For several years, DAN, the Divers Alert
Network, has studied the effect rapid ascents have
on decompression illness. Animal studies have
shown that fewer bubbles form at a 30 foot per
minute ascent rate, and in 1993 the U.S. Navy
changed their rate for their air divers from 60 to 30
feet per second.
As part of DAN's Project Dive Exploration, 47
divers contributed their depth-time profiles from
357 dives made during the course of 15 dive trips.
Diver's maximum depths during 20-second intervals
were recorded by their computers. While none of
the divers had DCI, up to one-third ascended faster
than the recommended 30 feet per minute. Half
took a safety stop of three or more minutes at 20
feet or less.
The results are a cautionary note to divers who
believe they ascend at the proper 30 feet per
minute rate: one-third don't. Researchers noted
that one reason divers exceed the ascent rate is that
computers with a 20-second interval recording rate
can detect ascent rates greater than 60 feet per
minute but are not entirely accurate at rates of less
than 60 feet per minute for ascents totaling less
than 20 feet.
These researchers believe that computer
manufacturers should change the monitoring
interval to five seconds. Meanwhile, divers should
be careful to ensure a slow ascent and not depend
entirely on computer monitoring.