The radioactive gas radon is a hazard in many homes and workplaces. Breathing in radon is the second largest cause of lung cancer in the UK resulting in up to 2000 fatal cancers per year. However radon hazards are simple and cheap to measure and relatively easy to address if levels are high. Under UK regulations all employers must review the potential radon hazard in their premises.
Radon affected areas in Scotland
Indicative map of radon affected areas in England and Wales
Radon is a naturally occurring radioactive gas that can seep out of the ground and build up in houses and indoor workplaces. The highest levels 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 sub-soil underneath buildings to enter through cracks and gaps in the floor.
Radon (more properly known as radon-222) comes from uranium which occurs naturally in many rocks and soils. Since granite contains relatively high levels of uranium many people think that it is only granite areas of the UK, such as the South West of England, that have high radon levels. This is untrue and, as shown on the map above, many parts of the country have high radon levels.
Most radon gas breathed in is immediately exhaled and presents little radiological hazard. However, the decay products of radon (radon daughters) behave more like solid materials than a gas and are themselves radioactive.
These solid decay products attach to atmospheric dust and water droplets which can then be breathed in and become lodged in the lungs and airways. Some decay products emit particularly hazardous radiation called alpha particles which cause significant damage to the sensitive cells in the lung.
Radon is now recognised to be the second largest cause of lung cancer in the UK after smoking. Lung cancer is also the biggest cause of cancer related death in the UK and only 5% of all lung cancers are curable.
Radon contributes by far the largest component of background radiation dose received by the UK population (see chart below) and, while the largest radon doses arise in domestic dwellings (due to the longer time spent there), significant exposures are possible in workplaces. Epidemiological studies on occupational groups with known high exposure to radon show a significantly increased risk of lung cancer. A recent study which pooled the results of 13 European case-control epidemiological studies of people exposed to radon at home (Darby et al, 2005) has confirmed the risks and refined their accuracy. It also showed that the risk from radon is approximately 25 times higher for cigarette smokers than for non-smokers.
Contributions to the average UK annual radiation dose (HPA/-RPD-001, Ionising Radiation Exposure of the UK Population: 2005 Review; ISBN 0-85951-558-3)
Radon is measured in units of becquerels per cubic metre, Bq/m3 (ie concentration of radioactivity in air).
The UK has been extensively surveyed by the Health Protection Agency (HPA) and British Geological Survey. The highest radon areas have been defined by Government as radon Affected Areas and employers and householders may consult the definitive radon dataset at www.ukradon.org to see if their premises are located in one of these Areas.
In addition to the dataset, an atlas indicating the approximate locations of radon Affected Areas in England and Wales (HPA-RPD-033) is available to download at from the HPA website. This indicative atlas, shown above, was published in November 2007 and replaces the 2002 NRPB Radon Atlas (W26). The darker the colour the greater the likelihood of significant radon levels within buildings in that area. Affected Area maps for Scotland radon map and Northern Ireland are also available on the HPA website.
Underground workplaces such as basements mines, caves and utility industry service ducts can have significant levels of radon as can any above-ground workplaces in radon Affected Areas. All workplaces including factories, offices, shops, classrooms, nursing homes, residential care homes and health centres can be affected. Whilst employers who only occupy parts of buildings from the first floor and above are unlikely to have significant radon levels, employers who use cellars, basements and poorly ventilated ground floor rooms are far more likely to have problems with radon levels.
Although the radon data used in production of the indicative atlas above comes from measurements in homes, the maps indicate the likely extent of the local radon hazard in all buildings. The information in this atlas is therefore relevant to employers in assessing workplace risks. 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. The Management of Health and Safety at Work Regulations 1999 require the assessment of health and safety risks and this should include radon in the following circumstances:
For the vast majority of above ground workplaces the risk assessment should include radon measurements in appropriate ground floor rooms where the building is located in a radon Affected Area. Employers usually take a conservative approach and undertake measurements in all premises located in a 1-km grid square that is shaded in the indicative atlas. (Ie. Measurements are not usually required in above ground workplaces located in the white areas of the indicative atlas.) If employers wish to be more specific they may choose to consult the definitive HPA radon dataset online (a small fee is charged) to identify the Affected Areas status of a particular building or buildings.
For occupied below ground workplaces (for example occupied greater than an average of an hour per week/ 52 hours per 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 above ground Affected Areas status.
The Ionising Radiations Regulations 1999 (IRR99) come into effect where radon is present above the defined level of 400 Bq/m3 and employers are required to take action to restrict resulting exposures. The HSE and Local Authorities are responsible for enforcing these regulations in particular types of workplace.
Risk assessment for radon should be carried out in relation to:
Radon surveys should be conducted in any building or basement where its location and characteristics suggest that elevated levels may be found and significant exposures to employees and/or other persons are possible. Inexpensive surveys can be carried out by leaving small plastic passive detectors in rooms of interest. The HPA website contains up-to-date details of validated laboratories capable of supplying such detectors for undertaking radon measurements. Delivery and return of the dosemeters is usually by post.
The Building Regulations 2000 ( England and Wales), the Building (Scotland) Regulations 2004 and Building Regulations Northern Ireland (as amended 1990), supported by BRE reports BR211, BR376 and BR413 respectively require that buildings and buildings extensions (workplaces and dwellings) constructed after 2000 in radon Affected Areas have protective measures installed during construction. These measures are described below. However, since 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, employers must still test as described above.
Experience has shown that radon concentrations in adjacent buildings, even adjoining ones, can differ by as much as a factor of ten (for reasons including local geology or building design and construction), so measurement results from neighbouring properties are not reliable indicators.
Where the workplace measurements show radon levels below 400 Bq/m3, as is the case for the majority of employers, then the only further action required is to decide when the risk assessment will be reviewed. This figure of 400 Bq/m3 is comparable with the Action Level of 200 Bq/m3 for homes, taking into account that most people spend much more time in their home than at work. For occupied areas with levels above 400 Bq/m3, the employer may need to immediately take steps to manage occupational exposures pending any decision they may take to reduce the radon levels by engineered means. A Radiation Protection Adviser with radon experience should normally be consulted about how best to manage radon exposures but, if the employer plans to immediately remove the radon so that the IRR99 do not apply, it is better to consult a specialist radon removal (remediation) contractor in the first instance. The specialist will be able to advise on the most cost effective engineered means of reducing radon levels. It is usually appropriate to continue monitoring in these areas at least until the reduction measures have been put in place.
The seasonal adjustments applied by testing laboratories to measurements carried out at other times of the year are normally good indicators of the worst-case winter levels. It is good practice to consider methods of restricting the radon exposures immediately if the seasonally adjusted figures are significantly greater than 400 Bq/m3 and not wait for measurements of worst-case winter levels, as this would incur additional radiation doses to persons within those premises.
HSE and some Local Authorities are aware of some workplaces such as factories and shops that have measured radon levels significantly in excess of the 400 Bq/m3 action level. Worst cases have shown levels over 17,000 Bq/m3 !
Radon enters a building primarily by airflow from the underlying ground and protection measures for reducing levels inside workplaces vary depending upon the severity of the problem and the type of building construction. New buildings can be protected during construction by installing a ‘radon proof barrier/ membrane’ within the floor structure and, in more seriously affected areas, provision of a ventilated sub-floor void or a 'radon sump'
A radon sump is a small, bucket sized, cavity under the floor with an electric pump drawing air from it. This reduces the normal under floor pressure with respect to radon in the soil and vents the radon gas outside the building where it quickly dissipates.
Radon pump diagram
In existing buildings, it is not possible to provide a radon proof barrier and so alternative reduction measures are used depending upon the severity of the problem. Such measures include improved under floor and indoor ventilation in the area, sealing large gaps in floors and walls in contact with the ground, positive pressure ventilation of occupied areas, and installation of radon sumps and extraction pipework. Descriptions of radon solutions are described on the BRE website and in report BR 293, detailed below.
If it is necessary to reduce radon levels by engineered means, the employer should ensure that the radon levels in the area are remeasured immediately after installation in order to verify its effectiveness.
As with all health and safety risk assessments, their applicability should be kept under review. Where significant changes are made to the fabric of a building or to the work processes carried out within it, then the need to remeasure the radon levels should be considered. In any case, it is still good practice to assign a maximum period upon which remeasurement of the radon levels will occur. Whilst it is the employer, in consultation with the Radiation Protection Adviser where appropriate, who is best placed to determine the frequency of any remeasurements, HSE suggests the following guidelines:
If engineered systems are fitted to reduce levels then procedures must be in place to ensure that they remain mechanically operational and kept switched on.
In radon Affected Areas employees could also be receiving significant exposure at home. Employers are strongly encouraged to recommend home testing to their employees who live in the radon Affected Area. Domestic radon testing is provided free of charge in some areas: Local Authorities can provide information about schemes they run. In other areas measurement laboratories make a charge of typically £40 per house.
All diagrams supplied courtesy of the Health Protection Agency (HPA)