An intercomparison of passive radon detectors was held at the National Radiological Protection Board, now part of Public Health England, in 2004. Thirty eight laboratories submitted 53 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. Twenty four percent of the laboratories achieved the highest classification for accuracy, while 28% were in the lowest category. The proportion of laboratories achieving very good results was lower than that seen in recent intercomparisons; this may have been due to a number of laboratories introducing new detector systems.