Radon levels in abandoned metalliferous mines, Devon, southwest England

Radon levels underground in two abandoned mines in Devon, United Kingdom, are reported and analyzed. Extremely high levels have been noted, 7,100,000 Bq m−3 being the highest level recorded. This is approximately 89 times higher than the highest published radon level for caves and mines in Devon and Cornwall, England, which is 80,000 Bq m−3. These levels have significant health implications for both casual and occupational mine explorers