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Post by luis on Mar 29, 2008 5:51:56 GMT -8
OBTW, a lot of the research comes from the space program.
Astronauts have to decompress to work in their space suits. The pressure inside the space suits is kept to a fraction of an atmosphere (with a high O2 content to sustain life). The lower pressure in the suits allows more flexibility of the suit. I think the absolute pressure in the suit is about 5 psi (about 1/3 atm), but I may be wrong.
Therefore, astronauts have to decompress into that lower ambient pressure at a rate that allows the out gassing of inert gas without causing DCS…just like a diver.
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Post by Deleted on Mar 29, 2008 6:45:52 GMT -8
Y'all have had a fascinating debate/conversation here.........which has reminded me of stuff I had forgotten or stuff I did not know. Luis, your aquired knowledge of the current thinking by researchers is to be admired........John (searat) your extensive experience in the past decades can not be ignored.........
I've been in and out of the water for 41 years, some of you are probably pushing 50 years of diving or more.......and we have survived all this increase in knowledge and continue to dive.....amazing!
All this info is great comfort to know that it is out there and someone uses it to our advantage, however, I feel I am more like Chuck.........a SPORT DIVER........vintage or modern double hose....does not matter........all this info just tell me.......not to worry.....follow your bubbles and your dive plan and don't stay down to long to deep. Stop at 10 or even 30 if it is in your dive plan.........and have fun........ Now.......what does all this have to do with a horse collar BC and Co2 cartridges?
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spectrum
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Post by spectrum on Mar 29, 2008 7:19:57 GMT -8
Interesting discussion. As mentioned some of this is semantics....
Is there an element of decompression in any dive? Sure there is.
Do all dives require a deliberate or inherent stop to ascend safely, surely not.
Can you get into some level of DCS on a shallow dive? There are certainly plenty of reports of "undeserved hits" and plenty of unreported incidents.
I have had 2 occasions early in my short time as a diver that are of interest. Both dives were in the 25-30 foot depth range. Neither was especially long in duration 25-40 minutes. We were thermally well protected, hydrated and in good health. On both dives there were several trips to the surface from near max depth and while not "out of control" they were much faster than I care for. In each case myself and my buddy that shared the profile found ourselves profoundly exhausted shortly after the dive. Lacking other telltale signs of concerns we napped it away which in hindsight may have not been the brightest move either. After some study I came to the conclusion that we probably suffered sub clinical DCS.
The take-away for me is that anytime we venture beyond 1 ATM there are effects on our body than must be managed. Fortunately most are controlled with nothing more than good diving practice. The effects may be transparent, but they are there.
Pete
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Post by SeaRat on Mar 29, 2008 14:03:31 GMT -8
Y'all have had a fascinating debate/conversation here.........which has reminded me of stuff I had forgotten or stuff I did not know. Luis, your aquired knowledge of the current thinking by researchers is to be admired........John (searat) your extensive experience in the past decades can not be ignored......... I've been in and out of the water for 41 years, some of you are probably pushing 50 years of diving or more.......and we have survived all this increase in knowledge and continue to dive.....amazing! All this info is great comfort to know that it is out there and someone uses it to our advantage, however, I feel I am more like Chuck.........a SPORT DIVER........vintage or modern double hose....does not matter........all this info just tell me.......not to worry.....follow your bubbles and your dive plan and don't stay down to long to deep. Stop at 10 or even 30 if it is in your dive plan.........and have fun........ Now.......what does all this have to do with a horse collar BC and Co2 cartridges? I like that comment, "...and we have survived all this increase in knowledge and continue to dive......amazing." Yes, actually it is. One of the reasons I dive shallow, and enjoy it a lot, is that there is a lot to see that no one looks for, especially in fresh water. I have seen the Umpqua northern pike minnow spawning, and have photographed this in about 15 feet of water: I have seen mussels spawning, again in about 10 feet of water, and last year presented these photos to a group of biologists who had never witnessed it: But I could have gone a different path. In 1973 I was part of the Warm Mineral Springs Underwater Archaeological Project, with Sonny Cockrell and Larry Murphy. A number of very well known cave divers were there, including Sheck Exley. I met Demetri Ribikoff too. But it was the cave divers that I had met in Florida, including Hal Watts, who were dominant in the Florida diving community. Many became famous, but their fame sometimes carried a very high price. Here's what happened to Sheck Exley: www.wired.com/wired/archive/3.11/divers_pr.htmlThis is why I wonder about the deep diving community, and their addiction to depth. What does this have to do with CO2 inflators on a vintage BC? Well, those are largely out of favor because they are not used by these deep divers. This is because these deep divers simply cannot afford to come to the surface. If they do, they will die, it is as simple as that. They do not have a recompression chamber standing by, like the Cousteau team did (probably still does). Their safety is totally dependent upon almost flawless diving technique, triple-redundant systems, and either propulsion vehicles or down-up type diving (not much horizontal swimming with all those bottles hanging off you). So CO2 inflators on a BC are considered a hazard, and they are not at all worried about surface rescue. To these divers, the surface is not their friend, but their enemy until they can get their required decompression completed. It is a different mindset, and one I'm not ready to endorse, even if I have dived with these people. John
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Post by luis on Mar 29, 2008 15:17:06 GMT -8
Now.......what does all this have to do with a horse collar BC and Co2 cartridges? In post number 25 I wrote this: "The original reason I brought this up was because an uncontrolled rate of ascend with any BC (with a CO2 cartridge or not) is not a good thing. Even if you don’t have a deco stop obligation and you avoid any barotraumas to your lungs, you may still be violating the maximum recommended rate of ascend and/or any safety stop (either can get you into trouble). Granted, DCS can be treated…drowning can not. This is just something to keep in mind."
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Post by Deleted on Mar 29, 2008 16:39:01 GMT -8
Now.......what does all this have to do with a horse collar BC and Co2 cartridges? In post number 25 I wrote this: "The original reason I brought this up was because an uncontrolled rate of ascend with any BC (with a CO2 cartridge or not) is not a good thing. Even if you don’t have a deco stop obligation and you avoid any barotraumas to your lungs, you may still be violating the maximum recommended rate of ascend and/or any safety stop (either can get you into trouble). Granted, DCS can be treated…drowning can not. This is just something to keep in mind." Luis, I agree with your statement. There have been many times in my early diving days when my little Maywest vest that I used sometimes to adjust bouancy propelled me to the surface the last 10 or so feet much faster than I wanted.......a couple of times I remember laying on my back face up, spreadeagled to slow my accent...... Happened a couple of times also with my Seatec horse collar.... Just can not dump any air with a Maywest quickly and the horsecollar did not have a over pressure dump either......my old Zeagle wings bc does and so does my new Reef Rider........ I am like John for diving now days..............shallow is prefered....there is more color and more abundant life in the shallows........plus you get to stay longer.......... Thoses wrecks I dove on in Brasil were in 30 feet or so......only issue was the tidal surge as these wrecks were 300 yards from shore.........but the marine life was abundant........as I stated.......I'm a sport diver, not a techie, not commercial or some ricky recon guy..........I dive for sport as a lot of folks do. Going to 60 or 70 is more than enough and not normally that deep.....nothing much past that but a few big fish, wrecks or coral caves etc...............if they are there I might make a dive like the wreck I missed diving on in Brasil due to illness from bad food, but it is not something I do every year. Still, paying attention to what one is doing is paramount.....you can get into trouble in 5 feet of water just as easily as 50........ This was a good string......................................
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Post by SeaRat on Mar 29, 2008 21:16:52 GMT -8
Well, I guess I am the only one on these boards who has done a buoyant ascent from 35 feet. It was a requirement for us to pass the U.S. Navy Underwater Swimmer's School in Key West, Florida. We used the "blow and go" technique of continuously expelling air. This was standard Navy training for all divers, and submariners, as they would need to do a similar buoyant ascent to escape from a submarine. Because of this, and the fact that I'm an "ol' coot," I probably am not as sensitive to ascent rates from shallow dives as I should be. I have just re-read Lee D. Sommers, PhD, The Depth and Gas Dilemma, from the Conference Proceedings for the 1991 NAUI International Conference on Underwater Education[/B], where he explains that: So it is apparent that this discussion has helped me, and maybe some others, understand the importance of slow ascents, and regarding all ascents as a form a decompression. (Who says that ol' coots never change. ) But, I have also been doing some other research on the topic. I have just re-read the last part of the book, The Last Dive, by Bernie Chowdhury, describing the fatal dive of Chris and Chrissy Rouse, who were diving to 230 feet, and spent greater than 40 minutes at that depth while diving on a submarine wreck (as I remember it). None of my tables from NAUI, Dacor, or NOAA go beyond 130 feet, so I had to look it up in the U.S. Navy Tables in my NOAA Diving Manual (vintage copy, from 1975). Under those tables, the "Total Ascent Time (min:sec) for that dive (using 50 minutes bottom time) was 202:50. That's 3.375 hours. They died of fatal cases of DCS. It took six people to pull Chrissy out of the water because of all his gear; they had to cut his dad, Chris, out of his gear to get him up the ladder. It is obvious that these two divers had a huge decompression obligation that they never met, and had a much greater than 2:1 partial pressure differential to overcome too. They could not, and both divers died. I have also looked at Michael R. Ange's book, Diver Down, Real-World SCUBA Accidents and How To Avoid Them[/B]. In it Mr. Ange shows several accidents, including decompression accidents. But none of these are the result of buoyant ascents. One case involved a malfunctioning BC, but it was a case where the BC had been reassembled without an O-ring for the jet dump. The diver went into the water way overweight and was not able to inflate his BC. He ended up out-of-air at about 175 feet on a reef, and was recovered by the dive master, only to die subsequently. The other involved two tech divers who had problems, and made errors in their dive resulting in one missing his decompression and surfacing confused and disoriented. Again, no buoyant ascent, but missed decompression obligations. The British SubAqua Club has assembled a very interesting report, and in it they discussed reported in 2007 91 incidents associated with "abnormal ascents," down slightly from the year prior. "...the great majority of these incidents relate to poor buoyancy control and rapid ascents, often resulting in missed decompression stops. Better training is the key; BCD and drysuit control, and the use of associated equipment, especially delayed SMBs...Many DCI cases have their roots in these problems; they have been recorded under the DCI heading but the causal factors are often the same, so the actual number of abnormal ascents will be significantly higher than shown above." See; www.scubaboard.com/forums/accidents-incidents/172010-bsac-uk-2006-accident-report-out.htmlI think that there has been no reduction in ascent-related problems as the CO2 cylinders were dropped from equipment lists. But there may actually have been an increase. Consider this proposition--when a CO2 inflation mechanism goes off, the BC fills with 25 grams of CO2. That is a specific amount, but the volume is dependent upon the ambient pressure. It has already been reported that at 90 feet, there is little influence in buoyancy. But even at 20 feet (where I have done tests on my Para-Sea BC, using breath-holding techniques and poped the CO2) where there is a sufficient amount of gas to cause a buoyant ascent, it is a constant amount (the volume changes, but the amount in the CO2 cylinder is the same). So if it is discovered, it can be dumped rather quickly. Now consider a BC or dry suit inflation malfunction (especially without the "jet dump" which bypasses the BC). Here you have a constant addition to the dry suit or BC, which must be constantly dumped. If someone is already in a buoyant ascent, the dump mechanism probably cannot handle both the expanding gas and the addition from the inflation mechanism. So looking at it this way, the CO2 mechanism on a BC without a power inflator is probably a safer configuration than a power inflation mechanism without a "jet dump." I think that the BC itself would still need to be dumped, even with the "jet dump" feature (I'm not real familiar with this, and will have to go to the dive shop to see). My observation is that many divers get into trouble by not being familiar with the basics of buoyancy control, and one of these is to be neutral in the water at the surface. Vintage divers, or divers who learned in the 1960s and 1970s, learned these techniques. Now, especially with the extremely heavy tanks (compared to the single 72), divers are more and more dependent upon the BC for their buoyancy, and when it malfunctions, they are in trouble. John
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Post by Deleted on Mar 30, 2008 9:37:41 GMT -8
Well, I guess I am the only one on these boards who has done a buoyant ascent from 35 feet. It was a requirement for us to pass the U.S. Navy Underwater Swimmer's School in Key West, Florida. We used the "blow and go" technique of continuously expelling air. This was standard Navy training for all divers, and submariners, as they would need to do a similar buoyant ascent to escape from a submarine. Because of this, and the fact that I'm an "ol' coot," I probably am not as sensitive to ascent rates from shallow dives as I should be. If someone is already in a buoyant ascent, the dump mechanism probably cannot handle both the expanding gas and the addition from the inflation mechanism. So looking at it this way, the CO2 mechanism on a BC without a power inflator is probably a safer configuration than a power inflation mechanism without a "jet dump." I think that the BC itself would still need to be dumped, even with the "jet dump" feature (I'm not real familiar with this, and will have to go to the dive shop to see). My observation is that many divers get into trouble by not being familiar with the basics of buoyancy control, and one of these is to be neutral in the water at the surface. Vintage divers, or divers who learned in the 1960s and 1970s, learned these techniques. Now, especially with the extremely heavy tanks (compared to the single 72), divers are more and more dependent upon the BC for their buoyancy, and when it malfunctions, they are in trouble. John John, Your not the only Ol' Coot here ..........I was put thru what was called a "free ascent training" in Okinawa to be allowed to dive. The training was NAUI sponsored and approved by the island Provost Marshall. A airforce staff sargent named Tom Eskow taught the course. You may have known him perhaps. Your other statement about old bc's, dry suits is accurate from my experince as I said in my other response. Now my question is: what effect have you ever noticed from increased rapid ascents for the last 6-10 or so feet, expelling air as we were taught?
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Post by nemrod on Mar 31, 2008 8:31:17 GMT -8
I thought everyone knew you don't pop the CO2 at depth. Goes to show what gets lost with disuse- knowledge. Apparently it's a good thing this was brought up. By the way, maybe a distinction should be made between "decompression" and "outgassing". I think the term "decompression" has been overused and abused to the point that people think it is one and the same as "outgassing". Though related, they are not the same. I take "decompression" to be when something goes from a higher state of compression to a lower state. Even when your body and the gasses within it are at a steady pressure (as during a standard SIT), you continue to outgas until equilibrium is reached. You aren't really still "decompressing". I know it's nitpicking, but a clarification of the terms may have resolved the misunderstanding. The problem with keeping the CO2 inflator intact is that they are known to fire at a bad hair time. They tend to hang up and corrode and then when you need them not operate--all in all a bad thing. I would not have wanted the CO2 cartridge to fire during my hang after this 140 footer to the Mighty O. I love this stuff, I dove 30% Nitrox in an aluminum 80, I was first in and last out, everybody other than myself (maybe one other guy) was on steel 95s with Nitrox. I was well past a square profiled no deco dive on the tables, computer was one bar in the red. It cleared to yellow at my 30 foot stop and went back into green after a ten minute (slightly less) hang at 15. Back on boat with 500 psi. Max depth was 140 feet. A side note, the O is too deep for 80 cf tanks. The minimum should be a 95 with at least a 19 cf pony. Last year the captain told me they brought 17 divers up flat out of air below 100 feet. It is just a matter of time. This dive is an advanced dive due to extreme depth potential and the usual strong currents, potential large wildlife encounters and long distance from shore and "hugeness" of the wreck itself all work to destroy your sense of scale. An 80 is simply not enough for margin even for experienced divers. I would not have done it had I not had a cocked and loaded pony. Nem
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Post by nemrod on Mar 31, 2008 8:47:23 GMT -8
Luis, I agree mostly with what you say, but there are some dive profiles in which gas loading is really minimal. Here is one of my dive profiles from April of 2006. I have consulted my dive tables, and I have a number (2 NAUI versions, one NOAA, a Dacor table from 1971-vintage), and all of them start their loading at 40 feet, or 12 meters. My Suunto Reduced Gradient Bubble Model[/B] publication that came with my Suunto Cobra computer shows a table that shows the "Personal Mode" settings. For the "9 metres," using their PO mode (Ideal Conditions, which is the default), it shows "--" indicating an infinite number of minutes available. In "P1" mode, it is 163 minutes available, and in "P2" mode, it is 130 minutes. This publication also discusses the "decompression floor," and "decompression ceiling." That last paragraph helps me understand how Nemrod's dive (see above) in choppy water can be conducted safely. But my contention is that for some dive profiles, probably like mine above, the "decompression ceiling" and the waters surface are the same. In other words, no decompression is necessary. I realize that this may be just semantics, as Luis may say that in fact by swimming the last 22 or so minutes of this dive at less than ten feet, I was decompressing. But I spent maybe 8 minutes below 20 feet. So uptake of nitrogen would be pretty minimal, and I was not purposely decompressing. I was swimming the river bottom. Note that I was working in heavy current at the time and wearing twin 50s. Usually in this area, when I dive a single 72 under these medium to heavy current conditions, I'll go through it in 30 to 45 minutes. Even using the "personal Mode P2, at 9 meters I have about 130 minutes (and I have several of those factors, age, wet suit, cold, heavy current) to justify the P2 mode. What does this have to do with wearing a vest or not. Not much, but a poorly-designed vest can add drag in heavy current, which can affect work load (mine adds a little, but not like the vintage vests). This would be one factor to add into the personal profile when using a dive computer. John PS--Here's the log of the dive from above. It explains the dive profile. [/quote] Did any of these "dives" actually occur underwater . I am just messing with you ;D. Nem
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Post by duckbill on Mar 31, 2008 22:41:35 GMT -8
James, that looks like a fun dive you had on the USS "O". I wish I could get a dive in on the beast.
One thing, though- if your CO2 were to let loose at 140 feet I don't think you'd have any trouble at all burping that tiny bubble from your BC.
It's true that the cartridge and trigger need maintenance that most of us who still have them on our BCs forget to do. I'm glad this thread has served as a reminder to disassemble, rinse and grease it once in a while (fresh water diving), and after each saltwater weekend. I haven't wired my triggers yet like John mentioned, but it's a pretty good idea.
Oh, and Luis- I think you are right about the definition of decompression on a molecular level when partial pressures are considered. I think you and John were just using different definitions for "decompression". Simple semantics. Glad it got straightened out.
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Post by nemrod on Apr 1, 2008 5:29:41 GMT -8
James, that looks like a fun dive you had on the USS "O". I wish I could get a dive in on the beast. One thing, though- if your CO2 were to let loose at 140 feet I don't think you'd have any trouble at all burping that tiny bubble from your BC. It's true that the cartridge and trigger need maintenance that most of us who still have them on our BCs forget to do. I'm glad this thread has served as a reminder to disassemble, rinse and grease it once in a while (fresh water diving), and after each saltwater weekend. I haven't wired my triggers yet like John mentioned, but it's a pretty good idea. Oh, and Luis- I think you are right about the definition of decompression on a molecular level when partial pressures are considered. I think you and John were just using different definitions for "decompression". Simple semantics. Glad it got straightened out. No, but as I said, at the stop/deco hang it would matter especially if I had my hands full. If it can happen then sooner or later it will happen, usually at the worst time. The next day I went over to the Destin area, this was the hang after a dive on live bottom at about 90-110 feet. Seas running about three, strong current. Not a good place to have your CO2 cartridge fire. Now, if your max depth is three feet like for our famous friend here, no worries. Don't have a clue as to if the CO2 is armed or not for this lovely old SeaTec, I know mine is not. Nem
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Post by luis on Apr 1, 2008 6:13:07 GMT -8
Oh, and Luis- I think you are right about the definition of decompression on a molecular level when partial pressures are considered. I think you and John were just using different definitions for "decompression". Simple semantics. Glad it got straightened out. I know that I am wasting my time, but I am glad you think that I am right. I would hate to have to tell all those researchers with their PHD and MD degree that they have a poor command of the English language. On the other hand, I am not a native English speaker so decided to look up the word decompression in the dictionary. Actually, some of those researches are not native English either like Dr Petar J. Denoble, from DAN (who I met at Boston Sea Rovers and ended having a discussion about double hose regulators among other topics). Decompression: 1. pressure decrease: a decrease in surrounding or inherent pressure, especially the controlled decrease in pressure that divers undergo to prevent decompression sickness 2. (comput) computer data expansion: the expansion to full size of compressed electronic data 3. (surgery) surgery to reduce pressure in organ: a surgical procedure to reduce pressure in an organ or part of the body caused, e.g. by fluid on the brain, or to reduce the pressure of tissues on a nerve Of particular interest are definitions 1 and 3. The human body is a pressure vessel and within it we have a high pressure hydraulic system called the circulatory system. This hydraulic system can produce pressures of several psi and the base pressure (diastolic pressure) is rarely less than 1 psi. Some suggested optimal blood pressures are 120 / 80 mmHg (or the same as 2.3 psi / 1.5 psi) for Systolic over Diastolic pressures. The circulatory system doesn’t run at hundreds or thousands of psi, but that doesn’t make any less formidable than the hydraulics in a tractor. In the case of diving decompression, the pressures we are talking about are far from being in a “molecular level”. We are talking about bubbles and micro bubbles that can be measure in a totally different scale than a molecule. Some of them could probably be seeing with minimal magnification. These bubbles are pressure vessels and the analysis I started to read about (in a book about decompression, RGBM, and diving science) calculates hoop stresses just like I would on a steel pressure vessel. Therefore, IMHO, this is not about semantics…this is about the correct use of the word decompression. But, I am fairly sure that John did get it.
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Post by luis on Apr 1, 2008 6:14:16 GMT -8
Nemrod those are some great pictures.
On a related horse collar/ BC subject, I recall some big debates in the early 70’s about the use of a horse collar as a BC (or any type of BC). There were many at the time who consider adding any air to a horse collar underwater as an advance technique and only experience divers should ever actually use BC (there was no mention about specialty courses at the time…this was pre PADI multi-course evolution).
A “blow and go” and to some extent a buoyant accent was discussed and practiced in our advance class. But, the normal use of a horse collar as a BC was not common and considered potentially dangerous to a beginner diver (just do to a potential of an uncontrolled ascend and the potential barotrauma). Some units had over pressure relief valves, but the addition of quick air dumps was just starting to show up.
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Post by nemrod on Apr 1, 2008 6:42:47 GMT -8
Yeah, off subject but the master, David Haas was correct, digital is easy.
Both Joe and I dove our Seatec horsecollars at Ginnie and environs because we did not want to get banned from Florida for a fourth time. A good horsecollar BC performs very well for this kind of diving. As long as your not overweighted and especially with aluminum tanks you can get good horizontal trim or good enough anyways. I rarely put more than a puff or two in mine. The SeaTec is fully modern in that it has both a power inflator and a rapid dump pull.
Nem
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