An intercomparison of passive radon detectors was held at the National Radiological Protection Board, now part of Public Health England, in 2003. Forty nine laboratories submitted 65 sets of passive detectors to this intercomparison. The exercise included 3 exposures to radon and its decay products at different equilibrium factors. After exposure, the detectors were returned to their originating laboratories for assessment. Participants reported the estimated exposure for each detector before they were notified of the exposures given to the detectors. The results obtained by participating laboratories were classified according to the spread of results from detectors exposed together and by the difference between the mean result of each group and the actual exposure given. Forty two percent of the laboratories achieved the highest classification for accuracy, while 23% were in the lowest category.
The proportion of laboratories achieving very good results was comparable to that seen in intercomparisons carried out prior to 2000. This was despite the fact that since 2000 these exercises have included a very low radon exposure, causing larger random errors in exposure assessment. This continued improvement therefore represented a significant achievement by the participating laboratories.