313 meters - Now that's Deep! Part 1
Posted By Mark Ellyatt on 30 July 2004
I like to dive deep; I like a challenge and it’s rewarding to do something difficult and return safely. In February 2003, I almost dived my last dive, and this was my first major diving incident in almost 3000 dives. This dive was to 260m as a practice dive for a deeper one scheduled soon after. The ascent plan was aggressive time-wise, but I had built confidence in this particular decompression algorithm and had dived it “deep for long” many times. How mistaken could I have been? The decompression schedule proved woefully inadequate and the injuries I sustained will probably take a lifetime to fully recover from. During my rehabilitation I couldn’t do much but read books and try to make the best of it. I went over my dive plan again and again; it was not until after the dive that I discovered that although it was commercially available dive software, It was not tested, in any way, and had no place suggesting it could provide an ascent solution from a depth well within its stated specifications.
My doctors had advised me against diving again, but what had become a career for 10 years was proving very hard to simply discard. If I had not been able to return to the sport I love, then the depression that was sure to follow would be harder to endure than any physical injuries I might suffer.
As time went by, my health improved and over the months I became proficient in dive table design and had reworked a dive plan; I felt this plan covered all of the weaknesses of the February plan. Now I can build my own dive plans, incorporating years of deep dive experiences - its not rocket science, at all. With all the information freely available and man tested long before most of us were born.
If it’s new (as I found out to my cost) it has not been tested outside of a PC or Petri dish. The dive plan software I worked on, together with a colleague knowledgeable in programming skills, reflects information actually tested by commercial divers in the past. It utilises data from large dives that have not worked recently and includes matrixes to avoid counter diffusion problems. It has already received interest from military and governmental academics. Even more so with its recent success on predicting the ascent solution from the deepest solo dive to 313m without DCI. I believe that now, safe, extreme scuba doesn’t need luck.
In my opinion dives below 300m need a rapid descent. This causes HPNS which can be minimised by using a high Equivalent Nitrogen Depth (END) value. I used an END over 70m and kept the oxygen high on this dive (PO2 was 1.6+).
The reasons for this are as follows.
- The exposure was short, so not problematic (for me).
- Keeping the helium as low as possible in the bottom mix has many benefits. It also makes it easier to derive the next Trimix decompression gas.
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- what are these?
