Reference value

A reference value is used to enable the assessment and comparison of radon concentrations. In German Radiation Protection Act, the reference value is established at 300 becquerels per cubic metre indoor air.

What is a reference value?

In public debate, the reference value is often confused with a limit value or a guide value. There are crucial differences here:

• A limit value is a value that must not be exceeded.
• A guide value is a value that should be aimed for. It should be adhered to, so as to avoid actions that are negligent or grossly negligent. In radiation protection, guide values apply to parts of a situation where people are exposed toradiation. Guide values should ensure that a limit value is not exceeded when a person is affected by many radiation sources independently of one another.
• Under Radiation Protection Act, a reference value serves as a "standard for testing the suitability of measures". According to Radiation Protection Act, "a reference value is not a limit value".

A "standard for testing", as stated in Radiation Protection Act, particularly does not mean that this standard and the testing begin only at the reference value.

Why a reference value and no limit value for radon?

A limit value is always sensible when the extent to which people are exposed to radiation can be controlled at any time – for example if during a planned activity with artificial radioactive sources

• the quantity of radioactive substance can be adjusted,
• the duration of handling the radioactive substance can be minimised,
• screening measures or other protection measures (breathing masks, special clothing) can be adopted.

Handling radon is not comparable because

• radon occurs naturally,
• the source of the radiation is therefore not removable and every person is unavoidably exposed and
• a risk is demonstrable even at normal concentrations.

If there was a limit value for radon concentrations in buildings, it would be obligatory to implement measures there. These would include usage restrictions or obligatory remediation measures in private buildings.

International radiation protection experts consider that the measures required by a limit value would be unreasonable and are therefore in agreement that a reference value and not a limit value should apply to radon.

How are reference values defined around the world?

There are different definitions of the term "reference value" around the world.

• The World Health Organisation WHO sees the reference value as a maximum acceptable radon concentration in residential buildings.
• For the International Commission on Radiological Protection ICRP and the International Atomic Energy Agency IAEA, the reference value is a risk level. Its planned occurrence should be seen as inappropriate and optimisation measures should be planned below this.
• The European Atomic Energy Community EURATOM sees the reference value as the concentration above which exposure is considered inappropriate, even through it is not a limit value which must not be exceeded.
• Under German Radiation Protection Act, the reference value is a stipulated value that serves as a standard for testing the suitability of measures. The law further explains that a reference value is not a limit value.

Common to all definitions is that action should not be left until after the reference value has been exceeded. Measures are sensible beneath the reference value too.

In exceptional cases, concentrations above the reference value must also be accepted if measures to reduce this are unreasonable, for example because they clash with other provisions or their expense would be considerably too high. For example, radon protection measures could clash with monument protection restrictions, i.e. in old forts and castles, or specific hygiene provisions, e.g. in waterworks, and so be implemented only with great effort.

The radon reference value is 300 becquerel per cubic metre air

Why 300 becquerels per cubic metre?

In radiation protection act, the legislator has established the reference value in Germany both in buildings generally and in workplaces at 300 becquerels per cubic metre. In this decision, the federal government and the federal states considered

• the findings of medical investigations that have demonstrated a measurable increase in the risk of lung cancer from a concentration of 100-200 becquerels per cubic metre and
• the fact that in Germany, the radon concentration is not evenly distributed. This means that there are regions that are particularly affected by radon because there are high radon concentrations in the soil that cannot be eliminated.

The radiation protection act requires that the Federal Environment Ministry submits a report after 10 years regarding the effect of the reference value on protection against radon.