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I just got the last two issues of Underwater Speleology, the news letter of the Cave Diving Section of of the NSS. The Jan/Feb 1993 issue has short reports on several technical diving accidents. In one accident several flagrant violations of diving procedure and common sense by a diver using trimix at 215 feet ended with a rapid ascent to the surface, omitting decompression. He developed symptoms of decompression sickness while being transported to a hospital in a Coast Guard helicopter, without oxygen. The last two sentences of the report however contain an encouraging message. "Clearly this incident was a 'blow up' and cannot be counted as a traditional DCI case. To date there appears to have been only one known incident of decompression illness involving trimix in approximately 500-600 recent U.S. 'technical' dives." That is a rather impressive safety record. I don't know how many cases would be expected in 500-600 deep air dives, but statistical analysis of the risk using USN, Royal Navy, and Canadian air tables to the limits indicates much higher risk than this. It seems that a lot of technical divers are doing something right. The Nov/Dec 1992 issue has a list of safety recommendations for "extended range" diving by Michael Menduno and Billy Deans. This is a reprint from a presentation at NAU ICUE in Oct. 1992. Among the recommendations are: 9. Maintain your PO2s below 1.5 atm (recommended 1.2-1.45 atm depending on workload) during the "working phase" of the dive and any time more than "light work" is being done, boosting the oxygen levels to 1.6 atm, with care, during resting decompression. Take regular "air breaks" as a safety hedge every 20-25 minutes. [Comment: I think 1.2 may be overly conservative as an upper limit, but maybe not for a long hard working dive. He may actually be saying to maintain your PO2 at 1.2 as a *minimum* during the deepest part of the dive, using a hyperoxic mix if necessary, to limit inert gas exposure.] 10. "Just Say No" to nitrox mixes, specifically "air," beyond about 180-200 fsw or less, depending on the operation and environment. [Comment: With the controversy over nitrox in the recreational diving world I find references calling air "nitrox", which it is, amusing.] 12. Utilize a "hyperoxic mix" for decompression (ex. suitable EAN mix(es) and/or oxygen) whenever an equivalent "air decompression" would exceed about 15-20 minutes. I had already decided that, for myself, there is no sense in decompressing on air (very deep stops excepted), apart from logistics. I might have set the limit of air decompression from convenience a bit longer. The same issue also has an excellent article on Jim King's exploration of Dean's Deep Blue Hole to a depth of 663 feet last year. Bill Mayne
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