How Far Do You Push Your Scrubber?

LS_DK

No, I dont think that is the right explanantion. If I sit at my desk here now, I can choose to breathe either through my nose or mouth. Works fine.
If I dive without working hard, I can control it aswell. Breathing control works fine here too. However, if I work hard I loose control. I cannot choose to only breathe through my mouth.. Something makes me go into that mode. I beleive it is directly linked to Co2 buildup.. Not in the loop... But in my body. Co2 levels in inspired gas can be very low, at the same time Co2 levels in the body are high(ish).

Cheers,
Lasse

dave t

yes I know you can choose but what does your body do naturally breathe via mouth or nose?

Sutty

I get the involuntary nose-breathing thing too, but its getting less of a problem with experience. At first I just couldn't stop it at all! Its not enough to lose gas, just to push mask in and out like a bellows. I never had a problem with this on O/C.
I find a good way to stop it is to blow into your DSV (even move your lips as if pursing), imagine you are blowing up a balloon or something. If that doesn't work partially block your mouthpiece with your tongue and blow against the resistance. The key seem to be to blow not just breathe.

May not work for anyone else but it does for me

LS_DK

Yeb, the natural thing is to breathe through the nose..
But why do I loose control of it in the first instance? that is the question... I can stop at depth and try all I can to control it, but it wont go away, until after a couple of minutes with deep breathing.

Cheers,
Lasse

Sutty

Regarding involuntary nose-breathing, I've opened a new thread, please reply to that, but I've wondered whether its related to static lung loading, ie whether there is -ve or +ve pressure at the mouth. If you have this problem (or even if not) what sort of Rebreather do you have? What do you do about it? etc

link here

grahamsp

Before I crossed over to the Dark Side, I dived OC using a Vytec with wireless air from which I got a very good handle on my air consumption over 50+ dives. With that number I was able to calculate my O2 consumption CO2 production rates. My air consumption averaged a shade under 15 lpm (though I use 18 lpm for all dive planning); at 4.5% by volume (approx; source Wikipedia) this implies a CO2 production rate of 0.68 lpm or 0.8 lpm for planning purposes. Note - this is 50% of the rate used by APD in setting the 2 hour limit on the Evo's scrubber.

To take your statement as written, not spending £2.00 by deferring scrubber changeout increases the risk (of a serious hypercapnia incident, I assume) by a factor of 2. At 100 metres, working like a Trojan in 4 degree C water, you're almost certainly correct. At 50 metres in warm water not working hard, I don't think you are - you'd have to push the scrubber an awfully long way to double the risk. The problem is, lacking good hard data on how the scrubber responds to the multiple variables that affect its performance over time, I can't tell you (and APD won't if even if they know) how far that is.

Graham

divetheworld

It s a risk assessment Graham, one you do for yourself. Quantifying the risk is vital to make an informed decision. I really dont know all the variables, and a CO2 hit is a bit too sneaky for me to not treat it with the ultimate respect. I dive in very cold water, and often have a good fight with non-ferrous or things with claws. I know for a fact that there is quite significant headroom on the suggested scrubber durations but that just gives me the extra room to manouver when (not if) it all goes t1ts-up. When I'm a bit squeezed inside a wreck or a fair distance from an exit, I want to know I have that extra third in reserve. C'est la vie. Each to their own.
We dont disagree so much on the available usage, just that I will make all attempts not to use it.


Brent.

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grahamsp

Spot on. And to do that we all need good quality, objective data.

Fair enough, can't (and wouldn't want to) argue with what you say. And, after the 'by the book' regimentation of the RN and to a lesser extent that of the PADI system, I really like the way in which CCR diving does in the end come down to each diver taking personal responsibility for what they do and how they do it.

Graham

Sutty

I'm very doubtful whether the 4.5% (exhaled CO2/consumed O2) figure is reliable in a diving scenario. This is about right for a normal person breathing normally on the surface, however experienced divers have been shown to have a modified response to CO2, and therefore may have higher expired CO2% but with a lower air comsumption/min. Even non-divers will put up their CO2 with increased WOB.
If this figure is your basis for determining your scubber duration it may well be seriously flawed.

Neil

CCR900

I am all for personal choice and personal risk assesment, trouble is people are still dieing on CCR and by all accounts some of these incidents are CO2 related. So somewhere somehow people are getting their risk assesments wrong. The trouble is that (being very selffish) their loss could be detrimental to the prolifiration of CCR in the diving community.

F