Why Is It Dangerous To Hyperventilate Before Diving Underwater?

Hyperventilation is a dangerous sign that can lead to hypoxic blackout, hypoxia, or shallow water blackout. It is a form of over-breathing where the body’s breathing exceeds its demands, causing the diver to stay underwater longer. This is particularly dangerous for breath hold divers, who start with low carbon dioxide content and often perform five or more large deep breathes before diving.

However, hyperventilation is generally easy to treat on dry land by having the person breathe into a paper bag or other type of bag. The number two rule for freediving safety is never to hyperventilate, as it can cause sudden loss of consciousness and death. Hyperventilation can be provoked by hyperventilating just before a dive, as a consequence of pressure reduction on ascent, or a combination of these.

The danger of hyperventilation applies to all breath hold divers, including snorkel divers and people swimming lengths underwater in pools. The reduction in CO2 pressure during hyperventilation reduces the urge to breathe, which can result in hypoxic or shallow water blackout caused by a loss of consciousness while underwater due to a lack of oxygen, which can lead to drowning.

The problem with hyperventilation is that it does not supersaturate the blood and tissues with oxygen, as previously hypothesized. Instead, it depletes the oxygen reserves in the blood and tissues, cutting off time underwater. Hyperventilation has been tested and shown to be harmful to both the body and the environment.