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Radon: the risks


Radon, a natural radioactive gas, is a hazard in many homes and workplaces. Inhaling radon is the second largest cause of lung cancer in the UK, causing more than 1100 lung cancer deaths each year. Gordon Tranter considers the risks from radon in the workplace.

A radioactive decay product

Radon is a naturally occurring odourless and tasteless gas formed from the radioactive breakdown of uranium. Radon is a short-lived radioactive element with a half-life of 3.8 days that decays by the emission of alpha particles to polonium, bismuth and lead in successive steps. The products of radon’s decay are not gases and their formation produces radioactive, solid decay products which attach to atmospheric dust and water droplets which can then be breathed in and become lodged in the lungs and airways.

Health effects

If inhaled, the radioactive dust produced by radon becomes trapped inside the lungs where it emits alpha particles which cause damage that leads to the only known health effect of radon — an increased chance of developing lung cancer. Radon is the second leading cause of lung cancer after smoking, causing over 1100 deaths each year in the UK. Half of these deaths are of current smokers. The risk from radon is approximately 25 times higher for cigarette smokers than for non-smokers. The dose-response relationship between the concentration of indoor radon and the risk of developing lung cancer appears linear; the greater the exposure, the greater the risk of developing lung cancer.

The risk

In the atmosphere, radon is present in low concentrations and is not a problem. However, radon can seep out of the ground and build up in houses and indoor workplaces and be a risk to health. The risk will depend on the level of radiation caused by radon and this will depend on the local nature of the soil and rocks on which the buildings are built, the nature of the building and whether there are protection measures in place.

Occurrence in the UK

Uranium is found in low levels within all rock and soils. However, the amount varies from place to place. Relatively high levels of radon emissions are associated with particular types of rock, particularly granite which naturally contains more uranium than other rocks. There are a number of radon hotspots in the UK, particularly the granite areas such as the South West of England, the Grampian and Helmsdale areas of Scotland, and the Mourne Mountains in Northern Ireland. However, it should be noted that it is not only granite areas of the UK where high levels of radon are found. Other areas with high levels of radon include Carboniferous limestones throughout the UK and some Carboniferous shales in Northern England, and sedimentary ironstone formations in the English Midlands.

The UK has been extensively surveyed by the Health Protection Agency (HPA), now Public Health England (PHE), and the British Geological Survey. The highest radon areas have been defined by the Government as Radon Affected Areas. Employers can consult the definitive radon dataset at the PHE website to see if their premises are located in one of these areas. In addition, an atlas indicating the approximate locations of Radon Affected Areas in England and Wales is available to download at the same site. Radon Affected Area maps for Scotland and Northern Ireland are also available at the PHE website.

Occurrence in the workplace

The highest levels in the workplace are usually found in underground spaces such as basements, caves and mines. High concentrations are also found in ground floor buildings because they are usually at slightly lower pressure than the surrounding atmosphere; this allows radon from the subsoil underneath buildings to enter through cracks and gaps in the floor. Where the only occupied parts of buildings are from the first floor and above, there are unlikely to be significant radon levels.


Under the Health and Safety at Work, etc Act 1974, employers must, so far as is reasonably practicable, ensure the health and safety of employees and others who have access to their work environment and the Management of Health and Safety at Work Regulations 1999 require the assessment of health and safety risks which should include radon.

Radon exposure and control for workplaces is covered by the Ionising Radiations Regulations 1999 (IRR) if the average radon gas concentration measured over a three-month period exceeds 400 becquerels per cubic metre (Bq/m3), after a mid-winter seasonal correction has been applied.

The test

The measurement of radon levels is simple. It uses an inexpensive test pack for radon which can be ordered through the PHE website. The survey involves leaving small plastic passive radon detectors in rooms of interest and returning them for analysis.

To measure or not to measure

The initial step in the radon risk assessment is to decide whether there is a need to measure the radon concentration.

Radon measurements should be carried out in all occupied below-ground workplaces (for example occupied for greater than an average of one hour per week during a year), or those containing an open water source, the risk assessment should include radon measurements. This applies to all below-ground workplaces in the UK, irrespective of the Radon Affected Areas status. If radon protection measures are already in place, the assessment needs to consider the need for monitoring their effectiveness.

Measurements should be carried out in most ground floor rooms if the building is located in a Radon Affected Area. In its guidance, the HSE advises employers to take a conservative approach and undertake measurements in all premises located in a 1km grid square that is shaded in the indicative atlas. Employers can obtain more specific information by consulting the definitive HPA radon dataset link to an external website online (a small fee is charged) to identify the Radon Affected Areas status of a particular building or buildings.

Acting on the test results

If the results show occupied areas to have radon levels exceeding 400 Bq/m3 the IRR, the regulations covering ionising radiations, apply. When PHE provides radon measurement results, it also provides advice to guide employers on the actions they can take to protect staff.

The Health and Safety Executive (HSE) provides guidance on its website regarding the steps to take when radon levels exceed 400 Bq/m3. This points out that in these circumstances the employer is obliged by the IRR to take action. This may involve taking immediate steps to manage occupational exposures pending any decision on what may be required to reduce the radon levels by engineered means. The HSE advises that a radiation protection advisor with radon experience should be consulted about how best to manage radon exposures. In those cases in which the employer plans to immediately remove the radon so that the IRR99 do not apply, the HSE recommends that in the first instance, a specialist radon removal (remediation) contractor should be consulted. In most cases it is advisable to continue monitoring in these areas at least until the reduction measures have been put in place. When PHE reports the radon measurement results, it also provides advice to guide employers on the actions that can be taken to protect staff.

Control of radon levels in buildings

The entry of radon into a building is mostly by airflow from the underlying ground. The protection measures required to reduce radon levels within the workplace will vary dependent upon the severity of the problem and how the building is constructed.

When extensions are made to existing buildings, or new buildings are constructed in high radon areas, the Building Regulations require that protective measures are taken against radon entering the building. A range of practical solutions have been developed to help reduce radon levels in existing buildings and to prevent radon entry into new buildings. The BRE REP 211 Radon: Guidance on Protective Measures for New Buildings provides guidance for radon reduction in new builds, conversions, extensions, and refurbishments of domestic and non-domestic buildings.

In existing buildings it is not possible to provide a radon-proof barrier and so alternative solutions for reducing radon levels in existing buildings must be used. Alternative solutions include:

  • installing radon sumps

  • sealing large gaps in floors and walls in contact with the ground

  • increasing underfloor ventilation

  • installing a whole building positive pressurisation or a positive supply ventilation system

  • improving the ventilation of the building.

Re-measuring the radon levels

Once the results have been assessed and a decision on the actions required has been made, the risk assessment needs to be reviewed at intervals. It needs to consider the need for future measurements of radon levels. This should consider whether there have been changes to the construction of the building or alterations to heating and ventilation which could have caused the radon levels to alter. The HSE suggests that the radiation protection advisor is best-placed to determine the frequency of any re-measurements.

The HSE recommends that in the absence of a radiation protection advisor, it is good practice to assign a maximum period upon which the measurements should be repeated.

  • For buildings where the initial measurement is significantly less than 400 Bq/m3, the suggested period for re-measurement might be in the order of once every 10 years.

  • For buildings where the initial measurement is just below 400 Bq/m3, the period for re-measurement will be less than 10 years.

  • For buildings where the initial measurement is above 400 Bq/m3 and measures have been taken to reduce radon exposures, the re-measurement periods will very likely need to be significantly more frequent in order to verify their continuing effectiveness.

Employees in radon hotspots

It is possible that employees working in Radon Affected Areas could also be receiving significant exposure at home. The HSE strongly encourages employers to recommend home testing to their employees who live in the Radon Affected Area. In some areas domestic radon testing is provided free of charge (local authorities can provide information about schemes they run). In other areas, measurement laboratories make a charge of typically £40 per house.

Last reviewed 17 February 2017

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