Back to main document OC 560/50
1 This guidance is issued by the Health and Safety Executive. Following the guidance is not compulsory and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance as illustrating good practice.
2 Radon-222 (referred to as radon throughout this document) is one of the decay products of uranium-238 which occurs naturally in rocks and soils. Radon is a gas and high levels within the air in soil (soil gas) are possible if the local rocks contain high levels of uranium. Granite tends to have high levels of uranium and so radon levels are high in some granite areas within the UK ( see Figure 2 ). However, it is important to recognise that high radon levels are sometimes found outside granite areas (for example on the limestone of the Derbyshire Dales) and, conversely, that not all granite areas are associated with high radon levels.
3 Where radon is present it can build up in confined spaces, particularly underground, eg in basements of buildings, caves, mines, etc. High concentrations can also be found in buildings, because they are usually at slightly lower barometric pressure than the surrounding atmosphere and so tend to suck in radon (from the soil) through cracks or gaps in the floor.
4 Radon has a four day half life (the time taken for half of the radon atoms present to undergo radioactive decay), which is long compared with the residence time of air in the lungs. So, if it is breathed in, most will simply be exhaled again. Only a very small fraction will decay in the body and irradiate tissue. However, the decay products of radon (radon daughters) are solid and are themselves radioactive, decaying with half lives of less than half an hour. These short lived decay products attach to atmospheric dust and water droplets and can become lodged in the lungs and airways when breathed in. They are thus likely to decay within the respiratory tract. Radon daughters are alpha emitters and will cause significant damage to the cells of the respiratory tract. The relative amount of radon daughters present with radon gas depends upon ventilation, well ventilated areas containing relatively fewer radon daughters. Radon gas is measured in Becquerels per cubic metre (Bqm-3,ie air activity concentration).
5 Radon contributes by far the largest component of background radiation within the UK (see Figure 1) and, while the largest radiation doses arise in domestic dwellings (due to the longer time spent there), significant exposures are possible in workplaces within radon affected areas. Occupational groups with known high exposure to radon, upon which it has been possible to complete epidemiological studies, show a significantly increased risk of lung cancer.
Figure 1: Contributions to the average UK annual radiation dose (NRPB publication: 'Living with radiation'; 1998; Chilton, UK; ISBN 0-85951-419-6)
6 The counties most seriously affected by radon are Cornwall and Devon. However, surveys of radon levels indicate substantially increased radon levels in Northamptonshire and parts of Derbyshire, Somerset, Grampian and the Highlands of Scotland (see Figure 2). Elevated levels have also been found in small pockets in other areas.
Estimated percentage of houses above the Action Level (200 Bq m-3)
7 Underground workplaces such as mines, caves and utility industry service ducts can be significantly affected by radon. In addition, any above-ground workplaces in radon affected areas (see Figure 2) might be affected, though it must be noted that radon levels between adjacent buildings in affected areas can vary by orders of magnitude (due to a number of factors such as local geology or building design and construction). Detailed surveys indicate that typical buildings with elevated radon levels have small rooms and low ventilation rates. Some examples are offices, classrooms, nursing homes, residential care homes and health centres. Whilst employers only occupying parts of buildings from the first floor and above are unlikely to have significant radon levels, employers utilising cellars, basements and poorly ventilated ground floor rooms are far more likely. Generally, significant levels are less likely to exist in larger workshop-type premises such as engineering works, joineries and large bakeries, often because the nature of the process requires enhanced ventilation. Smaller rooms, offices, stores, etc around these larger workshop premises may still be higher.
8 Radon surveys should be conducted in any building where its location and characteristics suggest that elevated levels may be found. Inexpensive surveys can be carried out by leaving integrating dosemeters in rooms of interest. The National Radiological Protection Board can be contacted for information on measurement services.
9 Radon levels vary widely, throughout any given day and from season to season. For these reasons measurements are usually made over a period of three months and the annual average estimated using seasonal correction factors.
10 Where the workplace is occupied for a normal working day and extended measurements show radon levels below 400 Bqm-3, no further action is likely to be required. This figure of 400 Bqm-3is comparable with the Action Level of 200 Bqm-3in homes, taking into account that most people spend much more time in the home than at work. For levels above 400 Bqm-3the employer may well need to take action to reduce potential exposure.
11 New buildings and buildings extension: In England and Wales, the Building Regulations 2000 require that 'precautions shall be taken to avoid danger to health and safety caused by substances found on or in the ground to be covered by the building.' Similar requirements are contained in the Building Standards (Scotland) Regulations 1990 (as amended). In radon affected areas, therefore, new buildings (workplaces and dwellings) must be designed and constructed so as to deal with the risk. Generally, it isn't possible to accurately assess the severity of a radon problem on a particular site until the building has been constructed and occupied. Therefore, precautions should be taken on the basis of where problems are most likely to occur rather than where they actually occur: remediation is easier during rather than after premises construction. The BRE report lists, by parish, the areas in which precautionary measures are required.
12 In the areas with the highest risk, full radon precautions are required. This means providing both primary (radon proof barrier) and secondary measures (radon sump and extract pipe or a ventilated sub floor void). A radon sump is a small cavity under the floor with a small electric pump sucking air from it. This reduces the normal under floor pressure with respect to radon in the soil and results in much less being sucked up into the building through cracks in the flooring material.
13 In areas with a lower risk only secondary measures, for example provision for future sub-floor extraction (radon sump and extract pipe or ventilated sub floor void), are required.
14 In areas where there is little or no possibility of an enhanced level of radon there is no need to provide secondary measures during construction; for example, the subsoil may be such as to prevent the passage of radon or it may be permanently saturated.
15 The areas listed in the BRE report are subject to periodic revision as and when new research data become available. Local authority Building Control departments should be able to provide information about the location of affected sites within their district.
16 Existing buildings: radon remediation might consist of installation of under-floor sump plus fan and/or improved ventilation.
17 In workplaces where it has been found necessary to take action to reduce radon levels, employees could also be receiving significant exposure at home. Employers are encouraged to recommend to their employees to have their homes tested.
18 The Buildings Research Establishment Ltd (BRE), Garston Watford WD2 7 JR. Telephone 01923 664707; e-mail email@example.com. BRE can provide advice on radon in the workplace, dwellings with cellars and basements, major alterations and conversions and various methods of radon remediation.
19 National Radiological Protection Board (NRPB), Chilton, Didcot, Oxon OX11 0RQ. Telephone 01235 822622; Fax 01235 833891; e-mail firstname.lastname@example.org; website Http://www.Nrpb.Org. NRPB can provide a range of information relating to occupational exposure to radon.
20 The Radon Council, PO Box 39, Shepperton, Middlesex TW17 8AD; Telephone 01932 221212; Fax 01932 229 779; e-mail email@example.com. The Radon Council have a list of organisations providing radon remediation services (www.radoncouncil.org).
In 1991 NRPB announced a validation scheme for laboratories making radon measurements in homes. The government departments with responsibility for radon in dwellings have requested local authorities and the Northern Ireland Housing Executive to give favourable consideration only to grant applications which are supported by measurements carried out by laboratories successfully participating in the scheme. The validation scheme requires rigorous tests of the laboratory, and requires that measurements in homes are carried out over at least a three month period. A list of validated laboratories, which includes NRPB, can be made available. Further details of the validation scheme are given in NRPB-M1140,Validation scheme for laboratories making measurements of radon in dwellings: 2000 revision, which is available from the Information Office on payment of an administrative charge of 5.00 per copy. A current list of laboratories that have been validated is at:http://www.nrpb.org/services/radon/validation.htm