Rn – Radon

In brief:

Radon is a radioactive noble gas that occurs naturally in soil and in building materials made from it. From these materials, radon can enter buildings. When radon decays, radioactive substances are formed that, when inhaled, increase the risk of lung cancer. The study by the RIVM (National Institute for Public Health and the Environment of the Netherlands) shows that 100 becquerels of radon per cubic metre in homes is feasible as a national reference level for the Netherlands.


  • Radon is radioactive. It occurs almost everywhere in buildings
  • Radon is the second most common cause of lung cancer after smoking.
  • There are no visible traces of radon
  • Extended ventilation as key measure to combat radon

What is Radon?

Many people have no idea of the danger posed in their homes. In their buildings, radon collects in basements and threatens the health of adults and children. Radon is the second most common cause of lung cancer in the Netherlands. Only smoking is more dangerous. According to the RIVM, 3-5% of all lung cancer cases are due to the invisible gas.

Radon is a radioactive gas that emits alpha radiation during decay. The gas is found in the soil – but it is also in building materials. Human senses do not perceive radon, as it is tasteless and colourless and odourless. Of all natural radiation sources, radon is the largest contributor to radiation exposure.

Normally, exposure to radon in fresh air is low. Values range from 2-40 Becquerels per cubic metre of air (Bq/m3). However, the gas can accumulate in buildings, creating radon concentrations that are hazardous to health. In severe cases, values in basements and living spaces are 1,000-10,000 Bq/m3 – or higher. No later than now, remediation measures are needed to prevent unnecessary health risks.

How is radon formed?

Radon is formed wherever uranium or thorium is present in the soil. When these elements decay, radon-222 (Rn-222), among others, is released, which has a half-life of 3.8 days. During the formation of radon-222, other radon isotopes are also produced (e.g. Rn-220 or Rn-219). However, their half-life is so short that they pose no danger to humans. The situation is different with radon-222: With a half-life of 3.8 days, Radon-222 has enough time to reach the earth’s surface and accumulate in spaces such as basements or ground-floor rooms. When Radon-222 decays, alpha radiation is released. The secondary products of Radon-222 are also radioactive and also decay (mainly) by emitting alpha radiation.

Am I affected by radon?

Pretty sure. Yes. Because every one of us in our lives is always in places contaminated by radon. At work, at school or at home: there is probably hardly anyone who has not been exposed to high levels of radon.

Besides the radon concentration, the decisive factor for a health risk is mainly the duration of exposure to the radioactive gas and its secondary products. Anyone who inhales radon in high concentrations over a long period of time significantly increases their risk of developing lung cancer.

How does radon get into my house?

Radon is formed in the ground, where it rises to the surface. In fresh air, it is quickly depleted. However, when the gas hits buildings, it enters through cracks, joints and crevices and can accumulate in lower rooms (basement, ground floor). Through sucking effects (open windows, heated rooms), radon reaches the upper floors.

However, radon cannot enter the house only through leaks. Other possibilities include:

  • Drinking water: Water-soluble radon is also found in drinking water. When taking a shower, for example, the radon can be over-fertilised. The increased radioactivity is often clearly measurable after showering.
  • Building materials: Some building materials contain large amounts of radioactive isotopes. The decay of radium-226 produces radon-222.

Both building materials and drinking water can significantly increase the radon load in a building. However, radon usually enters the interior of a building through the ground.

How to measure radon?

Different measurement methods are available for each medium examined (room air, soil air, water). Active and passive measuring systems are commercially available for measuring radon.

Active measuring devices measure electronically and have a display that shows the values. Most active devices are used for short-term measurements.

Passive measuring devices record the decay on a plastic film, which is evaluated in a special laboratory after the measurement. Passive measuring systems are particularly suitable for long-term measurements. In addition, there are measuring devices that detect radon directly in the air, while others record the decay products of radon.

Radon values vary depending on the time of year or day. To obtain meaningful measurements, radon measurements with active measuring devices should last at least 4-10 days, with passive measuring devices at least 1-12 months.

Why do radon values fluctuate?

Radon measurements need to be long-term, as radon concentrations often fluctuate. Measurements depend on daily and seasonal fluctuations. However, what matters in a radon measurement is the long-term average value. Short-term measurements are extrapolated to an annual average value.

Fluctuations in measurements in buildings during the day are caused by changes in temperature, wind conditions and air pressure. In addition, living habits also play a role in radon concentrations. Is there frequent ventilation or does the basement have no windows? Do you open doors often or less frequently? All these factors affect average radon exposure. Over night, values tend to increase. During the day, levels decrease due to increased activity (opening and closing doors) and increased air exchange (ventilation, opening and closing doors, etc.) in the building.

Seasonal fluctuations are caused by changes in soil structure due to ground frost. The gas seeks other paths in frozen floors, often entering building interiors. At the same time, there is less ventilation in winter than in summer. Due to the suction effect that occurs when buildings are heated (rising air), radon is increasingly drawn from the soil into the building, increasing radon concentration. At the same time, the rising air also causes radon to reach the upper floors.

How dangerous is radon to my health?

A sustained increase of 100 Bq/m3 in indoor air radon concentration leads to a 16% higher risk of lung cancer. In the Netherlands, about 400 deaths a year are attributable to radon gas. Across the EU, authorities assume that 20,000 deaths a year are caused by radon gas.

Radon itself is not toxic. Inhaling radon does not cause symptoms such as headaches or dizziness. It is the radioactivity that makes the gas so dangerous. When radon decays, it releases alpha radiation that damages the human body. Moreover, its decay produces secondary products (e.g. radioactive lead, bismuth and polonium), which in turn are mainly alpha emitters. When inhaled, the radioactive derivatives reach the lungs together with aerosols (radioactive derivatives attach to dust water droplets), where they damage lung tissue.

Could radon also cause skin cancer?

A Swiss study suggests that radon, in addition to UV radiation, increases the risk of skin cancer. According to this study, the alpha radiation produced during the decay of radon-222 has a similar skin-damaging effect as UV radiation. The study also found that young people are more affected by this effect than the elderly. (link)

How dangerous is radon for my children?

In general, radioactivity is more dangerous for children than for adults. Their tissues react particularly sensitively to ionising radiation. This is why children, for example, are X-rayed as rarely as possible.

Cancer often results from a triggering event (e.g. increased radiation). However, cancer can sometimes take decades to break out. When old people are exposed to increased radiation, they often do not live to see the onset of cancer. In younger people, the body has more time to develop tumours during their lifetime. Moreover, a child’s body is generally more sensitive to radiation because the cells of the child’s body divide more frequently. Cell division is an important condition for cancer development.

In relation to radon, this means that children should not be exposed to increased radon exposure. It is therefore important that children’s rooms are checked for radon. Moreover, schools and kindergartens should pay attention to thorough radon testing.

Which buildings are particularly affected by radon?

It is difficult to predict which types of buildings will be increasingly affected by radon. Radon is present almost everywhere and can be found in new buildings as well as in old buildings, schools or kindergartens.

However, buildings with cracks in the building envelope or a leaking floor slab are generally particularly uncertain about radon ingress. If you find natural soil in your basement or the basement consists of natural stone, then a radon measurement is certainly useful. Even if you live in a radon risk area, you should not delay a radon measurement for too long. However, because radon values fluctuate widely even within a region and often even vary significantly from house to house, indoor air analyses are basically recommended for all people in the Netherlands.

Why does radon accumulate in basements?

In many houses, there is always a slight negative pressure as warm, heated air rises to the top and causes a slight suction. The negative pressure pulls radon from the ground into the building. All areas in contact with the ground, such as the basement or ground floor, are affected. The radioactive gas enters the lower areas of a building through existing cracks and leaks such as pipe and duct penetrations. Because radon is heavier than air, it accumulates in the lower rooms. To the amount of gas entering the building through the leaking building envelope must be added the amount of gas escaping from the building materials. Radon is also almost always dissolved in tap water, which can then be gassed when showering, for example.

Once radon reaches the basement, it can also rise to the upper floors. The gas can also reach the upper living spaces through suction effects, such as those caused by heating or ventilation. Air currents and thermal mixing mechanisms pull the radioactive gas upwards, especially if the basement doors are not closed or leaky.

What can I do against radon?

First of all, you should carry out (or have carried out) a radon measurement. With modern, electronic measuring instruments, this should not be a problem. After only a few days, you will get an overview of the radon situation in your home.

You have detected elevated radon levels in your home? Then you can reduce the radon concentration with some immediate measures:

Open windows and doors and make sure there are draughts in your home. With modern measuring instruments, you can see an immediate decrease in radon concentration. Make sure you get plenty of fresh air into your home regularly! If radon levels remain high, corrective measures may be necessary.

When do remediation measures become necessary because of radon?

When simple ventilation is no longer sufficient, remediation measures are necessary. Various techniques are used for remediation measures:

  • Installation of ventilation systems
  • Sealing of cracks and crevices in the basement
  • Sealing of all radon entry points such as pipe and line penetrations
  • Sealing of cellar doors and windows

What are the limit values for radon?

Currently, there is no limit, only a national reference value for radon.

European member states are free to choose their own national reference level, but it cannot exceed 300 Bq/m3 (EU European Union 2014). In the Netherlands, national reference levels have now been set and have been included in the Basic Safety Standards for Radiation Protection Decree (Bbs Besluit basisveiligheidsnormen stralingsbescherming ) since 6 February 2018. Both for homes, workplaces and public buildings, national reference levels for the annual average radon concentration of 100 Bq/m3 have been set in the Netherlands. Exceeding the reference level should be avoided as much as possible.

Request a radon testing

    Radon testing