The Suitability of Short-term Measurements of Radon in the Built Environment

摘要

Although domestic and workplace radon concentration levels often show marked diurnal/short-termvariation, overall health risk is determined by the long-term average level, and many national protocols advocatethe use of long exposure periods, usually three months, to assess long-term risk. Simple passive measurementtechniques, e.g. track-etch, activated charcoal and electret, can, however, provide reasonably accuratedeterminations with exposures as short as one week, and there is pressure from users and stakeholders forassessments within this time period. We report evaluation of the effectiveness of one-week, one-month and threemonthexposures over a period of one year in a designated Radon Affected Area in the United Kingdom (UK).Although short-term exposures did not compromise measurement accuracy, short-term radon variability renderedone-week measurements less reliable in predicting annual average radon levels via the conventional methodology.Analysis permitted estimation of the maximum and minimum short-term measured domestic radon concentrationsat which there was 95% probability of the predicted annual average being below or above the UK Action Level of200 Bq·m~(-3) respectively. Between these limits, the short-term result is equivocal, requiring repetition, and the'equivocal range' for one-week measurements is significantly wider than for three-month exposures. In anygeographical area, domestic radon concentrations are distributed lognormally, with many properties having lowaverage levels; a small number exhibit excessive levels, and this distribution must be considered when definingexposures for a radon measurement programme. In low-radon areas, where 1% of houses might exceed the ActionLevel, a one-week assessment will find that fewer outcomes are equivocal. For high-radon areas, with 20% ormore houses over the Action Level, more than 50% of one-week outcomes will be equivocal, requiring repeats.The results of this work will be presented, together with a suggested policy for the use of short-term and long-termmeasurements in different areas and for chosen Action Levels.