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Cavers risk cancer from underground radon

from:  New Scientist, 12 September, 1992

William Bown

Radon gas in Britain's caves is exposing thousands of potholers and other cave users to levels or radiation up to 800 times the official safety limit in homes.  Radon increases the risk of contracting lung cancer.  The Health and Safety Executive is considering what action to take after a survey team recorded the world's highest radiation reading for a natural limestone cave in Britain.

     In a letter to New Scientist this week, Robert Hyland, a PhD student and a member of Manchester Polytechnic's Limestone Research Group, reports the conclusions of a year-long survey of 40 British caves.  Hyland found the average level of radiation was 2900 bequerels per cubic metre.  The limit at which Britain's National Radiological Protection Board recommends action to remove radon form home is 200 bq/m³.

     The highest figure averaged over the year was 46 000 bq/m³ for the Giant's Hole in Derbyshire.  Readings at this cave peaked at 155 000 bq/m³ during the summer when airflow is reduced and radon, released by uranium in rocks, remains trapped under ground for longer.

     This figure is the highest ever recorded for a natural limestone cave.  By contrast, the highest figure for a limestone cave in the US is about 54 000 bq/m³.  Hyland  wants all cavers to know the risks before they go underground.  "Children and people on management training courses are not always told of the risk," he says.

     The 1985 Ionizing Radiation Regulations limit workers to a dose of 15 millisieverts a year.  Such a dose increased lung cancer by 0.05 per cent.  This is about four times the annual risk of being killed in a road accident.  With radioactivity of 155 000 bq/m³, a caver would pick up this dose in around 13 hours.

     Over a year, keen potholers can clock up hundreds of hours underground.  Dave Edwards, chairman of the National Caving Association's working party on radon, cut his time underground from 200 hours a year to about 26 hours in the past year as he became aware of radon's effects.  He sees no reason for anyone to stop caving entirely, but says:  "We are changing our habits."

     He has advised outdoor centres using Britian's 20,000 caves "to quietly, find out about radon levels and informally change the caves they use".

     The Health and Safety Excutive, still waiting to see the full results of the survey, is considering whether employers who send people underground are liable for any health problems caused by the radiation.

     Local education authorities may be at risk for the school children they send caving on trips and holidays.  The Department of Education has provided no guidance and most education authorities are unaware of the risk.  Derbyshire County Council, however, recently stopped school parties from visiting caves while it checked radon levels in the Peak District.

     Installing fans will reduce radon in caves.  And the HSE is satisfied that the installation of fans has averted any problems at tourist caves with high levels of radon.