PADI vs SDI
#16
Posted 26 December 2009 - 11:37 PM
While I definitely agree with what everyone has posted here regarding the instructor being a huge factor as to which kind of course you'll get, *you* are also a deciding factor. Read the material and make sure that you *understand* the material. If a concept isn't clearly presented in the book, ask the instructor. If you're not comfortable with the instructor's answer, there's a wealth of scuba knowledge on this board, and we are more than happy to proffer second opinions.
And remember that, like every other dive skill, the skills you learn in the Nitrox course will atrophy with neglect. So keep your skills fresh by diving often.
Mark
#17
Posted 27 December 2009 - 09:34 AM
I think it's all been said. Nitrox doesn't just improve your overall safety but for most people considerably improves their comfort and fatigue levels. Even if you're on a boat where dive times are determined by other divers on air, if you're on nitrox you can maybe stay a bit deeper for longer, or you can do exactly the same dive as the air guys and feel significantly fresher afterwards. One thing that everyone agrees on is that if it's available it's almost always a no-brainer to use nitrox. It'll cost a bit more, but put that in context of your overall costs for your dive trip.
Let me just clarify what I said maybe a bit too succinctly about learning formulae. What I mean is that you should seek an instructor who will teach you to understand the material, not just to regurgitate it and pass the exam. The formulae in the PADI nitrox manual for example to me typify the worst possible approach to teaching this subject. I always tell my students not even to read that chapter until after they've completed the course to my satisfaction. Then if they wish they can look at it, and I hope will come to the same conclusion as I did when I first saw it. The other thing I always tell my students is to do all nitrox calculations in metric, converting from/to imperial outside the main calculations if they need to. The problem with using imperial is that the maze of numbers totally disguises the simplicity of what's actually going on.
WOW! ,shadragon & Peter,This is some real information to apply.Your comment about PADI is interesting,in that I was always under the impression that since PADI was the 1st recognized organization to set/establish some curriculum ,that they were more strict/thorough.Regardless,you both & others have added a plus to understanding some of the basics.
:
E= pluribus Forum Enjoy the view. ,Do unto others:respect
#18
Posted 27 December 2009 - 09:58 AM
1. Not a cure-all, not suitable for all diving, downright silly for diving in the local mud-pond. Some of us won't dive EAN in water deeper than the partial pressure limit for the mix even if we intend to stay above the MOD for example.
2. Not to downplay the risk of decompression sickness, but the numbers of DCS hits are so low on both air and EAN, that there is no statistical evidence to date that EAN is superior to air in preventing DCS. Further, I haven't seen evidence there is a differential in "undeserved DCS hits" for EAN divers so remember - NOTHING can GUARANTEE your dive may not result in a DCS hit - be ever vigilant even though the odds are extremely remote, know the symptoms.
3. The health and feel-good benefits are widely acclaimed, but undocumented - although I'd love to see some solid research on those reported phenomenon
4. You REALLY should get good training, and shop for a computer you can grow into - think of the future - what kind of diver do you want to be - there is nothing more expensive than a piece of gear you don't use - e.g. a single gas computer once you decide to take advanced EAN training and start deco diving
5. If you take a Flower Gardens trip, or almost any gorilla-diving (4-5 dives a day) liveaboard - it's almost impossible to max out your dives on air
6. Differing SACs will differentiate bottom times for most divers more than EAN/air so don't fret too much about being the only EAN diver, even if your buddy is on air - you are buying yourself significant nitrogen loading benefits even if you have to follow your buddy's air profile. Again, I know divers who use EAN, but keep their computer set to 21% (I STRONGLY don't recommend this, but wanted to mention it because it does happen - MOD is MOD regardless)
Bottom line - get the training, use the devil gas when appropriate. At your earliest point of comfort, take an advanced EAN course for using > 40% mixes
Edited by Capn Jack, 27 December 2009 - 12:01 PM.
Jacques Yves Cousteau
#19
Posted 27 December 2009 - 11:47 AM
3. The health and feel-good benefits are widely acclaimed, but undocumented - although I'd love to see some solid research on those reported phenomenon
My 2 psi: Maybe we can start some testimonial research here and pass it on to DAN?? I'm not a scientist, but I CAN testify that diving 3x or 4x per day for a week on 21% regular air, I'm usually feeling very fatigued by the end of the week, and doing the same number of dives on EAN 32% to 34%, I feel no fatigue by weeks end. Unscientific testimony to be sure, but it must count for something!
Don't follow that air breather too deep if you're on EAN! He gets too far below 100 feet, and he'll be leaving ME behind because I dive a very conservative MOD.6. - you are buying yourself significant nitrogen loading benefits even if you have to follow your buddy's air profile. Again, I know divers who use EAN, but keep their computer set to 21% (I don't recommend this, but wanted to mention it)
Not changing the Nitrox percentage on your computer is just asking for trouble if you rely on the computer for dive depth limits & no deco limits, IMHO. If you're going to dive mixed gasses, get a computer that can handle them, and set them properly!
I'm sure Kamala has a lovely computer deal worked out with Cochran dive computers!
#20
Posted 27 December 2009 - 12:04 PM
Why I mentioned that some EAN divers will not dive a mix over a bottom that is beyond their MOD. Wall dives are a good example.Don't follow that air breather too deep if you're on EAN! He gets too far below 100 feet, and he'll be leaving ME behind because I dive a very conservative MOD.
Jacques Yves Cousteau
#21
Posted 27 December 2009 - 07:37 PM
Point one Find an instructor that has tech training or better yet a tech instructor, if possible. You will probably get the unabridged course content and the explanations of why you should get in the habit of doing things a certain way.
I absolutely agree that once you have your basic Nitrox cert get comfortable in the application of it.
Get a MOD chart, I made mine in Excel. It is laminated in the front of my log book. That way you can analyze your gas, look up the MOD and don't dive it any deeper then that.
My 2psi is that the Advanced Nitrox class is one of the best courses I’ve taken. After AOW and Rescue anyone looking for more diving education should take the Advanced Nitrox class. It is a bit challenging but the content is great! You’ll learn to use a 7 foot hose, the nitty gritty of oxygen and nitrogen diffusion in and out of suspension, and how to throw a lift bag. Two very usable skills and a bunch of great information.
The advice about getting a computer for the diver you want to be and not the diver you are now is perfect, I wish I had said it!!
Nitrox when used to limit your nitrogen uptake on multiday trips is a very useful tool to keep you as far removed from the repetitive dive No Decompression Limits as possible.
When you use it to extend your bottom time on a NDL dive the extended bottom Time is real. Here in NC on a standard two tank boat dive the max depth is about 115 FSW. With air as my back gas my Cochran computer, with 25% Conservatism, gives me:
12 min NDL at 110FSW and 9 min at 120FSW
When I run the numbers for 30% I get:
20 min NDL at 110FSW and 15min at 120FSW.
That's more then a 50% increase in available time at depth for the same Nitrogen uptake. Those are real numbers. Then add to that a switch to 80% O2 at the appropriate depth and a nice long safety stop I can get out of the water with a very short time to fly time. My computer tracks time to fly as a function of nitrogen loading not just a countdown timer. I get a lot more off gassing at 15FSW on 80% O2 (or pure O2 for that matter) then I get on air sitting on the boat.
In Cozumel there was a SNAFU with my Nitrox order one day. Most of the week I was able to finish up the day with about 18hours time to fly while diving Nitrox. After one day of air dives mid week I finished up with over 36hours time to fly.
Anything you can do to limit the amount of nitrogen absorbed by your body is a good thing.
Sorry for the Tech detour but this is where Nitrox can take you and the things it can do for you if you learn how and when to use it.
Each wreck has a tale to tell about its life and its demise.
If you are observant while diving in dark places listen to the account each has to tell, You cannot come away unaffected.
Changes in Latitude, Changes in Attitude
#22
Posted 27 December 2009 - 07:54 PM
I started this regime just diving air, and on several occasions I was forced to stop the car on the way home for a couple of hours' sleep before I could continue. Rarely would I ever unload the car when I got home, but I'd leave it till the next day and hope that a potential thief would be put off by the damp dank smell!
Then I started using nitrox, and the difference was profound. I'd take down a side sling of 32% or 36% for use on the first dive when I was shallow enough. I still used my air computer so was underwater for the same time, but I felt an awful lot better when I surfaced. In those days we didn't have lifts to get out of the water on (they're almost universal now) and I was really concerned about the tremendous effort needed to haul a twinset plus a sidesling, plus a very heavy drysuit and an enormous amount of lead. There weren't always people to help, and when the sea was rough (pretty common) it was very arduous. Once I started using nitrox this became much easier.
The second dive would normally be on nitrox, ideally 36%, and despite the beer I had with my meal and the very late start for the return journey I always thereafter cleared out the car and rinsed all the gear when I got back. To me there's no question about it - nitrox makes you feel MUCH fresher after a day's hard diving.
Some comments on statements made. I don't have a problem using or having someone else use an air computer with nitrox. Why is this undesirable?
When I teach nitrox, I impress upon my students that once they're kitted up and ready to go, there's only one difference between nitrox and air diving, and that's the maximum acceptable depth. I ask people what their maximum depth is for the forthcoming dive, and I expect two answers (for 1.6 and for 1.4). If I don't get those answers I read those divers the riot act there and then! For Americans it's actually a bit easier to remember than it is for people using metric depths - for 36% the two depths are roughly 90ft and 110ft, and for 32% they're (again roughly, but pretty close and erring on the side of conservatism) 110ft and 130ft. Very easy to remember. This information must be in your HEAD when you jump into the water, not just written down somewhere and certainly not written on the EANx label stuck to your tank, where of course it's completely inaccessible to you during the dive.
As to walls, if divers can't be relied on to remember and act on the maximum depths dictated by the mixes they're diving, AND to have the buoyancy control to make this easy and dependable, then they shouldn't be on the wall at all. In fact, they shouldn't be diving at all until they've got their skills up to an acceptable and safe level.
A couple more points having just read Jerry's excellent post. First, if you've had decent training (both formal and by example from your peers) you'll have learned long ago how to deploy and use a DSMB. I don't call them "lift bags" because they're completely different in construction and designed to do different jobs. In England most serious divers carry two DSMBs and two lift bags on every dive, with a separate reel for each. The red DSMB is for use on every ascent, the yellow DSMB is to announce to the people up top that you have a problem and (are likely to) need help, the first lift bag is to raise anything on the bottom that you decide would look good on your mantlepiece, and the second lift bag is for when you find that the first doesn't have enough lift to overcome the stiction
The advanced nitrox course is IMO badly named, because the nitrox bit of it is relatively marginal. It should instead be called "Intro Tech", as it principally covers equipment management and handling and scenarios you have probably never experienced before.
Caution needs to be employed when using lift bags (for their intended purpose). Unless you've planned a recovery dive, you probably have about the right amount of breathing gas for your dive, plus a safety margin. Once you start filling a lift bag it's remarkable how much gas it uses (you can work it out - there you are, your homework!). If you then need to resort to the second, that doubles what you use. If, as a friend of mine found, the two lift bags are still not enough you might be tempted to start using your DSMBs. He did, and just after he'd started filling his second DSMB he ran out of back gas. He was at the time on the bottom at about 270ft, quite alone, and with his next available gas 35%. That doesn't start becoming usable until around 115ft, so he had a fair way to go up before he could switch to it. He did it, skipping quite a few deco stops along the way, but then of course ran out of 35% long before he'd acquitted his (mentally recalculated) deco obligations. So up to (what depth?) so he could use his 80%. He couldn't of course send up his yellow DSMB or indeed any signalling device as he'd left them all on the bottom attached to the brass porthole he'd inadvertently left for the next diver (along with a nice present of four flotation devices and four reels). There was a fair current that day and the dive boat was tied into the wreck, so when he finally bolted for the surface, out of gas but still with 50 minutes of deco obligation, he was 3/4 of a mile away in a grey and choppy sea, clad all in black. Remarkably, because no-one was due to surface yet, the skipper happened to be looking in that direction and spotted him. By the time I surfaced the boat was back over the wreck and the chopper was on its way, and in due course it whisked him off to a chamber somewhere. Even more remarkably, he was back diving again within a month. He did something stupid on a CCR later, I heard, got away with it again, but then gave up diving. I think he took up a nice safe sport like base jumping or motorcycle racing.
Edited by peterbj7, 27 December 2009 - 08:37 PM.
#23
Posted 27 December 2009 - 08:33 PM
I like your position, and your approach to how we should dive, make no mistake about that. I am not trying to hijack this thread, but wanted to respond to these points.Some comments on statements made. I don't have a problem using or having someone else use an air computer with nitrox. Why is this undesirable?
When I teach nitrox, I impress upon my students that once they're kitted up and ready to go, there's only one difference between nitrox and air diving, and that's the maximum acceptable depth. I ask people what their maximum depth is for the forthcoming dive, and I expect two answers (for 1.6 and for 1.4). If I don't get those answers I read those divers the riot act there and then! For Americans it's actually a bit easier to remember than it is for people using metric depths - for 36% the two depths are roughly 90ft and 110ft, and for 32% they're (again roughly, but pretty close and erring on the side of conservatism) 110ft and 130ft. Very easy to remember. This information must be in your HEAD when you jump into the water, not just written down somewhere and certainly not written on the EANx label stuck to your tank, where of course it's completely inaccessible to you during the dive.
As to walls, if divers can't be relied on to remember and act on the maximum depths dictated by the mixes they're diving, AND to have the buoyancy control to make this easy and dependable, then they shouldn't be on the wall at all. In fact, they shouldn't be diving at all until they've got their skills up to an acceptable and safe level.
First - I personally don't dispute the improvement in energy etc - I've had similar sensations - but I'm at a loss to find a documented reference, so I don't push it too hard as a benefit of EAN.
Second - My aversion to diving an air computer is based solely on my observation that people are very reliant on their computer, and if it's not beeping, they think all is well. I agree that diving an air profile and obeying the appropriate depth limits for the mix in use gives one an added margin, and in that a regard is a good practice.
Second - On walls, it seems to me there is always someone who doesn't pay attention, and if I can, I get to them and help them back to a reasonable depth. On EAN, I lose that option - and while it's maybe an example of Darwin's principles - I don't like the feeling of not being able to assist if need be - or to risk a CNS event if I decide foolishly to chase the "improving the gene-pool" candidate.
Edited by Capn Jack, 27 December 2009 - 08:38 PM.
Jacques Yves Cousteau
#24
Posted 27 December 2009 - 09:00 PM
Did I ever tell the story of something I witnessed in the Egyptian Red Sea? I was with a friend, both of us new instructors, and we joined a large group (they're all cattle boats out there) led by a German instructor, a girl we both knew and had dived with before on previous trips. The group included about 20 divers, including us, and she had no supporting staff, so we told he we'd take up the tail of the group. I should add that the dive was at around 18mtr (60ft) and in her very comprehensive briefing she had warned of a down-current that might exist at one point, which could be expected to start at around 25-30mtr. At our depth we would be well clear of it.
She led from the front. Periodically she'd turn and scan the group, evidently counting the divers. We kept a general eye on the group from high at the back, primarily watching for any divers who might stray surface-wards. Then on one occasion she repeated her scan, and clearly something was wrong. We looked up and couldn't see anyone, and at the same time as her we looked down. Well below the group, at at least 30mtr, there were two divers, animatedly looking at the wall and seemingly oblivious of their depth. The guide signalled to us that she was going down, so we moved closer to the group. Clearly the divers were still descending, and by the time she reached them looked very deep. But she grabbed them and hauled them upwards - no finesse and no politeness! Because these two divers were now almost out of air and there had been no provision for staggered ascents, we all had to end our dive at that point. I found out afterwards that she had reached the two miscreants at around 55mtr, and that she was diving nitrox 36%. You work out what danger she put herself in to rescue these two Italians, who showed not the slightest remorse or even understanding of what they had done. At least the dive shop confiscated their cards and told all local operators the story, so their diving holiday was over. Would you have done what she did? Actually, she could have sent us down, because there were two of us and two of them, and we were on air. But she was working and we weren't, and I don't suppose her professionalism would have let her do that.
#25
Posted 27 December 2009 - 09:47 PM
I would do anything in my power to assist a diver in distress up to and probably including dying in the attempt. But severely risking my life in the attempt to rescue two blatantly stupid people......I don't know. An Oxygen seizure at 180FSW would undoubtedly be fatal.
Edited by Jerrymxz, 27 December 2009 - 09:48 PM.
Each wreck has a tale to tell about its life and its demise.
If you are observant while diving in dark places listen to the account each has to tell, You cannot come away unaffected.
Changes in Latitude, Changes in Attitude
#26
Posted 27 December 2009 - 10:05 PM
Sitting here, drink in hand, calmly thinking about this, I'd have to stick with the company line and say - "don't make 3 victims when you already have 2" - sadly, I'd probably have realized they were deeper than they should be, and pursued as she did without calculating the ppo2 (2.34 in this case). I would for sure have not sent you and your buddy down. So... short answer - yes - I might have tried a few tank bangs on the way down to get their attention, but at 50+ m, they were probably oblivious.I found out afterwards that she had reached the two miscreants at around 55mtr, and that she was diving nitrox 36%....Would you have done what she did?
Jacques Yves Cousteau
#27
Posted 28 December 2009 - 12:00 AM
#28
Posted 28 December 2009 - 12:20 AM
This made me dive (pun intended) for "the book" - a chamber ride following table 6 calls for going to 60 feet on 100% O2 - which would be real close to 3.0 ppO2. Of course this is in the chamber, so if you start doing the funky chicken it's not as immediately life threatening as it would be underwater.Navy divers in wartime are expected to work to 3.0, and most are expected to survive.
Jacques Yves Cousteau
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