Can you breathe in a cave?

One of the most common beliefs is that in caves the air is often stuffy, unhealthy, low in oxygen content and at times saturated with toxic gases.
As a matter of fact, this erroneous belief stems from the confusion between natural caves and mines. In the latter, due to artificial hollows that disturb the natural system, it is true that often air circulation is slow and needs a mechanical aid to guarantee the health of the miners working in them and to channel out waste substances produced by the machinery. Moreover, the galleries often get saturated with gases contained in the rocks and freed by the excavation work (like the much feared fire damp gas of carbon mines). Unlike mines, caves are complex systems that generally have more than one entrance and always communicate with the surface through a system of fractures and small conduits. Hence there is appreciable air circulation as a result of the differences in pressure and temperature at the entrances of the caves. The air currents that form inside a cave become more intense when the disparity between the entrances increases, and also when the difference between the internal and external temperatures increases. Often strong air currents at the entrance of a cave are a clue to the possible existence of a karst system. Hence the air inside a cave is continually mixed and there is never the problem of a lack of air or oxygen.
Only in some particular caves precautions are necessary. In some closed chambers, especially in tropical climates, air pockets rich in CO2  may form cyclically as a result of biological activities: an excessive sense of fatigue and exhaustion and the acetylene flame that just will not keep alight are usually good warning signs. Other gases, such as ammonia, can be formed due to decomposing organic deposits (an example is bat guano, that in some tropical caves can reach a thickness of tens of metres): in this case a strong, pungent smell warns the explorers. However,  in volcanic caves, in lava tunnels in the areas closer to the crater or those with active smoke-holes,  and in particular caves, such as those dug in ice in contact with active volcanic terrains (like those found in Iceland), or even caves with sulphur springs inside (such as the famous Cueva de Villa Luz, in Mexico)  specific precautions must be taken, such as oxygen bottles for breathing and particular  measuring instruments (Draeger apparatus) to keep the quality of the air monitored at all times. Even during the exploration of caves beyond siphons and flooded galleries a check must be made before breathing the air. In certain tropical caves, especially if they are very dry, the fungus, Histoplasma capsulatum, can grow on bat guano and its spores can provoke serious breathing pathologies when inhaled: in this case it is necessary to protect oneself with a mechanical filter respirator capable of holding back the spores. Apart from these particular cases, however, in caves the air is adequate for breathing and oxygen bottles and gas masks are unnecessary. Indeed, due to elevated levels of humidity that make the atmospheric dusts settle and  also the absence of allergens, air in caves is often very clean, so much so that in the last century many caves, especially in Austria, were transformed into speleotherapy centres to cure respiratory illnesses.

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