Is there any reason to do a Nitrox 'course'?

[MaxBottomtime]

I must be misunderstanding your point, because I can't believe you wouldn't understand the intrinsic connection between bottom time duration and nitrogen absorption.... The relative level of nitrogen on-gassing and off-gassing being the crux of whether DCS symptomatic bubbles occur...

If you have less nitrogen inside, you have less risk of bubble formation in any given scenario. Nitrogen leaving saturation at a rate exceeding its transport from the body being the root cause of DCS. That might easily be interpreted as 'less risk of DCS'.

Again, the intrinsic link between the level of nitrogen saturation and DCS risk is well understood.

In addition, there are known benefits in respect of increased PPO2 in limiting and/or collapsing bubbles that may have begun to form. Again, this might easily be interpreted as 'less risk of DCS'.

I understand all of that. I was referring to your comment that there was a signicant reduction of risk. With the low risk of DCS when following proper ascent profiles at less than one per cent of the dives made, any reduction would be minimal, not significant.

 

[DevonDiver]

I understand all of that. I was referring to your comment that there was a signicant reduction of risk. With the low risk of DCS when following proper ascent profiles at less than one per cent of the dives made, any reduction would be minimal, not significant.

As mentioned before, it's only insignificant if you're not one of those who gets unlucky.

That said, pretty much all of us do dive whilst effected by one, or more, pre-disposing factors to DCS. Many divers do experience improper ascent profiles, accidentally or otherwise. A significant proportion of divers do also present physiological factors that may increase DCS likelihood, such as PFO. Likewise, a significant number of divers also push the boundaries with aggressive dive profiles, without compensation through their ascent plan.

"According to the PDE data collected between 1998 and 2004, the decompression sickness (DCS) incidence rate among warm-water dives fluctuated from 0 to 5 cases per 10,000 dives." DAN


http://dspace.rubicon-foundation.org/xmlui/bitstream/handle/123456789/3962/12964853.pdf?sequence=1

Also, bear in mind that virtually every study done on DCS statistics makes some note that statistics have a tendency to under-represent the incidence of DCS, because it is believed many divers fail to report, or access treatment for, minor DCS symptoms. This is substantiated somewhat by comparison between studies based on treatment figures compared to diver questionnaires etc. There is a high probability that the issue is considerably "more significant" than the published numbers suggest.

Secondly, also bear in mind that studies tend to deal only with symptomatic DCS. Any discussion on the benefits of nitrox use might be well advised to consider the implications of sub-clinical (non-symptomatic) DCS presentation. Just how 'significant' is that post-dive fatigue?

 

[Dan Sumners]

Are you sure that your issue isn't just unfamiliarity with computer operation. I just don't see any difference between plastic (analogue) or electronic (digital) tables - other than the in-water flexibility offered by the digital. It's all just algorithms... and both methods offer easy and precise dive planning according to those numbers.

Why do you think that?

Does a plastic table provide more "patterns in data" than a computer downloadable graph showing actual calculated tissue compartment saturation across the length of a dive profile, in relation to actual depth and duration?

Really, this argument doesn't have any more logic than demanding a return to the tuition of medieval abacus in maths class. It's an old technology, superseded by the digital age... modern tools do the same functions and more... and it, in reality, reflects the way most people choose to do it.

Why not continue this discussion by paper-mail and stamps... if you really don't appreciate the benefits of electronic mediums and feel the need to have something tangible 'in front of you'? Or would you acknowledge draw-backs to that suggestion?

No at all, I'm very much in favour of technology and use it extensively (including having a computer), but feel the fact it generally works and works well shouldn't be an excuse to abdicate responsibility for understanding, which it often is. For example, most people have no idea what to do when their PC etc develops a fault, and I think that's a shame (as well as expensive). In the same way, I think it's useful to be able to do mental arithmetic, which came before the abacus.

As for dive computers, I go back to an earlier point; the fact people don't even plan with their computer could be the result of a shift of attention from planning with tables to saying, 'everyone has a computer so just learn how to do that', coupled with the fact it's easy to just let it do everything for you, ie that habit is less likely to develop.

 

[RJP]

As for dive computers, I go back to an earlier point; the fact people don't even plan with their computer could be the result of a shift of attention from planning with tables to saying, 'everyone has a computer so just learn how to do that', coupled with the fact it's easy to just let it do everything for you, ie that habit is less likely to develop.

The fact of the matter is, before computers became popular... most people didn't plan with tables. They didn't plan at all. Once a year they dusted their gear off, took a plane to a vacation destination, got on a boat, and listened to a briefing during which they were told that "the plan" was to be back on the boat in 45min with 500psi in their tanks.

With computers, if they still don't plan, at least they'll know during the dive whether that actually makes sense.

 

[DevonDiver]

...the fact it generally works and works well shouldn't be an excuse to abdicate responsibility for understanding, which it often is.

Surely that's an argument for computer training?

I don't see what "understanding" a set of plastic dive tables gives someone. If someone wants to better understand deco theory, then they should seek a proper source - for instance, Mark Powell's 'Deco for Divers'. They'd learn more from that book than a decade of staring at numbers on plastic...

...most people have no idea what to do when their PC etc develops a fault,..

I think they do. I also think they occasionally might ignore that knowledge and seek to compromise safety in terms of convenience. Dive computer failure contingencies are taught in all courses that now have a 'computer option'.

In the same way, I think it's useful to be able to do mental arithmetic, which came before the abacus.

So, by that logic, most divers should just carry a flash-card with the following...

​

Pcomp = Pbegin + [ Pgas - Pbegin ] x [ 1 - 2 ^ ( - te / tht ) ]​

where:

Pbegin = Inert gas pressure in the compartment before the exposure time ( ATM )
Pcomp = Inert gas pressure in the compartment after the exposure time ( ATM )
Pgas = Inert gas pressure in the mixture being breathed ( ATM )
te = Length of the exposure time ( minutes )
tht = Half time of the compartment ( minutes )
and ^ stands for exponentiation
1 ATM = 14.7 psia ( 1 Atmosphere, or sea level standard pressure )
x all the compartments you wish to apply...

I go back to an earlier point; the fact people don't even plan with their computer could be the result of a shift of attention from planning with tables to saying, 'everyone has a computer so just learn how to do that',

Exactly. Perhaps people don't use computers as effective dive planning tools because they were never taught to do so. Instead they (previously) learned to plan on plastic tables, which they never used subsequently. The training did not match the usage.


If those people had (and are) trained from the offset to plan dives effectively using the computer, then they are more likely to make best use of their computers - completing proper pre-dive planning.... rather than just 'flying' the computer once in the water.

 

[Bob DBF]

I have never done a BSAC course in my life, but when I got my original PADI OWD certification in 1984 the tables clearly provided for non-accelerated decompression. The implication was, once you were certified you could go ahead and conduct small deco obligation dives, although they never claimed to "teach" deco. Now they explicitly prohibit planned deco diving.

I had a similar experience when I got my ticket punch for OWD in 1980 in a NAUI/PADI class. The training was not to make deco dives but to give you the proper information on returning to NDL should you go into deco for any reason. The emphasis was on having enough air left to use this information. The class was a lot longer than they are now so they had to be filled with something, and he chose useful. As I remember the tables were cut off of the Navy diving tables of the day, since I don't remember having to memorize new markers for adjusting my plan to reality on the fly.

As for Nitrox, I mainly use it on multiday multidive trips because I feel better after, as opposed to air. And before you site the "it doesn't do that study", go read the study, in fact no study I've seen has done multidive, never mind multiday, study on nitrox. Once you read the methodology, you will wonder why anyone cites it. I actually agree with it that when diving (they actually didn't dive) one tank, there is no discernible difference between air and Nitrox.

Anyone could learn more about Nitrox than any alphabet class can teach, but without the card access to Nitrox can be denied. If you want to use Nitrox, get the card.



Bob
--------------------------------------
"If you don't like it, go on the internet and complain." Brian Griffin

There is no problem that can't be solved with a liberal application of sex, tequila, money, duct tape, or high explosives, not necessarily in that order.

---------- Post added June 15th, 2013 at 08:33 AM ----------

Surely that's an argument for computer training?

So, by that logic, most divers should just carry a flash-card with the following...

​

Pcomp = Pbegin + [ Pgas - Pbegin ] x [ 1 - 2 ^ ( - te / tht ) ]​

where:

Pbegin = Inert gas pressure in the compartment before the exposure time ( ATM )
Pcomp = Inert gas pressure in the compartment after the exposure time ( ATM )
Pgas = Inert gas pressure in the mixture being breathed ( ATM )
te = Length of the exposure time ( minutes )
tht = Half time of the compartment ( minutes )
and ^ stands for exponentiation
1 ATM = 14.7 psia ( 1 Atmosphere, or sea level standard pressure )
x all the compartments you wish to apply...

Now that's funny, I don't care who you are.

Exactly. Perhaps people don't use computers as effective dive planning tools because they were never taught to do so. Instead they (previously) learned to plan on plastic tables, which they never used subsequently. The training did not match the usage.

I must admit, I don't see much dive planning going on these days. Depending on the dive, I may not put a lot of work into planning but I do like to know where I am in relation to NDL, depth, time and gas before the splash. I fly the computer in the water, but will head shallower or surface if my plan and the computer are diverging, did the same on tables years ago.

 

[Kharon]

Going to Bonaire for 2 weeks in November. I've had my first six days of dives planned (from tables) for quite a while now. I might diverge from the planned dives but at least I have some idea what I want to do re. where, how deep, how long, SI, objective. I also did the calcs for Nitrox-32 to see what that would buy me over the course of each day. Am I obsessive - nope. Just a lot of time before I leave, I know how to do it, and what does it hurt to evaluate? At least I shouldn't get any surprises re. SI requirement and I'll be doing my diving efficiently.

 

[RJP]

Going to Bonaire for 2 weeks in November. I've had my first six days of dives planned (from tables) for quite a while now. I might diverge from the planned dives but at least I have some idea what I want to do re. where, how deep, how long, SI, objective. I also did the calcs for Nitrox-32 to see what that would buy me over the course of each day. Am I obsessive - nope. Just a lot of time before I leave, I know how to do it, and what does it hurt to evaluate? At least I shouldn't get any surprises re. SI requirement and I'll be doing my diving efficiently.

I'll bet the one thing you haven't planned for is how close the sites are to each other.

:d

My buddy planned all the dives for our trip and we threw than plan out the window by the second dive. The logistics of getting around the island and from site to site are hard to understand fully until you're actually there. Most of the sites are contiguous, so it becomes a bit silly to do a dive to the left, come back to your truck, sit an hour, and then do the same dive to the right.

Also, there's a point at which the main road along the shore becomes one-way, heading north. Issue becomes that if you want to go to a second dive south of your first one... it's quite a ride all the way back around.

 

[Madacub]

Also, there's a point at which the main road along the shore becomes one-way, heading north. Issue becomes that if you want to go to a second dive south of your first one... it's quite a ride all the way back around.

Ah! Finally! Now I see the importance of planning your dives - and that's even without tables or computer!

 

[Abaco24]

I can't believe this thread has 10 pages for the OP's post....no matter the depth I love Nitrox, its like a "O2 treatment" on every dive, gives me energy and makes me feel great after a day of diving. I actually suck up some at home on the couch just to get an O2 treatment before my refill or if I have a headache. So I would say YES, get Nitrox and enjoy all the benefits. Remember the O2 bars that opened, it works.