Translation — the French version prevails.
The invisible pollutant that cannot be seen or smelled
Radon is a naturally occurring radioactive gas that rises from the ground. It is invisible, odourless and leaves no obvious material trace in a building. Yet it can accumulate in indoor spaces and become a major public health issue.
Radon requires a shift in perspective. The question is not to locate a contaminated material : it is to read the relationship between a building and its ground, between its structural weak points and the way air circulates, stagnates or is renewed.
Le radon est un risque du bâti sans être un matériau du bâti : il vient du sol, pénètre par les points faibles de l'enveloppe basse et s'accumule dans les locaux mal ventilés.
Deuxième cause de cancer du poumon après le tabac, le radon transforme la lecture d'un bâtiment en sujet de mesure, de zonage et de décision technique.
« Radon is the opposite of a spectacular pollutant: the more dangerous it is, the less perceptible it is without instrumented methods. »Batiscan — Diagnostic synthesis
Lung cancer
2nd cause after tobacco — IARC Group 1 (definite carcinogen)
Linear dose-response relationship
No threshold below which risk is zero (WHO 2009)
Multiplicative effect with tobacco
Risk ×25 for a smoker exposed to radon (EPA)
200–300 deaths/year in Switzerland
OFSP estimate based on measured concentrations
From uranium mines to living rooms : how radon became a public health issue in residential buildings.
The discovery of radium opens the door to identifying naturally occurring radioactivity phenomena. Radium-226 is the parent nuclide of radon-222 through alpha decay.
Source : Pierre & Marie Curie, Comptes rendus de l'Académie des sciences, 1898
Friedrich Ernst Dorn identifies the radioactive 'emanation' from radium as a distinct radioactive noble gas. It would be named 'radon' in 1923. It is the only radioactive noble gas occurring in nature.
Source : F.E. Dorn, Abhandlungen der Naturforschenden Gesellschaft zu Halle, 1900
Lung cancers among uranium miners in Schneeberg (Saxony) and Joachimsthal (Bohemia) are systematically documented. The excess mortality from lung cancer is striking, but the link to radon would not be formally established until later.
Source : Arnstein, 1913 / Rostoski et al., 1926
American, Canadian and European nuclear programmes generate epidemiological monitoring of tens of thousands of uranium miners (Colorado, Ontario, France). Radon is formally identified as a lung carcinogen. The dose-response relationship is linear: the longer and more concentrated the exposure, the greater the risk.
Source : Lundin et al., 1969 — Colorado Plateau Uranium Miners
The US EPA and mining authorities set the first occupational radon exposure limits in underground environments. The concept of the 'Working Level Month' (WLM) is introduced to quantify cumulative exposure.
Source : EPA, Federal Mine Safety Standards
Stanley Watras, a technician at the Limerick nuclear power plant (Pennsylvania), routinely triggered radiation detectors on his way into work. Investigation revealed that the contamination came from his own home: radon concentrations of 100,000 Bq/m³ — more than 300 times the current reference level. This was the first public awareness that radon is not solely a mining hazard.
Source : EPA, The Watras Case — Turning Point for Indoor Radon
The International Agency for Research on Cancer (WHO) classifies radon and its decay products in Group 1 — definite human carcinogen. Evidence is established from miners' data, but extrapolation to residential settings is underway.
Source : CIRC, Monographie Vol. 43 — Radon, 1988
Switzerland establishes a limit value of 1,000 Bq/m³ for radon in existing dwellings and 400 Bq/m³ for new constructions. The first systematic measurement campaigns begin, revealing elevated concentrations in the Jura, the Pre-Alps and certain alpine valleys.
Source : Ordonnance sur la radioprotection, Suisse, 1994
Large European case-control studies (Darby et al., BMJ 2005) demonstrate that radon increases the risk of lung cancer in ordinary dwellings, even at moderate concentrations. The risk is linear with no threshold, and the combined effect of radon and tobacco is multiplicative.
Source : Darby et al., BMJ 330:223, 2005
The WHO 'Handbook on Indoor Radon' recommends a reference level of 100 Bq/m³ for dwellings, with a ceiling of 300 Bq/m³. This document becomes the global reference for national radon prevention policies.
Source : OMS, Handbook on Indoor Radon: A Public Health Perspective, 2009
Directive 2013/59/Euratom requires member states to establish a national radon action plan, including risk-area mapping, measurement programmes and reference levels. Switzerland, not an EU member, draws on this framework to revise its own regulations.
Source : Directive 2013/59/Euratom, Conseil de l'Union européenne
The entry into force of the new Radiation Protection Ordinance (ORaP) lowers the reference level from 1,000 to 300 Bq/m³ for habitable and occupied spaces. Above this threshold, the competent authority may require remediation measures. For new constructions, cantons may impose protective measures in risk areas.
Source : ORaP (RS 814.501), art. 164-167, entrée en vigueur 1er janvier 2018
The subject is no longer the preserve of radiation protection specialists. It has become a diagnostic input for buildings in contact with the ground, particularly in risk areas. Measurements are multiplying in schools, nurseries, public buildings and residential dwellings.
The OFSP annual radiation protection report indicates that approximately 150,000 buildings had been measured for radon in Switzerland by the 2020 review. The radon map is regularly updated with this data.
Source : OFSP, Rapport annuel radioprotection 2020
In practice, the right question is no longer 'is there radon?' but 'does this building need to be measured, how, where and when?'. Radon is becoming a decision-support issue for building managers, property administrators and public authorities.
Radon is not a material added to the building. It is a gas that comes from the ground and penetrates through weak points in the lower building envelope. The building acts as an amplifier.
Shrinkage cracks, construction joints and slab-wall interfaces — preferential pathways for the gas.
The interface between the slab and the foundation walls is rarely perfectly airtight.
Every penetration of a slab by a pipe, cable or sleeve creates an entry point.
Unventilated space between the ground and the first floor slab — a natural accumulation zone for radon.
Below-grade spaces in direct contact with the ground. Maximum concentrations occur at the lowest levels.
Risers, lift shafts and service ducts create a stack effect that draws radon upward through the building.
Lower ground floors, semi-buried garages and spaces in partial contact with the ground.
The absence of extraction in basements, combined with the negative pressure created by heating systems, draws radon up from the soil.
Radon is not managed like an adhesive, a sealant or a contaminated panel. It is not sampled from a substrate : it is measured in an operational building, taking into account its contact with the ground, its airtightness defects and its actual ventilation.
For Batiscan, radon is therefore a decision-support matter. Should measurements be taken ? In which rooms ? Over what period ? Is this a simple uncertainty, a regulatory check, a building in a risk zone, or a structure whose lower levels show obvious entry pathways ?
Karstic and fissured limestone soils that promote radon migration to the surface.
Granitic and gneissic terrain with high natural uranium content.
Risk varies according to local geology. Localised areas of elevated concentration.
Depends on local subsoil. Certain municipalities at the foot of the Jura are in risk zones.
In Switzerland, radon is both a territorial and a building issue. Geology matters, but is not sufficient. Two neighbouring buildings can present very different situations depending on their slab, cracks, service penetrations, ventilation and level of occupancy.
The issue takes a very concrete form : FOPH mapping, reference level of 300 Bq/m³, inhabited buildings, living spaces, cellars, lower floors, schools, dwellings, public buildings and targeted remediation interventions.
The reference level is set at 300 Bq/m³ for residential and living spaces (previously 1’000 Bq/m³). Above this threshold, remediation measures may be required by the competent authority.
The canton may require protective measures against radon (waterproofing membrane, sub-floor ventilation) for new constructions in identified risk zones.
Radon measurement may be required in schools, nurseries and radon-exposed workplaces. The canton sets the specific obligations according to the local situation.
Measurement is carried out by passive dosimetry over a minimum of 3 months (heating season, October–March). Dosimeters are provided by the FOPH or accredited laboratories.
Techniques : sub-floor ventilation, mechanical extraction under the slab (radon sump), sealing the slab and penetrations, building pressurisation. The choice depends on the measured concentration and the building configuration.
« With radon, the question is not only 'what does the building contain?' but 'how does the building breathe in contact with the ground?'. »Batiscan — Site synthesis
Official page of the Federal Office of Public Health on radon in Switzerland.
Interactive map of radon measurements by municipality (150,000+ measurements).
Global reference document for radon prevention policies in residential settings.
Classification of radon in Group 1 — definite human carcinogen.
Swiss legal basis: 300 Bq/m³ reference level, measurement and remediation obligations.
European study demonstrating the risk of lung cancer associated with residential radon.
US reference guide on radon in residential buildings.
Describe the building, the planned works and the timeline. We will get back to you with the recommended scope of intervention.
