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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.

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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.

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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

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Karen van den Oever Continues to Push the Depth at Bushmansgat: Her New Record—246m

Karen van den Oever recently broke her own world cave diving depth record by a little more than 10m/33 ft at Bushmansgat cave in South Africa. The S.African cave diver conducted the 8 hour 14 min high-altitude dive on open circuit scuba, breathing trimix 4/90 bottom mix, and suffered mild High Pressure Nervous Syndrome (HPNS). Here former world depth record holder, Nuno Gomes who was van den Oever’s cave instructor, offers the details of her record setting dive along with a short history of the women’s depth records.




By Nuno Gomes. Images courtesy of Karen van den Ever.

Karen van den Oever and her husband Francois Bain

Karen van den Oever, from Johannesburg, South Africa, has dived to a depth of 246.65 m/809 ft. This is equivalent to a dive to a depth of 296 m/971 ft when corrected for an altitude of 1550 m/5,085 ft above sea level. The dive was conducted on October 27, 2022, in Bushmansgat cave, South Africa, and is a new women’s world record cave dive. Karen bettered her own previous world record to a depth of 236.04m/770 ft  (283 m/924 ft correcting for altitude), also accomplished at Bushmansgat cave in 2021.

I actually felt really good after the dive, a little tired but overall, quite good. I felt much better after this dive than the previous one. I’m happy that the dive went well, just thinking about what comes next. I have no definite plans going forward, we are looking into diving some of the caves in Namibia and also exploring some of the caves not yet dived in Zambia but no concrete plans yet.”—Karen van den Oever

Karen and Theo van Eeden, with the signed tag.

Women have been making record deep dives for quite some time. Back in 1981, one of the first deep diving records was made by Sheck Exley’s wife, Mary Ellen Eckhoff (USA). She used a dive propulsion vehicle (DPV) to travel into Wakulla Springs cave, as well as staged tanks for decompression purposes. Mary Ellen dived on open circuit, together with Paul DeLoach and John Zumrick, and they reached a distance of 363 m/1192 ft and a depth of 80 m/260 ft, which was a major dive at the time.

In 1996, Dr. Ann Kristovich (USA), a friend of Jim Bowden, considerably extended the record, reaching a depth of 167 m/548 ft on open circuit at Zacaton cave, Mexico. Ann’s world record dive would remain in place for a long time.

It was not until the year 2000 that another woman, Claudia Serpierri (Italy), would beat the previous record, but this time in the sea (Mediterranean Sea). Claudia would reach a depth of 211 m/692 ft on open circuit, diving from a support ship. This dive remains the deepest sea dive by a woman to date.

Toward the end of 2001, Verna van Schaik (South Africa), was ready to challenge the women’s record. First, she did her deepest dive by reaching a depth of  186 m/610 ft  (223 m/732 ft correcting for altitude), on open circuit, at Bushmansgat cave in South Africa. This was not enough for her, and during her next expedition on October 25, 2004, Verna would go back to Bushmansgat cave to become the first South African woman to get her name in the Guinness Book of World Records by reaching a depth of  221 m/725 ft  (265 m/870 ft altitude corrected), on open circuit. Her deep support diver was the late Dave Shaw (Australia), on closed circuit, who died of respiratory insufficiency at a sub-250 m dive at Bushmansgat in 2005.

View of the surface pool of Boesmansgat cave.

Following Verna van Schaik’s dive at Bushmansgat cave, two women divers died trying to break her record, as follows: 

In May 2010, French diver Brigitte Lenoir, died in Dahab, Egypt during a dive in the Red Sea. The accident took place at 147 m/482 ft while ascending from a 200 m/656 ft, on closed circuit. Her body was recovered with an ROV. 

In September 2017, Bulgarian technical diving instructor trainer, Teodora Balabanova, died attempting a dive to 231 m/754 ft, on open circuit, while her husband, Mihail Balabanov, suffered from decompression sickness. 

Karen van den Oever is a science graduate from the University of Witwatersrand in Johannesburg, South Africa, where she currently resides. Like Verna van Schaik, who now resides in New Zealand, she is a CMAS diving instructor, and also a former member of the University of the Witwatersrand Underwater Club. 

Her original cave, trimix and blending training was with me. I also trained her husband Francois Bain. 

Unstoppable Karen van den Oever

Karen had previously dived to 201 m/660 ft (241 m/792 ft altitude corrected) on open circuit in Bushmansgat cave in South Africa’s Northern Cape province on February 27, 2020. That dive’s total dive time was 7 hours and 21 minutes. On March 26, 2021, Karen dove to 236.04 m/770 ft (283 m/924 ft), on open circuit, at Bushmansgat cave, using a bottom gas of trimix 6/85. The total dive time was 7 hours and 18 minutes. That dive is the current deep diving Guinness World Record (women).

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Karen’s new world record dive, done on October 27, 2022, was made to a depth of 246.65 m/809 ft (296 m/971 ft), in Bushmansgat cave. The dive was done on open circuit, using a bottom gas of trimix 4/90, and with a total dive time of 8 hours and 14 minutes. The dive would not have been possible without a large team of support divers. 

Karen’s dive computer. Actual depth from rope measurements by independent witnesses was 246.56m/809 ft.

Peter Reid was at 209 m/686 ft (251 m/823 ft); this was his personal deepest dive on closed circuit, and his total dive time was 6 hours and 20 minutes. Don Hauman did deep support at 110 m/361 ft (132 m/433 ft). Her husband Francois provided shallow support and surface support, together with the other team members.

Karen’s support team.

Karen’s Total Narcotic Depth (TND) was 48.06 m/158 ft; the Equivalent Narcotic Depth (END) considering nitrogen only was 9.49 m/31.14 ft, and her maximum Partial Pressure of Oxygen (PO2) was 1.03 Atm. Gradient factors: 40/75.

There were no serious incidents during the dive except that Karen suffered some mild High Pressure Nervous Syndrome (HPNS), which ultimately did not prevent her from going any deeper. Karen had some difficulties recovering the evidence tag from her maximum depth because of the tremors that she was experiencing as a result of the HPNS, but in the end she turned the dive mainly because she ran out of bottom time. 

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Dive Deeper

InDEPTH: South African Cave Diver Karen van den Oever Sets New Women’s Deep Cave Diving Record

InDEPTH: Diving Beyond 250 Meters: The Deepest Cave Dives Today Compared to the Nineties

InDEPTH: Extending The Envelope Revisited: The 30 Deepest Tech Shipwreck Dives

InDEPTH: Opinion: Don’t Break That Record

InDEPTH: Fact or Fiction? Revisiting Guinness World Record Deepest Scuba Dive

Nuno Gomes is a professional civil engineer, a CMAS technical diving instructor and a commercial diver. He was born in Lisbon, but his family relocated to South Africa during his youth. He now lives permanently in New York with his family. He has dived all over the world.

He used SCUBA (open circuit) to dive to a depth of 321.81 meters (1,056 feet), inclusive of rope stretch, in the Red Sea off the coast of Egypt near Dahab, in June 2005. The total dive time was 12 hours and 20 minutes. The descent took 14 minutes with two minutes spent at the bottom.

He also used SCUBA (open circuit) to dive to 282.6 meters (927 feet) in the Bushmansgat cave, in South Africa, in 1996. The cave is located at an altitude of 1,550 meters (5,086 feet) above sea level, which resulted in a decompression schedule for an equivalent sea level dive to a depth of 339 meters (1,112 feet) in order to prevent decompression sickness. The total dive time was 12 hours and 15 minutes with four minutes spent at the bottom of the cave.

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