The radiation doses received from radon by recreational cavers using caves in the mendip hills, UK

Raised radon gas levels are known to exist in mines and Show Caves, and in the United Kingdomthe Ionising Radiations Regulations 1985 require the employer to take action to reduce radonlevels by improving ventilation or restricting access, because significant radiation doses can bereceived by workers.In the Mendip Hills, where the underlying rock gives rise to raised radon levels in domesticdwellings, there are a number of cave systems with unrestricted access to recreational cavers;including youth groups. A number of individuals regularly act as professional guides.We have measured radon levels in a number of these cave systems. In most, the levels are modest,but in one extensive system, the entrance system has levels consistently over 10,000 Bq.m-3. Whilstcavers would only receive a modest dose on a single visit, those who use the caves regularly forhalf a day each month could receive around 4 mSv each year, and the guides, using the cavesseveral times each week could receive annual doses up to 66 mSv.Thus the dose received by some recreational cavers can exceed the radiation dose limits for theworkplace, and so are significant. A survey to identify all affected caves, and action to developsome means to limit access by regular cavers to affected caves, are appropriate.