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Ascent Rates
Slowing Down
By David Holt NAUI #15465

The U.S. Navy’s original 1915 dive tables were based on the work of the Scottish physiologist John Haldane (you Master Scuba Divers remember Haldane’s theory, don't you?). He developed the first decompression tables for the Royal Navy in 1908.

Early Navy hard hat diver originally ascended a slow rate of about 25 feet per minute. A faster ascent rate was virtually impossible, because bringing a fully equipped hard hat diver to the surface by pulling hand-over-hand was slow and hard work for the dive tenders. The possibility of Decompression Sickness for ascending to rapidly was never even considered, very few divers got bent.

Several decades later, with the introduction and refinement of self contained diving, it became possible to increase the diver's ascent rate. During World War II, the newly formed U.S. Navy "frogmen" needed to ascend at a much faster rate – about 120 feet per minute. The problem was that 60% of them got bent. Opps, not to good for our public relations during a war.

A compromise was reached by splitting the time in half, and an ascent rate of 60 feet per minute emerged as the Navy’s new standard. It is important to note that this new "standard" did not emerge as a result of extensive research and testing, it was simply a best guess. However, it had the benefit of simplifying ascent rate calculations in actual rate use.

More recently, research conducted favor an ascent rate of 30 feet per minute and mandatory safety stops at 15 feet. The studies showed that evidence of decompression sickness existed in the tissues of the body, without symptoms – especially with cerebral neurological involvement (that means your brain) following dives below 65 feet.

Is it possible that we have all been "bent" and didn't know it? I, for one, will start ascending at a much slower rate and take time for a safety stop every dive.

Safe dives are fun dives …….
 
 
 


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