Health risks of radon in buildings

01Apr / 2015

Health risks of radon in buildings

What is radon?

Radon is a gas produced from the decay of uranium, a naturally occurring element in the earth’s crust. Radon is radioactive, emitting harmful alpha radiation when it decays.

Radon is present in outdoor and indoor air, usually in small amounts. We breathe it in and out all the time. If a radon atom decays while inside our lungs, the alpha radiation released may damage lung cells. This has the potential to cause lung cancer. It is estimated that 1,100 people die prematurely every year from radon exposure, just in England and Wales.

Radon gets into buildings through a variety of routes, including directly through floors or walls in contact with soil or through the water or gas supply.

Where is it?

Radon is known to be associated with rocks and soils which include granite and shale. The probability of encountering high radon levels has been mapped for the UK in the ‘Indicative Radon Atlas’. Shaded parts of the radon atlas are classed as ‘Radon Affected Areas’. It is important to remember that the atlas is indicative; the only way to know if radon is present is to test for it.

Testing for radon

Radon is commonly tested for using passive ‘track etch’ detectors. To observe the likely worst case radon levels, testing in the winter months is recommended. Tests should be done in areas of highest occupancy to get an indication of actual exposure. Radon concentrations are highly variable and affected by weather, geology, building use, heating and ventilation systems. A time averaged concentration is therefore a more reliable measure of long term exposure; this test is typically taken over 90 days. Within larger buildings, a good spread of detectors is usually needed as radon concentrations often vary from room to room. Interpretation of radon testing results is key.

Legal requirements

High radon levels within buildings can be considered an engineering fault. Therefore employers have a legal duty, under the Ionising Radiation Regulations 1999, to ensure that employees are not exposed to concentrations exceeding the workplace Action Level of 400 Bq m-3. Should radon levels exceed this, provision should immediately be put in place to reduce Radon levels or manage exposure.

In the home, there is an Action Level of 200 Bq m-3; there is no legal requirement to reduce elevated levels, but it is recommended.

Radon and your safety policy

Radon Sump

Radon sump retrofit, ducting to match existing downpipes

If a workplace is located within a radon affected area, radon testing is a legal requirement. If a workplace falls close to a radon affected area, or if a precautionary approach is taken, radon testing should be considered as part of a building’s safety policy. Most buildings or parts of buildings fall below action levels; however testing may show that something needs to be done about radon – remember that the radon atlas is indicative, so there will be areas which are affected which were not identified through mapping.

Radon mitigation

Where radon levels are elevated within a building, effective retrofit solutions are available to reduce these levels and to reduce risk to building users. A popular solution is the installation of active radon sumps. This involves the removal of a small volume of fill from beneath a building, with pipework sealed into this void and actively exhausted to the outside air with an in-line electric fan. The fan creates an area of negative pressure beneath the footprint which radon will preferentially migrate to. Exhausts are typically above the building eaves (where practical) and away from windows or doors.

Contractor choice

The installation of radon protection systems may appear basic, but in practice it is not always easy to reduce radon levels to below exposure limits, due to the multitude of factors which affect radon ingress. Choice of contractor is essential in increasing the chance of mitigation systems working in the first instance. Specialist radon contractors will be experienced in installing the most appropriate systems for the building type, size and measured radon levels. Many specialist contractors will use pressure or smoke testing to demonstrate effective seals within the system. Radon monitoring equipment is also sometimes used to immediately indicate effectiveness of systems and to identify whether they need to be fine tuned. Expect to pay more for a specialist radon contractor, but use one to give you peace of mind that building occupants are being suitably protected, as well as reducing the risk of needing multiple mitigation attempts. A list of Radon Council approved contractors and consultants can be found on the Radon Council website:

Maintaining active systems

Active radon sumps have moving parts; therefore need to be maintained to ensure effective long term operation. The expected life of an active sump system should be at least 5 years, but this is dependent on the fan speed required for the building. An inspection and maintenance plan can be written into the general maintenance procedures for the building. Radon sump fans make an audible whirring sound, so an audible inspection is suitable. Ducting should be physically tested for integrity to ensure it remains firmly fixed and sealed. Visible lights on circuit breakers can be used for a quick check to show that the fan is still connected to the mains supply.

Some specialist radon contractors will offer telemetry systems and battery backups in the event of a power outage. Telemetry units will alert (by email or SMS) designated individuals of faults with the mitigation system, such that these can be quickly repaired.

Radon telemetry unit

Telemetry unit to alert users of a system fault


Whichever system is used (manual inspections or telemetry); a procedure for maintenance and repair should be produced for the building. Depending on the extent of the repair required, this could be undertaken by the building maintenance contractor or a specialist radon contractor. Major system repairs should be followed by re-testing of the internal radon levels, as a change to the system may affect the dynamics of radon ingress.







Radon mitigation measures, both in new and existing buildings, do not always work first time. Buildings should be tested for radon after measures are installed to demonstrate that they work. This commonly involves the use of passive track etch detectors. Should levels still be unacceptably high, mitigation systems may be modified or extended to improve their effectiveness.

Long term verification

Within managed buildings or in any building with particularly high radon levels in the first instance, long term validation testing may be prudent. This can be undertaken on an annual, or 14 month (to identify seasonal trends) basis.

Retesting of an affected building should also take place following any change to:

  • The building structure, e.g. extensions
  • The heating or ventilation systems
  • The building use


  • Radon is a naturally occurring radioactive gas.
  • Radon causes an estimated 1,100 premature deaths from lung cancer, in England and Wales alone, every year.
  • Employers must ensure that their employees are not exposed to unacceptable levels.
  • Solutions are available to reduce radon. They can be effectively retrofitted to existing buildings or installed as preventative measures in new buildings. Active systems need to be maintained in the long term.
  • Radon mitigation measures don’t always work first time; verification monitoring should be undertaken to demonstrate their effectiveness.

Add your comment