User:IntoCaves/sandbox/"Foul Air" in Caves

"Foul Air" in Caves, sometimes called "Bad Air", is an atmosphere which has a noticeable abnormal physiological effect on humans.

Limestone Caves
"In limestone caves, ‘foul air’ can be described as an atmosphere which causes a noticeable physiological affect on humans. Fouls air usually contains greater than 0.5% carbon dioxide (CO2) and/or lower than 18% oxygen (O2) by volume". Foul Air is not found in all caves, however if present, it is usually found in deep caves which have little air movement, thus increased concentrations of CO2 and reduced O2 can accumulate in the lower levels of the cave. An elevated concentration of CO2 being the the most common foul air encountered in limestone caves which is threatening to human life, as opposed to reduced O2 concentration.

Sources of CO2 in Caves
There are a number of possible sources from which CO2 can enter a cave and influence the composition of its atmosphere.

Naked Flame Test
The 'naked flame test' involves carrying a lit candle or lighting a match or cigarette lighter in the cave atmosphere. The behaviour of the burning flame or lack of flame, was erroneously used by cavers to determine the concentration of CO2 in the atmosphere. The flame test is actually indicating the O2 concentration which may indicate that the CO2 is elevated. This becomes evident when considering the elements which are required for combustion to occur. ie. fuel, heat, oxygen.