Radon exposure risk: strengthening the risk prevention approach

What is radon? And why is it a health risk? We explain everything in this article.

Juliette Virly
Consultante HSE
Publication : 
22.07.2024
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Please note: This article concerns French legislation. The requirements described may not apply in other countries.

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What is radon?

Radon is a naturally occurring radioactive gas found throughout France: in the air, soil, and water, at concentrations that vary from one location to another. It is found in high concentrations particularly in granitic and volcanic regions. Radon quickly disperses in outdoor air, but it can accumulate significantly in enclosed spaces such as buildings.

Radon poses a health risk; it is classified as carcinogenic and is the primary source of natural exposure to ionizing radiation in France.

Radon potential zones have been defined at the municipal level. Municipalities are thus divided into three zones for which radon exposure prevention measures must be implemented:

  • Zone 1: low radon potential zones;
  • Zone 2: low radon potential zones, but where specific geological factors can facilitate the transfer of radon into buildings;
  • Zone 3: significant radon potential zones.

The zoning by municipality is available on  the website of theIRSN.

Employer Obligations

Radon represents an occupational risk of worker exposure due to its potential accumulation in the air of enclosed spaces. Employers must therefore assess the risks of worker exposure to radon in their single occupational risk assessment document (DUERP). The risk assessment must enable the employer to determine whether the radon concentration in the air is likely to exceed the defined reference level of 300 becquerels per cubic meter (Bq/m3) in ground-floor and basement premises.

For establishments located in municipalities within radon potential zones 2 and 3, it is recommended to measure the radon concentration in the air to ensure that the reference level is not exceeded. Furthermore, measurement will be necessary if the risk assessment results do not allow for a conclusion of no exposure risk.

Based on the measurement results, the employer must implement preventive measures aimed at reducing the radon concentration level in the air, such as improving ventilation or the airtightness of the premises.

Strengthening Preventive Measures

To improve the prevention of workers' exposure to radon originating from the ground (i.e., radon generated directly by ground rocks or secondarily by water circulating in these rocks or materials extracted from them), the decree of May 15, 2024, strengthens the preventive measures that employers must implement.

Risk Assessment and Action Plan

Henceforth, whenever the results of the risk assessment indicate that the radon activity concentration in the air is likely to reach or exceed 300 Bq / m3 as an annual average (reference level), the employer must carry out measurements of the radon concentration in the air using integrated, delayed-reading measuring devices, supplied and operated by an accredited organization.

If the measurement results reveal a radon concentration in the air equal to or exceeding the reference level, the employer must establish an action plan aimed at lowering the radon concentration in the air below the reference level, such as, for example, implementing work processes that do not expose or result in less exposure; modifying the design and layout of workplaces and workstations to reduce exposure to ionizing radiation; improving the building's airtightness against radon entry points or renewing the air in the premises; choosing a work organization aimed at reducing the duration and intensity of exposures, particularly by controlling access to delimited areas.

This action plan must be implemented within 3 years. If the radon concentration in the air exceeds 1,000 Bq/m3, the action plan must be implemented within 1 year.

After these deadlines, if the measures implemented are not effective and do not allow for remaining permanently below the reference level, the employer must establish a radon zone and reinforced preventive measures.

Establishing a Radon Zone

Establishing a radon zone involves:

  1. appointing a radiation protection advisor to delineate the radon zone;

  1. reporting and notifying this zone to the IRSN;

  1. have an initial check carried out by the radiation protection advisor to ensure that workplaces adjacent to the radon zone do not contain an airborne radon concentration exceeding the reference level. A new check must be performed for any significant modification to work methods, conditions, or workplace layout that could affect workers' health and safety.

  1. establish a program of periodic checks, taking into account activity within the radon zone and adjacent workplaces. Checks must be carried out at least every 5 years (annually if the airborne radon concentration exceeds 1,000 Bq/m3). When workers are present in the radon zone, the employer may choose to implement continuous radon monitoring instead of the checking program.

  1. visibly mark the "radon zone" at the entrance to the area. Additionally, an information sheet on radon risk, accompanied by a diagram specifying the zone's boundaries, as well as safety instructions for accessing the zone, must be visibly displayed at the zone's access points.