One Quarter of a Kilometer Down at Bushmansgat

It is well-known that Bushmansgat, in the Cape Province of South Africa (1600 meters - 5240 feet - above sea level), is one of the deepest water-filled caves in the world and that at 284 meters of fresh water (865 feet) it is at least the third deepest water-filled cave in the world.

According to the late Sheck Exley, this cave is the largest water-filled cave in the world with an estimated water volume of 4.5 million cubic meters (156.2 million cubic feet), almost four times larger than the next largest known water-filled cave, Dean's Blue Hole in the Bahamas, USA.

• How much deeper does this cave get?
• How much bigger does it become?

A team of divers set out to try and answer these questions. They had ten days (from September 24 to October 3, 1994) to come up with some answers. The team of divers consisted of Nuno Gomes, Craig Kahn, Craig Newham, Liz Gomes, Verna van Schaik and the newcomer to the team, Paul Pretorius.

Before any serious diving could take place, it was first necessary to carry out build up dives. These dives included the retrieval of the old decompression line which needed to be taken out and put back into place since the planned decompression stops were changed from the previous expedition. It had been decided to have the decompression stops at 10 meter intervals at depths greater than 100 meters, at 5 meter intervals at depths between 100 meters and 20 meters and at intervals of 3 meters from 18 meters to the surface. Once this task was completed it was time to start using the submersible sonar. The unit consisted of a Hummingbird Wide Vision with 300 meters range (100 feet) and a narrow beam transducer housed in a 100 meter (330 feet) waterproof case. This apparatus was called the "GIZMO" for short.

In order to get any meaningful readings it was necessary to do dives in excess of 60 meters (200 feet). We decided to do dives in the 75 meter (250 feet) bracket. The highest reading which I measured was 296 meters (970 feet) which was somewhat higher than Craig Newham's reading of 285 meters (935 feet). These readings were obtained by swimming horizontally at a certain depth, pointing the sonar down and adding the reading to the present depth. These readings are not final in any way and the cave could be still deeper.

The next part of the expedition included solo deep dives to a planned depth of 260 meters (853 feet) by the author supported by the other team members. Craig Newham would be the deep support at 110 meters (361 feet) followed by Craig Kahn at 60 meters (200 feet) and Paul; Liz and Verna would support at shallower depths.

Before the dive could take place it was necessary to place diving cylinders at various depths, with different gas mixtures, for the purpose of decompression, on the 130 meter (426 feet) marked decompression line. Twelve cylinders in total would have to be placed on the deco line; this excluded the oxygen which was surface-supplied from two 50-liter storage tanks. Although the first decompression stop was at 130 meters, the first cylinder would be placed at 120 meters (394 feet). In order to place this deco cylinder at 120 meters, Craig Kahn and myself had to do a special dive. The cylinder at 90 meters (295 feet) was put in place by Craig Newham and Paul Pretorius, Verna van Schaik and Liz Gomes followed to a depth of 50 meters (164 feet) as backup.

The following day I did no diving. It was during my day off that Debbie van Zyl, the teacher (wife of Andries van Zyl, the owner of the farm) and the children from the local school paid us a visit at Bushmansgat to find out more about cave diving as well as the geology of this Karst type structure. The children (about 40 of them) and teacher alike were full of questions and kept me busy for well over an hour. The rest of the day was fairly peaceful and my tissues were given the opportunity to rid themselves of inert gas.

With the next day came the opportunity to dive and finally put the plan to the test as well as the theories which had been postulated. Final preparations for the dive started at 8:00 a.m. on September 30; the dive, however, would only begin at 10:16 a.m. It takes a long time to get kitted up for a dive such as this. One item that was missing was the p-valve, which unfortunately only arrived in South Africa one week after the dive, compliments of Alan Riggs from the USA. It will be used the next time, even through the nappies which were used were very effective.

10:16 arrived and so did the point of no return; it was time to go and test my metal against the black depths of Bushmansgat. The dive started using air as the breathing medium. After getting through the crack and once at 36 meters (118 feet) some lead, which had helped me get this far, was removed and placed on the descent line. The Poseidon dry suit and Arctic undergarment had created a lot of buoyancy which for the most part was lost at depth. At 70 meters (230 feet), 3 minutes into the dive, it was time to switch to my first Trimix mixture (travel mix) which would take me to 152 meters (500 feet); the old Poseidon Cyclone 300 was still going strong (it had done it before when I did a dive to 153 meters in March 1993). At 8 minutes into the dive I changed to the bottom Trimix mixture and thus to the Cyclone 500 (the plan was to go to 260 meters (853 feet). At this stage High Pressure Nervous Syndrome (HPNS) was not obvious. It was at this depth that I lost one of my Pelican Mightylights which I chased for a long time, passing 177 meters (581 feet), which I had done in September 1993 when Sheck Exley was at this cave, down to 200 meters (722 feet). Upon reaching this depth, my previous deepest (February 1994), I decided to slow down as this was new territory, one had to be on the alert, anything could go wrong - equipment and myself - thinking that I would get the Mightylite at the bottom.

From this point onwards the contents gauge of the main gas supply (2x18 liter Cressi cylinders or 280 cubic feet) was watched very frequently for the critical pressure or turn around pressure (in this case 120 Bar or 1700 psi). The bottom time was now 12 minutes. I looked at the gauge and it read 110 Bar and in a moment of stupidity I decided to try to reach the bottom. At 825 feet (251.4 meters) and only 9 meters (30 feet) from the bottom, at the shallowest part of this cave system, sense prevailed and I stopped descending (at this depth one used 650 liters of free air per minute). I looked back towards the black bottom and tried to spot Sheck's diving tank which he had lost at this cave in September 1993. I could not see it. Maybe it was just as well (it could have resulted in a fatal mistake being committed had I seen it). Both my computers now showed 14 minutes and so did my Casio DW6300 Frogman. The Parkway Legend Computer showed a depth of 825 feet (251.4 meters), while the UWATEC Aladin Pro Computer showed a depth of 815 feet (248.5 meters) or an average depth of 820 feet (250 meters).

The planned turn around time (bottom time) of 14 minutes had been reached; the gas supply was below the critical pressure. I paused for a moment, took a look towards the bottom once again, using the 4 Sabrelites mounted on my helmet, and started filling my Diverite Wings. While this took place I became aware of HPNS in the form of Helium tremors (nothing to be alarmed about). After a while I had enough lift to ascend. The ascent went without problems; when I reached my first stop at 130 meters (426 feet) the SPG showed 40 Bar (588 psi). I had cut it very fine.

From this depth I could see Craig Newham at 100 meters (328 feet). When I got to 100 meters (361 feet) he was there. He asked me if I was OK, had a look at my computers and after a little while left to do his own deco stops.

When I reached the 60 meter (197 feet) deco stop, 46 minutes into the dive, I was greeted by Craig Kahn, who asked me if I was OK and then started taking photos. He took a number of photos, stayed with me for quite a long time, supplied me with air to flush my drysuit of Trimix and then had to leave to carry out a lengthy decompression of his own.

At 30 meters, 86 minutes into the dive it was Paul and Liz's turn to keep me company and look after my welfare. It was at this depth, after switching to Nitrox 35, that I became aware of tinnitus. Thinking that I could be experiencing oxygen toxicity, I switched back to air for a while until the symptoms seemed to improve. Then I switched back to Nitrox 35. Paul, Liz and Verna followed and monitored my progress up the decompression line and through the different mixtures for a long time until I went onto pure oxygen at 6 meters (18 feet) and 277 minutes into the dive. During their stay they took turns in supplying me with hot Sustagen energy drinks from a plastic bottle and with chemical heat packs which were placed on the inside of the hood of my dry suit (the water temperature is 19degrees C or 66 degrees F at Bushmansgat).

The 6 meter (18 feet) stop on pure oxygen was nearly 1.5 hours. During this time I was supplied with more Sustagen and heat packs and was asked many questions by means of using their slates. Eventually it was time to move to the next stop, 3 meters above, very, very slowly.

Craig Kahn took over the vigil as well as the supply of hot Sustagen and heat packs at 3 meters (10 feet) for the remainder of the dive. The last 2.5 hours of the decompression were carried out for the most part at night. Entertainment was found in the form of following the trajectories of the frogs in the pond with a torch. Finally, it was time to surface very slowly. It was 7:37, the dive had lasted 9 hours and 21 minutes. I had used 31,278 liters of 7 different gas mixtures (thanks to Air Liquid). This was equivalent to 16 10-liter cylinders charged to 200 Bar, assuming one would use them until they were totally empty.

Upon surfacing, I became aware that my hearing was far from right. It felt as though someone had placed 2 tin cans over my ears. Apart from that I felt very well, much better than I had felt after my 220 meter (722 feet) dive earlier this year.

Realizing that I was suffering decompression sickness, I went onto pure oxygen straight away for 3 hours. During this period I had tested negative for all other symptoms of DCS, type I and type II. At the end of this period my hearing had improved slightly; on the other hand, my Oxygen Tolerance Units or OTUs were well in excess on 1,000 (the recommended maximum is 650 OTUs). It was close to 1:00 a.m. and time to rest for a while. I had earned a short sleep.

Early the next morning I left for the chamber for treatment with Craig Newham, breathing oxygen all the way to Johannesburg. The other members of the team finished the diving which had to be done and packed up camp. That evening, thanks to Doctor Franz Cronge, I was in the Institute for Aviation Medicine's chamber in Pretoria. The oxygen treatment, performed in the chamber, was to last a week. Audiograms were performed after each spell in the chamber, which confirmed the success of the treatment (3 weeks after the dive I had regained a subjective 95% of my hearing back), nothing short of a miracle.

The diving expedition would not have been possible without the assistance of the following people and companies:

1. The divers in the team, Craig Kahn, Craig Newham, Liz Gomes, Verna van Schaik and last but not least, Paul Pretorius.
2. Dr. Franz Cronje, Sergeant Major Alan Pletschke and Sergeant Lowuis Bewsher as well as all the other staff of the Institute for Aviation Medicine in Pretoria who were willing to help with my Hyperbaric Treatment.
3. Wilber Ellis - The donation of a wide vision Hummingbird sonar and transducer.
4. Aquas Divers International & Poseidon Sweden - Donation of a dry suit and a Triton regulator.
5. Air Liquid S.A. - The donation of 5 helium and 4 oxygen cylinders.
6. Clive Nicol - The construction of special instruments needed for the dive.
7. Divetek - The donation of a UWATEC Aladin Pro dive computer.
8. Deeken Services - The donation of 4 Pelican diving torches.
9. National Panasonic - The donation of 480 torch cells.
10. Larry Holding - Development of a decompression program based on the Buhlman algorhythm "TRICOMP."
11. University of Witwatersrand Underwater Club - Loan of a compressor and diving equipment.
12. Cave Diving Club of Southern Africa - Loan of 200 meters of high pressure hose.
13. Casio - The use of previously donated diving watches.
14. Ian Riphagen - Loan of his Toyota Hilux 4x4. Ian has been part of this diving team since 1988 when I carried out a dive 123 meters (403 feet). Due to an unforseen accident outside of diving he was unable to be part of this trip. He will join the next one.