Posted by Ken Kurtis on October 31, 2000 at 00:05:04:
Since we've been discussing a lot of hypotheticals lately, I pulled out my copy of the D.A.N. "2000 Report on Decompression Illness & Diving Fatalities" (based on 1998 data) to see what they said about type of gas used during dives that resulted in accidents. Here are the raw numbers (without comment). Draw your own conclusions.
Also be aware that D.A.N. seems to have changed their reporting criteria in 1998. In 1997, the report was based on 972 cases (820 DCS- I & II, 68 AGE, 84 not classified). In 1998, D.A.N. sarted using the form called DIRF (Diving Injury Report Form) but only collected data on 431 divers. Nowhere in the report does it say that they assume the accident rate suddenly dropped in half.
Here's the stuff. (Remeber this is only bends and embolisms - these numbers don't include the 83 fatalities in 1998 - and they don't seperat bend and embolsims this year as they have in the past):
BREATHING GAS USED BY INJURED DIVERS (421 responses)
Air - 90.5%
Nitrox 6.7%
Heliox - 0.7%
Other - 2.1%
DIVE PLANNING (422 divers)
Computer - 60.9%
Tables - 23.7%
Followed Dive Guide - 10.2%
Other - 5.2%
Perhaps more interesting and comprehensive are the numbers from D.A.N.'s Project Dive Exploration (PDE) which basically consist of people volunteering to be monitored during their dive excursions (frequently, but not always, diving vacations). D.A.N. freely admits that these people may not be representative of the general diving population, but the results are interesting nonetheless. The group consisted of 1,234 divers who made a total of 12,849 dives.
BREATHING GAS USED BY PDE DIVERS (data from 7397 dives)
Air - 83.3%
Nitrox - 14.0%
Combination - 2.0%
Trimix/heliox - 0.6%
There were no fatalities among these divers. The report states that, "In two years of PDE data coillection, 76 divers reported symnptoms which were classfiied as . . ."
Not DCS - 62 divers (81.6% of those reporting symptoms)
Ambiguous (possible DCS but not recompressed) - 11 (14.5%)
Recompressed - 4 (6.5%)
4 hits out of 12,849 dives yields a hit rate 0.03%, or one hit per 3212 dives. The quoted summary of each hit is:
1. A 43-year-old female diver with 10 years diving experience made 10 dives in four days to depths as deep as 140fsw. 26 hours after her last dive, she flew home by commercial air. During the flight, she developed right shoulder pain and tingling of her left forearm. She was treated on Table 6 the next day with complete resolution of her symptoms.
2. A 43-year-old female diver with extensive experience made 20 dives in 6 days to as deep as 110fsw. Shortly after dive 20, she developed skin changes and swelling in unspecified locations. Her symptoms were relieved by recompression.
3. A 30-year-old female diver with 3 years of diving experience made 20 dives in 5 days to depths as deep as 110fsw. On day 5, she developed pain in her left shoulder and back but continued diving on day 6. . . . Her symptoms resolved completely after several days treatment . . .
4. A 54-year-old male diver with 30 years experience made six trimix dives in 6 days on the USS Monitor. Only the last two profiles were recorded by dive compouter. The last dive was to a depth of 220fsw. 38 minutes after the dive, the diver developed vertigo and vomited twice. . . . The diver was recompressed . . . (and symptoms) cleared with two additional treatments over the next two days.
There you have it. Actual, real (raw) numbers. Draw whatever conclusions you deem appropriate.
Ken Kurtis
NAUI Instr. #5936
Co-owner, Reef Seekers Dive Co.
Beverly Hills, Ca.