4: Remain Within the Operating
Limits for Your Breathing Media
Although only one in ten cave diving fatalities involves certified cave or cavern divers, 90 percent of these fatalities take place on dives in which participants expose themselves to an Equivalent Narcotic Depth (END) of 130 feet or more. At these depths, factors such as nitrogen narcosis, high partial pressures of carbon dioxide — and physiological mechanisms that experts have yet to understand — can either lead directly to a diver’s demise, or contribute substantially to his or her death.
With the increased use by technical divers of breathing media other than air, there has also been an increase in fatalities caused by oxygen toxicity (exposure to too much oxygen, such as would result from breathing an oxygen-rich Nitrox mixture at too deep a depth), and from hypoxia (exposure to too little oxygen, as might result from breathing certain Trimix combinations in water that is too shallow).
For these reasons, the major cave-diver training organizations recommend that divers remain within a limiting PO2 of 1.4 atmospheres while diving, and 1.6 atmospheres during decompression. They further recommend that divers not exceed an Equivalent Narcotic Depth (END) of 130 feet. In so far as experts believe both oxygen and nitrogen have the potential to cause impairment at depth, this mandates the use of Trimix (a combination of nitrogen, oxygen and non-narcotic helium) at depths below 130 feet.
It is important to note that, while small groups of highly trained, highly experienced cave divers are currently exploring cave systems at depths exceeding 300 feet, the average recreational cavern or cave diver can spend a lifetime exploring north-central Florida’s more popular dive sites and never have the need to exceed a depth of 130 feet.
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