Diving Nitrox to increase safety AND bottom time!

[beaverdivers]

SDI COMPUTER NITROX COURSE: Traditionally, becoming a Nitrox Diver required long hours in the classroom, learning how to work obscure formulas and use complex dive tables. No more. Through SDI's on-line training program, you can complete most of the required academic study in the comfort and convenience of your home or office. And, as with all SDI programs, you'll learn to dive Nitrox the modern way, using Nitrox-programmable dive computers instead of arcane formulas and complicated tables.

I went to my LSD for our I think 2 hour course and he didn't even mention tables. The he asked if we had any questions..... Uh yah, how do you use the tables? He spent another half hour with all of us to go through it but I was pretty floored that it wasn't covered in class. That's when I looked deeply into the Above course description.. Should've skipped it althogether and gone straight to advanced nitrox. I'm sure that would break some rules of not paying for all the classes! Arcane formulas and complicated tables? Really? Just shove them off the gunnel with a $200 computer..... They'll be fine.....

Wolfie,

You signed up for the wrong course for what you wanted. The name of the SDI Computer Nitrox Course and the course description implies that it will be dive computer based.

I would have steered you to the TDI Nitrox course - Dive Tables, Formulas & long hours in the classroom.

I teach both.

I have 100 SDI Computer Nitrox students for every (1) TDI Nitrox student.

 

[DaleC]

Mike, I agree with what you said. That is why I have stopped diving Nitrox for most of my dives. I find they are already conservative enough that I don't need the buffer or the extended BT. But I can think of some dives that do put people closer to DCS and in those cases EAN should/could be considered (along with other mitigation).

My argument (in the greek sense) is that EAN does increase safety from DCS (over air) when one moves closer to the edges of the spectrum and deliberately not addressing that point is not what I would expect when paying a professional to give me all the facts about the subject.

 

[Moonglow]

My argument (in the greek sense) is that EAN does increase safety from DCS (over air) when one moves closer to the edges of the spectrum and deliberately not addressing that point is not what I would expect when paying a professional to give me all the facts about the subject.

This represents why I carefully choose my students.

 

[doctormike]

Mike, I agree with what you said. That is why I have stopped diving Nitrox for most of my dives. I find they are already conservative enough that I don't need the buffer or the extended BT. But I can think of some dives that do put people closer to DCS and in those cases EAN should/could be considered (along with other mitigation).

My argument (in the greek sense) is that EAN does increase safety from DCS (over air) when one moves closer to the edges of the spectrum and deliberately not addressing that point is not what I would expect when paying a professional to give me all the facts about the subject.

Point well taken! And I do agree with you from a practical point of view. I think that we are basically saying the same thing, and I'm probably just being a bit irritating by trying to be overly scientific in my comments. But that makes sense since I tend to be a bit irritating in person as well...!

I guess the bottom line is that the research behind diving practices are much less scientifically rigorous than that behind, say, rocket science or pharmaceutical development, because we don't have the abilities to do big experiments with huge sample sizes. In drug research, you have millions of dollars for testing and an inexpensive model initially (animal tests), and then clinical data on thousands of human subjects once your project reaches that stage. In engineering, we have computer models that precisely mimic reality, so we can try endless permutations of variables, in every conceivable combination, to figure out how a spaceship or a building will respond to stress in the real world.

In scuba diving, there is not much money for research, very limited animal testing and no completely accurate computer model, so we are left with drawing conclusions from historical data, accident reports and collected profiles. That's why I was just saying that we don't really know how much the safety is increased... For example, if I knew that all I was getting from nitrox was a reduction in the undeserved hit rate from two in a million to one in a million (a 50% reduction!), I probably wouldn't bother to use it if I wasn't going to extend my BT.

Dive safe!

M

 

[TheDeuce]

Just for fun I checked out the SSI Nitrox Course online description. Here's the quote that caught my attention:

Combine other specialties while taking the ENRICHED AIR NITROX course! WRECK DIVING or DEEP DIVING are great add ons. The possibilities are limitless!


I'm being totally candid when I say that combining an EAN course with a Deep Diving course didn't leap to mind when planning my extended training. "All right students! Everyone got their tank of N32 strapped on? Great, see you at 130 feet! Remember to keep an eye on your buddy for signs of oxtox..."

Now there's a practical component.




m.

 

[doctormike]

Just for fun I checked out the SSI Nitrox Course online description. Here's the quote that caught my attention:

Combine other specialties while taking the ENRICHED AIR NITROX course! WRECK DIVING or DEEP DIVING are great add ons. The possibilities are limitless!


I'm being totally candid when I say that combining an EAN course with a Deep Diving course didn't leap to mind when planning my extended training. "All right students! Everyone got their tank of N32 strapped on? Great, see you at 130 feet! Remember to keep an eye on your buddy for signs of oxtox..."

Now there's a practical component.




m.

Hah! But as with most things, the devil is in the details, and in this case, in the definition of "deep".

SSI defines deep for the purposes of this course to be below 100 feet. And while oxtox is a risk when you approach the MOD for any mix, there isn't much point in diving nitrox at very shallow depths, you simply don't extend BT enough to make the cost worthwhile. The nitrox sweet spot is in the depths just above the MOD, since that's when you get the most bang for your buck. So it makes a lot of sense to combine nitrox and deep diving, as long as you are above the MOD, right?

For example - on Saturday, I went to the wreck of the Coney Island off NJ, about 110 to the deck, no deco. I was diving EAN 28, which gave me 20 minutes at depth. If I had been diving air, the NDL would have been 16 minutes. OK, it's just four minutes, but that's a 25% increase in dive time for each of two dives, and I thought that was worth it. I usually fill my tanks with 28 if I don't know where I'm going to dive next, since it's less limiting, but if I had know that I was doing this wreck when I filled them, I could have chosen a richer mix as long as I stuck to the deck and suprastructure. I once had 30 in my tanks and then ended up doing the Oregon, so I had to stick to the engine and the top of the boilers (still a great dive!).

 

[TheDeuce]

Hah! But as with most things, the devil is in the details, and in this case, in the definition of "deep".

SSI defines deep for the purposes of this course to be below 100 feet. And while oxtox is a risk when you approach the MOD for any mix, there isn't much point in diving nitrox at very shallow depths, you simply don't extend BT enough to make the cost worthwhile. The nitrox sweet spot is in the depths just above the MOD, since that's when you get the most bang for your buck. So it makes a lot of sense to combine nitrox and deep diving, as long as you are above the MOD, right?

For example - on Saturday, I went to the wreck of the Coney Island off NJ, about 110 to the deck, no deco. I was diving EAN 28, which gave me 20 minutes at depth. If I had been diving air, the NDL would have been 16 minutes. OK, it's just four minutes, but that's a 25% increase in dive time for each of two dives, and I thought that was worth it. I usually fill my tanks with 28 if I don't know where I'm going to dive next, since it's less limiting, but if I had know that I was doing this wreck when I filled them, I could have chosen a richer mix as long as I stuck to the deck and suprastructure. I once had 30 in my tanks and then ended up doing the Oregon, so I had to stick to the engine and the top of the boilers (still a great dive!).

Now, from what I've seen it's unusual to dive N28. Until now I've only been peripherally attentive to nitrox mixes but it seems like the various dive shops I've used gave you a choice of N32 or N32 or, for those special dives, N32. It's the old SNL John Belushi skit- "Cheeseburger cheeseburger cheeseburgercheeseburgercheeseburger". Is EAN underutilized? If I'm doing 5 dives a day I'd like to be able to choose my mixes based on my dive plan, not dive a plan dictated by the only available mix. Starting my day in the Blue Hole? I'll take some N27 or so. Wrapping up at Hol Chen? 100 cubes (as a sop to making BT=NDL) of N40, if you please. Casual reef diving in between? N32 works for me.

That said, I don't know if I'm on board with your contention that "there isn't much point in diving nitrox at very shallow depths, you simply don't extend BT enough to make the cost worthwhile" since I haven't enrolled in either the "extended bottom time only" or the "greater safety" camp. Indeed, what I'm hoping to get out of using nitrox is less fatigue. I get to do a hard-core dive trip once or twice a year and I want to squeeze every dive I can into it and what I've found my limiting factor to be is exhaustion. My ideal dive day is a sunrise dive, breakfast, two boat dives, lunch, nap, two boat dives, nap, sunset dive, dinner, chill on the dock, night dive, sleep like a log, repeat. This ideal isn't realistically achievable but there's a lot of days when I'm not even close. Even if I scrub the sunrise dive I find the 'two afternoon dives' and 'sunset and night dives' become an either-or situation. If the only benefit I get diving nitrox is added energy I'll be a happy diver.



m.

 

[vladimir]

Indeed, what I'm hoping to get out of using nitrox is less fatigue. I get to do a hard-core dive trip once or twice a year and I want to squeeze every dive I can into it and what I've found my limiting factor to be is exhaustion. My ideal dive day is a sunrise dive, breakfast, two boat dives, lunch, nap, two boat dives, nap, sunset dive, dinner, chill on the dock, night dive, sleep like a log, repeat. This ideal isn't realistically achievable but there's a lot of days when I'm not even close. Even if I scrub the sunrise dive I find the 'two afternoon dives' and 'sunset and night dives' become an either-or situation. If the only benefit I get diving nitrox is added energy I'll be a happy diver.

Forgive me for perhaps stating the obvious: I would not expect breathing nitrox and pushing your diving to the new, longer NDLs, to give you less fatigue or less DCS risk. In essence, you will have spent your "nitrox credit" on more dive time. If you dive air profiles and breathe nitrox then you are spending it on less fatigue, and less DCS risk. And, of course, there's some middle ground, where you can exceed air NDLs but be well within 32% (or whatever) NDLs, and then you hopefully get a little more time underwater as well as less fatigue and less risk.

 

[doctormike]

Now, from what I've seen it's unusual to dive N28. Until now I've only been peripherally attentive to nitrox mixes but it seems like the various dive shops I've used gave you a choice of N32 or N32 or, for those special dives, N32. It's the old SNL John Belushi skit- "Cheeseburger cheeseburger cheeseburgercheeseburgercheeseburger". Is EAN underutilized? If I'm doing 5 dives a day I'd like to be able to choose my mixes based on my dive plan, not dive a plan dictated by the only available mix. Starting my day in the Blue Hole? I'll take some N27 or so. Wrapping up at Hol Chen? 100 cubes (as a sop to making BT=NDL) of N40, if you please. Casual reef diving in between? N32 works for me.

Most of the dive shops around here that do nitrox will blend whatever mix you like. I usually ask for 28, which gives me a bit more bottom time at the typical depths around here, but will let me dive to 126 feet, which seems like a pretty good compromise. Yup, it's hard to plan ahead sometime, so that's one of the benefits claimed about a CCR - you always have the right mix at any give depth. I'm not going there any time soon, though...

That said, I don't know if I'm on board with your contention that "there isn't much point in diving nitrox at very shallow depths, you simply don't extend BT enough to make the cost worthwhile" since I haven't enrolled in either the "extended bottom time only" or the "greater safety" camp. Indeed, what I'm hoping to get out of using nitrox is less fatigue. I get to do a hard-core dive trip once or twice a year and I want to squeeze every dive I can into it and what I've found my limiting factor to be is exhaustion. My ideal dive day is a sunrise dive, breakfast, two boat dives, lunch, nap, two boat dives, nap, sunset dive, dinner, chill on the dock, night dive, sleep like a log, repeat. This ideal isn't realistically achievable but there's a lot of days when I'm not even close. Even if I scrub the sunrise dive I find the 'two afternoon dives' and 'sunset and night dives' become an either-or situation. If the only benefit I get diving nitrox is added energy I'll be a happy diver.



m.

Right, as has been mentioned upthread, and in many, many other threads, lots of people feel better diving nitrox, and no amount of scubaboard discussion or data is going to change that. So I agree, if you feel better when you dive nitrox at shallow depths, then you should do that.

 

[TheDeuce]

Forgive me for perhaps stating the obvious: I would not expect breathing nitrox and pushing your diving to the new, more liberal NDLs to give you less fatigue or less DCS risk. In essence, you will have spent your "nitrox credit" on more dive time. If you dive air profiles and breathe nitrox then you are spending it on less fatigue, and less DCS risk. And, of course, there's some middle ground, where you can exceed air NDLs but be well within 32% NDLs, and then you hopefully get a little more time underwater as well as less fatigue and less risk.

Now this is getting into the areas that I'm looking forward to experiencing first hand. My armchair-only nitrox experience tells me that there are three benefits to diving nitrox:

1. More NDL time
2. Reduced DCS risk
3. Reduced fatigue

Now correct me if I'm wrong, but those benefits flow from the following:


1. More NDL time - a result of there being less nitrogen in the tank hence less nitrogen in your system
2. Reduced DCS risk - as above, at least until the point where you've ongassed the same nitrogen as you would have on air
3. Reduced fatigue - a result of more oxygen in the tank

Benefits number one and two are a see-saw. The more advantage you take of one, the less you glean from the other. Push your bottom time to the max and you'll have the same DCS risk that you'd have on air (notwithstanding the middle ground I discussed in my OP). But point number three is different. It stands alone. It's not dependent on either of the first two benefits nor is it included in the aforementioned trade-off. So I don't automatically agree with your first point where you say "I would not expect breathing nitrox and pushing your diving to the new, more liberal NDLs to give you less fatigue or less DCS risk". I can see how pushing the new NDL's will reduce my DCS risk reduction (#awkwardsentences) but I don't see how it would affect the added energy benefit. More oxygen is more oxygen, period.

That said, the added energy aspect seems to vary from diver to diver. I've read of divers who indeed feel slightly energized after diving EAN, others who've noted no difference. Different results for differing physiologies, I suppose. I'm doing the Cayman Aggressor from October 20-27 (my first diving since getting my EAN card) and plan to dive, dive, dive so that should be a good litmus test to demonstrate any energetic benefit that nitrox will provide me with. I'll be sure to share my findings.



m.