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Scuba Forum / General / August 2006Nitrox Certification - with whom?
hey, i just got my ow and aow back to back (btw, people saying you should get some experience between taking the two.. nonsense. aow is just five fun dives with an instructor hanging around.. ) and am now looking to get my nitrox certification followed by rescue diver sometime when i've got some more dives under my belt. my question is, i've read some things on here about how some agencies teach a better nitrox class than padi, some of these threads were really old though so i'm just wondering, is there anything wrong with the padi class? what do these other classes teach that padi doesn't? if i was to take a class from a different agency which would the 'best' one? would certification from this agency afford me the same ability and access to nitrox fills as a padi certification? and finally, would padi recognize my certification from another agency? thanks! It isnt agencies, it is instructors. Nitrox is no big deal, you are breathing 21% nitrox right now (unless you are in Denver or Tibet). Very simple math and discipline. > It isnt agencies, it is instructors. > > Nitrox is no big deal, you are breathing 21% nitrox right now (unless you > are in Denver or Tibet). > > Very simple math and discipline. ???????? THe percentage of Nitrogen and oxugen changes with altitude???  Signature“TANSTAAFL” "One day I will leave this world and dream myself to Reality" Crazy Horse 1874 ____________________________________________________________________________ "A prudent man foresees the difficulties ahead and prepares for them; The simpleton goes blindly on and suffers the consequences." - Proverbs 22:3 > > It isnt agencies, it is instructors. > > [quoted text clipped - 6 lines] > > THe percentage of Nitrogen and oxugen changes with altitude??? No, but the partial pressures do. They do change just a little with humidity though, at least according to the manual of my analox O2 analyser Frank > ? Scott wrote: > ? > <stebed@gmail.com> wrote in message [quoted text clipped - 16 lines] > > No, but the partial pressures do. > They do change just a little with humidity though, at least according to the > manual of my analox O2 analyser That's a "feature" of the sensor, not a characteristic of the air. > Frank > [quoted text clipped - 18 lines] > > > > No, but the partial pressures do. > They do change just a little with humidity though, at least according to > the manual of my analox O2 analyser I suspect you'll find that it's the measurement of the O2 percentage that changes rather than the actual content. On the other hand, the area you are in may change the percentage enough to be measurable. I imagine the percentage of O2 in say, downtown NY would be lower than it would be in the middle of a forest. >> ? THe percentage of Nitrogen and oxugen changes with altitude??? Maybe. Oxygen is produced by photosynthesis, around ground level. While it certainly mixes to a relatively constant level, I would expect there would be at least some difference at high altitudes. Lee > hey, i just got my ow and aow back to back (btw, people saying you > should get some experience between taking the two.. nonsense. aow is > just five fun dives with an instructor hanging around.. ) You were ripped off. Come on out and I'll show you an AOW course. and am now > looking to get my nitrox certification followed by rescue diver > sometime when i've got some more dives under my belt. [quoted text clipped - 6 lines] > and access to nitrox fills as a padi certification? and finally, would > padi recognize my certification from another agency? thanks! Agencies differ in their standards that MUST be taught. What actually IS taught will differ with the comfort and skill level of the instructor. PADI is not and no matter how much deep air crap they put in their tech classes will never be a tech agency. As such their instructors, unless they are also trained by and teaching outside PADI, will never be technical instructors. You will find instructors who will range from teaching the bare minimum of "use this computer and here's how to read your MOD from a chart and sign for your gas" to those who teach you theory, work on your buoyancy, even teaching helicopter turns and finning backwards (well you have to do SOMETHING on those dives!) help you streamline your gear, and teach enough skills to be an intro to tech course. You need to decide what you want from the class. Some here will argue that the first option is all you need (sign for gas on the shop's analysis-HORRORS!, find MOD, set computer and go diving). Whenever a student works with me, I will share with them whatever is necessary to help them be a better diver, whether or not its part of the class standards, in a mentorship situation. Guess which type of class I teach. * >>hey, i just got my ow and aow back to back (btw, people saying you >>should get some experience between taking the two.. nonsense. aow is >>just five fun dives with an instructor hanging around.. ) > You were ripped off. Come on out and I'll show you an AOW course. That might be a subjective viewpoint. Considering those that are new to diving and not have many dives under their "belt", the next step for them is, in PADI, AOW. While there are a lot of shops that "push" this right after someone is certified, there are those that don't. Considering again that these are new divers still learning and developing their skills, AOW just introduces them to other areas of diving. It's an introduction to these areas of diving not known to them, not a course to make them really really excellent in the 5 "specialities" they are introduced to. >>looking to get my nitrox certification followed by rescue diver >>sometime when i've got some more dives under my belt. [quoted text clipped - 5 lines] >>and access to nitrox fills as a padi certification? and finally, would >>padi recognize my certification from another agency? thanks! > Agencies differ in their standards that MUST be taught. What actually > IS taught will differ with the comfort and skill level of the > instructor. If that instructor wants to remain in a particular agency, they had better teach the "standards". Nothing like having a lawsuit on your hands if you didn't. While there is the technical side to Nitrox, it's still not difficult, and in PADI (who used to think Nitrox was voodoo gas), it's made for the masses. > PADI is not and no matter how much deep air crap they put in their tech > classes will never be a tech agency. As such their instructors, unless > they are also trained by and teaching outside PADI, will never be > technical instructors. I personally don't know any PADI "tech" instructors. But, I do know a lot of PADI divers that are tech divers. They go outside of PADI for the more "technical" diving instruction. PADI does not offer tri-mix or anything with helium yet. They will find a way to make it "easier" for people to get their certification, "if" there is money to be made. And, they will make it safe enough to avoid litigation. > You will find instructors who will range from teaching the bare minimum > of "use this computer and here's how to read your MOD from a chart and [quoted text clipped - 8 lines] > help them be a better diver, whether or not its part of the class > standards, in a mentorship situation. All this in a $99 Nitrox level 1 course? As for using a shops analyzer, why not? You check it against (as you would even your own) an air (21%) tank and calibrate. That is what I was taught when I took PADI Nitrox when it was first introduced. I guess I was fortunate in the instructors I have had. They all shared their experiences and ways to be a better diver. The mentoring came from other divers with far more experience than myself. The instructors can only handle so many people at one time. And most of the time, they were teaching. One of the best things taught to me was just keep diving. another question, i don't own a dive computer yet.. is it a bad idea to dive nitrox without one or is it just a matter of doing your tables? > another question, i don't own a dive computer yet.. is it a bad idea to > dive nitrox without one or is it just a matter of doing your tables? It's never wrong to learn tables, but get the computer soon as you can. Get a cheap one if you need to, nitrox capable, and keep it for a spare or trade up later. SignaturePopeye I have discovered that all human evil comes from this, man's being unable to sit still in a room. -Pascal www.finalprotectivefire.com >> another question, i don't own a dive computer yet.. is it a bad idea to >> dive nitrox without one or is it just a matter of doing your tables? > > It's never wrong to learn tables, but get the computer soon as you can. He should learn the tables first, in order to understand what the computer is telling him. > Get a cheap one if you need to, nitrox capable, and keep it for a spare or >trade up later. Signaturedillon JAFO stebed@gmail.com wrote > I don't own a dive computer yet.. is it a bad idea to > dive nitrox without one or is it just a matter of doing your tables? It's easier to do with a computer and, just like when diving on air, you often get to dive longer because the computer credits time spent at shallower depths, but there's nothing wrong with diving nitrox based on tables. The gas you use and the way you use the tables will determine how easy it is to do with tables. There are tables made for the standard nitrox mixes, 32% and 36%. If you use only the standard mixes and the tables to go with them, the only difference between nitrox and air is that, with nitrox, you also have to watch your maximum depth. If you use mixes other than the standard ones, as several of us do, you can calculate an EAD, equivalent air depth, and then use air tables for the dive. This ability, by the way, will come in handy if you eventually decide to move up to trimix. EAD and END, equivalent nitrogen depth, are closely related concepts. Having said all of that, I agree with Popeye and Dillon. Learn to do the calculations, learn to use the tables, but get a nitrox capable computer when you can. Lee > It's easier to do with a computer http://tinyurl.com/rjuhg ;-) >> It's easier to do with a computer > http://tinyurl.com/rjuhg > ;-) 8^) It's still easier to do with a computer . . . usually. Next Monday, I'll be off on my annual "death to all edible creatures" trip to the Tortugas. If it's like most trips, we'll do 6 dives the first day, 7 the second day and 3 or 4 on the way back on the third day. Depths will vary between about 45 and 100 fsw depending on the site and what there is to hunt. We hunt black grouper from midwater, descending only for the shot. Lobster, hogfish and red grouper are normally hunted on the bottom. Snapper and other fish are targets of opportunity while hunting for blacks, reds, hogs and lobster. The dives last anywhere from a few minutes (occasional small patch reefs) to about 45 minutes (pretty much the norm). About half of us use nitrox. The other half use air. All of us user computers. This kind of diving simply isn't practical any other way. You don't know when, where or how deep the next dive will be until just before you start it. Even when you hit the water, you don't know whether you'll hunt from mid water, on the bottom, or some combination of both. There's no time for planning individual dives or, sometimes, even for figuring what your RDG is. Often, there's barely enough time to switch tanks. I love Magilla like a brother, but I would not buddy up with him for diving like this unless he used a computer too. Lee > Next Monday, I'll be off on my annual "death to all edible creatures" trip > to the Tortugas. <snip> Are you going on that boat out of Ft Meyers? I've done some of the deep wrecks in the Gulf about 100 mi north of the Tortugas, and they were really thick with fish. > This kind of diving simply isn't practical any other way. I differ with you on that, but do what is comfortable for you. > when, where or how deep the next dive will be until just before you start > it. Even when you hit the water, you don't know whether you'll hunt from [quoted text clipped - 4 lines] > I love Magilla like a brother, but I would not buddy up with him for diving > like this unless he used a computer too. I've done this kind of diving many times with no computer. I'm not calculating RDG's, and I doubt that Magilla is either. I didn't just one day accept and start using the method; I experimented and worked up to it gradually, with mentoring from Mike Rodriguez, who I believe understands decompression as well as or better than anyone in the non-commercial community. What you really need to be careful of is that your computer will happily "let" you do bounces that are unwise, which is asking for big trouble. > Are you going on that boat out of Ft Meyers? I've done some of the deep > wrecks in the Gulf about 100 mi north of the Tortugas, and they were > really thick with fish. We use the Playmate, out of Stock Island. The boat leaves Key West after midnight. We sleep through much of the trip, waking somewhere in the neighborhood of the Marquessas. We dive and hunt from there to the boundaries of Ft. Jefferson, usually spending a night in the harbor there. >> This kind of diving simply isn't practical any other way. > I differ with you on that, but do what is comfortable for you. > I've done this kind of diving many times with no computer. I'm not [quoted text clipped - 3 lines] > understands decompression as well as or better than anyone in the > non-commercial community. I don't know how you'd manage it. As it is, on 32%, I spend most of the trip at, or near my no deco limit. I get closer still around the middle of the second day to accomodate my computer's CNS clock. Lee > We use the Playmate, out of Stock Island. The boat leaves Key West after > midnight. We sleep through much of the trip, waking somewhere in the > neighborhood of the Marquessas. We dive and hunt from there to the > boundaries of Ft. Jefferson, usually spending a night in the harbor there. sounds like a great trip. what gun are you using these days? > I don't know how you'd manage it. As it is, on 32%, I spend most of the > trip at, or near my no deco limit. I get closer still around the middle of > the second day to accomodate my computer's CNS clock. It's not at all difficult, once you accept a few things. Have a good trip - if you see anything unusual, take a picture and then let me know how it tastes. > sounds like a great trip. what gun are you using these days? It's made better by the company, most of whom have been taking the trip for years, and the food, which is top quality and quantity. The spearfishing and lobstering, of course, is good. That's why we're there. My buddy and I usually limit or slightly more on lobster. The limit is annoying. You're only allowed 6 per day and have a posession limit of two days catch, a total of 12 lobster each. Since the count is done by the boat, we sometimes benefit from the less than stellar hunting skills of other participants, bringing home our fair share and some of theirs. We don't let anyone come home empty handed, but we don't exactly divide everthing equally either. We generally put enough fish in the freezer to last until the next trip. I don't normally hunt lobster, or with a speargun except for this one trip. The downside is that 6 to 7 dives a day is a stressful pace. Given a choice, I'd probably choose a bit less agressive schedule. Of course, I could sit out a dive now and then, but guys being guys, pretty much everybody does every dive. This year is beginning to look like a problem. There's a tropical storm, potential hurricane, that looks like it will hit Key West just about the same time as I do. Getting on and off the boat in 6 foot plus seas is no picnic, especially when carrying a stringer full of fish, bag full of lobster and all the equipment used to harvest them. I've still got a 3 inch scar on my leg to prove what can happen when the boat moves unexpectedly. It jerked me up and pulled my buddy, on the tag line, under and into me. My right leg found the tip of his speargun. Lucky for me, he let the speargun move during the encounter. If he hadn't, it might well have gone through my leg rather than cutting the surface. I shoot a twin band 42" AB Biller with 48" shafts. I considered a Riffe, but we normally shoot freeshaft, without a line, and you can't do that with Riffes. On the Riffe, the line holds the front of the spear on the gun. The longer shaft is to make up for the shorter gun. I could shoot a 48" gun, which is what my buddy has, but at the end of the day, the extral length gets to me. >> I don't know how you'd manage it. As it is, on 32%, I spend most of the >> trip at, or near my no deco limit. I get closer still around the middle >> of >> the second day to accomodate my computer's CNS clock. > It's not at all difficult, once you accept a few things. You'll have to explain some day. I literally plan dives during the dives, changing my average depth according to my N2 load and hunting conditions. Of course, I could do identical dives without the computer, but I'd have a hell of a lot less confidence that I had not exceeded my limits. I've been mildly bent twice. That's at least once more than enough. > Have a good trip - if you see anything unusual, take a picture and then > let me know how it tastes. Maybe. I usually take a surface camera with me, but the best stuff is normally found below the surface. Last year, we encountered a Jewfish the size of a Volkswagen. As I was marveling at his size, my buddy poked his tail. He gave one of those grunts that Jewfish are famous for. In his case, it felt like an earthquake. If sharks dislike human waste, I was sharkproof for the remainder of that dive. 8^) Lee > I shoot a twin band 42" AB Biller with 48" shafts. I considered a Riffe, > but we normally shoot freeshaft, without a line, and you can't do that with > Riffes. On the Riffe, the line holds the front of the spear on the gun. > The longer shaft is to make up for the shorter gun. I could shoot a 48" > gun, which is what my buddy has, but at the end of the day, the extral > length gets to me. I have a 48" Riffe, and am planning on buying a Rhino 52" commercial freeshafting gun for the ledges. The Riffe is ok for wrecks, and is deadly accurate, but as you point out, is NG for freeshafting. > I have a 48" Riffe, and am planning on buying a Rhino 52" commercial > freeshafting gun for the ledges. The Riffe is ok for wrecks, and is > deadly accurate, but as you point out, is NG for freeshafting. I've seen the Rhino guns around. As near as I'm able to tell, the essential parts of the classic Sea Hornet guns are identical to those of the Billers. In fact, one of my friends had a Biller repaired and it came back with a Sea Hornet trigger mechanism. I'm not sure what advantage you get from the coating on the Rhino model and when I looked for it, I didn't see a one piece Rhino. Sea Hornet and Biller both make a one piece wood gun. In fact, that's what my buddy shoots. I could shoot a 48. There's no way I'd get a 52" gun. The biggest I'd go is a 48 with a 52" spear. I don't see a significant advantage to the Rhino over what I shoot now. What are the weights on the line for and why should I not assume that they will slow the spear? I recommend against the spare shaft design. I bought the two spare shaft system for my Biller. It did a few things that I had not planned on. It made the gun very nose heavy. I'm not sure how it would have been in the water, but I could not point it one handed on land. It also made the gun quite negatively buoyant. Originally, I planned to put my powerhead on the second shaft, arranged so that it extended slightly forward of the loaded spear, effectively turning my speargun into a combination speargun and bangstick. That part worked, but wasn't enough of an advantage to warrant the problems I created. I took the system off, purchased some tips that are the same diameter as the inside of the powerhead and settled for putting the powerhead on the end of the spear when needed. Of course, I hope I never need it when my spear is not in the gun. If you want to try the system on something, let me know. I suggest you do it on something you don't mind patching holes in. I don't think you'll like it. Lee Al Wells wrote > I have a 48" Riffe, and am planning on buying a Rhino 52" commercial > freeshafting gun for the ledges. The Riffe is ok for wrecks, and is > deadly accurate, but as you point out, is NG for freeshafting. It's too late for this year, but we do this trip about this time every year. Are you interested in the future? Lee > It's too late for this year, but we do this trip about this time every year. > Are you interested in the future? I guess it depends on where I am next year, but yes, I would be interested if there is space. > What are the weights on the line for and why should I not assume that they > will slow the spear? They keep the line from fouling, since it doesn't wrap. Some of my Sc buddies are spearo fanatics, and between them they have owned every gun ever made, and they all ended up with the Rhinos. They go to the Fl tournaments and kick a.s. The next time I'm down there hunting, I will try one of the Rhinos. Most of the hunting is on live bottom and ledges, so freeshafting is the method that works. I've done ok with the Riffe though - I can't remember the last time I pulled the trigger and didn't get groceries. > I don't know how you'd manage it. As it is, on 32%, I spend most of the > trip at, or near my no deco limit. I get closer still around the middle of > the second day to accomodate my computer's CNS clock. I just remembered something - I started to look at the file you sent me, and so far have found no errors. I will remember to finish it tonight. al Thanks > I just remembered something - I started to look at the file you sent > me, and so far have found no errors. I will remember to finish it > tonight. > >> It's easier to do with a computer > [quoted text clipped - 8 lines] > Next Monday, I'll be off on my annual "death to all edible creatures" trip > to the Tortugas. Did you read the book yet? :^) >> Next Monday, I'll be off on my annual "death to all edible creatures" >> trip >> to the Tortugas. > > Did you read the book yet? > :^) No. It's still sitting on my night stand. Maybe I'll take it with me. Lee >> >> It's easier to do with a computer >> [quoted text clipped - 8 lines] >> Next Monday, I'll be off on my annual "death to all edible creatures" trip >> to the Tortugas. How is Chris going to affect the trip? >Did you read the book yet? >:^) > Signaturedillon How much power does it take to run a server farm? A googlewatt. >another question, i don't own a dive computer yet.. is it a bad idea to >dive nitrox without one or is it just a matter of doing your tables? I have never bothered. I dive either 32 or 36, but I dive to my standard air tables. >>another question, i don't own a dive computer yet.. is it a bad idea to >>dive nitrox without one or is it just a matter of doing your tables? > > I have never bothered. I dive either 32 or 36, but I dive to my > standard air tables. And do ya dive trimix to nitrox tables? >>>another question, i don't own a dive computer yet.. is it a bad idea to >>>dive nitrox without one or is it just a matter of doing your tables? [quoted text clipped - 3 lines] > >And do ya dive trimix to nitrox tables? I am strickly recreational, I have never dived tri-mix >>>I have never bothered. I dive either 32 or 36, but I dive to my >>>standard air tables. >> >>And do ya dive trimix to nitrox tables? > > I am strickly recreational, I have never dived tri-mix My point was this: dive the tables (profile) for the gas yer using, not for some arbitrary other mix. Dive air on air profiles. Dive nitrox on nitrox profiles. Dive trimix on trimix profiles. Dive heliox on heliox profiles. The idea of diving 32 or 36 to 21 profiles is idiotic. That's three very different profiles - use the correct one, or stay home. m >>>>I have never bothered. I dive either 32 or 36, but I dive to my >>>>standard air tables. [quoted text clipped - 13 lines] > >m I understand what you are saying. The reason I dive nitrox on air tables, is an increase in safety factor. >>My point was this: dive the tables (profile) for the gas yer >>using, not for some arbitrary other mix. >> >>The idea of diving 32 or 36 to 21 profiles is idiotic. That's >>three very different profiles - use the correct one, or stay home. > I understand what you are saying. The reason I dive nitrox on air > tables, is an increase in safety factor. Some say that certain factors, including age, can affect ones natural ability to exchange nitrogen through respiration. Compensation is possible by using the air table (or computer) and diving with nitrox. Your logic is sound. The same logic applies to decompressing using oxygen or oxygen enriched air. The only guy complaining is the guy waiting for you to get back on the boat so the boat can return to shore. (Rec.scuba regulars omitted, of course.) (The "natural" was thrown in for Star because she eats that concept.) >> I understand what you are saying. The reason I dive nitrox on air >> tables, is an increase in safety factor. > Some say that certain factors, including age, can affect ones natural > ability to exchange nitrogen through respiration. Assuming you are correct, does it not affect the exchange in both directions? If so, is not the risk the same? > Compensation is possible by using the air table (or computer) and diving > with nitrox. There's nothing to compensate for. > Your logic is sound. His logic is questionable. Yours is flawed. > The same logic applies to decompressing using oxygen or oxygen enriched > air. True enough. Using nitrogen allows you to remain underwater longer without increasing your nitrogen load or by shortening your surface interval. Decompressing using oxygen allows you to spend a greater portion of your dive at the depth you choose, shortening the time required for decompression, including the surface interval. > The only guy complaining is the guy waiting for you to get back on the > boat so the boat can return to shore. (Rec.scuba regulars omitted, of > course.) If you use nitrox according to air tables or oxygen to decompress, you're back on the boat sooner. The guy waiting to return to shore probably won't complain about how much shorter your dive turned out. You, however, might complain about the fact that you're on the boat by yourself while others, who used nitrox standards for nitrox use. are still enjoying their dive. Lee >>> I understand what you are saying. The reason I dive nitrox on air >>> tables, is an increase in safety factor. [quoted text clipped - 4 lines] > Assuming you are correct, does it not affect the exchange in both > directions? If so, is not the risk the same? Maybe. No, the risk to taking on nitrogen slower and off-gassing nitrogen slower are separate and their associated risks are opposite. Taking nitrogen on slowly is seen as a benefit. Nitrox is fiddling with air for the specific purpose of taking on less nitrogen. Off-gassing nitrogen slowly is a detriment because the "pool" of nitrogen in the body can bubble after you surface. The ideal would be to discharge excess nitrogen rapidly and not allow it to build up in the body. >> Compensation is possible by using the air table (or computer) and diving >> with nitrox. > > There's nothing to compensate for. The nitrogen in your body needs to be expelled. One can compensate for the decreased ability to off-gas by spending more time off-gassing. The time to decompress will always be equal to or longer using air tables or setting your nitrox compatible dive computer to 21%. When the interval is longer the extra time is compensation. >> Your logic is sound. > > His logic is questionable. Yours is flawed. Actually, it's not my logic. It what you learn in class. >> The same logic applies to decompressing using oxygen or oxygen enriched >> air. [quoted text clipped - 4 lines] > of your dive at the depth you choose, shortening the time required for > decompression, including the surface interval. I'm unsure of what you are saying. Nobody I know uses nitrogen to stay under water longer. You mean oxygen? I'm unsure of what you're saying. Using oxygen you decompress faster or take on nitrogen slower, depending on what point you start the higher oxygen level. >> The only guy complaining is the guy waiting for you to get back on the >> boat so the boat can return to shore. (Rec.scuba regulars omitted, of >> course.) > > If you use nitrox according to air tables or oxygen to decompress, you're > back on the boat sooner. I'm unsure of which air tables you're refering to but it's not true with the air tables I use. If you use oxygen to decompress you're back on the boat sooner if you use the oxygen table for decompression. > The guy waiting to return to shore probably won't complain about how much > shorter your dive turned out. You, however, might complain about the fact > that you're on the boat by yourself while others, who used nitrox > standards for nitrox use. are still enjoying their dive. We must be talking apples and oranges. Time at depth is set at whatever you want, the variable is decompression. From personal experience, for equal dives, I'm the last one to decompress. But, of course, my nitrox computer was set at 21% while everyone else adjusted for the higher oxygen gas. > The nitrogen in your body needs to be expelled. One can compensate for the > decreased ability to off-gas by spending more time off-gassing. The time to > decompress will always be equal to or longer using air tables or setting > your nitrox compatible dive computer to 21%. When the interval is longer > the extra time is compensation. This logic is the same logic used by some to drive 30 mph on the interstate. Lower speed = less risk. Your suggestion is to set yer speedometer gearing to indicate 70 when you are actually going 30. In fact, it doesn't work that way at all. On- and off-gasing are functions of partial pressure. Within the limits (and especially within the ridiculously conservative limits used by recreational divers) you are compensating for a DCS risk that does not exist, while ignoring oxtox risks that are real. That's stupid. That's dangerous. Don't do it. >> The nitrogen in your body needs to be expelled. One can compensate for >> the decreased ability to off-gas by spending more time off-gassing. The [quoted text clipped - 4 lines] > This logic is the same logic used by some to drive 30 mph on the > interstate. Lower speed = less risk. I see no similarity in this analogy. In practice, lower speed = more risk. > Your suggestion is to set yer speedometer gearing to indicate 70 when you > are actually going 30. [quoted text clipped - 5 lines] > recreational divers) you are compensating for a DCS risk that does not > exist, while ignoring oxtox risks that are real. People diving within established limits take "hits". It's a risk of the sport. If the risk does not exist, end of discussion, all points are rec.scuba: they just don't matter. The fact is there is a risk, however small, and that risk can be reduced even further if one so chooses. Oxygen toxisity is a very real risk and, I'm told, quite unpleasant. I agree with you that the recreational limits are safe and conservative. > That's stupid. > > That's dangerous. > > Don't do it. These warnings apply to rec.scuba! >> This logic is the same logic used by some to drive 30 mph on the >> interstate. Lower speed = less risk. > > I see no similarity in this analogy. In practice, lower speed = more > risk. We know you don't see it. If you did, we wouldn't be having this discussion. It's not a bad analogy at all. In practice, lower speed = different risk. If the risks are dealt with appropriately both fast and slow are equally safe. If the risks are dealt with appropritely when using nitrox, using it based on air no deco limits or nitrox no deco limits are equally safe. Regardless, there are different risks. > Oxygen toxisity is a very real risk and, I'm told, quite unpleasant. I > agree with you that the recreational limits are safe and conservative. Only if you plan for them. The MOD at PPO2 of 1.4, the max recommended by most diving agencies, for both 32% and 36%, are well within recreational limits. Diving nitrox like air, is not adequate planning for them. Lee >>> This logic is the same logic used by some to drive 30 mph on the >>> interstate. Lower speed = less risk. [quoted text clipped - 15 lines] > most diving agencies, for both 32% and 36%, are well within recreational > limits. Diving nitrox like air, is not adequate planning for them. Another good example of why it's easy to love rec.scuba. One chooses the meaning of posts based on his or her response to the post. Of course, that helps to explain why the information, if one can be so bold as to call it information, is uninformative. >>> Oxygen toxisity is a very real risk and, I'm told, quite unpleasant. I >>> agree with you that the recreational limits are safe and conservative. [quoted text clipped - 8 lines] > that helps to explain why the information, if one can be so bold as to > call it information, is uninformative. This is a discussion of breathing nitrox as though it is air. Your statement that the recreational limits are safe and conservative, in this context, does not address the issue of oxygen toxicity. My statement simply points out that the generally accepted point, beyond which nitrox is not recommended, is within what is normally referred to as recreational diving limits. The 132 fsw/4 ata limit for recreational diving is not conservative if you're breathing either of the standard nitrox mixes. This is not a trick, not a twisting of meaning, it's plain and simple fact. If you find it uninformative, perhaps it is you that is interpreting things to suit your personal bias. Lee > People diving within established limits take "hits". It's a risk of the > sport. If the risk does not exist, end of discussion, all points are > rec.scuba: they just don't matter. The fact is there is a risk, however > small, and that risk can be reduced even further if one so chooses. There is indeed a risk of a hit within the tables, the "undeserved hit". The fact is that this risk is equal regardless of the profile within the tables, in other words that risk cannot be reduced by changing time and/or depth within the tables. It is a constant regardless of profile. The only way to reduce that risk is to stay on dry land. In article <bonAg.210328$mF2.181399@bgtnsc04-news.ops.worldnet.att.net>, mike gray <omgray@worldnet.att.net> wrote: > > People diving within established limits take "hits". It's a risk of the > > sport. If the risk does not exist, end of discussion, all points are [quoted text clipped - 7 lines] > tables. It is a constant regardless of profile. The only way to > reduce that risk is to stay on dry land. In other words, there's always a small positive offset to the curve? > In article > <bonAg.210328$mF2.181399@bgtnsc04-news.ops.worldnet.att.net>, mike gray [quoted text clipped - 17 lines] > > In other words, there's always a small positive offset to the curve? Yup. >> People diving within established limits take "hits". It's a risk of the >> sport. If the risk does not exist, end of discussion, all points are [quoted text clipped - 6 lines] > depth within the tables. It is a constant regardless of profile. The only > way to reduce that risk is to stay on dry land. The table is a range of values within specified parameters. To say that all values in the table have equal risk ignores the characteristics of the value. You believe what you say and that is well and good. We've kept "risk" within the parameters offered by the original poster so that pretty much covers it. >>>People diving within established limits take "hits". It's a risk of the >>>sport. If the risk does not exist, end of discussion, all points are [quoted text clipped - 12 lines] > "risk" within the parameters offered by the original poster so that pretty > much covers it. No, it doesn't. You still haven't grasped the fact that moving from x time to y time within the tables has no effect on DCS risk. There is one risk that has not been discussed here: current research indicates risk of lifetime exposure to high PPO2. By diving nitrox on air tables, you are increasing lifetime exposure without reducing DCS risk. In the near future, you will probably see NOAA develop a "lifetime exposure clock" which will require avoidance of hot mixes - like any nitrox on air profiles. > There is one risk that has not been discussed here: current research > indicates risk of lifetime exposure to high PPO2. By diving nitrox on air > tables, you are increasing lifetime exposure without reducing DCS risk. Please cite your reference(s). > > There is one risk that has not been discussed here: current research > > indicates risk of lifetime exposure to high PPO2. By diving nitrox on air > > tables, you are increasing lifetime exposure without reducing DCS risk. > > Please cite your reference(s). Bad day or simply no sense of humor? >>>There is one risk that has not been discussed here: current research >>>indicates risk of lifetime exposure to high PPO2. By diving nitrox on [quoted text clipped - 6 lines] > > Bad day or simply no sense of humor? It's OK. I'm sending him a bill for research assistance. > It's OK. I'm sending him a bill for research assistance. What is the hourly bill for Dive Guru now days? >>There is one risk that has not been discussed here: current research >>indicates risk of lifetime exposure to high PPO2. By diving nitrox on air >>tables, you are increasing lifetime exposure without reducing DCS risk. > > Please cite your reference(s). Ongoing research by Dr. Christian J. Lambertsen, US Navy Experimental Diving Unit, under the general topic "The Inevitability of Oxygen Poisoning, and the Practical Use of Oxygen at Toxic Pressures". >>> I understand what you are saying. The reason I dive nitrox on air >>> tables, is an increase in safety factor. [quoted text clipped - 34 lines] > >Lee I have found that when I dive in the 45 to 60 FSW area and my bottom time is over an hour I start prossing the NDL limit on the second dive. To my knowledge there are 3 things I can do, Increase my surface interval, not always a possability depending on who I am diving with. Dive shallower Reduce the amount of nitrogen I breath. > I have found that when I dive in the 45 to 60 FSW area and my bottom > time is over an hour I start prossing the NDL limit on the second [quoted text clipped - 3 lines] > Dive shallower > Reduce the amount of nitrogen I breath. Sounds like you should be using nitrox, on nitrox profiles! >>>My point was this: dive the tables (profile) for the gas yer >>>using, not for some arbitrary other mix. [quoted text clipped - 9 lines] > by using the air table (or computer) and diving with nitrox. Your logic is > sound. No, his logic is not sound. 1. My air tables let me go to 240fsw. Not a good idea on 40%. 2. There is no reduction for anyone, young or old, in the risk of DCS using nitrox to air limits. None. This practice is an old wives' tale from the late '80s that just won't die. Dive air and save money, or dive nitrox and extend bottom time. Nitrox on air tables is just foolish. > Dive air and save money, or dive nitrox and extend bottom time. And for those places that sell nitrox and air at the same price, you can do both... > 2. There is no reduction for anyone, young or old, in the risk of DCS > using nitrox to air limits. None. This practice is an old wives' tale from > the late '80s that just won't die. "Some of the benefits are: 1. EANx, when used with standard dive tables or computers, provides a tremendous safety factor. In fact, when utilized in this fashion, the actual nitrogen accumulation is that for a 10 to 20 feet (3 to 6 meter) shallower dive. This application of EANx is ideal for divers who simply wish to be more conservative individuals who are not "as young as they once were" or those who may not be in the peak of physical fitness." http://www.iantd.com/iantd6.html "There are two ways to utilize EANx. The first is termed the "physiological" advantage. This means breathing EANx while using whatever sport diver tables/computer (based on air) you currently use. Since you are breathing a mix that employs less nitrogen than air, you will accumulate less nitrogen than you would breathing air on the same dive profile. Since you have accumulated less nitrogen than your air table/computer has calculated, you have a "physiological" safety factor; you are at less risk for a decompression sickness hit than you would be breathing air on the same dive." -- Larry "Harris" Taylor, PhD http://www.mindspring.com/~divegeek/stuff.htm "Nitrox diving may extend bottom times or decrease the possibility of decompression sickness, depending on how it's used . . ." http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=35 "[A] given dive using nitrox as the breathing gas but with a decompression table based on air will be more reliable or have a lower predicted decompression sickness incidence (PDCS)." -- Dr. R.W. Bill Hamilton http://www.cisatlantic.com/trimix/AQUAcorps/mix/RWHNitrox.htm Now I'll grant you that Hamilton concedes: "Finally, a word about "safety." Recreational decompression procedures are all "safe" in the sense that there is an extremely low probability of encountering DCS, and in particular of being injured by it. Enriched air reduces that probability still more. Calculations notwithstanding, it seems ludicrous to promote that this is "safer" when the difference in incidence could not be detected except by a controlled test program involving hundreds or even thousands of dives." But that means that it would be detectable in a controlled test program involving hundreds or thousands of dives. Ludicrous or not, nitrox on air tables makes a diver safer. >>2. There is no reduction for anyone, young or old, in the risk of DCS >>using nitrox to air limits. None. This practice is an old wives' tale from [quoted text clipped - 10 lines] > > http://www.iantd.com/iantd6.html This is an old wives' tale from the 80's that just won't die. > "There are two ways to utilize EANx. The first is termed the "physiological" > advantage. This means breathing EANx while using whatever sport diver [quoted text clipped - 7 lines] > > http://www.mindspring.com/~divegeek/stuff.htm Ditto. The fact is that, within the recreational limits, reducing nitrogen accumulation has ABSOLUTELY NO AFFECT on the risk of DCS. Zero. None. > "Nitrox diving may extend bottom times or decrease the possibility of > decompression sickness, depending on how it's used . . ." > > http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=35 That's true. "..depending on how it's used..." For example, nitrox used outside the air table limits decreases the possibility of DCS. That's why we use it. > "[A] given dive using nitrox as the breathing gas but with a decompression > table based on air will be more reliable or have a lower predicted > decompression sickness incidence (PDCS)." -- Dr. R.W. Bill Hamilton > > http://www.cisatlantic.com/trimix/AQUAcorps/mix/RWHNitrox.htm This is not true, and has been debunked by any number of researchers including NOAA, DAN, DCIEM, and Hamilton himself. > Now I'll grant you that Hamilton concedes: "Finally, a word about "safety." > Recreational decompression procedures are all "safe" in the sense that there [quoted text clipped - 3 lines] > "safer" when the difference in incidence could not be detected except by a > controlled test program involving hundreds or even thousands of dives." It certainly is ludicrous to promote that this is "safer" when the difference in incidence could not be detected. And the fact is that NO DATA HAS EVER BEEN PRESENTED THAT INDICATES THAT A LEFTWARD SHIFT ALONG THE TIME LINE WITHIN RECREATIONAL LIMITS HAS ANY AFFECT ON INCIDENCE OF DCS. Period. > But that means that it would be detectable in a controlled test program > involving hundreds or thousands of dives. Ludicrous or not, nitrox on air > tables makes a diver safer. Unfortunately, it has never been detected, by anyone. And check the dates on the above cites... >> NO DATA HAS EVER BEEN PRESENTED THAT INDICATES THAT A > LEFTWARD SHIFT ALONG THE TIME LINE WITHIN RECREATIONAL LIMITS HAS ANY > AFFECT ON INCIDENCE OF DCS. Period. Let's examine this assertion by moving left on the time line to its origin. Many have said that zero time in the water equates to zero chance of DCS, perhaps you agree. So, move a bit farther to the right, say one minute, and compare that to say 90 minutes. Would your chance for DCS be greater with 90 minutes at 20 feet or 1 minute at 20 feet? (This is a recreational range.) If you say the risk is equal, then you proffer the risk at zero throughout the recreational dive range. When you "know" the risk is zero there is little one can offer as proof to increase the risk. You're probably even willing to do something 1,000,000 times riskier without blinking an eye. This is rec.scuba where your risk is anything you want it to be. >>>NO DATA HAS EVER BEEN PRESENTED THAT INDICATES THAT A >> [quoted text clipped - 13 lines] > > This is rec.scuba where your risk is anything you want it to be. No, the risk is a simple and statistically proven curve. Yes, the risk of DCS when not diving is zero. Yes, the risk of DCS increases the instant you enter the water. No, the risk of DCS does not increase over time until you exceed the recreational limits (by a considerable amount) until a point where the curve turns upward. That turn is very sharp and reaches near vertical very quickly. No, the risk is not anything you want it to be. The shape and magnitude of the risk curve has been studied for at least 118 years and is pretty well defined. It is a bit fuzzy in the area where it turns, but not very. Other points on the curve are defined very narrowly; the flat portion is very flat and equal to the incidence of "undeserved hits" (which in many data includes diagnosed DCS which may not be DCS at all) and the near vertical portion is, essentailly, 1.000 Yes, anywhere within the tables your risk = "undeserved hits", a number that varies from data set to data set, but does not vary with points within the tables. There is then a very narrow range of time/depth profiles starting somewhere outside the tables where risk increases from near zero to near certainty. Then there is a section of the curve where you get bent regardless of whether you smoke air or nitrox. That's where you shift to another gas like trimix or heliox and use tables for the gas yer diving. > No, the risk is a simple and statistically proven curve. > > Yes, the risk of DCS when not diving is zero. Unless you are a space cowboy. Matthias > Yes, the risk of DCS increases the instant you enter the water. > > No, the risk of DCS does not increase over time until you exceed the > recreational limits (by a considerable amount) until a point where the > curve turns upward. That turn is very sharp and reaches near vertical very > quickly. These factoids are interesting. You imply that DCS will affect equally 10,000 students sucking air at the bottom of the pool or 10,000 divers down 100 feet in Lake Tahoe. Five minutes in the pool at 10 or five minutes in the cold at 100 is all the same as far as the DCS clock is concerned. If it ticks on you, your alarm goes off. I wonder if DAN incidence reports bear that out. > No, the risk is not anything you want it to be. The shape and magnitude of > the risk curve has been studied for at least 118 years and is pretty well [quoted text clipped - 3 lines] > includes diagnosed DCS which may not be DCS at all) and the near vertical > portion is, essentailly, 1.000 Some of the best and brightest medical minds studied the problem of sickness and determined that people could be healed by opening their arteries and draining blood from their bodies. It wasn't that many years ago that bleeding was a medically recognized cure. Sometimes you need to use common sense in order to survive. > This is an old wives' tale from the 80's that just won't die. Maybe because, like lots of old wives' tales, it's true. > This is not true, and has been debunked by any number of researchers > including NOAA, DAN, DCIEM, and Hamilton himself. Cite? > It certainly is ludicrous to promote that this is "safer" when the > difference in incidence could not be detected. And the fact is that NO > DATA HAS EVER BEEN PRESENTED THAT INDICATES THAT A LEFTWARD SHIFT ALONG > THE TIME LINE WITHIN RECREATIONAL LIMITS HAS ANY AFFECT ON INCIDENCE OF > DCS. Period. So many things have indicated they may have an effect on incidence of DCS: ascent rate, safety stops, post-dive exertion, post-dive flying, post-dive hottubbing. Using nitrox on air tables means that the diver has less residual nitrogen which means that ascent rate isn't as critical, safety stops are less mandatory, post-dive exertion, flying, and drinking beer may be rendered safer. Safer. Period. > Unfortunately, it has never been detected, by anyone. Cite? I'm not aware of a controlled study involving thousands of dives. Are you? Let's get 10,000 divers together. Have half dive air to the limits of air tables, say at 90'. Have the other half dive 36% to the same profile. Let's make the ascent rate 60' per minute, like it's still taught by PADI, and let's skip the safety stop since they're optional. Immediately after the dive, all divers will then sit in a 103-degree hot tub (we'll have to find a big hot tub) and down a six-pac of beer. Finally, everyone flies home 12 hours after the dive. I posit that my group, the 36%ers, will have less incidence of DCS. > And check the dates on the above cites... It's not exactly rocket science, but simple common sense. Less nitrogen = less risk of harmful nitrogen bubbling. I think it was Bert or Haldane who first figured this out. Those are some really old cites too. Unless you're aware of more recent developments, say controlled studies involving thousands of dives? > Cite? I'm not aware of a controlled study involving thousands of dives. > Are you? There have been a number of studies of undeserved hits, including DAN and USN. All have shown no corelation between incidence of hits and profile. Undeserved hits are totally random. > Let's get 10,000 divers together. Have half dive air to the limits of air > tables, say at 90'. Have the other half dive 36% to the same profile. [quoted text clipped - 5 lines] > > I posit that my group, the 36%ers, will have less incidence of DCS. And you posit wrong. >> I posit that my group, the 36%ers, will have less incidence of DCS. > > And you posit wrong. I'm willing to stake money on it. And booze. >>>I posit that my group, the 36%ers, will have less incidence of DCS. >> >>And you posit wrong. > > I'm willing to stake money on it. And booze. what kind of booze??? >>>> I posit that my group, the 36%ers, will have less incidence of DCS. >>> [quoted text clipped - 3 lines] >> > what kind of booze??? Let's make it $1 and a bottle of Appleton's. I just can't take advantage of a guy whose T-shirt reads "Trust Me, I'm a Lawyer". >> I posit that my group, the 36%ers, will have less incidence of DCS. > > And you posit wrong. More cites: > (for you newbies, 10footstop is the only diving medical source worth a > sh.t, and a {free} subscription is mandatory for all divers that have even > the slightest interest in their health.) -- Mike Gray, 7/11/06 "Some people believe that you should gradually reduce the depth and times of dives as you grow older; others feel that you should lengthen safety stops and surface intervals. The only proven ways to reduce your risk of DCS are using nitrox on air tables and not diving at all." -- Ern Campbell, M.D., 11/28/05 http://tenfootstop.blogspot.com/2005/11/questions-we-answered-for-scuba-diving.html Did I hear Campbell say "proven"? > >> I posit that my group, the 36%ers, will have less incidence of DCS. > > [quoted text clipped - 16 lines] > > Did I hear Campbell say "proven"? Remember, Mike - he's a lawyer, and he's good.... > No, his logic is not sound. > > 1. My air tables let me go to 240fsw. Not a good idea on 40%. Depth wasn't the issue raised by the original poster. If it had been then the MOD would have been discussed. Not a good idea on 40% and questionable on 21%. 205' sticks in my mind as a safer depth but one must question the wisdom of that should the opportunity present itself. > 2. There is no reduction for anyone, young or old, in the risk of DCS > using nitrox to air limits. None. This practice is an old wives' tale from > the late '80s that just won't die. It won't die until it's out of the lesson plans of instructors. It seems to me that you are saying it is not safer to devote more time to decompression. When an oxygen table calls for 3 minutes of decompression at 10 feet and air table calls for 8 minutes, you're saying there is no reduction of risk of DCS if you decompress for 8 minutes on oxygen instead of 3 minutes. You're saying this is true even if your bodies ability to expel nitrogen is impaired. If that's your position it's counterintuitive and contrary to popular teaching. > Dive air and save money, or dive nitrox and extend bottom time. Nitrox on > air tables is just foolish. Dive air and save money. That's good advice. >> 1. My air tables let me go to 240fsw. Not a good idea on 40%. > Depth wasn't the issue raised by the original poster. You can't talk about safe or safer without including depth. Depth is always an issue in diving. > Not a good idea on 40% and questionable on 21%. 205' sticks in my mind as > a safer depth but one must question the wisdom of that should the > opportunity present itself. Great example of why diving nitrox based on air tables is a poor idea. You'd be dead on 40% and beyond what most people t hink is wise on 21%. The limit for 21% at a PPO2 of 1.4 is 187 fsw, at a PPO2 of 1.5 is 203 fsw and at a PPO2 of 1.6 is 218 fsw. The same limits on 32%, the lowest standard nitrox mix, are 111 fsw, 122 fsw and 132 fsw. Note that all of these O2 limits are within normal recreational limits. A nitrox computer, set for nitrox would tell you. An air computer, or a nitrox computer set for air, would not. Still feel safer using nitrox with an air computer? > It won't die until it's out of the lesson plans of instructors. It seems > to me that you are saying it is not safer to devote more time to [quoted text clipped - 4 lines] > expel nitrogen is impaired. If that's your position it's counterintuitive > and contrary to popular teaching. Diving at, or beyond no deco limits is not the same as diving within no deco limits. Nevertheless, if Mike were to say, as I think he would, that diving within your no deco limits, or with the appropriate amount of decompression time is equally safe no matter what the gas, I would agree. I think you would too. Enough is enough. Anything more than enough may make you feel better about your risk, but it doesn't make you any safer. > Dive air and save money. That's good advice. Until nitrogen begins to be the factor that limits how much diving you can do. Those with consumption similar to Mike and I can get into deco territory in a single air dive. If we were to dive air, we'd throw half of it away after many of our dives. The problem gets worse on subsequent dives. Depending on the mix, nitrox may offer more than twice the no deco time, time we are able to make good use of on the first dive, and on every one thereafter. I have often said that the time to seriously consider nitrox is when your no deco time rather than your available gas supply, begins to be the factor limiting your dive time. Lee >>No, his logic is not sound. >> [quoted text clipped - 4 lines] > on 21%. 205' sticks in my mind as a safer depth but one must question the > wisdom of that should the opportunity present itself. You cannot divorce depth and time. That's what all profiles are, x depth for y time. And you are correct that 240, and even 205, is playing at the point where that flat risk curve begins to curl upward. Over the years, the table limits for all forms of diving have been moved well to the left of the beginning of the curve, largely because that curve goes nearly vertical very quickly - a small error can have big consequences. Conservatism, therefore, dictates that we stay well into the flat part of the risk curve. However, once well within the flat part there is nothing to be gained by moving even further to the left, as by diving nitrox on air tables. > I understand what you are saying. The reason I dive nitrox on air > tables, is an increase in safety factor. Know a lot of people bent while within the tables do you? Save your money. Lee >>>>>I have never bothered. I dive either 32 or 36, but I dive to my >>>>>standard air tables. [quoted text clipped - 16 lines] > I understand what you are saying. The reason I dive nitrox on air > tables, is an increase in safety factor. There is no increase in safety gained by diving nitrox on air tables. To be safe, dive nitrox on nitrox tables. >>>>>> I have never bothered. I dive either 32 or 36, but I dive to my >>>>>> standard air tables. [quoted text clipped - 20 lines] > > To be safe, dive nitrox on nitrox tables. Granted the air tables do not take into account oxygen toxicity, but as long as you did not exceed your MOD for your gas and doing multiple dives, why would there not be the added margin of safety of a higher EAD? i.e.- You are diving a 32% mix. You dive to 90ft. Your EAD is 73ft. If you dive the air tables your maximum NDL is 24 minutes. If you dove it referring to your EAD of 73 ft, your maximum NDL is now 31 minutes. So by diving nitrox but using air tables to determine bottom time, you are actually ascending 7 minutes ahead of your NDL. Then factor in a SI based on air and you have increased your margin of safety even more. As mentioned, Oxygen toxicity is not taken into account, but the times I have dove nitrox, I have never even come close to any ox tox issues. > Granted the air tables do not take into account oxygen toxicity, but as > long as you did not exceed your MOD for your gas and doing multiple dives, > why would there not be the added margin of safety of a higher EAD? I presume you mean a shallower EAD. Either way, the falacy is in your question. What makes you think a lower EAD is safer? Dive nitrox according to nitrox standards, nitrox according to air standards (with consideration for O2 time and depth issues), or dive air according to air standards. All are safe. Safe is safe. To put it in a different context, a rec.scuba context, Popeye has a .45 that does not go off. I have a .40 that does not go off. Which was safer? > As mentioned, Oxygen toxicity is not taken into account, but the times I > have dove nitrox, I have never even come close to any ox tox issues. Are you sure? Don't forget that CNS toxicity is not only a depth issue. It's also a time issue. What was your 24 hour exposure? Lee >> Granted the air tables do not take into account oxygen toxicity, but as >> long as you did not exceed your MOD for your gas and doing multiple dives, [quoted text clipped - 17 lines] > >Lee I said I dive Nitrox to air tables, I did not say I ignored MOD ot CNS clock. Those get factored in. But enough, you have given me food for thought. >>Granted the air tables do not take into account oxygen toxicity, but as >>long as you did not exceed your MOD for your gas and doing multiple dives, >>why would there not be the added margin of safety of a higher EAD? > > I presume you mean a shallower EAD. Either way, the falacy is in your > question. What makes you think a lower EAD is safer? Correct. Shallower is a better term. You had two divers enter the water. One goes to 90 ft and stays 24 minutes and ascends. The other diver stays at 73 ft for 24 minutes and ascends. Which one has a less liklihood of DCS? > Dive nitrox according to nitrox standards, nitrox according to air standards > (with consideration for O2 time and depth issues), or dive air according to > air standards. All are safe. Safe is safe. > > To put it in a different context, a rec.scuba context, Popeye has a .45 that > does not go off. I have a .40 that does not go off. Which was safer? Not a great analogy. One of you could have a 2000lb bunker buster that doesn't go off. However, I will congratulate you for turning a diving question into a gun thread. :) >>As mentioned, Oxygen toxicity is not taken into account, but the times I >>have dove nitrox, I have never even come close to any ox tox issues. > > Are you sure? Don't forget that CNS toxicity is not only a depth issue. > It's also a time issue. What was your 24 hour exposure? I figured it both on tables and my computer. Showed a maximum of 15%. Not anywhere close. > Correct. Shallower is a better term. You had two divers enter the water. > One goes to 90 ft and stays 24 minutes and ascends. The other diver stays > at 73 ft for 24 minutes and ascends. Which one has a less liklihood of > DCS? What are they breathing? 90 feet for 24 minutes is the air no deco limit according to my computer. If you intended a no deco dive, you blew it. You're going to have a deco obligation before the end of the dive. If you're using a Suunto computer, you're going to have a long deco obligation. Hope you brought enough gas. Pushing whatever you perceive the limits to be is not a great idea and using a limit and non limit dive to make your point is not a fair comparison. Using two limit dives, 90 feet for 24 minutes versus 70 feet for 40 minutes, my response would be, the risk is approximately the same. Both are no deco limit dives according to my computer. Both will incur a deco obligation before you're done. Both can get you bent if just the right set of conditions exist. Taking your 90 foot depth for the example, my maximum for a no deco dive on air would be a maximum of about 10 minutes. That puts my computer right at the edge of the caution zone, but still in the green. I think I'm safe. I think you'd agree. Using 36%, I would still be safe at the end of 10 minutes, but no safer than I would have been doing the same on air. Safe is safe. At a setting of 36%, I'd still be safe after about 22 minutes. Safe is still safe. Spending the money for nitrox, to dive it like air, O2 exposure issues aside, is a waste of money. You're either bent, or you're not. If you're not, you're safe. >> To put it in a different context, a rec.scuba context, Popeye has a .45 >> that does not go off. I have a .40 that does not go off. Which was [quoted text clipped - 3 lines] > doesn't go off. However, I will congratulate you for turning a diving > question into a gun thread. :) I thought it was a perfect analogy. In diving, you're either bent or you're not. With guns, you're either shot, or you're not. If you're not, you're safe, no matter what caliber gas, or gun, you weren't bent/shot with. I thought you'd like the transition. I considered using a law enforcement context, but the gun one is more appropriate here. 8^) > I figured it both on tables and my computer. Showed a maximum of 15%. Not > anywhere close. I would agree. I have to wonder, however, why you don't apply the same standard to O2 issues that you to do N2 ones. Why do you consider "not even close" to nitrogen limits safer on nitrox than on air, but not also consider "not even close" to oxygen limits to be less safe on nitrox than air? Lee |
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