Relevant Radon properties

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2 Relevant Radon properties Radon is a natural gas and has a half life of 3.8 days. This means that if a box was full of radon gas, half of it would have decayed into something else after 3.8 days. It has a boiling point of C, so is always present as a gas. Radon is a large atom, a long way down the periodic table. It has many more neutrons than protons; this gives it a large and unstable nucleus. Radon is colourless, odourless and tasteless, so human detection is impossible. Radon is produced from the radioactive decay of Radium, which itself is a decay product of Uranium. These first two steps take many years. Radon undergoes a series of decays which produce radon daughters. Each new element produced is unstable so decays further, until a stable element is produced. This is lead. All of the elements on this decay chain are solids (at room temperature) except for radon itself.

3 Either an alpha or a beta particle is released during radioactive decay of radon and its daughters. Alpha particles are not very penetrating; therefore they lose all of there energy over short distances, this is potentially damaging. Beta particles penetrate further, passing straight through human tissue. The most widely used measurement unit is the Becquerel per cubic metre. 1 Bq m -3 is equivalent to 1 decay event per cubic metre per second. On average there is 20 Bq m -3 indoors and 4 Bq m -3 outdoors. Radon occurrence The radon map shows the probability of a domestic house having elevated radon concentrations (darker colours mean higher probability). Radon is encountered in areas where the geology naturally contains uranium. Uranium is usually found with granites, ironstones, phosphatic rocks and organic rich shales. The radon atlas is based largely on geology, and amended with data from actual radon measurements. It s important to remember that the atlas is indicative. There will be some buildings in the dark brown areas with low radon concentrations and some in the white areas with high concentrations. The only way to really know is to measure Source: Indicative atlas of Radon in England and Wales, Indicative Atlas of Radon in Scotland, HPA 2007.

4 Radon concentrations are highly variable. They are affected by Geology Amount of uranium, amount of weathering / fracturing, permeability, hydrogeology Weather Temperature, rainfall, wind speed / direction, atmospheric pressure Building construction & use The way the building is constructed, e.g. foundation type, ventilation, heating will all affect radon within the building. Building use is also key open windows and doors. The Radon HAZARD Radiation is often associated with X-rays, nuclear power stations, nuclear fallout, astronauts and flight crew. In reality, 50% of our radiation dose comes from exposure to radon. In fact, the risk from living in a house at the currently accepted Action level is about 10 times higher than working in a nuclear fuel plant.

5 REGULATION

6 Under the H&S at work act, employers are required to ensure workplace concentrations are below the action level (400 Bq m -3 ). The action level of 400 Bq m -3 must not be exceeded when averaged over an 24 hour period. This helps to inform us of how radon should be measured. If there are no plans to immediately reduce levels below the action level, employers must appoint a Radiation Protection Advisor. They are able to produce strategies to limit employees exposure to radon, such as implementing room restrictions. Measuring radon Track etch detectors house a small square of plastic within a casing. The square is similar to the material used in spectacles. When alpha particles collide with this plastic they form a pit. These pits can be counted and a time averaged concentration calculated. Advanced analysis software can determine whether the pit has been made by decay of radon itself, or one of its daughter products. Bare face detectors will allow entry of radon and radon daughters, whereas closed cup will only allow radon itself to enter.

7 Radon should be measured: Over long timescales (3 month average measurement is a typical duration) In the winter (concentrations tend to be higher) In closed house conditions (to give worst case) In the most frequented areas, e.g. lounge and bedroom In workplaces or buildings with large footprints, radon measurements in every other room is advised. Variability between rooms requires interpretation of results. Electronic detectors are available to continuously monitor radon concentrations. When radon is measured at the same time as environmental parameters such as atmospheric pressure, temperature or rainfall, drivers of radon may be identified. Continuous detection throughout a mitigation project can show the immediate effects of mitigation.

8 Protection & mitigation Basic radon protection involves laying a radon proof membrane across a building footprint. This is a requirement for all new buildings in radon affected areas. As with any ground-gas membrane, this must be installed correctly and seams should be adequately bonded. Use of a specialist contractor and integrity testing should seriously be considered. In some high risk areas, full radon protection is required. This involved installing a radon sump (pictured below) beneath the building footprint, with pipework to the edge of the footprint and venting to the atmosphere. Should post-construction radon measurements show that concentrations are still elevated, an electric fan can be connected to the sump to extract air from beneath the building, to exhaust at the building eaves. This creates a negative pressure beneath the floor and is often effective in reducing radon build up within the building.

9 There are many thousands of existing buildings which may contain elevated radon concentrations. Measurement of radon concentrations within these houses requires acceptance of the problem. Perhaps declaration of radon concentrations should be a requirement within the conveyancing process, as it is within the USA. There is a range of techniques which can be effectively applied to existing buildings, either as standalone solutions or in conjunction with other methods. The active sump is often effective where radon concentrations are high. This involves coring beneath the building floor from outside the footprint, excavating a small amount of fill and actively extracting air from beneath the floor slab.

10 Case study and validation Within this building in Aberdeen, concentrations of up to 23,000 Bq m -3 were detected. Concentrations showed significant diurnal variations (pictured below). A series of active radon sumps were installed (pictured below). In order to validate the effectiveness of the radon sump system, further monitoring was undertaken using both continuous monitoring and track etch detectors. Validation monitoring is essential in determining whether mitigation measures have been successful. In certain situations it may be sensible to use a 3 rd party for this. Further validation testing, e.g. annually is often used as an indication that concentrations are remaining below the Action Level. This should be undertaken following any change in building structure or occupant use. To Test is Best Radon Council

11 In this case, continuous monitoring was employed before and after the sump system was installed. This showed a rapid reduction in concentrations and success in the short term. Longer term track etch monitoring was also undertaken and continues to take place on an annual basis. This demonstrates that concentrations continue to remain below the workplace Action Level. Radon is a large, unstable atom. When it decays it emits alpha particles, which can damage human tissue. Radon prevalence has been mapped, largely according to underlying geology Radon concentrations are variable and dependent on geology, weather, or building structure The risk from radon is relatively high, when compared with working in a nuclear fuel plant Action levels have been set for the home and workplace, and a target level set for the home Radon can be measured through passive (track etch) or electronic means New buildings can be protected with membranes and radon sumps Existing buildings can be successfully mitigated with a variety of methods, including active radon sumps. Radon is a natural phenomenon, but the radon problem is one created by construction a human invention.

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