Radon is a radioactive noble gas. It forms in the ground as a decay product of uranium and radium, has no smell, no colour and no taste, and is the second most common cause of lung cancer after smoking (WHO). You can neither see nor smell it. The only way to know the level in your own home is to measure.
At ETH Zürich we used uranium-lead decay chains to date rocks, among them lunar and Mars samples. The same understanding of radioactive decay lies behind the question of how much radon accumulates in living spaces. This text summarises what is documented about radon in Austria.
What radon is and why it is dangerous
Radon itself is mostly exhaled again. The danger comes from its short-lived decay products, above all isotopes of polonium, lead and bismuth. They attach to dust particles, reach the lungs when inhaled, and irradiate the tissue with alpha radiation. The International Agency for Research on Cancer (IARC/WHO) classifies radon as a Group 1 carcinogen, that is, as carcinogenic to humans.
How large the risk is was shown by a joint analysis of 13 European case-control studies (Darby et al., BMJ 2005): the risk of lung cancer rises by about 16 percent per additional 100 Bq/m³ of radon in indoor air. The relationship is linear and shows no apparent threshold, so there is no level below which the risk is demonstrably zero. For smokers the absolute risk is many times higher, because the two factors reinforce each other.
Why Austria is affected
Radon comes from the geological subsurface. Rocks with elevated uranium content, such as granite, gneiss and certain schists, release more radon. Large parts of Austria sit on such ground, and this shows in the measurements: in the Austrian national radon project (ÖNRAP), the geometric mean of indoor radon is around 110 Bq/m³, roughly three times the global average of about 40 Bq/m³. About 6 percent of Austrian households exceed the reference level of 300 Bq/m³.
The gas enters the building through the ground. In winter the stack effect is at work: warm air rises and escapes in the upper floors, a slight negative pressure builds up in the lower level, and radon-laden soil air is drawn in through cracks in the foundation, pipe penetrations and leaky basement walls. This is why basement and ground-floor rooms are most affected, and why the values are highest during the heating season.
The radon map: orientation, not diagnosis
AGES provides an interactive radon map for all of Austria (geogis.ages.at). It is based on the radon potential, a combination of geological data and actual measurements, and assigns each municipality a rating: green for low, yellow for medium, orange to red for high potential.
What matters is what the map does not show. It gives an average per municipality, not the value for an individual house. Local geology varies within a municipality; your house may stand on granite and the neighbouring house 200 metres away on gravel. The construction is missing entirely: the age and condition of the floor slab, cracks, pipe penetrations, basement use. Ventilation habits play a part too. In practice we regularly see values above 300 Bq/m³ in green-rated municipalities and low values in red ones. The map gives orientation, not a diagnosis.
Regardless of the map colour, a measurement makes sense for old buildings with inhabited basement rooms, for houses on a slope or on granite, before buying a house, and wherever people spend many hours a day in rooms near the ground, that is, in kindergartens, schools and care homes.
Measuring correctly: how long, where, how many
A snapshot is useless, because the radon concentration varies strongly within a few days depending on weather, air pressure and ventilation. The reliable method is long-term measurement with passive track-etch dosimeters, small capsules that need neither power nor maintenance.
- How long: at least three months, ideally during the heating season (October to March). Anyone below the reference level during the heating season is below it in the annual mean as well. Electronic short-term measurements over 24 to 72 hours are suitable only as a first screening, not as a substitute.
- Where: in the most-used living room on the ground or lower floor, not in the kitchen or bathroom, where there is a lot of ventilation. In the room at about 1 to 1.5 metres height, at least 20 cm from the wall, not at the window, not on the heater, not behind furniture.
- How many: at least one in the most-used room. For a complete picture two to three, for example basement, ground floor and bedroom.
What the values mean
Measurement is in becquerel per cubic metre (Bq/m³).
- Below 100 Bq/m³: unremarkable, no action needed.
- 100 to 300 Bq/m³: simple measures worthwhile, such as regular ventilation and sealing obvious entry paths in the basement.
- Above 300 Bq/m³: remediation measures recommended. 300 Bq/m³ is the reference level of the Radon Protection Ordinance.
The legal framework
Radon in Austria is governed by the Radiation Protection Act 2020 (Strahlenschutzgesetz, BGBl. I No. 50/2020) and the Radon Protection Ordinance (Radonschutzverordnung, RnV, BGBl. II No. 470/2020) based on it, both implementing the EU basic safety standards (Directive 2013/59/Euratom). The ordinance sets a reference level of 300 Bq/m³ as an annual mean, both in living spaces of residential buildings and at workplaces. This is not a limit in the legal sense, but the value above which measures are foreseen.
On the basis of the data, Austria has designated 104 municipalities as radon protection areas (Radonschutzgebiete), municipalities whose predicted mean radon concentration exceeds the reference level. There, special requirements apply: for new buildings a radon-proof floor slab is foreseen, and for workplaces in basement and ground-floor rooms there is a measurement obligation.
What can be done
Radon is among the most manageable pollutant problems in a building: the measurement is cheap and unambiguous, and the countermeasures work. For moderately elevated values, better basement ventilation and sealing cracks and pipe penetrations often already help. The most effective active measure is a radon sump, a sub-slab depressurisation system that captures the gas before it enters the house; its design and installation belong in expert hands. For new buildings in radon protection areas the radon-proof floor slab is standard anyway.
Sources
- AGES, interactive radon map Austria: geogis.ages.at
- Radon Competence Centre / „Radon in Österreich" (ÖNRAP): radon.gv.at
- Radon Protection Ordinance (RnV), BGBl. II No. 470/2020: ris.bka.gv.at
- WHO Handbook on Indoor Radon (health effects): ncbi.nlm.nih.gov
- Darby et al., „Radon in homes and risk of lung cancer", BMJ 2005: pubmed.ncbi.nlm.nih.gov/15613366
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