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 deep dive was to 260m as a practice dive for a deeper one 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.

As time went by my health improved, and over the months I became proficient in dive table design and had reworked a dive plan, which I felt covered all the weaknesses of the February plan. 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.

Anyways…now I can build my own dive plans incorporating years of deep dive experiences and its not rocket science at all with all the information freely available and man tested long before most of us were born. If its 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, 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 ever, at 313m without DCI. I believe that now, safe, extreme scuba doesn’t need luck.

Right…less of the sobering stuff and more information on the dive…

(I think) A dive below 300m needs a rapid descent. This causes HPNS and this can be minimised by using a high Equivalent Nitrogen depth (END) value. I used an END over 70m. I kept the oxygen high on this dive also (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, and it 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 down 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 n2 to complicate matters and is fast to decompress with. I managed oxygen toxicity by keeping PO2 low from 6m. No “air breaks” were needed (call them what you want)     Air breaks work OK in a o2/n2 (chamber) environment…but are possibly suicidal on a Trimix / Heliox dive.  Trimix “air breaks” or Heliox “air breaks” are just as bad, for the same reasons. Managing Po2’s to the 1.3 level 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 point, also breathing heliox on open circuit for multiple hours is difficult. It might be “easy” to breath but the body wastes energy heating it (as it arrives in the lungs cooler than a typical nitrogen/oxygen mix and overall heat loss can reach unsustainable levels. (Helium has a high capacity to bleed heat from the body, which is strange for such a light gas)

I chose the heliox route, to avoid counter diffusion problems only (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 on this almost 7 hour dive, I had to drink 2-3 litres every hour and this was difficult. A CCR would be the better alternative on the heliox deco (warm and moist) A dropping set point would be my choice also 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 then…who knows, although a drop in vital capacity was measured for 25days + after the dive.This may have been in fact, 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.

Since completing this deepest solo dive, I received numerous emails, mostly well wishes, but a few from would be “Extreme Explorers” less impressed. A few mails were from Explorers angry with me for not sharing information. My purpose for attempting this deep dive, was to find some answers and prove some theories.

Deep Explorers who are only interested in going on previously trodden ground, are not explorers but thrill seekers. If these divers want thrills then…diving with an un-proven ascent plan is as thrilling as anyone could want! If people would like some tips on deep diving then of course I am happy to help in a professional level, the information I have at the moment has commercial value, and I will treat it as such.

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.

( For the complete dive report, please visit inspired-training)

I got out of the water after 6 hours 36 minutes in it. I had got down deeper than any solo diver before me. I had surfaced under my own strength and more importantly without decompression illness. Although I was exhausted I was very happy.

copyright Mark Ellyatt