This page was last edited on 5 February 2018, at 20:36. Victims are often established how to blackout text in pdf free of breath-hold diving, are fit, strong swimmers and have not experienced problems before. Freediving blackout has a high fatality rate, and mostly involves males younger than 40 years, but is generally avoidable.
Risk cannot be quantified, but is clearly increased by any level of hyperventilation. Blackout during a shallow dive differs from blackout during ascent from a deep dive in that deep water blackout is precipitated by depressurisation on ascent from depth while shallow water blackout is a consequence of hypocapnia following hyperventilation. The mechanism of deep water blackout is hypoxia, arising from the rapid drop in the partial pressure of oxygen in the lungs on ascent as the ambient pressure drops and the gas in the lungs expands to surface volume. Hypoxic blackout which occurs where all phases of the dive have taken place in shallow water where depressurisation is not a significant factor. This is often referred to by breath-hold divers as shallow water blackout.
And mostly involves males younger than 40 years, the mechanism for blackout on ascent differs from hyperventilation induced hypocapnia expedited blackouts and does not necessarily follow hyperventilation. Which will deplete carbon dioxide — surface blackout occurs just after the diver exhales on the surface, many drownings unattributed to any other cause result from shallow water blackout and could be avoided if this mechanism was properly understood and the practice eliminated. Because ascent blackout occurs as the diver approaches the surface from a deep dive, carbon dioxide builds up in the bloodstream when oxygen is metabolized and it needs to be expelled as a waste product. When the urge to breathe comes on near the end of the dive, the mechanism is essentially that for shallow water blackout but hypoxia is delayed by pressure at depth and sets in only when the pressure drops while surfacing. While the diver is still unconscious underwater, they should be continuously monitored until out of the water.
These blackouts typically occur in swimming pools and are probably driven only by excessive hyperventilation, with no significant influence of pressure change. This is an alternative term for blackout on ascent when used by free divers. As it is also used for other purposes, ascent blackout is the less ambiguous option. This is a recommended term for cases where hyperventilation is known or suspected to have been a contributing factor in either shallow water blackout or deep water blackout. This describes the precursor to blackout on ascent where the partial pressure of oxygen remains sufficient to maintain consciousness, but only at depth, under pressure, and is already insufficient to maintain consciousness at the shallower depths that must be encountered on ascent. This refers to loss of consciousness during a dive associated with blackout at a shallow depth.