Short and long-term radon measurements in domestic premises: reporting results in terms of the HPA action and target levels

In the UK, the Action Level for radon gas in domestic buildings has stood at 200 Bq.m-3 for many years. Some years ago, our group made an extensive study of 7-day, 1-month and 3-month measurements in thirty-four un-remediated dwellings in a high-radon area over a full year. It was shown that one-week exposures were less reliable indicators of the long-term radon level, but that this variability was related to the changes in radon level, due to occupancy, weather changes and other influences. Our analysis reported the confidence limits for each detection period, and recommended a protocol for reporting. Short-term measurements can be reliable indicators in low-radon areas or for new properties, but in high-radon areas, the use of three-month exposures is indicated. In 2010 the UK Health Protection Agency (HPA) recommended the introduction of a lower Target Level of 100 Bq.m-3, with the intention of encouraging those most at risk from radon to consider remediation of their homes, even if the long-term average is between 100 and 200 Bq.m-3. We have reviewed the results of the previous survey in relation to the new Target Level, and report on the limits of confidence established for establishing whether a short-term result is over the target level, and proposes a reporting scheme