Unknowingly, radon had been cited as the cause of lung cancer in miners in the sixteenth century publication `De Re Metallica’ (Arricola, 1556) in which he noted that `critics say further that mining is a perilous occupation to pursue because the miners in the Ore Mountains of central Europe are sometimes killed by the pestilential air they breathe … sometimes their lungs rot away’. Two decades earlier, Paracelsus (Translated by Temkin et al, 1941), in his `On the miners’ sickness and other miners’ decease’s, had written the first treatise on the disease of an occupational group. Paracelsus appeared to believe that the origin of the disease of the lungs is to be sought in the air, although these early writings lack the conceptional framework within a modern account would be placed.

It was not until 1895 when Roentgen discovered x-rays and in the following year Becquerel discovered radioactivity that the understanding about ionising radiation grew, by 1900 adverse health effects attributable to radiation had been reported. The discovery of radon in 1900 by Dorn and its isolation as an element in 1908 followed from Marie Curie’s discovery of radium in 1898. The first measurements of radioactivity in ambient air were reported by Elster and Gaitel in 1901. Thus commenced studies of atmospheric radioactivity that have continued with increased intensity to the present.

In 1956 a study of natural radiation in Swedish housing was published which noted the elevated concentration of radon-222 and its decay products in indoor air compared with those concentrations in the open air. Since then studies have taken place of the incidence of radon-222 and its decay products in dwellings and other buildings in countries including the UK. In most countries the vast majority of buildings sustain radon-222 concentrations between a factor of two and ten higher than the concentrations in the open air.

Risk estimates for radiation were first evaluated by scientific committees in the starting in the 1950’s. The most recent of these committees was the Biological Effects of Ionising Radiation Committee Five (BEIR V, 1990). Like previous committees, this one was charged with estimating the risk associated with radiation exposure. The BEIR IV (1988) committee established risks exclusively for radon and other internally alpha emitting radiation, while BEIR V (1990) concentrated primarily on external radiation exposure data.

The National Radiological Protection Board (NRPB) was set up by the Radiological Protection Act 1970 primarily to advise Government on the risks of radiation. It’s remit was altered under the Health and Safety Act 1974 to provide for consultation with the Health and Safety Executive. Until 1980 there has been relatively few measurements of radon concentrations in UK dwellings. However, in the early 1980s NRPB set up a programme to investigate this subject. It was found that the mean radon concentration was around 20 Bq m­³ but that there was very large variation with a significant number of homes having radon concentrations of 1000 Bq m­³ or more (Brown, Cliff and Wrixon, 1981).

Following the International Commission of Radiological Protection (ICRP) Publication 39 (1984) and the Tenth report of the Royal Commission on Environmental Pollution (1984) the NRPB in 1987 proposed that action should be taken to reduce levels of radon in dwellings where levels were high and that building practices in selected high radon areas should be modified to reduce the levels in new dwellings (NRPB, 1987a; NRPB 1987b). This advice was accepted by government.

In 1990, NRPB updated and simplified its advice on radon in homes and introduced the concept of radon Affected Area – a part of the country where an appreciable fraction of the dwellings were likely to have concentrations of radon above the prescribed Action Level, which was set at 200 Bq m­³ (NRPB, 1990). The NRPB recommended that steps should be taken to reduce radon concentrations in dwellings found to be above the Action Level and that the appropriate authorities should delimit localities within the Affected Areas for preventative measures against radon in new dwellings.

In 1991 the House of Commons Environment Committee reviewed radon in a report on indoor pollution (House of Commons Environment Committee, 1991). It recommended that the government should commit itself to ensuring the identification of the majority of homes above the Action Level by the year 2000.

The UK is not alone in the identification of indoor radon as a potentially serious problem in public health. There are similar radon programmes in other European countries. The Commission of the European Communities (CEC) made a recommendation on the control of radon in dwellings in 1990 (CEC, 1990). A reference level of 400 Bq m­³ was put forward for existing buildings above which remedial measures should be considered; preventative measures in new buildings should be aimed at ensuring that 200 Bq m­³ was not exceeded.

The ICRP, Publication 65, surveyed the accumulated evidence on the risks of exposure to radon and on the practicability’s of controlling exposures. In authoritative recommendations it has refined its previous approaches to controlling doses from radon in both the domestic and occupational settings. (ICRP, 1993). The ICRP recommendations allow national authorities a significant degree of autonomy in setting Action Levels. However, it’s suggested ranges of 200-600 Bq m­³ in dwellings and 500-1500 Bq m­³’ in workplaces are consistent with the UK and European Action Levels in dwellings and very similar to the Action Levels for workplaces.

The NRPB in it’s 1994 Publication reviewed the risks of radon exposure, the factors affecting radon concentrations in buildings and how these concentrations can be measured. The NRPB defined the radon Affected Areas where appropriate authorities may declare that radon preventative measures are needed in new houses and where existing houses with high radon levels should be identified and rectified. (NRPB, 1994).

Radon protection measures where first introduced into the Building Regulations in 1994 under Regulation C2 “Preparation of site and resistance to dangerous and harmful substances”. This regulation specifies the radon Affected Areas of Northern Ireland where radon protection measures must be taken. These areas included the Southeast corner of Northern Ireland where radon levels greater than 200 Bq m­³ may be found.

The Department of the Environment in conjunction with the British Research Establishment in March 1997 produced a draft Technical Booklet to cover the radon regulations. This draft is currently out for consultation and will become part of the Building Regulations (England and Wales) at the beginning of 1998. This document uses a different method of calculating the financial cost of the regulations and has proposed that two levels of radon protection are provided. In radon affected areas above 6% probability full protection is provided and in all other areas basic protection is provided to all new dwellings.