PADI Enriched Air Certification.... a little fishy.

[mala]

By PADI course materials mod is 1.4. Contingency is 1.6.

that is correct.
other agencies use similar numbers.

at the end of the day the diver decides what is mod for each gas based on experience and knowledge.

 

[hypertech]

30% nitrox.

surface pp02 is .3
at 10 m .6
20m .9
30m 1.2
40 m 1.5
50m 1.8

i think the boat would need to rock quite a lot not to be able to do the maths.

You picked an easy multiple, used meters when most have depth guages that measure in feet, and only identified the PP02 and did not identify a MOD at, for example, 1.4.

I can do it too, but for many, its quicker and more reliable to just look at the table than do it in their head.

 

[mala]

You picked an easy multiple, used meters when most have depth guages that measure in feet, and only identified the PP02 and did not identify a MOD at, for example, 1.4.

I can do it too, but for many, its quicker and more reliable to just look at the table than do it in their head.

most dive computers can be set to metric by pressing a button.
i agree it was an easy example.
without doing any math i would guess that 1.4 would be nearer 40m than 30 m(37m maybe?)who knows and what does it matter given thats its all theoretical based on the reading of an 02 analyser that reads 1% out when the cells are good and may read much worse if the cells are on there way out.

you have to agree its so much easier in metric than american.

 

[hypertech]

Yes, the math is easier. Except that americans don't think in meters they think in feet. The dive briefing was probably also done in feet. Knowing a mod is 37m doesn't help if you don't know how many meters the dive site is.

 

[mala]

Yes, the math is easier. Except that americans don't think in meters they think in feet. The dive briefing was probably also done in feet. Knowing a mod is 37m doesn't help if you don't know how many meters the dive site is.

i'm familier with both .
one is easy and one is not.



its a lot cooler to dive in feet as the depth in meters always seems so lame.

 

[billgraham]

Is it? I can calculate a MOD at any PPO2. Or, I can look at the chart at the fill station after I analyze my tank and just write it down from the 1.4 or 1.6 column for whatever mix I actually ended up with in the tank.

It was admittedly a long time ago when I took nitrox and advanced nitrox (TDI) but I was taught that maximum operating depth was the maximum depth you can safely breath the mix -- 1.6. Maybe they teach it differently now. The PP02 for the dive is something different.

---------- Post Merged at 07:16 PM ---------- Previous Post was at 07:06 PM ----------

I have no need/desire to support your position.

PS - You're arguing against a position that no one else is taking. I'm just saying that your examples don't support your point. If someone shows up at the boat with the wrong mix because the destination was changed it doesn't whether they used a table, Dalton's Diamond, or an abacus to calculate their mix -- it's the wrong mix, and how they calculated their mix doesn't matter. The guy who knows his math inside and out is going to be left at the dock just the same as the guy who relied on a nitrox table.

Actually, if you read the whole thread, most people are arguing that it's not necessary to know the theory because they'll never need to know it. I'm trying to come up with examples of why it's useful to know it, that's all. My point was more, how do they even know it's the wrong mix? (I know, you look at a table . . .) If you think people don't need to know it, fine. There have been three or four threads about whether the course is adequate, started by people who just took it, so I think there's some question in their minds about it.

 

[FoxHound]

MOD is kind of a written in jello thing though......I say this because if you look at the NOAA o2 exposure times that has a lot to play in the dangers too.

what happens if i plan on doing a dive that's over an hour in duration......a mix that would keep me at a 1.6 pp02 is most certainly not an good mix and the MOD is kind of moot and doesn't work. However if I was doing that exact same dive but for a shorter duration, say 40 min, then i'm good to go, but i've pretty well maxed out my 02 exposure for the day.

So in saying that, would I dive a 34% for a dive to 130 ft. (1.68ppo2) Yes because I understand whats going on and its highly unlikely that I will spend the entire time at 130ft.....plus I will know not to really exert myself and keep the bottom time short. Its all about risk analysis and understanding the physics behind it......not just blindly programming a computer. But I suppose that is the difference between nitrox and adv nitrox......the understanding of the physics.

 

[MaxBottomtime]

I don't know anyone who makes money teaching.

Fixed.

 

[billgraham]

MOD is kind of a written in jello thing though......I say this because if you look at the NOAA o2 exposure times that has a lot to play in the dangers too.

what happens if i plan on doing a dive that's over an hour in duration......a mix that would keep me at a 1.6 pp02 is most certainly not an good mix and the MOD is kind of moot and doesn't work. However if I was doing that exact same dive but for a shorter duration, say 40 min, then i'm good to go, but i've pretty well maxed out my 02 exposure for the day.

So in saying that, would I dive a 34% for a dive to 130 ft. (1.68ppo2) Yes because I understand whats going on and its highly unlikely that I will spend the entire time at 130ft.....plus I will know not to really exert myself and keep the bottom time short. Its all about risk analysis and understanding the physics behind it......not just blindly programming a computer. But I suppose that is the difference between nitrox and adv nitrox......the understanding of the physics.

My understanding of the term MOD is the absolute deepest depth you can breathe the gas. As in, Oxygen - MOD 20 feet marked on the tank. Obviously, you're going to do the dive at 1.4 or less.

 

[FoxHound]

My understanding of the term MOD is the absolute deepest depth you can breathe the gas. As in, Oxygen - MOD 20 feet marked on the tank. Obviously, you're going to do the dive at 1.4 or less.

That is true but playing devils advocate a bit, how deep can you actually breathe a 100% mix......i'd be willing to bet you can make a switch from your back gas to 100% at 30ft and make it to 20ft without incident. But then again if im being very conservative maybe my MOD for oxygen would not be 20 because I maybe want to keep a pp02 of 1.2 or less.

You can breathe any gas at any depth........doesn't really mean its a good idea.....the MOD is really just a guideline that experiments in diving has told us is possibly a safe depth (i say possibly because since everyone is different, what works for me may ox tox or bend someone else)

IMHO conservative is the best way to go but when the $**t hits that fan, im not gonna feel bad about breathing a gas a few feet below its marked MOD



at the end of the day i guess what Im trying to say is you have to have an understanding of how the gas works and why MODs are what they are.....not just following a chart blindly