narcosis question.

SBOD

i hope my query is taken seriously as i can't find any answers anywhere, so here goes ....

i have read (on another diving forum) that using a CCR enhances narcosis but this was a rather broad statement in that depth, gas mixtures and dive time were omitted.

i would appreciate any helpfull comments as to the validity of this statement, particularly in the 30-40M range with air dil. (CCR).

thanks.

EBT

Hmmmm two approaches;

- Approach 1. Residual loop CO2.

If there was residual CO2 in the loop, there would be enhanced CO2. We run the units within limits defined for the scrubber to ensure there is no residual loop CO2.

- Approach 2. Sticking to Air Dil.

Assuming a setpoint of 1.3 (for the sake of argument) and a dive depth of 40m (1.3/5), we get a loop FO2 of 26%, leading to 74% FN2. So, thats less narcotic than air. However if you take air dil deeper (say 60m... which should be trimix country but thats a different debate). Your loop FN2 @ 1.3 setpoint would be 81%. So thats more narcotic.

Both those approaches are very purist in view, but most of us chuck in a bucket load of helium (technical measurement), since its easy and cheap. So this sort of removes that whole narcosis debate, since we seem to be diving trimix at any depth.

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Retardboy

I don`t own or dive a breather, but I do know that a cc loop will have a slightly higher level of CO2 (one of the bad drug-boys you know than when diving OC. Technically I guess it affects the diver at any depth, but If on a calm, normal dive I dont know if CCR VS OC on 30-40m makes much difference. As I said, I probably should not answer your question

wedivebc

I think you will find that statement is not true. In fact the reduced CO2 in a Rebreather loop is thought to be the reason why most RB divers report less narcosis effect when diving CCR than OC, myself included.

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richc

absolutely. CCR makes narcosis a lot more fun....

deanc

It can be done if you try hard enough.

Say you're at 40 m with air diluent, thats a PO2 of 1.05. Now you turn off the O2 and breathe it down.

When the PO2 gets to 0.7 you're depleting the oxygen, and oh my gosh you're increasing the fraction of nitrogen. To how much?

Ptotal = 5 ata = Po2 + Pn2
Po2 = 0.7
Pn2 = 5 - 0.7 = 4.3
END = 10 * (4.3 / 0.79 - 1) = 44 m

So that feels like 44 m
at 0.4 it feels like 48 m
at 0.21 it feels like 51 m

Thats if you did let it go down like that. btw thats just thinking N2 is the only narcotic.

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Mixaddict

This point was recently discussed (argued on Rebreather World). You can probably find the thread by doing a search. In any event, my personal experience shows me that I am in need of helium at a shallower depth on CCR than I am on OC. I don't totally understand why. I have several theories, including increased task loading, but I'm not sure there is any scientific proof to it one way or another. I just know for me, the narcosis starts slightly shallower on CCR than it does on OC.

Regards,
Randy

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Randy Thornton (MixAddict)
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Retardboy

Ok. Do you know where I can find any data/tests showing that the CO2 level in the loop during diving is lower than in a OC tank of air from a decent compressor? Doesn`t look like the other answers support your theory.

EBT

Test graphs seem to show an acceptable level of Co2 post scrubber (the point of measurement).

Now the question is "whats the level of CO2 in the DIVER from the elevated WOB thats typical on CCR's" (dont forget oc is not really passive, once you crack the valve the gas is slightly pressured). Personally I 'suspect' its slightly higher, but its a bugger to measure.

Anyway, its all bollocks. I refer you to the previous statement about the real world where most ccr divers dive mix all the time. The Air dil brigade will always exist (as will OC deep air) but its so cheap to dive trimix on a ccr that even the tightest of jocks do it <pointed look in a certain direction>. Dont forget that ccr's do require more monitoring/vigilance than OC, so a low narc level is desirable anyway.


ps. Yak.

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zepp

Which it isn't but thats another argument

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