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.