PerroneFord:
A buddy of mine uses a shop like this, but they are smart enough to link the unlimited fills to a single tank. A shame really - otherwise he could fill my tanks for me
nitrox MOD/TOD
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A buddy of mine uses a shop like this, but they are smart enough to link the unlimited fills to a single tank. A shame really - otherwise he could fill my tanks for me
swisstrav
Contributor
hey guys
lets get a few things strait. mod goes always together with a certain ppo. in nowadays it is teached that ppo 1.4 is the thing to do. and for any given ppo is a mod. this is clearly regarded a safe limit for everybody the dive industry turns out. i.e. let's say 4 deg c (37 f ????)watertemperature, phisycally unfit divers with about 60 pounds of overweight.
if i would dive in cold water i would calculate my mod with a ppo of 1.4. i'm fit, not overweight and dive in watertemperatures 26 to 30 deg c. (70 - 80???)
so it is nothing wrong with asuming a ppo of 1.6. and even going higher will not kill you immediately.
besides that if you ever get bent and have to go to recompression camber (dcs typ2), you will be exposed to a ppo of 2.8. although there is a catch with that 2.8 in the camber but im not going to tell you. so stay within a mod of 1.6 as a max.
conclusion: a mod is always a relation to a given ppo. whether or not there is a sticker on your tank does not make any difference. however it is important to analize your tank by yourself and program your computer accordingly. doing that, your computer will scream like h... should you exceed your depth.
lets get a few things strait. mod goes always together with a certain ppo. in nowadays it is teached that ppo 1.4 is the thing to do. and for any given ppo is a mod. this is clearly regarded a safe limit for everybody the dive industry turns out. i.e. let's say 4 deg c (37 f ????)watertemperature, phisycally unfit divers with about 60 pounds of overweight.
if i would dive in cold water i would calculate my mod with a ppo of 1.4. i'm fit, not overweight and dive in watertemperatures 26 to 30 deg c. (70 - 80???)
so it is nothing wrong with asuming a ppo of 1.6. and even going higher will not kill you immediately.
besides that if you ever get bent and have to go to recompression camber (dcs typ2), you will be exposed to a ppo of 2.8. although there is a catch with that 2.8 in the camber but im not going to tell you. so stay within a mod of 1.6 as a max.
conclusion: a mod is always a relation to a given ppo. whether or not there is a sticker on your tank does not make any difference. however it is important to analize your tank by yourself and program your computer accordingly. doing that, your computer will scream like h... should you exceed your depth.
Jonnythanjonnythan:
I am intending to take a nitrox class, if only for my own safety.
I am going to buy a gas analyzer, if only for my own safety.
Whether I will bother to spend the money to replace dive computer, etc and dive nitrox is still open to question.
Given my air consumption a single alu80 gives me a 1 hour dive with an initial descent to 25m and a leisurely swim along the reef to 100 bar followed by a gentle return rising up the reef to the drop-off at 8m.
Without going to twin tanks I doubt whether I would have sufficient gas to stay down any longer at 25m.
I accept that nitrox may allow me a shorter surface interval, I will find out in the course. However if it is a 2 tank boat dive this will not make any difference unless everybody is on the same profile.
Currently I do all my diving on vacation so I dont have my own tanks. I am hoping this will change in the near future and then nitrox might be more interesting.
I'm sorry - I would strongly disagree.swisstrav:
An MOD goes together with a mix. The Maximum Operating Depth is the theoretical maximum depth a given mix is safe to dive to - it has nothing to do with the PPO2 EXCEPT for the argument/divergence of views as to which PPO2 is safe or not. This has led to different agencies producing different tables because they are using a different PPO2 as the maximum that they consider safe, but depending on who is talking there is only one MOD for any given mix. My IANTD tables are based on a PPO2 of 1.6, which was true for almost all tables several years ago. I may CHOOSE to be more conservative by using a lower PPO2 such as 1.4 but I MAY go deeper than that for short periods of time as long as I stay within the MOD limits from the tables, and the NDL for that depth. AFAIK everybody agrees that beyond 1.6 becomes dangerous. In any event the MOD is based on the Maximum that is considered safe to dive - not any lower PPO2.
What IS a function of desired PPO2 though is what is being referred to in this thread as TOD (Target Operating Depth)
Dive shop fill logs are to provide the shop with some documentation that you know what gas you have and have an idea of where and when to use it. I doubt that many care whether you use 1.4 or 1.6.
Whether you use the terminology "MOD and contingincy depth" or "TOD and MOD" may not matter much in a recreational diving context. However when we mark a tank with MOD, we want those big bold letters to tell us the maximum depth at which that gas can be used. In the case of decompression gasses that MOD is also where we usually begin using the gas.
For the record I think TOD and MOD make a lot more sense. Using MOD and contingincy is like saying maximum and more maximum...or maximum but not really...or that your max but you can go deeper with it...kind of stupid aint it? Where TOf says this is where I intend that most of my dive take place but I can go to "here" if I want or need to.
Whether you use the terminology "MOD and contingincy depth" or "TOD and MOD" may not matter much in a recreational diving context. However when we mark a tank with MOD, we want those big bold letters to tell us the maximum depth at which that gas can be used. In the case of decompression gasses that MOD is also where we usually begin using the gas.
For the record I think TOD and MOD make a lot more sense. Using MOD and contingincy is like saying maximum and more maximum...or maximum but not really...or that your max but you can go deeper with it...kind of stupid aint it? Where TOf says this is where I intend that most of my dive take place but I can go to "here" if I want or need to.
PerroneFord
Contributor
For me, the move to nitrox had nothing to do with surface intervals (I'm working on not having to have ANY mandatory surface intervals) nor did it have to do with increasing bottom time. For me, the move to Nitrox was all about reducing nitrogen absorbtion and thus making me feel better and hopefully bubbling less. When I got nitrox certified I didn't even own a computer, so there is absolutly no need for you to buy a new computer. Simply do the EAD (equivalent air depth calculation) and dive your air tables or computer. Or, just dive according to your air computer as is, and pretend there is air in the tanks.
In your two-tank boat dive, you may find that you can splash first and get a bit more time below (with a buddy) than the other divers who will be more limited. Thus giving you a longer bottom time, and a shorter surface interval if you're the last to come back to the boat.
All up to you.
In your two-tank boat dive, you may find that you can splash first and get a bit more time below (with a buddy) than the other divers who will be more limited. Thus giving you a longer bottom time, and a shorter surface interval if you're the last to come back to the boat.
All up to you.
victor:
PerroneFord
Contributor
MikeFerrara:
But Mike, isn't this like saying you can't take that 50 bottle below 70ft or you can't get on the oxygen below 20? Sure you can. So true MOD is dependent on many factors. We've all just arbitrarily agreed that 1.6 is where that limit is. I'm quite sure that those doing o2 deco in the ocean have violated 20ft at some point or another.
I'm not saying this to be argumentative, it just seems strange to condemn the process of TOD/MOD but them label an MOD and dip below the floor from time to time. Deep air guys are the epitome of this, though I don't agree with doing what they do.
This is basically how I think - I'll dive 1.4 and use that 'limit', but know that I can go to 1.6 if I need/want to.MikeFerrara:
The NOAA single exposure limit for a PPO2 of 1.6 is 45 minutes. One question I have for the deco divers here - do you stay within that 45 minute limit using 100% O2 at 20 ft? (I've seen that most use the PPO2 1.6 limit at this depth for deco)
swisstrav:
Read this story I posted awhile ago on another board. I was diving multi dives every day. Just two years prior I had been doing annual Oxygen Tolerance tests annually in a chamber and didn't think a PPO2 of 1.6 was an issue. I was wrong.
"lets see, in 97 was solo on 36% taking some macro shots while in Cayman at 90 some feet. I was hunkered in not moving for at least 10 mins. My legs started to tingle so I thought to myself "self move your legs they are tired from being in position so long" so I did and went back to the damn gobbie. Then a little alarm went off in the back of my head that said "holy **** I'm starting to tox, I had that happen in the chamber once on my yearly O2 tolerance test just before I did the funky chicken". I then put actually used my inflator as the up button so as to not exert myself and the tingle went away at 60 feet.
Stopped pushing 1.6 on nitrox and also stopped solo after that.
good lesson and bad judgement"
serambin:
I guess that we have to disagree on both of your points. First, the "truth of a thing" if you mean the definition of a word or term can be more than one thing (note the multiple meanings listed in any dictionary listing). Second, it has not been established that NOAA is the originator of the term, although you could argue easily that they popularized it for the scientific diving community, but even if they did originate it, that is still no reason for anyone else to only use it exactly like NOAA uses it. As long as everyone on a dive team agrees on what they mean by MOD, it doesn't matter what anyone else means by it.
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