nitrox MOD/TOD

[limeyx]

I don´t really see the label as that important...MOD/TOD/MIX

I just put mix in big numbers and my initials on the tank.
If it´s a single, I won´t be able to read it anyway (its behind me), same goes for dubbles.

If it´s a decobottle, all the label is for is to make sure I don´t use the wrong bottle. The depth at which I´ll breath it will be written in my decoplan. I have multiple other, redundant systems, to make sure none of those to things happen (wrong gas/wrong depth)...I´d think that would be true of any trained diver form any agency...

YMMV...

On the deco bottle, I think you should have the MOD clearly marked on the bottle so that you and your team can read it. Writing it in your deco plan is a recipe for disaster (in my opinion)

 

[limeyx]

I mark MOD at 1.6.

I think the present trend towards teaching 1.4 as MOD is a mistake - it's designed to keep people with poor depth control or judgement from going to truly crazy ppO2's. I mean no disrepect to individual instructors who are required to teach MOD=1.4 by their agency.

WHy do you think it's a mistake? I think that it could be one reason why 1.4 is used for sure, but I think reducing average PPO2 for the bottom portion of a dive is a pretty good thing in general.

Changing the definition of MOD to fit poor skills however, is not really a good solution

 

[limeyx]

Where do these ideas come from?

why, do you like them?

 

[Kim]

however, that is NOT what we were talking about. we were talking about MOD, in other words, the maximum operating depth for a particular gas being dependent on what PPO2 you chose to live by.

And this is my point. It doesn't really matter whether you choose 1.6 or 1,4 PPO2 to make your MOD if that is your absolute limit. That will depend on your personal belief as to where the acceptable risk ends. However, you seem to be suggesting that if for some reason you decide on a given day to use 1.2 PPO2 (which will give a new maximum depth) then you can call that new depth the MOD. This is not true.
It's like having a car that can drive at 100mph. You may decide that 80mph is as fast as it's safe to drive, and on a given day decide that 60mph is the limit for today due to road conditions or whatever - the car will still remain capable of the 100mph.
The MOD of a given gas is a fixed depth...it's simply that not everyone agrees which depth it should be. Any given agency that produces tables though only produces one MOD for any given mix.

 

[H2Andy]

The MOD of a given gas is a fixed depth...

i think i see where we do not agree. i would say the following:

the MOD of a given gas is not fixed, but is dependant on what PPO2
you chose. there will be different MODs depending on what PPO2 is used.

and with that, i throw in the towel and go off to taunt PETA fundamentalists

:10:

 

[Kim]

Maybe, as someone already pointed out, the problem is one of linguistics. There are no hard and fast certainties, only best guesses/practices. Using a word like 'maximum' suggests a certainty that doesn't really exist. This is why for instance that recently in another thread, someone who was obviously trained using 1.4 ppo2 was convinced that if you went deeper you would automatically tox at 1.6. This displays a basic lack of understanding of the issues involved. The same can be said of the word 'limit' in NDL. Again, there is a situation where different tables will give different times at the same depth according to which model/algorithm/software program is used - there is nothing 'absolute' about the 'limit'. The problem is that if you don't teach this stuff in terms of 'maximums' or 'limits', then a lot more theoretical and background knowledge is required for anyone to make an informed decision as to what is safe or not.

As far as the piece you chose to quote form my last post - maybe you'd agree better with:
"The MOD of a given gas is a fixed depth depending on which agency/who is making the tables."

 

[grazie42]

Originally Posted by limeyx
On the deco bottle, I think you should have the MOD clearly marked on the bottle so that you and your team can read it. Writing it in your deco plan is a recipe for disaster (in my opinion)

For me it´s more important that the label is big and clear, than cluttered...

I think everyone knows the mods for their decomixes by heart, kinda like the multiplication-tables you learned in school.

I don´t know how you dive but I always memorize my stops and switchpoints before I get in the water. the decoplan is my backup (and tables the backup to that).

In metric the math is also very easy and I´m comfortable I could do it even while semi-stressed.

And your team is always your backup-brain...

I respect your opinion but I disagree with it...

 

[limeyx]

For me it´s more important that the label is big and clear, than cluttered...

I think everyone knows the mods for their decomixes by heart, kinda like the multiplication-tables you learned in school.

I don´t know how you dive but I always memorize my stops and switchpoints before I get in the water. the decoplan is my backup (and tables the backup to that).

In metric the math is also very easy and I´m comfortable I could do it even while semi-stressed.

And your team is always your backup-brain...

I respect your opinion but I disagree with it...

My plan is memorized too.

Switching to the wrong mix is one of the easiest ways to kill/injure yourself underwater, so my training has been to make the process as foolproof as possible.

That includes having a team member watch you while you switch to a deco bottle, and not involving any calculations or math to figure out which bottle to switch to.

Before the dive, the gas in deco bottles is analysed to ensure it meets the PPO2 requirements for the depth at which it will be breathed. After that, the analysis is irrelevant. The only relevant thing is the "MOD" sticker on the tank which is on both sides of the tank in 3" letters that are easily seen.

Switching then becomes easy -- check your depth at your gas switch, locate the bottle with that depth marked on it, and proceed from there. Easy. No thinking "Hmm, this mis is 53.6% nitrox, that means at x number of meters/feet the PPO2 is y" -- all that stuff is left to the above water part of the dive where you can take your time and you aren't in a stressful situation. The whole team uses the same definition of MOD and the same gases, so we all switch at the same time and at the same depth.

I am a bit unsure on how you identify the bottle you are switching to -- are you saying you read the analysis sticker? Or you have some other method to make sure you pick the right one?

 

[Atticus]

...That includes having a team member watch you while you switch to a deco bottle, and not involving any calculations or math to figure out which bottle to switch to.

Before the dive, the gas in deco bottles is analysed to ensure it meets the PPO2 requirements for the depth at which it will be breathed. After that, the analysis is irrelevant. The only relevant thing is the "MOD" sticker on the tank which is on both sides of the tank in 3" letters that are easily seen.

Switching then becomes easy -- check your depth at your gas switch, locate the bottle with that depth marked on it, and proceed from there. Easy. No thinking "Hmm, this mis is 53.6% nitrox, that means at x number of meters/feet the PPO2 is y" -- all that stuff is left to the above water part of the dive where you can take your time and you aren't in a stressful situation. The whole team uses the same definition of MOD and the same gases, so we all switch at the same time and at the same depth...

This is the method I use as well. My opinion is that reading analysis stickers during a dive is both non-standard and more error prone than using clearly labeled MOD's. The team should agree on the gasses / ppO2's / switch depths and all be on the same page.

The MOD's should marked with large numbers and preferably done with decals or painted on. I have seen more than one team get confused trying to read one anothers chicken scratch on duct tape (yes, I used to this myself). It's important that the buddy check during gas switch is more than a head nod without real verification - and that requires that the buddy be able to clearly understand what gas you're switching to.

 

[grazie42]

I agree that switching to the wrong decogas is one of the easiest ways to kill/hurt yourself.

When it comes to the procedure, I agree with you, noone puts a new reg in their mouthbefore giving and recieving an ok-sign from a buddy. And the team does breath the same gas and follow the same schedule...

About what term to use as label:
I dive with both imperial and metric divers. Mix is the only label we´ve come up with that makes instant sense to all. MOD´s for the common decomixes are one of those things I´d be able to recite instantly if someone woke me up in the middle of the night. If I see a MOD in ft, I´ll really need a calculator and the formula isn´t ingrained, of course the opposite is true for the imperial diver. Labelling with MOD doesent work for me or the people I dive with...

How to label:
The labelling you guys use is only reasonable if your decobottles are dedicated to a certain mix. Mine, for various reasons, aren´t. I write mix in big numbers on the tank neck (this is the primary way of identification). I also use different rigging for my different bottles and different first stages with one bottle always containing the deepest gas and always located in the same place in the "stack" (in case I´m not able to see the label, for whatever reason).

That´s how I do it, I´m not convinced your way is better but I find the discussion interesting and I may learn something I hadn´t thought about...