Deep Water Blackout - Deep Water Blackout and Nitrogen Narcosis

Deep Water Blackout and Nitrogen Narcosis

Some scuba divers use the term deep water blackout loosely to refer to the final stage of nitrogen narcosis. Nitrogen narcosis is a neurological impairment caused by dissolved blood nitrogen under pressure. The progressive signs and symptoms of nitrogen narcosis are:

• Impairment of reasoning, judgement, memory and concentration;
• Sense of well-being and levity;
• Anxiety;
• Loss of coordination and physical dexterity;
• Hallucination, terror and vertigo;
• Unconsciousness and death.

The onset of symptoms may start around 30 metres and unconsciousness may occur at around 90 metres. Because free-divers start and finish the dive with only a single lungful of nitrogen to absorb, nitrogen narcosis has long been assumed to be an issue only for divers on compressed air. However, this issue may be more complex than that and needs to be resolved. There is a lot more to nitrogen narcosis than blackout and it is imprecise and probably not helpful to use the term deep water blackout to refer to a single aspect of it. Therefore, for the purposes of this article deep water blackout refers to latent hypoxia at depth and is unrelated to nitrogen narcosis.