Radon exposure: all businesses are affected

Radon, a carcinogenic radioactive gas, imposes new obligations on businesses. The reference level has been lowered to 300 Bq/m3, and a risk assessment is now required.

Marie Faucon
Consultante HSE
Publication : 
06.12.2018
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Please note: This article concerns French legislation. The requirements described may not apply in other countries.

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Radon is a naturally occurring radioactive gas resulting from the decay of uranium and radium, which forms in the subsoil (particularly in granitic and volcanic areas). It is present everywhere in France, with high concentrations found in granitic and volcanic regions (the Armorican Massif, the Massif Central, Corsica, the Vosges, etc.). Radon concentration in a building's air depends on soil characteristics as well as the building itself and its ventilation. This gas is classified as a carcinogen. Studies show thatexposure to radon is the second leading cause of lung cancer in France.

Since the publication of the decree on June 4, 2018, regulatory requirements for businesses have been strengthened. Here is an overview of the main legal obligations in this area.

Reference level

The reference level is the radon activity concentration above which it is considered inappropriate to allow worker exposure to ionizing radiation, even though it is not a strict limit that cannot be exceeded.

Since July 1st , 2018, the reference level for radon activity concentration in the air has been set at 300 Bq/m3 as an annual average (compared to 400 previously).

Affected businesses

All businesses must account for the risk of radon exposure. Specifically, this applies to businesses:

  • conducting professional activities in basements or ground floors of buildings located in areas where radon exposure is likely to harm the health of workers,
  • in certain specific workplaces. A decree (not yet published) will establish the list of these locations.

Radon exposure risk assessment

Employers must assess the risk of worker exposure to radon to determine whether the radon reference level is likely to be exceeded. To do this, they must take into account the radon potential of their municipality and any measurements already taken.

The radon potential of municipalities is established by the decree of June 27, 2018, and is shown on a map available on the website of the IRSN (Institute for Radiological Protection and Nuclear Safety). Municipalities are classified into 3 categories:

  • Zone 1: areas with low radon potential;
  • Zone 2: areas with low radon potential where specific geological factors may facilitate the transfer of radon into buildings;
  • Zone 3: areas with significant radon potential.

A ministerial instruction dated October 2, 2018, specifies that for workplaces located in zone 1 (low potential area), if the employer is not aware of other factors, the risk may be considered negligible.

In zone 2, further investigation is necessary and may lead to the need for measurements. If the company is located in zone 3, it is strongly recommended to carry out measurements.

Radon concentration in the air is measured using radon dosimeters, which are inexpensive measuring devices. The dosimeter is a device that measures the concentration of radon present in the room for the entire period it is placed there. These dosimeters are analyzed by COFRAC-accredited organizations.

If the employer concludes that the assessment is likely to exceed the reference level, they must measure the radon concentration in the air and implement preventive measures. These measures include improving the building's airtightness to limit radon entry or improving ventilation to dilute radon in the air. If preventive measures do not result in a radon activity concentration in the air below the reference level, the employer must report the measurement results to the IRSN.

Note: the risk assessment must be recorded in the single document (DU), and this assessment and the measurement results must be shared with health professionals (occupational physician, medical assistant, nurse, etc.) and the Social and Economic Committee (CSE).

Identifying radon zones

Employers must identify areas where workers are likely to be exposed to ionizing radiation levels exceeding 6 mSv/year in terms of radon concentration in the air, calculated as an effective dose. These areas are designated as "radon zones." Note: these "radon zones" are distinct from the "radon potential zones" mentioned above, which are geographical areas identified by official decree.

If a radon zone is identified, the employer must:

  • appoint a radiation protection advisor;
  • signpost these areas;
  • restrict access to radon zones to classified workers or authorize non-classified workers based on an individual assessment;
  • conduct an initial verification by measuring radon activity concentration in the air within the radon zones upon commissioning the facility or following any significant change in working conditions that could affect the health and safety of workers. This verification must be performed by an accredited body.
  • periodically renew this verification, which is then carried out by the radiation protection advisor;
  • provide workers with personal protective equipment when collective protection measures are insufficient;
  • inform workers operating in radon zones, particularly regarding the risks associated with ionizing radiation and the organizational rules in place.
  • assess the individual exposure of workers accessing these zones prior to their assignment to the workstation.
  • implement dosimetric monitoring for the worker (using appropriate delayed-readout dosimeters) when the effective dose is likely to exceed 6 mSv over 12 months, and ensure they receive enhanced individual health monitoring.

Radon exposure: conclusion

All companies must consider the risk of their workers being exposed to radon. However, for the majority, a simple risk assessment will suffice. If this assessment has not already been conducted, we recommend first identifying the potential of the municipality where your workplaces are located:

  • if you are in zone 1 and are not aware of any other factors regarding the presence of radon, you can conclude that the exposure risk is negligible.
  • If you are in zone 2 or 3, or in the case of specific activities, further investigation must be conducted; in category 3 zones in particular, dosimeter measurements can assist you.

If necessary, actions such as improving ventilation or sealing must be implemented to reduce the risk of exposure and remain below the reference level.

In cases where radon is highly prevalent, it will be necessary to determine the areas where exposure exceeds 6 mSv/year and implement various organizational and preventive measures (radiation protection advisor, dosimetric monitoring, etc.).

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