Although very few cave fatalities involve certified cave divers, most of these took place on dives in which participants exposed themselves to an Equivalent Narcotic Depth (END) of 40 m/130 ft or more. At these depths, factors such as nitrogen narcosis and high partial pressures of carbon dioxide can either lead directly to a diver’s demise, or contribute substantially.
With the increased use of breathing media other than air, there has also been an increase in fatalities caused by oxygen toxicity (exposure to too much oxygen), and from hypoxia. This is exposure to too little oxygen, as might result from breathing certain Trimix combinations in shallow water.
For these reasons, most cave and tech divers remain within a limiting PO2 of 1.4 ATA while diving, and 1.6 ATA during deco. They further avoid exceeding an Equivalent Narcotic Depth (END) of 40 m/130 ft by adding helium to their gas mixture.
It is important to note that, while small groups of highly trained, very experienced cave divers are currently exploring cave systems at depths exceeding 100 m/330 ft, 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 40 m/130 ft.