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THE RADIATION DOSES RECEIVED FROM RADON BY RECREATIONAL CAVERS USING CAVES IN THE MENDIP HILLS, UK.

M. Sperrin †, A.R.Denman ‡ $, and P.S.Phillips R.
† Department of Medical Physics,
Princess Margaret Hospital, Okus Road, Swindon, SN1 4DB, UK.
‡ Medical Physics Department,
Northampton General Hospital, Cliftonville, Northampton, NN1 5BD, UK.
R School of Environmental Science, University College, Northampton,
Boughton Green Road, Northampton, NN2 7AL, UK.
$ Visiting Fellow in Medical Physics, University College, Northampton.

Raised radon gas levels are known to exist in mines and Show Caves, and in the United Kingdom
the Ionising Radiations Regulations 1985 require the employer to take action to reduce radon
levels by improving ventilation or restricting access, because significant radiation doses can be
received by workers.
In the Mendip Hills, where the underlying rock gives rise to raised radon levels in domestic
dwellings, 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 . Whilst
cavers would only receive a modest dose on a single visit, those who use the caves regularly for
half a day each month could receive around 4 mSv each year, and the guides, using the caves
several 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 the
workplace, and so are significant. A survey to identify all affected caves, and action to develop
some means to limit access by regular cavers to affected caves, are appropriate.

Key Words :- Caves, Radon, Radiation Dose, Mendip Hills