W2B-040 Radon in buildings-0.txt
Radon in Buildings *
J. Connell, B.Arch, MRIAI Senior Research Architect, Environmental Research Unit

1. Introduction

For several years now members of the international radiation protection community have been expressing anxiety about the effect of natural radiation on the health of persons. It is expected that this concern will be given concrete expression in this country when the Building Regulations are introduced. They are expected to call for precautions to be taken to avoid danger to the health of occupants of buildings caused by radioactive substances in the ground under buildings. This will include radon which is a radioactive gas.

Designers of buildings will be faced with a problem in complying with this requirement. This arises firstly, due to the difficulty in predicting prior to construction the likelihood of harmful levels of indoor radon occuring in the completed building and secondly, in advising on the type and extent of any precautions that should be taken at the design stage. There is also the matter of legal liability. It would be prudent at the present time for designers of houses, schools and certain other buildings of long time occupation, to raise the matter of radon protection with their clients, as otherwise, with the widespread awareness of the radiation problem, they could be held to be guilty of professional negligence.

2. Facts about Radon

About 13% of our total radiation exposure is made up from man-made nuclear and medical activities and the remaining 87% from natural sources. Exposure to any form of radiation may cause harm to the exposed person or his or her descendants and there is no intrinsic difference between artificial and natural radiation in their biological effects. In contrast to the demand for strict controls over exposure to artificial radiation sources, relatively little attention has been given to control of exposures to natural sources. This may have arisen partly from a feeling that what is natural is without harm and also from a lack of awareness about precautions which could be taken. However, in recent years there has been a growing concern among those dealing with radiation matters about the long terms effects of radiation at all levels and the circumstances where exposure could, and probably should, be reduced. This is particularly so in the case of indoor exposure to radon and its decay products which accounts for over 30% of our total radiation.

Radon is a natural radioactive gas that has no taste, smell or colour and requires special equipment to detect its presence. It is part of the decay chain of uranium, which is widely dispersed in the earths crust, and its best known decay product, radium, which is the immediate precursor of radon. Most soil and rock have traces of radon but the amount can vary in different parts of the country and at different times of the year. Being a gas, it can move through porous media such as fractured rock and soil and some is exhaled at the surface. When this occurs in the outdoor air it is dispersed in the atmosphere and diluted to low and harmless concentrations. However, once it percolates into a enclosed space such as a building it can accumulate to dangerous levels because dispersion is restricted by the limited ventilation. The concentration will depend on the radon levels in the soil gas, the construction details of the building and the available ventilation. Radon may also be introduced indoors in ground water supplied from a well, or from building materials containing traces of radium, but normally the amounts from these sources are not of any consequence in this country.

3. Entry Routes

The increase in indoor levels of radon in recent decades is due most likely to the search for "tighter" building enclosures in order to reduce energy consumption.

These levels depend mainly on the concentration of the sub-floor soil gas and the available entry points in the ground floor area of the building. As these factors usually vary from building to building each case must be considered separately. The more fragmented and porous the underlying rock and soil the greater the amount of radon gas that can rise to the surface. This gas can enter a building in a convective flow through cracks and holes in the floor area and any gaps around service pipes and cables (Figure 1). It is usually pressure-driven due to the slightly lower indoor air pressure compared with that under the floor, a result of wind and temperature difference. As might be expected, elevated levels of radon resulting from soil gas are found mainly in basements and at ground floor levels. Also, radon gas is nine times heavier than air, and therefore tends to remain close to the ground. Radon is not normally a problem in high rise buildings and if an elevated level is found it is likely to have been caused by emission from the building materials used.

4. Lung Cancer

The reason for concern about radon is its association with an increased risk of developing lung cancer. Radon being radioactive disintegrates and gives off decay products known as daughters or progeny which are also radioactive. These are minute particles which when released in the air may be inhaled and deposited in the lungs. As they in turn decay they give a radiation dose to the lung tissues which may eventually cause lung cancer. The risk is related to the level and length of exposure and is normally considered as a lifetime risk. While few people these days spend a lifetime in the same house it would be foolish to ignore the risk completely and for some, the predictions over a lifetime are likely to be significant.

5. Occurrence in Ireland

Radioactivity in air resulting from radon is measured in becquerel per cubic metre (Bq/m3). This unit of measurement means that radon is present at a concentration that emits one particle of radiation per second in a cubic metre of air. A survey carried out by Dr. J.P. McLaughlin of University College Dublin of a random sample of approximately 1300 houses in the State shows a median level of indoor radon of about 35 Bq/m3 throughout the country.

* The Editor wishes to apologise sincerely to Mr Connell for allowing the gremlins to wreak havoc with his excellent article when first published in the August/September issue.

However, levels in excess of 400 Bq/m3 were found in 1.5% of cases with individual peaks rising as high as 1700 Bq/m3. Most of these were located in parts of counties Clare, Galway, Mayo and Cork, but even in these counties the vast majority of the sample houses had a low radon level. A more recent survey of over 500 houses in some western countries was carried out by the Nuclear Energy Board and U.C.D. to identify the distribution of elevated concentration in these areas. The results indicate that about 2.8% had radon levels above 400 Bq/m3 and that 9.4% were above 200 Bq/m3.

6. Reference Level

Having a screening measurement carried out is the only way of knowing if a house has a radon problem. A recommended Reference Level for Ireland has been set by the Government at 200 Bq/m3 for the annual average radon gas concentration in an existing home. Above this level action should be taken to reduce it. The level of 200 Bq/m3 is also intended to apply to all future houses which ideally should be constructed so that radon concentrations are as low as reasonably practicable and be at least below this level. In existing houses, for levels up to 500 Bq/m3 it would be desirable to take action within a few years and where levels are over 1000 Bq/m3, within a year or so.

7. Risks

For most people, the risk of developing lung cancer from radon is insignificant compared with other everyday risks. Nevertheless, despite the lack of complete agreement among experts on the precise risk, it has been calculated that exposure to the Reference Level of an annual average of 200 Bq/m3 corresponds to a lifetime risk of lung cancer of about 2.5%. The normal lifetime risk of contracting lung cancer in Ireland is about 3%.

International estimates now suggest that between 5% and 10% of lung cancer deaths may be caused by indoor radon exposure. There is also strong evidence which indicates a much higher risk from radon for cigarette smokers that for non-smokers. The National Radiological Protection Board in the U.K. in a 1990 publication puts this risk at 10 times that for non-smokers at all levels of exposure. This arises from a synergistic or multiplicative interaction of both carcinogens, which means that the combined effect exceeds the sum of the two effects taken independently.

8. Methods of Detection

The two most common devices used for measuring indoor radon concentrations are the alpha track detector and the charcoal canister. The charcoal canister is a small container of activated carbon which absorbs radon. It is exposed in a living area for about a week and then sent to a laboratory for analysis. The alpha track gives a more accurate reading of the average exposure but must be left in place for a longer period, usually three months, to cover the widely fluctuating daily and seasonal variations. The detector consists of a small container which allows the alpha particles released by the radon to come in contact inside the container with a small piece of special plastic in which tracks are formed by the radiation striking it. After exposure for the recommended time it is also sent to a laboratory for analysis. The intial screening measurement may indicate that there is no need for further action, but in some cases it may be necessary to take measurements over a longer period to get a more accurate estimate of the average level. There are other techniques requiring operation by trained personnel which can be used to give "instant" reading, but they are more expensive and, due to the normal variation in concentrations over a short period of time, would be certainly less reliable in determining the average radon level.

It is possible to take radon measurements in the ground on a prospective building site, but the results may be of limited value. Alfa track detectors may be buried in holes about 600mm deep and recovered after exposure for one week. If high readings are found there is no doubt about the need for preventative measures. Low readings in the ground, however, may not be taken as a guarantee of low concentrations inside a future building on the site, as any excavation necessary during construction may increase the release of soil gas which could result in high indoor concentrations. After construction it would probably be necessary to have indoor measurements taken in both cases to find out the actual level inside the building.

9. Prediction of Concentration

One of the difficulties at present with the occurrence of radon gas is that no reliable method has been found for identifying the geographical areas most at risk. There is evidence linking high radon levels with underlying areas of uranium-bearing granite, shales, phosphate and certain sandstones, but this pattern is not entirely reliable which makes it difficult to prepare maps predicting areas of high concentrations based on geographical data. As an alternative, national surveys based on map grids are extremely expensive and lengthy exercises and result in only very general indications due to the variations in radon concentrations that may occur within small areas.

Measurements for individual buildings may be arranged by writing to either of the following -

Nuclear Energy Board Physics Department

3 Clonskeagh Square University College Dublin

Clonskeagh Road Belfield

Dublin 14. Dublin 4.
