Do you determine ICD when planning your bailout gasses for a certain depth?

[flymolo]

Go for Nitrox 25% and take a stage with 40% for 45 metres. Then try a bounce dive using air to 60 metres for 3 minutes bottom time. Take 32% Nitrox for deco stage. Write the dive plan on a wrist slate.

 

[rjack321]

The OP is thankfully gone, but the answer to the IBCD question is "no".

I keep my ENDs reasonable and there is no need to get all wrapped around the axle about a functionally irrelevant mathematical hypothetical issue. For a short 75m wreck dive dive 15/55 to EAN50 is no big deal (and 10s of thousands of divers have made this 21m/70ft switch with no adverse affects). For a long 75m dive with hours and hours of deco, you need an intermediate gas cause your 35-21m stops really add up. I have used both 35/25 and 21/35 depending on the dive. To reiterate, you need the volume anyway. Don't go doing trimix to deep air switches and use a reasonable gas with a max ~30m END and the IBCD question is moot.

 

[rddvet]

The fact that he was asking for lists of people's bailout gas below 200ft in multiple threads was a huge red flag. I'd like to hear the story behind the conversation the mods had with him while banning hin

 

[Blackfrogfeet]

The OP is thankfully gone, but the answer to the IBCD question is "no".

I keep my ENDs reasonable and there is no need to get all wrapped around the axle about a functionally irrelevant mathematical hypothetical issue. For a short 75m wreck dive dive 15/55 to EAN50 is no big deal (and 10s of thousands of divers have made this 21m/70ft switch with no adverse affects). For a long 75m dive with hours and hours of deco, you need an intermediate gas cause your 35-21m stops really add up. I have used both 35/25 and 21/35 depending on the dive. To reiterate, you need the volume anyway. Don't go doing trimix to deep air switches and use a reasonable gas with a max ~30m END and the IBCD question is moot.

Can you explain what OP was even asking to a non CCR diver? I'm assuming IBCD is isobaric counter diffusion. I haven't gone CCR yet (doing training in a few months) but on my GUE T2 class I never learned about planning your deep/intermediate deco gases to avoid IBCD or what it really was.

 

[KenGordon]

Can you explain what OP was even asking to a non CCR diver? I'm assuming IBCD is isobaric counter diffusion. I haven't gone CCR yet (doing training in a few months) but on my GUE T2 class I never learned about planning your deep/intermediate deco gases to avoid IBCD or what it really was.

For a CCR dive you need gas to get to the surface if the rebreather is broken. That will typically be a set of gases that is quite similar to the choice you make on OC, so a bottom mix and appropriate deco mixes. Note that the choices are not exactly the same as this ascent is an emergency and your constraints might be different to the ones you’d use day in and day out.

The question arises when changing from that hypoxic bottom gas which will have plenty of helium (especially as you only have 3l to fill in regular CCR configurations) the what would be the first deco gas OC or the second bailout gas in CCR. This might be a 40m switch from 15/50 or 12/70 to 32%. The question is “is that ok?” or should you use 30/30 or some such.

Quite a lot of a hypoxic CCR course is about dealing with these logistical questions as well as the skills involved in dealing with the extra cylinders and techniques to avoid being overwhelmed. A risk is that a mod1 level diver, especially with deeper OC experience, decides there is nothing to learn and just goes diving with an extra bailout. There was a recent FB thread about that sort of thing where I think someone ended up badly hurt.

 

[rjack321]

Can you explain what OP was even asking to a non CCR diver? I'm assuming IBCD is isobaric counter diffusion. I haven't gone CCR yet (doing training in a few months) but on my GUE T2 class I never learned about planning your deep/intermediate deco gases to avoid IBCD or what it really was.

this might help
Isobaric Counterdiffusion in the Real World - InDepth (gue.com)

 

[GF99/99]

The OP is thankfully gone, but the answer to the IBCD question is "no".

I keep my ENDs reasonable and there is no need to get all wrapped around the axle about a functionally irrelevant mathematical hypothetical issue. For a short 75m wreck dive dive 15/55 to EAN50 is no big deal (and 10s of thousands of divers have made this 21m/70ft switch with no adverse affects). For a long 75m dive with hours and hours of deco, you need an intermediate gas cause your 35-21m stops really add up. I have used both 35/25 and 21/35 depending on the dive. To reiterate, you need the volume anyway. Don't go doing trimix to deep air switches and use a reasonable gas with a max ~30m END and the IBCD question is moot.

Spot on.

For a 75m dive I would do the same 14/55 direct to 50% and there is no need to worry about IBCD.

Please not that the depth is note the only factor there are many factors that contribute to IBCD warnings but ultimately it is just an unacceptable increase in PPN2/PPHe I think most agree that greater than 0.5atm is that limit. For example if you were to do a 60m dive 20min bottom time on a 14/60 1.2 SP and BO to a 14/60 you could not switch directly to a 50% at 21m. You get an IBCD warning. Now the way around this is to switch to the 50% at 12m to soften the spike in PPN2 or you can also put some He in your 50% to make a 50/10 then you can switch direct to the 50/10 at 21m like normal.

 

[flymolo]

For a CCR dive you need gas to get to the surface if the rebreather is broken. That will typically be a set of gases that is quite similar to the choice you make on OC, so a bottom mix and appropriate deco mixes. Note that the choices are not exactly the same as this ascent is an emergency and your constraints might be different to the ones you’d use day in and day out.

The question arises when changing from that hypoxic bottom gas which will have plenty of helium (especially as you only have 3l to fill in regular CCR configurations) the what would be the first deco gas OC or the second bailout gas in CCR. This might be a 40m switch from 15/50 or 12/70 to 32%. The question is “is that ok?” or should you use 30/30 or some such.

Quite a lot of a hypoxic CCR course is about dealing with these logistical questions as well as the skills involved in dealing with the extra cylinders and techniques to avoid being overwhelmed. A risk is that a mod1 level diver, especially with deeper OC experience, decides there is nothing to learn and just goes diving with an extra bailout. There was a recent FB thread about that sort of thing where I think someone ended up badly hurt.

Any chance you have a link to the thread on FB? I would be interested in reading it.

 

[rsingler]

These particular threads, while not on FB, are fascinating!
Isobaric Counter Diffusion - Scuba Engineer
Sheck Exley Mexico Dive - Scuba Engineer

 

[Scuba Client]

I learn from the best I learn from the worst.

The thread is now closed.

In the mix: Closed circuit rebreather gas planning