Do people ever run out of air when exploring caves?

Yes, this can happen in very deep caves. The main problem is not running out of oxygen, though. It’s the danger of breathing in too much carbon dioxide. Caves often have high levels of carbon dioxide, and carbon dioxide is dangerous to humans. Too much can speed up breathing and make the heart work harder. Cavers may get headaches, feel tired or dizzy, or even pass out.

When carbon dioxide levels are more than one percent, the air is called “foul.” Luckily there is an easy way to test for foul air. Cavers can light a match or, if the cave is wet, use a butane lighter. If the flame goes out quickly, they know that the air is foul and they need to get out. Some caves may even contain poisonous gases like ammonia and hydrogen sulphide.