Altidude Diving

25th June 2008 Article by Nuno Gomes

The higher the altitude above sea level, the deeper is the relative exposure in terms of the sea level equivalent depth. When diving at altitude the actual depth, the ascent rate and the depth of the decompression stops has to be corrected because of the reduced atmospheric pressure at altitude (see table 1.0 below). The reduced atmospheric pressure at altitude is not able to keep the gases in solution, in the diver’s body, following a dive if the standard decompression procedures are followed.

TABLE 1.0 – ATMOSPHERIC PRESSURE AT ALTITUDES ABOVE SEA LEVEL

Much research has been carried out over the years by various researchers such as Buhlmann, Cross, Wienke and others on the topic of high altitude diving.

In Switzerland and other mountainous or plateau countries, located at ambient atmospheric pressures lower than the atmospheric pressure at sea level, it becomes imperative to correct the depth, ascent rate and decompression stops depths for altitude (see table 2.0 below), in order to avoid serious decompression sickness.

Dives at high altitude, because of the relative increased depths and thus longer total decompression times, carry a far greater risk than same depth dives at sea level.

TABLE 2.0 – ALTITUDE CORRECTION FACTORS

For example a dive to 100 meters (328.10 feet) at an altitude of 2700 meters  (9000 feet) above sea level:

Corrected depth is: 100 meters x 1.40 = 140 meters (for the calculation of deco times)

Corrected depth is: 328.10 feet x 1.40 = 459.34 feet (for the calculation of deco times)

Corrected ascent rate (Buhlmann): 10 meters/minute / 1.40 = 7 meters/minute

Corrected ascent rate (US Navy): 60 feet/minute/ 1.40 = 40 feet/minute

Corrected decompression stop depth: 3 meters / 1.40 = 2 meters (applies to all deco stops)

Corrected decompression stop depth: 10 feet / 1.40 = 7 feet (applies to all deco stops)

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