Radon in caves

What is Radon?

Radon is a naturally occurring radioactive gas. It is produced by the breakdown of uranium in soil, rock and water. All rocks contain some uranium, although most contain just a small amount. Certain types of rock, including granites, dark shales, light-coloured volcanic rocks, sedimentary rocks containing phosphate, and metamorphic rocks derived from these rocks, have higher than average uranium contents.

Why is it found in Caves?

Radon is continually seeping from the rock. In the outdoors, air currents, reducing its concentration quickly dissipate radon. Caves, on the other hand, will not generally have the same level of airflow and so radon levels can become concentrated. The main source for Radon in the Burren for example is the granite underlying the limestone. Radon is released from this and travels up through the cracks and natural fissures in the limestone to enter the cave cavity.

What risk is the caver taking?

In 1994, the International Commission on Radiological Protection recommended the adoption of a risk factor equivalent to a lifetime risk of death of 0.0001 for chronic exposure to a radon gas concentration of 1 Bq m-3. On this basis, the estimated risk of contracting fatal lung cancer as a consequence of exposure to 200 Bq m-3 is about 2 in 100.

Full text & More info: CavingIreland

Radon in caves: clinical aspects

Abstract:
Historical, experimental and clinical evidence is presented to suggest that radon constitutes a relatively small carcinogenic risk for casual visitors to caves. The risk is dependent on radon levels and the smoking of tobacco. Show cave guides, chronically exposed to radon, may be at increased risk for lung cancer due to the effects of radon, especially if they are smokers of tobacco.

"Despite solid evidence that radon is a carcinogen, and that the risk rises with time of exposure (usually many years) and increased concentrations of radon, expressed in Bequerel per cubic metre (Bq/m3) in confined spaces, such as homes and caves (Darby et al., 2005) the risk varies with climate and geographical location. Because of the short times that casual cavers are exposed to radon, the risk of developing a lung cancer for a non-smoking caver can be considered very small; the risk is compounded for smokers."

RISK ESTIMATES FOR CAVERS EXPOSED TO RADON

" (...) the authors estimated the recreational caver spending 50 hours per year caving to have a lifetime risk of 1 in 12500 or 0·00008. For professional cavers, the lifetime risk is estimated, assuming 600 hours per year caving, for premature death from lung cancer, to be 1 in 1000."

Full article: Craven S.A. and Smit B.J. 2006. Radon in caves: Clinical aspects.
International Journal of Speleology 35 (2), 93-101. Bologna (Italy). ISSN 0392-6672