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Abstract: Health implications of radon in British caves John Gunn, 1 Stan Fletcher 2 and Robert Hyland 1 1 Limestone Research Group, Department of Environmental and Geographica/Studies, Manchester Polytechnic, Chester Street, Manchester, M1 5 GD, England 2 Department of Chemistry, Manchester Po/ytechnic, England
Radon is a naturally occurring radioactive gas which has three isotopes, the most significant being radon 222. This is a member of the uranium 238 decay series and has a half-life of 3.82 days. More significant in terms of human health are the short-lived radon daughters which are isotopes of polonium, lead and bismuth. Environmental radon is associated mainly with the trace amounts of the immediate parent, radium 226, in the rocks and soils. The Ionising Radiations Regulations 1985 apply to all places of work where the radon daughter concentrations exceeds 0.03 WL and where concentrations exceed 0.1 WL a controlled area must be designated. Such an area may only be entered by classified radiation workers or others operating under a written system of work. Present legislation sets the maximum annual radiation dose for a classified worker as 50 mSv although an investigation is required if any worker exceeds 15 mSv, the limit for non-classified workers. The annual dose limit for 'Other persons' is 5 mSv. There are some 2,500 limestone caves in Britain varying in length from a few metres to over 60 km. Nineteen of them are open to the general public (show caves) and the remainder are wild caves which are visited by instructed groups, recreational cavers and speleologists (cave scientists). The first measurements of radon gas and radon daughters in British caves (as opposed to mines) were probably those undertaken by the Manchester University Radiological Protection Service (RPS) at several of the Castleton show caves during the early 1970s. Although these revealed high concentrations no follow up work appears to have been undertaken and few, if any, measurements were made prior to 1987 when a Draft Code of Practice (DCOP) covering exposure to radon was circulated to all show cave and show mine operators by the
Health and Safety Executive (HSE). This was followed by an Approved Code of Practice in 1989. Following the DCOP measurements of radon daughter concentrations were made by the authors and others in most of the tourist caves and mines and in some cases concentrations were found to exceed 0.1 WL for at least part of the year, generally the summer months. More detailed observations were undertaken in these caves and the radon dose received by visitors and employees assessed. It was found that in the worst affected caves visitors were exposed to radiation doses of up to 0.4 mSv, a relatively insignificant amount, but the dose received by guides was very much higher. This would have been somewhat mitigated by the fact that guiding was usually a relatively short term occupation rather than a career for life. Ventilation systems have now b e e n i n s t a l l e d in these c a v e s g r e a t l y r e d u c i n g concentrations and hence the radiation dose. There are far fewer data for wild caves but radon daughter concentrations are generally lowest in Devonian l i m e s t o n e s (< 0.5 W L ) , b r o a d l y s i m i l a r in the Carboniferous limestones of South Wales, the Mendip Hills and the Northern Pennines (0.01-2.85) and highest in the Peak District Carboniferous limestones where all caves so far investigated would be controlled areas for at least part of the year if they were places of work. Giants Hole near Castleton has what is probably the greatest recorded radon daughter concentration in any natural cave in the world, 42 WL (- 155,400 Bq m-3 equilibrium equivalent radon gas). As in the show caves, concentrations are generally higher in the summer and lower in the winter. Recreational cavers and instructors at outdoor pursuits centres who spend several hundred hours per year underground could potentially receive very high radiation doses and this is the subject of ongoing research.
Abstract: Health implications of radon in British caves John Gunn, 1 Stan Fletcher 2 and Robert Hyland 1 1 Limestone Research Group, Department of Environmental and Geographica/Studies, Manchester Polytechnic, Chester Street, Manchester, M1 5 GD, England 2 Department of Chemistry, Manchester Po/ytechnic, England
Radon is a naturally occurring radioactive gas which has three isotopes, the most significant being radon 222. This is a member of the uranium 238 decay series and has a half-life of 3.82 days. More significant in terms of human health are the short-lived radon daughters which are isotopes of polonium, lead and bismuth. Environmental radon is associated mainly with the trace amounts of the immediate parent, radium 226, in the rocks and soils. The Ionising Radiations Regulations 1985 apply to all places of work where the radon daughter concentrations exceeds 0.03 WL and where concentrations exceed 0.1 WL a controlled area must be designated. Such an area may only be entered by classified radiation workers or others operating under a written system of work. Present legislation sets the maximum annual radiation dose for a classified worker as 50 mSv although an investigation is required if any worker exceeds 15 mSv, the limit for non-classified workers. The annual dose limit for 'Other persons' is 5 mSv. There are some 2,500 limestone caves in Britain varying in length from a few metres to over 60 km. Nineteen of them are open to the general public (show caves) and the remainder are wild caves which are visited by instructed groups, recreational cavers and speleologists (cave scientists). The first measurements of radon gas and radon daughters in British caves (as opposed to mines) were probably those undertaken by the Manchester University Radiological Protection Service (RPS) at several of the Castleton show caves during the early 1970s. Although these revealed high concentrations no follow up work appears to have been undertaken and few, if any, measurements were made prior to 1987 when a Draft Code of Practice (DCOP) covering exposure to radon was circulated to all show cave and show mine operators by the
Health and Safety Executive (HSE). This was followed by an Approved Code of Practice in 1989. Following the DCOP measurements of radon daughter concentrations were made by the authors and others in most of the tourist caves and mines and in some cases concentrations were found to exceed 0.1 WL for at least part of the year, generally the summer months. More detailed observations were undertaken in these caves and the radon dose received by visitors and employees assessed. It was found that in the worst affected caves visitors were exposed to radiation doses of up to 0.4 mSv, a relatively insignificant amount, but the dose received by guides was very much higher. This would have been somewhat mitigated by the fact that guiding was usually a relatively short term occupation rather than a career for life. Ventilation systems have now b e e n i n s t a l l e d in these c a v e s g r e a t l y r e d u c i n g concentrations and hence the radiation dose. There are far fewer data for wild caves but radon daughter concentrations are generally lowest in Devonian l i m e s t o n e s (< 0.5 W L ) , b r o a d l y s i m i l a r in the Carboniferous limestones of South Wales, the Mendip Hills and the Northern Pennines (0.01-2.85) and highest in the Peak District Carboniferous limestones where all caves so far investigated would be controlled areas for at least part of the year if they were places of work. Giants Hole near Castleton has what is probably the greatest recorded radon daughter concentration in any natural cave in the world, 42 WL (- 155,400 Bq m-3 equilibrium equivalent radon gas). As in the show caves, concentrations are generally higher in the summer and lower in the winter. Recreational cavers and instructors at outdoor pursuits centres who spend several hundred hours per year underground could potentially receive very high radiation doses and this is the subject of ongoing research.
