Radon Levels in Caves
Normally, radon levels in natural environments, such as caves, are very low because the gas escapes into the air. This process is inhibited when the radon is trapped inside of caves, allowing levels to rise to a dangerous point. Because they are rich in uranium ore, caves are littered with fragmented pockets that disperse this gas and raising radon to deadly levels. When caves are located near silicic volcanic rocks or areas frequented by earthquakes, they have naturally occurring higher levels of radon gas.
With a lack of ventilation, long term exposure to high levels of radon in caves can be deadly. This health hazard was discovered in the 1940’s and 50’s during peak production times in mines, not only with uranium but other hard rock materials as well. These miners had significantly higher incidences of lung cancer deaths which led to improved ventilation in the mines in an attempt at lowering radon gas levels. Many countries have done studies to determine the possible health hazards of exposure to high levels of radon in caves. The U.S. participated in these tests due to concern for some of the highest levels of radon occurring through the middle and upper parts of Northern America.
Collection of data was done over a period of a year to determine how weather factors into changing levels of radon in caves. Scientists recorded daily and seasonal climatic changes and their effects on the radon levels inside the caves. What they found was that levels were lower in winter and higher in summer, suggesting that higher temperatures did not allow radon gas to dissipate quickly. The results also indicated that winds also play a role in lowering radon gas levels. In the summer when there is little circulation in the air, the temperature inside the caves is uniform. During the winter when the air blows directly into the caves it lowers the temperature inside thereby, lowering radon levels. This natural ventilation also occurs during heavy rainfall periods.
During these experiments, various techniques were used to collect radon gas; from simple cups with filters to sputum collection from national park employees. In addition, they tested caves with large bat populations because these areas are known to have low to medium levels of radon. In the end, the results were the same - although somewhat inconclusive. As the studies done decades ago had indicated, long term exposure to radon in caves is detrimental to one’s health. However the fluctuating seasonal data for short term excursion into caves had too many factors to determine an exact impact this, in part, is due to the fact that radon has a half life of only 4 days.