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The results of a survey of radon exposures in underground structures of the British Telecommunications (BT) network were summarized. Static radon concentrations were measured in a large number of manholes and underground access ports of the BT network in Cornwall, Devon, Northamptonshire, Somerset and parts of Derbyshire, Scotland, and Northern Ireland, United Kingdom, that were judged by the National Radiological Protection Board to be radon affected areas, defined as an area in which at least 1% of the homes were expected to have radon concentrations above 200 becquerels per cubic meter (Bq/m3). The measurements were made with track etch detectors that were kept in place for 90 days. Personal radon exposures were measured on 35 volunteers from each affected area who wore track etch detectors and kept personal activity logs of time spent in the manholes for 30 days while they worked. Kinetic measurements utilizing nitrous-oxide as a surrogate for radon and a radon progeny meter were made in several manholes to characterize the rate of disappearance of radon and radon daughters from the sites under natural and assisted ventilation conditions. The grand area mean static radon concentration was 1,416Bq/m3. The lowest reading was 9Bq/m3 which was measured in a manhole in Derbyshire and the highest was 13,639Bq/m3 which was measured in Cornwall. The radon concentrations measured by the personal dosimeters varied from below 0.1 to 0.9 millisieverts (mSv). This was equivalent to an estimated annual dose range of from less than 1.1 to 10.1mSv. Most of the estimated annual exposures were below 5mSv, the limit specified by the Health and Safety Executive. The kinetic data showed that assisted ventilation significantly shortened the time for the radon or radon daughter concentrations to decrease to 0.10 of their original values. The authors conclude that radon can build up to very high concentrations in manholes. The dosimeter data, however, show that personal radon exposures are much lower than what would be expected from the very high static concentrations. Possible reasons for this include the facts that manholes have small internal volumes which means that much of the air (including any radon present) will be displaced upon entry and they are usually partially filled with water which also displaces air.
Annals of Occupational Hygiene, 40(5):569-581, 1996. (10 references)
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