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Hi Errol, > A friend told me about Pyle's reports on the Bishop musuem's web site in > Hawaii, so I looked it up. Thanks for checking out our expedition web page. I was recently informed that it received record-high hits, so I guess it was fairly popular. Your message, forwarded to me by George Irvine, indicates to me that you have some misconcenptions about closed-circuit rebreathers, and what advnatages they have. Allow me to clarify on some of the innaccuracies: > In reviewing Pyle's dive of May 14, 1997 (today) I saw that he had a > failure on both his and his buddie's unit today! Actually, neither "units" failed at all - only their pilots did. In facat, only I failed - John made no mistake whatsoever. > Pyle's buddy arrived at 220 feet and informed Pyle that he was severly > narced. The Nitrogen was mixing too high as part of the dilutent. That's what we thought the source of the problem was too. However, after we analyzed his gas mixture, it became evident that the nitrogen partial pressure in his breathing gas could not have been more than what he would have experienced while breathing air at a depth of 140 feet; and in fact, was probably much less. We never could figure out what caused his perceived narcosis. He might have inadvertently had the diluent selected to the air supply instead of the trimix supply; but when you consider that he has been diving since 1957, has made several thousand dives to depths in excess of 200 feet, and has nearly 200 hours of dive time logged on that rebreather, I find this explanation extraordinarily unlikely. > Upon informing Pyle of > this, he left Pyle, Pyle continued the dive, dropped to 305 and entered > a small cave by himself for a few minutes. And this is precisely what our contingency plan was if either one of us felt uncomfortable with the dive. Our protocol is to do these dives in the only way I feel they can be done within adequate margins of safety: as solo dives, regardless of whether or not we happen to be in the water at the same time. > Upon exiting the cave he found it very hard to breathe, tried hard to > inhale but could not. Thus he was alone at 305 and had to bail out, all > the while his video camera caught the action > on tape. This is all correct. The video recorded the entire dive, including the bailout and subsequent recovery (and intervening sequence of catching fish). The housing I was using for the video had a reputation for being unreliable at depth, so I diconnected the controls, started the recording on the boat, and just let the thing run non-stop for the entire 64 minute duration of the tape. > Thus, he ascended to 220 where he left the rebreather trimix > bailout bottle This is not correct. The bailout trimix supply was with me at 300 feet. I chose to breathe from this supply for a variety of reasons, but I also had about 50 cubit feet of trimix attached to the rebreather. I used about 14 cubic feet out of the bailout supply returning to the nitrox cylinder at 120 feet, and that includes stopping at about 200 feet to film John collect fishes (incidentally, that footage was used on the local ABC affiliate last night, so it was worth the effort, what little effort it required). > at 100 feet, he realized he forgot to put a cap on his > CO2 scrubber, and had his buddy replace it. This is correct. > He then says, although his breathing loop was totally flooded, he flushed > it out, went back to closed circuit, and is planning to use the same > scrubber material tommorrow without even repacking. This is also correct. I did use the same canister of Lithium Hydroxide for the remainder of that dive, and again for the next dive, without repacking. Why would I need to repack? I had used only two and a half hours of a canister that is CONSERVATIVELY good for 12 hours, and for my physiology, appears to be good for more like twenty hours? We had, of course, intentionally flooded the breathing loop and recovered it in shallow water for training purposes, but nonetheless it was comforting to ascertain how easy it is to recover the loop in a real-world bailout situation. I don't know of any other rebreather that has this capability. > In reading all of Pyle's info, I wonder why he is using a rebreather to > begin with. As this was one of his longest dive's with the unit, why > not simply use open circuit. This is an easy question to answer. The main reason is has to do with the cost of shipping large quantities of helium to Palau. I haven't worked out the totals yet, but I can tell you that we used about 2 to 3 cubic feet of helium per dive. Even with bottom times of only 20 minutes or less at 300 feet, I'm not aware of anyone who can make the same amount of helium last as long on open circuit. Another reason has to do with constant-PO2 decompression capability. You'd be amazed by how much shorter the deco is on these shorter-duration deep dives when the gas mixture is dynamic. Another reason is the vastly increased margin for error, which contributed to the incredibly easy bailout. > For these short bounce dives, open circuit can provide > plenty gas supply. If Pyle's answer is it helps get closer to fish, > Ok. It does help get closer to some kinds of fish, but for the most part, not the kinds of fish I am interested in. > If his reply is the deco savings, I say BS. Then go ahead and say "BS". > His runtime for a bounce to 305 for 17 minutes is a whopping 2 hours and > 27 minutes. Using open circuit trimix, with only 2 gas changes I > calculated a total run time of only 1 hour 40 minutes. And I suppose you ran the profile using all the waypoints of the dive profile as presented on the web, with slow ascents, deep stops, staying 20 feet below the ceiling, bouncing back to 75 feet for a while during the 10-foot ceiling, etc. If you ran my actual dive profile on your software, you might find yourself with slighly different results. > Moreover, his deco schedule seems very strange. Do you mean my actual profile, or do you mean the ceilings as calculated by the dive computer? If the former, remember we are working on a vertical wall and are still doing science while on the deco, so we go up and down quite a bit. If the latter, remember that I switched to OC for a portion of the dive, and that the portion of the dive when I was not in OC mode was calculated based on real-time PO2. > Next I wonder why someone > would continue a dive when his buddy has a problem, and leave his > buddy. Another easy one - we do these dives solo, whether or not we are in the water at the same time. In effect, we were not "buddies". > Why would you leave your bailout bottle in the ocean, 90 feet above you? I don't know - why would you? I did not - my primary bailout was on my back, and my staged bailout cylinder was about 10 feet from me at the time of the loop flood. > Even more suprisingly, Pyle goes into a cave by himself and Murphy is kind > enough to let him out before flooding the scrubber. I suppose I should have used the more proper term "cavern", but at this depth, I suppose it technically is a "cave" (what was it? 120 feet direct line to the surface?) Anyway, with a whopping 3-foot penetration into the cave, Murphy didn't have much more to work with inside the whatever-you-want-to-call-it-hole-in-the-reef as she did outside (we are talking about Murphy Brown, aka "10 cents per minute", aren't we?) > With these problems, I do not see how Dr. Stone can use the Cis-Lunar > to dive Wakulla. I can envision the W2 project now, 2 divers enter Sorry Errol, I don't mean to be rude, but this is a pretty funny concept. A number of Florida cave divers with strong political motives like to try to lump what I do together with what Bill Stone's plans are. Please understand that I would make a miserable diving companion for any Florida cave diver, just as most Florida cave divers (the out-spoken ones, anyway) would make miserable dive companions for me. > Isn't it time for everyone to Do it Right, or Not at All? Yes, I should think so. Aloha, Rich Richard Pyle Ichthyology, Bishop Museum 1525 Bernice St. Honolulu, HI 96817-0916 PH: (808) 848-4115 / FAX: (808) 841-8968 email: deepreef@bi*.bi*.ha*.or* "The views are those of the sender and not of Bishop Museum" -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send list subscription requests to `techdiver-request@aquanaut.com'.
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