Loss of Consciousness: The confusion around Shallow Water Black-out

By Rik Rösken

Goal of this article:

In literature, especially from 'laymen' often different definitions are used when discussing the loss of consciousness with divers. In this article, I will try to give the reader some clear information on these definitions. The history behind Shallow Water Black-out can be quite interesting for those interested.

Shallow Water Black-out and Swimming Pool Black-out

Source of the confusion is the definition shallow water black-out and swimming pool black out. You would expect that these definition has the same meaning. This is not the truth however and this causes often the confusion.

Depending of the context where the words are used, does shallow water black-out is used to describe the loss of consciousness by the sudden decrease of oxygen pressure at the end of a dive. This sudden decrease is caused by the large pressure difference between 10 meters and the surface. The other meaning is that of carbon dioxide poisoning with rebreather divers.

Swimming pool black-out is often used to to describe loss of counciousness in the swimmingpool where hyperventilation plays a role. This can happen both underwater swimming (dynamics) and time diving (statics).

When these definitions are used in scientific literature, often there is less to worry. But outside of this, they are often confused by both laymen as less informed specialist. The problems that this caused in the research of drowning cases caused that the American researcher Craig developed a new definition in the seventies.

Ascent Black-out and Breath-hold black-out

For his research Craig made a difference between breath-hold black-out, using it for every other vorm of the loss of counciousness caused by prolonged breath-holding, and ascent black-out, where during the ascent the loss of consciousness happens.

Breath-hold black-out often happens in swimmingpools and other relative shallow water. Ascent black-out is more dangerous. The diver is often surprised during the last few meters. Both black-outs can lead to drowning without any assistance of a trained buddy.

Shallow water black-out en swimming pool black-out are still being used and confused. With this short article, I hope to have informed the reader how the terms should be regarded and be aware what the better alternative is.

Sources:

Henri Corriol, La Plongée en apnée : Physiologie et médecine, 3e édition, uitgeverij Masson 2002.

Albert B. Craig, JR., Summary of 50 cases of loss of consciousness during underwater swimming and diving. (Medicine and Science in Sports (1976) 8: 171-175