« Diving safety | Main | Another trip: testing cameras and some bad news »
February 10, 2007
Some things you'd rather not know
Well, I finished a review of the late Sheck Exley's "Caverns Measureless to Man" and posted it on the site. I also informed the publisher at cavebooks.com and he was nice enough to send me a complimentary email and alert me to another must-read cave diving book, "The Darkness Beckons" by Martyn Farr. I ordered it and anticipate its arrival with great interest.
One of the things that puzzled me about Sheck Exley's story was that he never used a rebreather, or at least he never mentions one in "Caverns." Exley frequently commented on scuba bubbles dislodging debris from the cave ceiling, reducing visibility. Low viz is never pleasant, and can be life-threatening in a cave. So I wondered why Exley apparently never used a semi-closed circuit rebreather that generates far fewer bubbles, greatly reduces the amoung of gas required, provides warm and moist breathing gas, and has other benefits that reduce decompression time. I am aware that while rebreather technology has been around for well over a hundred years, they've only become commercially available (and feasible) relatively recently. However, semi-closed rebreathers had been used in cave diving as early as 1956 and 57 at the Wookey Hole Caves in Britain, and in the early 1980 they were employed in extensive and heavy-duty cave diving in France, Mexico and the US. So I began searching the web for examples where rebreathers were used in cave diving and exploration. And quickly found a stunning example.
Deepcave.com is the website of David Shaw, an Australian living in Hongkong. He was born in 1955, is a pilot and was introduced to diving by his son and was immediately hooked. They did some wreck diving, then Shaw completed a cave diving course in Florida at Cave Excursions in Live Oak, FL, and became engrossed in the thrill of it. As his explorations became more elaborate he decided to use rebreathers. He got an Inspiration unit, but soon found it couldn't handle the increasing depths he explored. So he switched to a US Navy-developed Mk15.5 and modified it for his purposes, replacing analog with digital electronics and so on. Like other cave diving enthusiasts, Shaw's primary interest was exploring what had never been explored before, but found that this took him to ever greater depths.
Shaw's site then has a section on "recent dives," those including two at Boesmansgat in South Africa in 2004. In June he went down to 718 feet. That dive is explained in a 14 page report with 30 color pictures and even a dive computer profile that is downloadable as a PDF file. Shaw described the preparations for the trip, the trip, his equipment, the modifications he had performed on it, and the dive itself in an easy, conversational style. The many pictures make the story come to life. Yes, sometimes a picture says a thousand words. Shaw describes how they found Sheck Exley's line from ten years before, 1994, during some preliminary dives. He describes how he used a program called Z-planner to compute various alternates with varying safety factors to be used with his two VR3 dive computers. He also described the setup of his rebreather that included two three liter tanks, one with air for his wing and the other with argon for his DUI dry suit. Then he had two three liter spheres, one with air and the other with oxygen -- good for a ten hour maximum. That's all he had on him. [see complete equipment list and modifications]
So then he goes on this deep dive, calmly wondering if all the equipment would stand up to the great depth. Nothing failed, however, but at about 700 feet, after a ten minute decent, Shaw experienced tunnel vision which he interpreted as the start of HPNS (High Pressure Nervous System) syndrome. He stopped and looked at the vast expanse of very clear water, commenting that breathing with his Mk15.5 rebreather was as easy as it was at 20 feet and marveled at the performance of the device. His VR3 computer then gave him all the decompression stops and he describes how he used all the tanks with different gas mixes. He also describes the technique on how to eat and drink which he did while using a reguator rather than his rebreather. He went into other practical aspects, like urinating through a valve in the drysuit. Total dive time with all the decompression stops was 517 minutes. Shaw mentioned the very low gas consumption -- barely more than a tenth of the gas used in a 1996 open-circuit scuba dive in the same location -- as one of the great advantages of the rebreather. Though this was a record depth drive with a rebreather, Shaw reported no fatigue. In fact, they did some dry cave exploring the next day, then a scooter dive at about 260 feet the day after that. Just a pleasant trip, no big deal.
Four months later, Dave Shaw returned to Boesmansgat for another world record dive (link to PDF). He explains how his digital electronics were filled with medical grade paraffin to prevent implosion at great depths. And how this time he used oxygen instead of air for the suit inflation tank, so as to have an oxygen backup. He hadn't been sure how deep bottom was and that made planning more difficult, and also presented the danger of either shooting past the line, or getting stuck in the muck if the line was too long. This time he used the dive computers just for bottom timing and carried his plans for various depths on slates. Why various plans? Because each second at a depth of over 900 feet means an extra 70 seconds of decompression.
Shaw encountered no problems whatsoever. He arrived at the bottom at 885 feet and it was nice and rocky. One of his VR3s failed but he began swimming around, saying "I was relaxed and could almost not believe where I was." Well, that was when he found a body, that of another diver by the name of Deon Dreyer, a 20-yeard-old who had died there 10 months before, on December 17, 1994. "There was no shock on my part, but rather a decision making process of what to do," goes Shaw. It was easy for him -- try to recover the body. Unfortunately, Deon's big doubles were stuck in the mud and Shaw could not dislodge him. So he did the next best thing, tie a line to the body so it could be found later. The ascent and decompression was uneventful and the whole dive lasted nine hours and 40 minutes. A body recovery was then planned for January of 1995.
So I move to the "Future Plans" section of Dave Shaw's website. There he explains the scheduled body recovery, what mixtures he'll use and how many tanks. Once again he'll have his four small on-board tanks, then a total of 19 bailout tanks in case the rebreather failed, with seven different gas mixes, with the bailouts starting to be used at 500 feet. He praises the Scubapro X650 second stage that "breathes brilliantly at great depth." He goes on to the support divers and their roles. The report completes with "More to come as I get time....." But no report.
Well, at least I had my answer. Apparently rebreathers are a workable solution for this sort of diving, one with many advantages. I contemplated that, studied the equipment list and modifications with great interest, and wondered whether Sheck Exley would eventually have started using rebreathers had he lived.
But now I wondered how the body recovery project had gone and I poked around some more and found the report at the Technical Diving Africa website. To my great dismay, not far into the page I found this statement: "This page is dedicated to David Shaw who in the attempt to retrieve Deon Dreyer lost his own life at Boesmansgat in Southern Africa."
That really hit me hard. This had seemed like such a success story. A man in his 50s calmly doing all this incredible diving, the use of the rebreathers, the total lack of any real problems. And now he apparently had died as well. What had happened?
Once again, the entire operation is described and illustrated in detail, the plan covering everything from "D-Day" minus 9 to D-day plus 2. Dave Shaw was to be the leader, doing the body recovery. Don Shirley, his backup, was going to 700+ feet in case Shaw needed help.
Then the description of the dive. Shaw goes down at 6AM, a Sony vidcam mounted on a helmet to record the recovery. Shirley follows 13 minutes later to meet him at 220 meters. Shirley sees Shaw's light, but no bubbles indicating purging during ascent and no movement. He prepares to go down, but his rebreather's Hammerhead controller implodes, likely the result of losing a bit of oil during a repair the night before. Now he's on manual rebreather control and there's no way he can go deeper. Other support divers meet Shirley 43 minutes after Shaw had begun his dive. "David not coming back," writes Shirly on a slate. Two and a half hours into the decompression Don Shirley starts feeling awful and fights for his life, feeling vertigo and throwing up -- the result of an expanding helium bubble in his inner ear. Yet, he makes it through an almost 13 hour decompression and is placed into a recompression chamber. He recovers, but it takes a long while.
Amazingly, both dead divers were recovered as well. And the Sony camera had worked, showing what had happened. Apparently the recovery had been more difficult than David Shaw expected as the body, instead of being skeletal after all those years, was in an unexpectedly buoyant condition. He is working harder than he should, building up CO2 and incurring increasing narcosis. He is alert enough to abort, but then his free-floating dive light, which he couldn't put around his neck due to the unusual vidcam helmet, gets snagged in the line tied to the dead diver. The now exhausted Shaw tries to untangle it, but can't. That was all it took.
To me, apart from being sad to find another inspiring story end in tragedy, it reaffirms a basic truth: anytime you make an exception for anything or anyone, things tend to get fouled up.
Unbelievably, you can see the entire last dive on YouTube here.
[Read detailed report of the fatal rescue mission]
Posted by conradb212 at February 10, 2007 11:08 PM
