Dr. Merlin Tuttle, founder of Bat Conservation International, has spent a lot of time deep inside caves. When asked about close calls underground, Tuttle — in an interview for western Mexico's Subterráneo Newsletter — cited a near-death experience in a Texas cave.
Death by Carbon Dioxide
Tuttle and a friend had worked their way down to the lowest part of the cave. Suddenly each of them simultaneously mentioned that he was finding it difficult to breathe and feeling extremely tired. Fortunately, this reminded Tuttle of an article he had read on the symptoms people experience just before death by exposure to carbon dioxide.
Tuttle grabbed his companion and the two of them headed for the cave entrance, which they were barely able to reach in their weakened condition. They both collapsed outside the cave and were able to stand up only after several hours of breathing fresh air.
CO2 is Invisible and Odorless
Controversy surrounds the cause of CO2 buildup underground and both rotting vegetation and bats’ breath have been named as culprits. However, one thing is sure. Because it is completely invisible and completely odorless, an underground “lake” of carbon dioxide poses a mortal threat to cavers who don’t know how to detect it.
Symptoms of CO2 Asphyxiation
CO2 can kill simply by depriving air breathers of oxygen. The very first symptom a cave visitor feels in its presence is faster breathing. If he or she is on the move, this accelerated breathing may not be noticed at all. The next symptom is tiredness, which may be the last thing the visitor will remember, because the third symptom, unconsciousness, follows very quickly.
How does a cave explorer go about detecting an invisible enemy? One solution is to buy a costly oxygen meter. A far simpler and cheaper approach is to carry an inexpensive butane lighter whenever entering a cave.
A Simple Butane Lighter
Many US cavers have been doing this since July, 1989, when the NSS (National Speleological Society) News published a report stating that these lighters cannot produce a flame if there is less than 17% oxygen present. Since people tend to black out with less than 17% oxygen, an inability to “flick one’s Bic” could indicate a deadly situation.
The report also mentions that a curious one-inch gap appears between the lighter and the flame when the oxygen level is 17.5%, an excellent indicator that it is time to turn tail and leave the cave.
How frequently should underground visitors use their lighters to test the oxygen level? The typical practice among experienced cavers is to do this only when they feel some discomfort in breathing. Others may want to carry out this test more frequently, for example on reaching the bottom of a deep pit or before entering a downward-trending tight passage.
For many cavers, a butane lighter is part of the basic equipment they carry each and every time they venture underground.
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