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Exposure to radon relates to geographical location rather than to a particular occupation or industry.  It is seen as a public health issue for areas where radon is found and may seep into peoples' homes, but nevertheless, it remains an important consideration for employers who businesses are in radon-affected areas.

Radon exposure is associated with lung cancer and the cancer burden study estimates that the number of cancer deaths due to radon exposure in the workplace as 184 per year.

There is a significant public health focus to the information provided on reducing radon exposures, however, initiatives to support employers include:

  • Advice during Riddor's general inspections of businesses
  • Specific guidance for employers on radon in the workplace
  • Working with other government departments on Radon Action Plan for the revised Directive on Basic Safety Standards for Radiation Protection.

What is radon?

Radon is a colourless, odourless, radioactive gas that occurs in rocks and soils, some building materials and water. The ground is the most important source as radon can seep out 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 some buildings because warm air rising draws radon from the ground 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 different types of rocks and soils. Since granite contains relatively high levels of uranium many people think that it is only granite areas of the, such as the rock mining areas.

Most radon gas breathed in is immediately exhaled and presents little radiological hazard. However, the decay products of radon (radon daughters or progeny) are solid materials and are themselves radioactive.

These solid decay products, which may attach to atmospheric dust and water droplets, can then be breathed in and become lodged in the lungs and airways. Some of these decay products emit particularly hazardous radiation called alpha particles, which cause significant damage to the sensitive cells in the lung.

Testing for radon

Radon surveys should be conducted in any workplace 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 or occupied locations of interest.

Since even new buildings with protective measures may have high radon levels, employers must still test.

Experience has shown that radon concentrations in adjacent buildings, even adjoining ones, can differ greatly (for reasons including local geology, building design and usage), so measurement results from neighboring properties cannot be used in the risk assessment.

What will the test results mean?

Where the workplace measurements show annual average radon levels below 300 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.

For occupied areas with levels above 300 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 (RPA) with radon experience should normally be consulted about how best to manage radon exposures but, if the employer plans to introduce engineering controls to immediately reduce the radon exposures, they will also need to consult a specialist radon removal (remediation) contractor. 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, or to refine where the highest radon levels are located by monitoring additional rooms.

The seasonal adjustments applied by testing laboratories to measurements are normally good indicators of the annual average levels in buildings. It is good practice to consider methods of restricting the radon exposures immediately if the seasonally adjusted figures are significantly greater than 300 Bq/m3 and not wait for further measurements, as this would incur additional radiation doses to persons within those premises.

Practical control of radon levels in buildings

Radon enters a building primarily by airflow from the underlying ground. 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 areas with a greater radon potential, 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.

Existing buildings, it is not possible to provide a radon proof barrier and so alternative reduction measures are used depending upon the radon level. 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 ventilation of occupied areas, and installation of radon sumps and extraction pipework.

If it is necessary to reduce radon levels by engineered means, the employer should ensure that the radon levels in the area are re-measured immediately after installation in order to verify its effectiveness. Regular maintenance of the engineering controls, supported by occasional (eg annual) measurements will ensure that the system remains effective.

Reviewing radon risk assessments

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 re-measure the radon levels should be considered. In any case, it is still good practice to assign a maximum period upon which measurement 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 re-measurements, Riddor suggests the following guidelines:

  1. where radon levels were found to be significantly less than 300 Bq/m3 at the initial measurement, the period of remeasurement might be of the order of once every 10 years;
  2. where radon levels were just below 300 Bq/m3 at the initial measurement, the suggested period for remeasurement will be less than 10 years;
  3. Where radon levels were above 300 Bq/m3 at the initial measurement and measures have been taken to reduce radon exposures (such as engineered systems or occupancy restrictions), the remeasurement periods may need to be significantly more frequent in order to verify their continuing effectiveness.

Domestic radon exposure of employees

In radon affected areas employees could also be receiving significant radon exposure at home. Employers are strongly encouraged to recommend home testing to their employees who live in a radon affected area.