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.
There will always be a step up in nitrogen on open circuit, unless you have “yet another bottle”. Too many bottles adds to the risk and a support diver bringing gas to 150m+ is not ideal either! On the dive, my nitrogen “spike” was deep when critical tensions were not yet high. The 140m deco gas went up 10% nitrogen with a raise of 6% oxygen, this meant that the rest of the ascent gases could keep the same or more helium and critically…less nitrogen.
All the subsequent ascent gases kept the same helium content from 140m to 9m, the only changes were to increase oxygen and decrease nitrogen. At 9m, Heliox was used, it has no nitrogen to complicate matters and is fast to decompress with.
I managed oxygen toxicity by keeping PO2 low from 6m which meant no “air breaks” were needed. Air breaks are possibly suicidal on a Trimix / Heliox dive; but work well in a chamber environment. Managing Po2’s to a level of 1.3bar is by far the safest way to deal with long decompressions.
Having no “p02 breaks” (better term for air breaks) is hard from a pulmonary toxicity standpoint; also breathing heliox on open circuit for multiple hours is difficult. It might be “easy” to breathe but the body wastes energy heating it; since arrives in the lungs at a lower temperature than a typical nitrogen/oxygen mix. This results in overall heat loss possibly reaching unsustainable levels.
I chose the heliox route to avoid counter diffusion problems; the cause of all my previous dive problems and knew that its use was troublesome but less life threatening. To counter the enormous dehydration due to immersion diuresis during this almost 7 hour dive; I drank 2-3 litres every hour, which was difficult. A CCR would be a better alternative for a heliox decompression (warm and moist). Using a dropping set point would be my choice to counter the pulmonary toxicity and increased carbon dioxide complications. The longer times on deco that this would have caused would be worth enduring.
The OTU and CNS count on this dive was going to be high and managed, by not chasing the 1.6 Po2 mantra. If I had followed traditional 1.6 PO2 maintenance for the dive, then who knows! A drop in vital capacity was measured for 25 days + after the dive, howvere, this may have been lung fatigue from breathing un-heated, un-hydrated gases for long periods (my own view) or simply pulmonary toxicity.
This text is not a recipe for deep dives, but simply how I did it and (possibly) how it turned out so favourably. You will note that I did not mention ascent rates (critical), where the deep stops were (critical), also I didn’t mention any mix values or the stop depths/ times themselves.
Extreme deep diving successfully is a complex business. Its not really a competitive sport, in fact you are competing only with yourself…and if you lose, you lose the farm.
From what I read of previous deep dive accounts, they all seem to follow similar themes. Dropping to maximum depth like the US dollar and then ascend like a jet fighter on afterburner. I thought this was wrong the first time I read it; a rapid ascent would ensure problems for later, but also, from my previous experience, too long spent in deep water would need serious redress.
Deep water decompression is an emerging science. The benefits gained can be dramatic on the overall decompression by stopping deep for short periods, typically less than 30 seconds. Too many stops though below 200m though would add heavily to the overall decompression burden. I chose a relatively slow ascent rate from the bottom at around 18m per minute for my planned dive to 320m, the first stop was around 250m, with the next 4 within 18-20 metres of each other. I planned and planned this dive, fine tuning the gas mixtures so that the Nitrogen values would be dropping on the ascent after one initial spike early on in the ascent. Some bad gas choices on the ascent would impact heavily on the decompression, combined with too much and then too little decompression stops would have affects similar to my previous dive. The maximum depth gases for this dive would be largely helium with 20 per cent nitrogen and 5 per cent oxygen (ish). The relative ratios of the breathing gases can have a dramatic affect within the body as gases of different solubility and density jockey for up-take and/or eliminination hierarchies.
My purpose for attempting this deep dive, was to find some answers and prove some theories. If people would like some tips on deep diving then of course I am happy to help in a professional level. Divers at Explorer level will either be diving in un dived areas of sea, or diving in unknown areas of physiology. The latter category have over the years proved again and again what does not work, but still many are willing to embark on virtual suicide missions believing that strength or fitness rather than technique, will somehow over come the physical brick walls of extreme deep diving. I have always tried to embrace new ascent solutions, but these can be every bit as precarious as the old school techniques.
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