TDI Extended Range - last words of advice?

[Bismark]

How big of a contributor to CO@ production do you REALLY think WOB on open circuit is compared to:
- Stress
- Actual Work (e.g. intertia and drag from pushing heavy steel doubles and drysuit vs. AL80's and wet suit)

If somebody gets stressed and their breathing rate skyrockets, the WOB due to helium is not going to make a whole lot of difference. Pushing 70 more pounds of gear with a lot more drag is going to produce a lot more work than sucking air vs. mix. Of all the reasons to use helium, I think this argument is a weak one in the big scheme of things.

You are trying to separate the effects of one part of the "package" as it were, when they do not ever exist in isolation from each other. It is not a question as to which one of the parts of the package causes more problems, it is that they all work together and do not exist in isolation. You start with "if someone gets stressed and their breathing skyrockets" when C02 build up is already starting from a higher WOB with air which causes stress, which causes your breathing rate to increase....etc. You are starting part way down the chain of events, rather than at the beginning. Lowering your WOB lowers your stress, etc., thus contributing to lower C02 build up, further lowering your susceptibility to stress.

 

[battles2a5]

You are trying to separate the effects of one part of the "package" as it were, when they do not ever exist in isolation from each other. It is not a question as to which one of the parts of the package causes more problems, it is that they all work together and do not exist in isolation. You start with "if someone gets stressed and their breathing skyrockets" when C02 build up is already starting from a higher WOB with air which causes stress, which causes your breathing rate to increase....etc. You are starting part way down the chain of events, rather than at the beginning. Lowering your WOB lowers your stress, etc., thus contributing to lower C02 build up, further lowering your susceptibility to stress.

You are absolutely right, you cannot separate all of the effects of the "package". But rjack's comments seemed to suggest that WOB is some leading cause of CO2 build-up, which it is not. It is certainly can be a contributor CO2 build-up, but not as large as actual work, or the work required to push a much larger system through the water. And if you are so concerned about WOB and CO2 production, why aren't you diving heliox? Air is only 20% denser than 21/35 at 150fsw? Is that really more significant than pushing 60 more pounds of gear through the water?

My comment about stress was aimed toward the mindset of the diver. If you are inexperienced or prone to physical symptoms of stress (e.g. increased breathing rate) the additional CO2 produces will be much more than someone who can keep their head on their shoulders. So you can influence "the chain of events" by being an experienced and level-headed diver, regardless of the contents of your back gas.

 

[rjack321]

You are absolutely right, you cannot separate all of the effects of the "package". But rjack's comments seemed to suggest that WOB is some leading cause of CO2 build-up, which it is not. It is certainly can be a contributor CO2 build-up, but not as large as actual work, or the work required to push a much larger system through the water. And if you are so concerned about WOB and CO2 production, why aren't you diving heliox? Air is only 20% denser than 21/35 at 150fsw? Is that really more significant than pushing 60 more pounds of gear through the water?

My comment about stress was aimed toward the mindset of the diver. If you are inexperienced or prone to physical symptoms of stress (e.g. increased breathing rate) the additional CO2 produces will be much more than someone who can keep their head on their shoulders. So you can influence "the chain of events" by being an experienced and level-headed diver, regardless of the contents of your back gas.

Putting aside all N2 issues... You wouldn't get in the water with a poorly tuned reg, why get in with a poor gas choice making your reg perform marginally?

"Only 20% less dense" is potentially misleading since the WOB is not linear with density.

 

[battles2a5]

Putting aside all N2 issues... You wouldn't get in the water with a poorly tuned reg, why get in with a poor gas choice making your reg perform marginally?

"Only 20% less dense" is potentially misleading since the WOB is not linear with density.

Come on, now. If we went to 150ft with 5 stages w/ 5 different regs and different mixes I guarantee you can tune the difference out of them using cracking pressure adjustments alone. You are grossly overstating the case by saying that air makes a reg perform "marginally" at depth. Like i said, there are plenty of great arguments for helium. I am trained to use helium and given the choice I will always choose helium when appropriate but the WOB argument is pointless. This is one of those Georgisms that people keep recycling but its pointless. On closed-circuit w/ an ambient pressure breathing loop it's a valid argument, but not open circuit.

 

[Bismark]

So you can influence "the chain of events" by being an experienced and level-headed diver, regardless of the contents of your back gas.

How do you define "level headed"? While agree with your statement here I would ask you how "level headed" are you at 180' on air? I am pretty sure that if you took the current Formula driving champion and poured a few martini's down his throat, even he is going to suffer some impairment and be "off his game". I would go so far as to also suggest that for me anyways, "level headed" starts before I even get in the water. Choosing the right gases, the right equipment, the right training and the right dive teammates are just as much indicative of "level headedness" as is reacting properly to emergencies at depth. As I mentioned before, you simply cannot remove these items from the equation and assign arithmatic functions to them. 1 +1 does not always equal 2 when the values of the first 1 and the second 1 are not the same. (See Rjacks post above about linear density.)

 

[Bismark]

Come on, now. If we went to 150ft with 5 stages w/ 5 different regs and different mixes I guarantee you can tune the difference out of them using cracking pressure adjustments alone. You are grossly overstating the case by saying that air makes a reg perform "marginally" at depth. Like i said, there are plenty of great arguments for helium. I am trained to use helium and given the choice I will always choose helium when appropriate but the WOB argument is pointless. This is one of those Georgisms that people keep recycling but its pointless. On closed-circuit w/ an ambient pressure breathing loop it's a valid argument, but not open circuit.

Please provide some scientific references to validate and support your statment that the "WOB argument is pointless".

I also think you are thinking of WOB as only something that you can necessarily feel at a concious level of exertion. Regardless of what you are "feeling" biochemical processes are occuring that you will not feel physically but which are contributing to increase C02 load, which you will feel if you know what to look for. Unfortunately, most divers do not know what is happening. That is what makes this stuff so insidious. The gas mix doesn't have to feel "thicker" for your body to react. Our bodies are designed to work within a very low tolerance of C02 limits and it doesn't take much at all to tip over this apple cart. Perhaps Lynne can chime in here with some numbers so I don't have to look them up again.

 

[Reg Braithwaite]

I'm shocked,shocked I tell you that this has descended into a deep air bashing thread

Your air fills, Sir.

 

[battles2a5]

It's obvious that you two are in no way open to anything outside of your doctrine so I'm not going to argue this anymore. Just out of curiousity through, what kind of experience do you two have diving on air in order to build these arguments? Have you experienced deep air in clear, warm, water and found that you had trouble functioning or are you basing your position purely on anecdotal evidence or your training?

 

[battles2a5]

Please provide some scientific references to validate and support your statment that the "WOB argument is pointless".

I also think you are thinking of WOB as only something that you can necessarily feel at a concious level of exertion. Regardless of what you are "feeling" biochemical processes are occuring that you will not feel physically but which are contributing to increase C02 load, which you will feel if you know what to look for. Unfortunately, most divers do not know what is happening. That is what makes this stuff so insidious. The gas mix doesn't have to feel "thicker" for your body to react. Our bodies are designed to work within a very low tolerance of C02 limits and it doesn't take much at all to tip over this apple cart. Perhaps Lynne can chime in here with some numbers so I don't have to look them up again.

Where's your scientific evidence to validate and support your position? I never said it does not have an effect, I said there are so many other PRIMARY contributors that will make much of an impact that the difference in WOB between air and trimix. I don't need a lesson on how dangerous CO2 is, but I'd love to see some scientific evidence of where people "tipped over the apple cart" because their WOB was too high and could be directly attributed to breathing air.

 

[rjack321]

Come on, now. If we went to 150ft with 5 stages w/ 5 different regs and different mixes I guarantee you can tune the difference out of them using cracking pressure adjustments alone. You are grossly overstating the case by saying that air makes a reg perform "marginally" at depth. Like i said, there are plenty of great arguments for helium. I am trained to use helium and given the choice I will always choose helium when appropriate but the WOB argument is pointless. This is one of those Georgisms that people keep recycling but its pointless. On closed-circuit w/ an ambient pressure breathing loop it's a valid argument, but not open circuit.

Bull. There's a valid reason 20/80 is used at 1ATA medicinally and there's no "reg" or even water involved.

CO2 increases with work. Air creates more work. Helium lowers WOB as ONE piece of its overall benefit.