Air/Backgas breaks.

[turbanator]

Not sure if this is a DIR, Deco or RB question as it really arose during a discussion about rebreathers last night.

It seems fairly well recognised that air or backgas breaks go some way toward 're-setting' the CNS clock when decompressing, so I'd like to know if many of you OC and RB divers do this.

My guess would be that it's done with a dil flush on CC, but if yuo have any comments please post them.

[greekbird]

i wouldn't go as far as saying that air/back gas 'resets' CNS but it certainly helps lungs not get irritated by high ppo2... i personally dont do them as i dont spend that long on high ppo2s to increase CNS loadings or get irritated lungs...but if i was doing long deco on high ppo2 then i would...

[And]

Hi

If using 50% and O2 for deco then the 9 mtr stop becomes a backgas break whilst you tidy away the 50% and then deploy the o2.

O2 is breathed 12 mins on 6 off, one cycle being counted as 15 mins deco time.

Andy

[Mdemon]

IIRC, airbreaks are useful during prolonged periods on 100% to avoid possible lung irritation/damage. I think the periods were so long that they are of more use in the chamber that diving. Not sure what use they would be on lesser mixes and I'd be very dubious about "resetting" the CNS clock...




***Disclaimer - this could be rollocks!

[turbanator]

Originally Posted by Mdemon

"resetting" the CNS clock...

Well not completey in the times involved - note to self 'read oxygen and the diver' - again!!

One other theory/effect is that the time on air or low PO2 lets the lungs recover to allow better diffusion of gasses - obviously having more of an effect on whole body toxicity.

I done this to a theoretical 120% without airbreaks and was asymptomatic, what I was really wondering was is it common practice on RBs?

r
Paul

Edit - should read "120% WITH airbreaks"

[NotDeadYet]

I do every 10min on my O2 stop on my lowest gas if the stop is an hour or longer. Generally I'll do every 15min otherwise.

I don't know if it does any good but by the time I reach 6m I'm usually cold, tired and bored so I don't like taking the chance. I've also had pulmonary O2 toxicity once and it isn't pleasant (like a 24hr asthma attack).

I guess on your KISS it should be very easy, just switch the DSV to OC for a period and then back again. I think a KISS DSV is going to be my next big purchase.