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Thoughts on Diving To Great Depths



By Jim Bowden, March 7, 1998

Header image: Explorer Jim Bowden surveys Zacatón. All photos courtesy of Jim Bowden and Proyecto de Buceo Espeleologico Mexico y America Central

Deeper into, the abyss, knees bent and streamlined for speed. The feeling of space and the suspicion that the void goes on and on. The darkness closes in, embraces me, not hostile, not threatening, just black like eternity. My light, a sword with nothing to touch, only my line, and the limits that my fears decree.

Bowden’s Proyecto de Buceo Espeleologico Mexico y America Central logo

These last few years I have wondered about my comrades in arms who have experienced that immersion into great depths. In 1993, Sheck Exley published an article in aquaCORPS # 7 C2 titled, “Beyond 500 feet (150 m)” listing sub-500 ft/153 m open circuit technical dives. There were thirteen at the time, completed by six divers, five men and one woman. All but one were in fresh water and in caves, though Exley commented that the wreck divers were sure to ”catch up.” Other than general fatigue, and one case of skin bends, no DCS symptoms were reported. The decompression models used were customized and often proprietary. My intention here is to update the list of sub-500 ft dives/153 m. To date, at least thirty-seven have been completed in this range and technical diving is no longer the realm of the lunatic fringe, at least in comparison to a few years ago. This paper will embrace the sub-500 ft/153 m dives made to the present and the known physiological challenges to those who dare. At best, it is an incomplete report and it will be dated by the time it finds print. The participants are not always forthcoming with all the details of their activities (myself included) and not all the individuals involved in these dives are known. Not everyone is interested in sharing their passion with the world. It is an immensely personal endeavor whether they chose media coverage or not.

The dives in the chart Deep Dive List (1982-1998) [See: Diving Beyond 250 Meters] reflect the historical journey rather than a listing of progressively greater depths. To list them according to depth would imply a status that deeper is the greater accomplishment. The deepest depth is a coveted goal and I cannot exclude myself in this desire. However, some of these dives, such as Jochen Hasenmayer’s (sneak) dive in Vaucluse, Nuno’s difficult access and altitude, the cold and strong currents that some of the wreck divers must face, makes the distinction that just the volume of water over one’s head is a poor gauge of the individual’s accomplishment. It must be considered that many of these dives were preparation dives for a much more ambitious effort in the future. In Sheck’s article, I was one of the six divers in the sub-500 ft/153 m group. I was honored to be there. In less than six months I had made two more dives and found myself with the record. This is waiting to happen on the world scene. Somewhere someone—South African, French, German, Swiss—is on the brink of accomplishing the impossible.

Jim Bowden and Ann Kristovich reviewing their dive plans on site at Zacatón


Diving at the edge of the envelope obviously invites the possibility (probability) of decompression illness. “Bends is a statistical inevitability” says Bret Gilliam. The true pioneers in this exotic discipline were extremely exposed. Jochen Hasenmayer and Sheck Exley had little history to guide them in their efforts. Decompression software and models that would fit their particular techniques were not available, and everything was experimental. We have all benefited from their courage and their accomplishments.

Bowden preparing to make the jump

It is remarkable, considering the extreme nature of the dives, that there have been few incidents of DCS among the divers listed. The inert gas exposure facing each of these individuals is mind boggling, and the lack of CNS compromise in this series of dives is interesting. Jochen’s unfortunate incident occurred because of the cascading number of mistakes brought about by equipment malfunctions; he was also subject to inappropriate recompression treatment. My hit was multiple joint involvement, Nuno’s was inner ear, Gilberto’s was, by his report, the result of poor choices in the decompression profile. We have all recovered and are still diving aggressively.

Complicating the risk of DCI and the hope of resolution of symptoms is the remoteness of many of the dive sites. Nature is seldom kind enough to grant us sites that provide ease of excavation and treatment. In water recompression and/or aggressive medical management in the field are often the only options available for immediate DCI management.

High Pressure Nervous Syndrome

Sheck experienced HPNS on his August 1993, 863 ffw/265 mfw dive in Bushmansgat, SA. It occurred below 700-750 ffw/215-230 m. Descending at greater than 100 fpm/30 mpm, he first experienced visual disturbances at or just below 700 ft/215 m. His entire field of vision became a series of small concentric circles with black dots in their centers. Distant vision deteriorated, and objects began to blur. He slowed his descent and paused at 750 ft/230 m in the hope of relieving the problem. Around 800 ffw/245 m he experienced itching all over his body that soon became a stinging sensation (Inert gas counter diffusion?). Tremors ensued and increased in intensity until he reached the bottom at 863 ffw/265 m. According to Sheck, ”the tremors were quite intense by the time I reached the bottom, severe enough to make operation of my inflator difficult. Essentially, the bottom stopped the descent. My entire body began trembling, gradually escalating to uncontrollable shaking by the time I landed.” On ascent, all of his symptoms disappeared by the time he reached 400 ffw/123 m.

Sheck Exley with Bowden after making a 400 ft/123 m dive on air to loosen up his tissues (on Dr. Bill Hamilton’s advise) the day before his big mix dive.

Interestingly enough, Sheck did not experience HPNS during any of his dives in Mante, all of which were in excess of 500 ft/153 m (see chart below). His descent rate was slower than the 100 fpm/30 mpm rate in Bushmansgat due to the current, but still very fast compared to commercial protocol. He mentioned no problems with his 721 ffw dive in Zacatón in which his rate of descent was greater than 100 fpm. I dove with him that day, and I am sure he would have mentioned it. We were planning our future dive to the bottom of Zacatón, and we discussed every aspect of our plans and concerns. Sheck called it “addressing our fears.” Very appropriate and necessary on dives of this magnitude.

Zacatón revealed

Nuno Gomes reported on all his dives to 581 ft/178 m and on his recent dive to 925+ ft./284m. Nuno has made at least two other dives in excess of 500 ft, one to 754 ft/231 m and the other to 826 ft/253 m. I have no information revealing that he experienced HPNS on those dives. On his deepest dive he experienced tremors beginning at 600 ft/184 m but felt comfortable continuing his dive. “I had felt this before; therefore, I was not alarmed,” Nuno said.

Gilberto Menezes de Oliveira, diving Agua Milagrosa in Brazil, experienced slight trembling in his left arm which he presumed was HPNS. It occurred as he approached 500 ffw/153 m. He later made another dive to 592 ffw/182 m m the same system and did not experience HPNS.

Out of dives to 504, 648, 744, 800+ and 925 feet, I have experienced what I perceived to be HPNS on only one dive. On the dive to 800+ ffw/245 m I experienced tremors in my latissimus dorsi and my arms. It was noticeable but not serious enough to abort the dive. It occurred around 700 ft/215 m. I had been ill with the flu just prior to the dive. Other deep colleagues, Dr. Ann Kristovich, Terrence Tysall, and Mike Zee have not mentioned any problems with HPNS.

HPNS can occur as it pleases. Immunity one day does not insure that it will not occur on a subsequent dive. In some cases it can be mild enough to be tolerated. On brief technical dives, perhaps the worst effects of HPNS—nausea, vertigo, and convulsive jerking—would not take place. Without the saturation habitat environment used by commercial divers, the occurrence of these types of symptoms would probably be fatal. 

The whole concept of diving for records carries emotional responses that often confound and confuse the explorer/adventurer. The desire to excel in some way is a powerful drive that has existed since the beginning of civilization. Usually a solitary and driven individual, divers who find themselves suddenly thrust into their 15 minutes of fame, also find themselves both respected and vilified. Not only in diving to extreme depths but in almost all extreme sports the accomplishment of the task carries the burden of attention, both positive and negative. Divers who are kindly labeled pioneers, and brave adventurers are also labelled  thrill seekers, insecure individuals seeking attention, and just plain crazy.

Kristovich and Bowden preparing to dive

The situation is further confused by the public desire for a champion. I think  this is more of a European thing than here in the states. Competition becomes a factor. Accomplishments are often segmented to allow for champions in methods and degree of risk: a different, more difficult route climbed, a breath-hold dive made without assistance, or with assistance either on descent or ascent or freestyle. The media stokes the fire with the promise of a future story. In 1993, it was a simple catalogue of divers who made dives to deeper depths. Now there is talk of having different categories. 

My dialogue with divers throughout the world in researching this article revealed proposals that range from some degree of practicality to the absurd. Suggestions have come from the European community about categorizing records by scuba or surface supplied, requirements that all decompression gases be carried by the diver, the diver must have no help from the surface, extra tanks can be available but the diver cannot use them (I presume you could in an emergency). Other styles would allow surface support, deco gases hanging on a line, habitat use, heating, and so on. There is no “official” delineation but there is a trend in that direction. Perhaps this is inevitable. Already there are claims based on experts assessing the depth reached by the severity of HPNS symptoms. Give me a break. 

Nuno had HPNS on his shallowest sub-500 ft/153 m dive, look what he has done since. I had HPNS on my 800+ ft/245 m dive, but no noticeable symptoms on my dive 125+ ft/37 m deeper. When there’s talk about depths of 500 ft/153 m and greater, there is a difficulty of accurately recording the depth with existing technology. Already there have been mathematical calculations based on environmentally difficult premises. Sheck was never happy with the need to calculate his record depth at Mante. Allowing for errors, he estimated the depth of his dive between 867 ft to 880 ft/266-270m. Ever modest, he personally chose the lesser number. He wrote that his 863 ft/265 m dive in Bushmansgat was just four feet shy of his record. Those of us who admired him chose the latter.

Dr. Kristovich, out of respect and admiration for M. E. Eckhoff [Sheck’s widow], stated that she would not claim the woman ‘s record unless it was decisive. At 554 ft/170 m, her dive surpassed the record by 154 ft/47 m, but if it had been less than 100 ft greater/30 m, she wouldn’t have claimed it. I believe her. So the whole vague, confusing  and admirable issue of personal ethics clouds the question as well.

These were gear intensive dives

The depth of my dive was determined by the UWATEC computer I sent to the media representatives waiting for me to finish my greater than ten hours of decompression. Concerned and desperate to arrest my descent because of inadequate gas volumes to continue the dive, the 925 ft/283 m marker on the descent line passed through my hand. Where did I stop? Who knows? I was desperate to get out of there. The writer from Sports Illustrated and Discover Magazine chose my depth for me from the read out on the UWATEC, 925 ft/283 m. At the time, I was shocked and grief stricken over the loss of Sheck. It was hardly a time for rejoicing. For the next year both the criticism and the loss of my friend did not allow me to accept the fact that I had made a ”record” dive.

Nuno is the man of the time in my opinion. I will not concede that he went deeper, but if he had not bottomed out Bushmansgat, then he would have been the first man to make a sub-300 m dive. Nuno and I both have done more sub-500 ft dives than anyone else in the world. As fortune would have it, we are tied in that number. Fate is fickle and a tie carries about as much excitement as kissing your sister. The public and the media cry for a decisive champion. If succumbed to, then that pressure can kill you. I hope that we are both too smart for that.

Unfortunately, some of us will die in pursuit of great depth. The continued efforts in the face of danger is unanswerable to anyone but the participants. I do believe that every man and the one woman here would agree that the intense freedom of the now, a moment that is unique and life enhancing and the pushing oneself in order to find oneself is, indeed, a reaffirmation of life.

My colleagues, I salute you. We are brothers and sisters of a kind. A bond of having been in the belly of the beast. No one can understand who hasn’t been there.

Return to the main story: Diving Beyond 250 Meters


Diving Into The Famous Ressel Cave

Belgium service member, cave explorer and tech instructor Kurt Storms takes us for a dive into the Ressel cave system located in Lot. Get out your reels.




By Kurt Storms. Photos courtesy of K. Storms unless noted.

The Lot and The Dordogne areas of France have an abundance of beautiful caves suitable for all levels of diving expertise, situated in glorious rural locations. Sites are mostly found on three rivers: The Dordogne, The Lot, and Célé. The Lot area lies in the northern extremity of the Midi-Pyrenees region, which stretches from the confines of the Dordogne Valley to the highest peaks of the Pyrenees, forming the heart of South-West France. Cave divers from all over the world return to dive here year after year. With over 20,000 known caves, France is one of the premier cave diving areas in the world. One of the most interesting regions lies in the Southwest, around the rivers of Lot and Dordogne. Here you find a multitude of long and deep caves with mostly crystal clear and relatively warm water, offering superb diving conditions. The water temperature averages 14º C/57º F and the visibility normally varies between 5-30 m/15-100 ft.

Finally!!! We can go to the Lot again. The COVID conditions have thrown a spanner in the works. But because we are all now vaccinated, we can finally leave. This time, for a week of training and then a week of diving holiday with my wife Caroline Massie. Two students (Jo Croimans and Bram Van Gorp) are with me for the training. The next few days, they will be busy with skills and dry teaching. Theory has already been given in Belgium so that we can get the most out of our dives. 

Why the Lot?

The area in France is popular because most European divers take cave classes there so they don’t have to travel to Mexico or Florida. One of the most famous caves around here is Ressel. Ressel is located in the village of Marcilhac-sur-Célé, in the heart of the Lot. Most pictures you can see online show huge, dramatic  blocks of white rock, flat structures, and the shafts of this cave. The facilities are pleasant, we have a large parking area for our cars, and finally there is also a conveniently located building with a toilet. From the car park we have only to walk about 100 m/330 ft to get to the entry point on the River Celé where we can put all our equipment needed for our dive.

Ressel History

The Ressel was first dived in 1968, by two divers of the speleo club Auvergnat. Martin and Debras reached 150 m/492 ft. It was only in 1973 that the line was extended to 300 m/984 ft, with a maximum depth of 30 m/100 ft. In 1975, Fantoli and Touloumdoian reached Pit 4 and went to a depth of 45 m/147 ft. Further exploration continued over the years, especially by Jochem Hasemayer in the early 1980s, where at 1100 m/3609 ft into the system he planted his knife in the rock to which he attached his line. This knife is still there.

On August 12, 1990, Olivier Isler was the first to cross Sump 1. The total dive time back and forth was 10 h 35 min. End of Siphon 1 is at Lac Isler, and from there on you can continue to the next siphons. Ressel consists of 5 sumps, of which siphon 1 is the longest (1850 m/6070 ft) and the deepest (83 m/272 ft). From Pit 4 onwards, the deep section begins, which can only be done with trimix mixtures. In the following years, the further sumps were explored by gentlemen like Rick Stanton, Martin Farr, and Jason Mallison. In 1999, the end of Sump 5 was reached. The total length on the main line is 4415 m/14,485 ft.

Spectacular Views In The First Section

To be honest, the visibility is spectacular all around. More than 10 m/33 ft visibility, which was near zero before the start in the Celé River—quite a change. As soon as we got to the entrance, the water cleared like snow in the sun. The first thought that ever crossed my mind was: How on earth did they find this cave? How, with the visibility of the river, did anyone see a hole that is 6 m/20 ft below the surface on one side—which is frankly not that big. Enquiries with the locals revealed that when the cave is full of water, you can even see a geyser in the river! Another impressive detail. 

There is a rope that runs from the point where you get all the way into the cave, and it continues to the main line; you don’t need a primary reel here—it’s really easy to find the entrance, at 6 m/20 ft deep. Then there is a huge tunnel with white giant boulders, which is impressive.

The first dives were only up to the T (180 m/591 ft penetration), where the obligatory skills were practiced, so that later one can widen the comfort zone. This is also a very beautiful part, especially because of the large blocks that lie here. There are even two exceptional phenomena visible; these are two blocks consisting of white limestone, with a large black spot in it. You won’t find these black spots anywhere else. It is wonderful to be able to admire nature like this.

My wife, the students, and I got in, and on the first dive, with a sidemount set consisting of 2×80 cf (dual 11 ltr) tanks, we did the first T, taking the left corridor. On the next T, we continued toward the shaft to a maximum depth of 30 m/98 ft to take a look. It is so impressive! We felt like we were going to the abyss, and actually we were, to the abyss below ground and underwater. But now they were even more curious about the famous Pit 4 of the Ressel.

To be able to do this dive, we had to bring the right amount of gases. The first dive was with Jo Croimans, my student; he had his sidemount configuration with an extra 7 ltr along, I dived with my Divesoft Liberty SM rebreather. There we went, all prepared. The way there is about a 28 minute dive. On the way, I showed Jo the shunt that goes to the deeper part of the first loop. Enjoying the ride, we continued until we reached the point of the shaft. 

Here I asked Jo if everything was Okay, he indicated that it was, and we descended to a depth of about 40 m/131 ft. I could see in Jo’s eyes that he was enjoying himself. But we didn’t have much time to enjoy ourselves, because we had to go back again. If you have deco, you can do it all on the way back on a nitrox 50 (NX50). For the advanced divers, you can take your oxygen at 6 m/20 ft and finish any decompression on O2.

It’s actually a great dive, and the cave allows for a variety of dives, just by choosing different depths in the tunnels, to have different perspectives.

Once we got to the top, Jo couldn’t stop exclaiming about the amazing beauty of this cave, and especially Pit 4. This made Caroline want to go and have a look too. This dive was done a few days later, when both gentlemen had gone home. This time we did the dive by scooter, a big difference. In 13 minutes we were at the shaft, and again I saw a happy face. How nice it is as an instructor to be able to pass on your passion. This is what we do it for. Ressel is one of the most beautiful caves in Europe. It remains an easy, accessible system.

The Ressel is and will always remain a special cave. Last year, I did the deep loop (1160 m/3806 ft long, 73 m/240 ft depth) here with two friends. And I still enjoy it when I talk about it. We still have to come back to do the rest of S1.

Additional Resources:

X-Ray: Pushing the Ressel—A Cave Diving Expedition in Lot, France by Erik Wouters (2013)

YouTube: Cave diving in France: Emergence du Ressel (2016)

Facebook: Here is a cave exploration project also going on nearby in Lot, France https://m.facebook.com/thehiddenriverproject. Find their map: here. 

Kurt Storms is a member of the Belgium military, and is an underwater cave explorer and active technical/cave/rebreather diving instructor for IANTD. He started his diving career in Egypt when he was on vacation, and the passion never ended. Kurt is also founder and CEO of Descent Technical Diving.  He’s diving on several CCRs such as AP, SF2, Divesoft Liberty SM.

Kurt is also one of the pushdivers that is documenting a new slate mine in Belgium (Laplet). This project was news on Belgium Nationale TV. Most of his dives are mine and cave dives.  In his own personal diving, Kurt’s true passions are deep extended-range cave dives. His wife (Caroline) is also a passionate cave diver. In his free time he explores Belgium’s slatemines. When he is not exploring, he takes his camera with him, to document the dives.

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