, they irradiate the lung and increase the risk of developing lung cancer. This risk increases as the level of radon and the duration of exposure increases. High radon levels therefore need to be taken seriously and steps taken to ensure exposure to radon is kept as low as reasonably practicable.