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I wish I knew how to spell Aye-yai-yai-yai-yai (one of my Mom's expressions). Instead, I'll simplify and say "Yikes!". > What about different standards for "standard mixes"? > There is difference in standards beetween WKPP and GUE. Aren't GUE standards > developed from WKPP? > > For 0-190 ft WKPP recommends trimix 18/35 for bottom gas. Personally I see > no practical reason to use trimix for 50 ft dive for dives _I_ make. First of all, the WKPP is a specialized group, and they dive specific sites with particular needs. They have simplified to only a few gases for bottom gas for a number of reasons. Doing so provides a lot more flexibility on how team members might be deployed. Support divers have a hard bottom (in the cavern zone at Wakulla) of 190', so they need to be mixed to go that deep, if required. Not just for the WKPP, but for any diver, you always need to be mixed for the bottom, in case a failure or a diver assist requires you to go deeper than planned. If you CAN go deeper, then you have to be mixed for the bottom. GUE is planning on revising the recommended standard gases, but I don't yet know what they plan to change. For now, follow the GUE standard gases for dives shallower than 100' and use 30/30 trimix. For deeper dives, the 190' or 300' gas is appropriate, depending on the dive. Not having a plethora of gas mixes makes things a lot easier when you mix. If a dive gets cancelled or you don't use a cylinder for some reason, you can always use that gas on another similar dive, and you have a wider range of those dives for that gas. There is nothing worse than dumping a cylinder containing trimix because you need to mix a different gas for use in that cylinder. > ...some organisations and divers say 1,4 is safe limit. 1,2 is only for exceptionally long exposures... The limit has steadily dropped and dropped (from 2.0 to 1.8 to 1.6 to 1.4 and now 1.2). I don't really care if other agencies are promoting practices I consider unsafe, or at least, more risky than necessary. I like the 1.2 limit on PO2 because I want to avoid CNS O2 toxicity and I want to off-gas properly during the dive and during the deco, without compromising the respiratory system. Once the respiratory symptoms are obvious, the off-gassing is already compromised. Preventing it is the only smart thing to do (in my opinion). > ...Tech diving is risky activity and risk is what tech divers are used to live with. Risk mitigation is what divers need to live with, and plan for. Creating or accepting added risk is not something I need to do. There is nothing down there worth dying for. > ...I will not try to be smarter than tables because of actual experience. If > there is actual experience you state why there is no tables using this advantage? These tables are being developed. Diving is a new field; decompression theory is a new science, and is not completely understood. My information regarding how to work with the software and adjust the tables is cutting edge information. It is available in the GUE Tech 1 and 2 course. I also get a lot from listening to the right people and reading what they've written. > > Well, actually I felt the difference having 23% He... > ...nitrogen narcosis, and can detect it without problem. I did goof here when I mentioned 35% helium as a minimum. I use 30/30 trimix for recreational depth dives, and I do feel the advantage of the 30% helium even on these kinds of dives. I am definitely less narced, and I feel less decompression stress than when I dived air or nitrox in the past. Narcosis is insidious; its early effects are subtle and occur shallower than you'd imagine. I doubt you are completely aware of when you are narced. Expect that you are at least mildly narced even at 30'. The mixes I use are 30/30 or 18/45 for most of my dives. Note that the 45% helium is slightly higher than the WKPP minimim helium content for 190' gas, but it matches the GUE standard mix. I feel better with more helium. > > > ...Why to add 5 minutes for gas switch? The five minutes allows the deco gas to completely circulate from the lungs all through the blood. You want the window of time for this to occur during the deco. > Agree, but then there is reality. I don't know _any_ diver 40 km radius from > my city ever diving wreck on Baltic sea, same with trimix. Nearest diver > able dive tx whom I know lives about 90 km away and his schedulle make it > impossible to dive together. So maybe in Florida it's different situation > but not here. Most of my cave diving friends live in other locations, at least 400 miles away from me. I meet them at the dive site (400 miles from me). I come from Miami (south Florida), others come from North and Central Florida (300-500 miles away). My other regular cave buddies are in Tennessee, Georgia, Alabama, North Carolina, and a couple in South Florida 30-90 miles from me. We meet at the dive site. They don't need to live next door in order to have similar equipment, training, philosophy, standards of excellence, and passion for diving. My other wreck diving buddies are in Michigan (my previous home state - 1200 miles away). Besides traveling to dive, I arrange occasional recreational and tech dives in my own backyard, offering my friends lodging at my place. That's because the warm water ocean dives are at my doorstep here, as long as the winds are favorable. They come from Tennessee, north Florida, Michigan, etc. I just got back from a 10 day sailing/diving trip with friends from North Carolina, north Florida, Denmark, and Georgia. Proximity to other like-minded divers, helps, but is not essential. The main point is that you and other divers diving the sites where you dive can become a team. I belong to a dive club (in Michigan) that includes some very seasoned divers and some brand new ones. We have a very active program for mentoring the new divers so that they can progress from easy club dives to more experienced club dives. I personally mentor a number of people. It's a responsibility we must have to allow the new divers to be good buddies on the higher level dives. Surely you can do something like this with some of the divers you know. If you are a safe, knowledgable diver, then other divers will be happy to dive with you. Please let me repeat my advice from before: Look at the www.wkpp.org and www.gue.com web sites at the articles there on decompression, using helium, etc. Some of the articles are also on my web site: http://members.aol.com/jsuw3/wkpp_articles.html. There is a lot more information there than I can type in an email. Your arguments are all addressed. Ultimately, you can either say, "Yes, that's the smart way to dive", or you can say "It's too much trouble". I'm sure you can come up with a lot of reasons why you can't do the things I feel are much safer, but I hope you'll make the effort. If it's too much trouble to do things to promote safety, then you might want to consider finding another hobby. Best, Jan Sitchin --------------------------------------------- In a message dated 7/17/2003 1:09:02 AM Eastern Standard Time, janwer@fo*.co* writes: > > > ----- Original Message ----- > From: <Jsuw@ao*.co*> > To: <techdiver@aquanaut.com> > Sent: Tuesday, July 15, 2003 1:48 AM > Subject: Re: What ppO2 for bottom mix? > > > > Jan: > > > > Using standard mixes simplifies things. As someone else mentioned, you > begin to know the deco for the dive with that mix because you use it often. > It also helps your team of divers to have the same mix for a dive. That way > you are all staying a team and doing the same deco. > > What about different standards for "standard mixes"? > There is difference in standards beetween WKPP and GUE. Aren't GUE standards > developed from WKPP? > > For 0-190 ft WKPP recommends trimix 18/35 for bottom gas. Personally I see > no practical reason to use trimix for 50 ft dive for dives _I_ make. > > > The lower PO2 (e.g. 1.2) is to avoid both Central Nervous System Oxygen > Toxicity, but more importantly, to avoid seeing the respiratory degradation > which occurs with whole body oxygen toxicity. The respiratory effects will > cause inefficient off-gassing on long exposures. This is also the reason to > incorporate "back-gas" breaks during the deco. This is where you'd switch > to the lowest PO2 mix breathable at a given depth during deco. An example > of this for oxygen deco at 20' (6M) would be to breathe O2 for 12 minutes > and then the back gas for 6 and then O2 for 12, etc. This helps prevent the > respiratory effects. > > Yes, but for the same reason some organisations and divers say 1,4 is safe > limit. 1,2 is only for exceptionally long exposures. And there are always > exceptions when somebody can get a oxtox hit or something well before > reaching limits proposed by you but is it enough reason for others to > follow? Tech diving is risky activity and risk is what tech divers are used > to live with. > As for a oxygen breaks I agree. > > > > > Most decompression tables and programs are based on Buhlmann algorithms > for decompression modeling. Buhlmann assumed, without testing, that helium > would lengthen the decompression schedule. Actual experience with helium > mixtures proves otherwise. Helium on-gasses and off-gasses quickly, and can > be off-gassed very cleanly when doing "deep stops" and using slow ascent > rates. Not only will you be coherent on dives with helium, but you will > feel much better, less tired (and less other symptoms "decompression > stress"), etc. after the dive. > > I will not try to be smarter than tables because of actual experience. If > there is actual experience you state why there is no tables using this > advantage? It's bee a few years since we know it and still no programs and > tables??? Why??? New algorythms are developed and we still have to dive like > those legendary Egyptian divemasters diving 80 meters on air without > computers just counting on feeling good? :-) > > > You need at least 35% helium in the mix to make any real difference. Less > than that is a token amount and not effective enough. > > Well, actually I felt the difference having 23% He on my last dive to 43 > meters. I'm like most divers very aware of nitrogen narcosis, and can detect > it without problem. > > > When I plan a dive using software, such as DecoPlanner, I use the table > provided by the program, add deep stops, add time at gas switches to have at > least 5 minutes at a switch, and then I trim a few minutes from the > shallower stops, following the shape of the decompression curve. > > Why to add 5 minutes for gas switch? > > > As far as solo diving, I encourage you to develop a group of safety minded > divers that are qualified to do the dives you wish to do. Begin diving as a > team. By team, I do not mean independent divers in the water at the same > time. Plan your dives together. Execute the dives together. Support each > other during the dive. Watch each other perform gas switches, etc. It's > safer and more fun. > > Agree, but then there is reality. I don't know _any_ diver 40 km radius from > my city ever diving wreck on Baltic sea, same with trimix. Nearest diver > able dive tx whom I know lives about 90 km away and his schedulle make it > impossible to dive together. So maybe in Florida it's different situation > but not here. > > Thank you for a lot of info. > > Jan Werbiński O0oo....._[:]) bul, bul, bul > Strona domowa http://www.janwer.com/ [ http://pa54.zgora.sdi.tpnet.pl/jw/ ] > Nasza sieć http://www.fredry.net/ [ http://pa54.zgora.sdi.tpnet.pl/ ] > > --------------------------------------------- Visit my web page with underwater and other photos at http://members.aol.com/jsuw3/index.html -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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