Technical diving with oc versus ccr gas requirements

[rjack321]

what does that have to do with watching your O2 pressures? hint, absolutely f*cking nothing. Your O2 running out means you bail out. Why were they not watching their ppO2 for at least 10 minutes while it went from 1.0 down to less than .15? Sorry, not buying it. I feel for you having buddy's die, but that was their fault for not watching their ppO2, not for lack of an O2 gauge.

Shrugs
When it leaks or runs out on ascent, (or your solenoid/battery dies, or orifice clogs up, or 1st stage spring breaks etc etc) and almost assuredly there is some other problem or distraction happening at the same time - "just bail out" is not as simple as you seem to think. Especially since your brain is barely working as you're ascending and that ppO2 drops faster and faster. Anyone teaching MOD1 without gauges is not teaching to standards.

You are playing with fire not having an O2 gauge and the capacity to monitor it during the dive, but go ahead defend it as acceptable.

 

[PfcAJ]

If I were on a cave dive, I’d really like to know if I had an oxygen leak so I could turn around and go home before it became a bailout situation.

I mean that’s pretty simple and a dang good reason to have a gauge.... mitigate the issue before it becomes a real problem.

 

[broncobowsher]

I deleted my O2 gauge



But replaced it with a transmitter and have the O2 pressure displayed in the NERD. Also data logged.
It's a little number in the corner. Don't really pay much attention to it. But it will go red long before I am out or if it is off.

 

[rjack321]

Thanks - so practically speaking, how much longer bottom time does that translate to at a given depth (as a percentage, on average)?

Define longer?
On a square profile to 80m you will have more deco on CCR than on OC. So for the same 20mins, same GFs, your CCR dive will have a longer run time.
On a 30m max, multileveling dive for 4 hours you might not have any deco at all on CCR and have 30mins of deco on OC.

Longer is not really a useful metric

 

[tbone1004]

Define longer?
On a square profile to 80m you will have more deco on CCR than on OC. So for the same 20mins, same GFs, your CCR dive will have a longer run time.
On a 30m max, multileveling dive for 4 hours you might not have any deco at all on CCR and have 30mins of deco on OC.

Longer is not really a useful metric

That was a confusing response, I had to read it twice.

@Ghattas what he's saying is if you are going for the same total run time, you will get a few extra minutes on CCR since every deco stop can be done at 1.6 and if you don't have an ideal mix on OC, you can make it ideal on CCR which is nice.
If you are asking about how much longer you can go on CCR for bottom time when carrying the same bailout, it all depends on depth and your personal deco strategy. If you carry 1:1 on CCR and 1.5:1 on OC, then your total deco time can be 50% longer with the same deco bottles, but what that translates to in terms of bottom time will depend on depth. At 100ft it could be several hours, at 100m it may only be a few minute depending on your gradient factors

 

[DiveClimbRide]

Define longer?
On a square profile to 80m you will have more deco on CCR than on OC. So for the same 20mins, same GFs, your CCR dive will have a longer run time.
On a 30m max, multileveling dive for 4 hours you might not have any deco at all on CCR and have 30mins of deco on OC.

Longer is not really a useful metric

Sorry I don't understand. Why would the same square profile have a longer deco time on ccr?

 

[CptTightPants21]

Sorry I don't understand. Why would the same square profile have a longer deco time on ccr?

It depends on the profile and exact nature of the dive, but if an OC diver is diving very close to MOD on a mix then they are essentially mirroring the CC diver on the bottom portion of the dive who is running 1.2-ish. On Deco, the OC has the benefit of maxing out PO2s, especially the 1.6 at 20'. CCR divers will typically just deco at 1.3 or 1.4--it doesn't spike the CNS clock, they don't need air breaks, and it's easier to maintain.

 

[DiveClimbRide]

It depends on the profile and exact nature of the dive, but if an OC diver is diving very close to MOD on a mix then they are essentially mirroring the CC diver on the bottom portion of the dive who is running 1.2-ish. On Deco, the OC has the benefit of maxing out PO2s, especially the 1.6 at 20'. CCR divers will typically just deco at 1.3 or 1.4--it doesn't spike the CNS clock, they don't need air breaks, and it's easier to maintain.

Would I be correct in understanding that it's because the ccr diver will be running a lower ppo2 for the whole dive (perhaps due to CNS) than the oc diver at the bottom?

 

[grantctobin]

Bottom PO2s will likely be similar. Largely the discrepancy comes from the avg 1.4 deco PO2 on standard gasses open circuit and then 1.6 at 6M/20’ if oxygen is used vs vs a constant 1.2 on CCR

Would I be correct in understanding that it's because the ccr diver will be running a lower ppo2 for the whole dive (perhaps due to CNS) than the oc diver at the bottom?

 

[helodriver87]

Yeah, chasing 1.6 on your shallower stops is impossible. Super wasteful too. Since that's where most of your deco is, an OC diver has an advantage there since they can hit 1.6 on their 20ft stop and CCR will need to settle for 1.4. But the CCR diver can even it out on intermediate stops where the OC diver is working with a less optimal PO2. The real magic is on multilevel stuff. CCR will prevent a lot of deco from accumulating compared to OC by maintaining an ideal PO2 when away from the MOD. I did a 3 hour swim at Madison with some buddies on OC. They used 32% and ended up with 15 min of O2 time. I had no deco.