Ginnie Springs diver missing - Florida

[Capt Jim Wyatt]

Why is 32% used as diluent? I was always taught and used 21% as a diluent, often with a bit of Helium in it to ease the WOB.

Is this something new for sidemounted rebreathers?

 

[rddvet]

Why is 32% used as diluent? I was always taught and used 21% as a diluent, often with a bit of Helium in it to ease the WOB.

Is this something new for sidemounted rebreathers?

I was taught to use a dil closer to actual OC p02s for most typical cave dives. 32% is a little hot for me for a place like LR so we typically dive 30/30, 25/25, or 21/35. 30/30 is most common as it’s what I’d dive in OC. The way I was taught was it’s a balance of dil flush dropping p02 vs deco obligations if bailing out. I personally wouldn’t want to swim out of Ginnie for an hour on air and accrue a big deco obligation after having to bail out. 30/30 is a nice median of the two. But it’s a fine balance. Doing a dil flush with 32% at 100ft isn’t very efficient at all. My wife prefers 21/35 because she doesn’t like her p02 over 1.2 anymore. She’s finding she has an oxygen sensitivity which I understand is ,ore common in women. If she stays above a 1.2 for a long time she gets burning lungs.

side note: I am much more likely to get mild dcs symptoms than oxygen issues so a higher p02 if bailing out is a little more important for me. I found out 2 weeks ago I have a pfo I need to get fixed

 

[_Slacker_]

Why is 32% used as diluent? I was always taught and used 21% as a diluent, often with a bit of Helium in it to ease the WOB.

Is this something new for sidemounted rebreathers?

It is a trade-off when having only off board Dil and no onboard dil. So, SM CCRs generally (most but not all don't have onboard Dil) do this but also BM CCRs that configure without any onboard dil.

 

[tbone1004]

Why is 32% used as diluent? I was always taught and used 21% as a diluent, often with a bit of Helium in it to ease the WOB.

Is this something new for sidemounted rebreathers?

most of the CCR training I have seen as of late, especially amongst cave instructors has been to use the same dil as you would if doing the dive on OC. The higher ppO2 in the dil helps conserve oxygen use on the bigger dives but also allows you to take advantage of SCR mode without incurring nasty deco penalties

 

[Capt Jim Wyatt]

@rddvet @TBone @_Slacker_ Thank you.

I also agree the PO2's should be 1.2 max vs 1.4. We have a history of a couple of females toxing at 1.4. on O/C cave dives.

 

[rddvet]

@rddvet @TBone @_Slacker_ Thank you.

I also agree the PO2's should be 1.2 max vs 1.4. We have a history of a couple of females toxing at 1.4. on O/C cave dives.

Not sure how much it differs from instructor to instructor, but we're taught p02 of 1.0 for the majority of the dive if possible for longer dives 3-4 hours +. And a p02 of 1.2 if you prefer for shorter dives. I was also taught not to chase 1.4 or higher at deco. 1.2 is perfectly acceptable. If you're able to bump it up great, but unnecessary and often more of a waste of oxygen and a buoyancy annoyance

 

[tbone1004]

Not sure how much it differs from instructor to instructor, but we're taught p02 of 1.0 for the majority of the dive if possible for longer dives 3-4 hours +. And a p02 of 1.2 if you prefer for shorter dives. I was also taught not to chase 1.4 or higher at deco. 1.2 is perfectly acceptable. If you're able to bump it up great, but unnecessary and often more of a waste of oxygen and a buoyancy annoyance

especially annoying when doing OW deco. In a cave it's a lot less bad, but agreed on trying to chase high ppO2's on the shallow stops. Deeper ones I don't have much of an issue getting close, but the O2 stop is really annoying. My SOP is basically to bump up to 1.5 or so then let it bleed down

 

[rddvet]

especially annoying when doing OW deco. In a cave it's a lot less bad, but agreed on trying to chase high ppO2's on the shallow stops. Deeper ones I don't have much of an issue getting close, but the O2 stop is really annoying. My SOP is basically to bump up to 1.5 or so then let it bleed down

That's basically what I do as well. When I first started diving trimix on the unit I was really annoyed because I was too stupid to realize that during the initial part of deco it was ridiculously hard to keep a high p02 due to offgassing helium so rapidly. When it finally dawned on me what was happening deco became alot less annoying. It's really odd to see as offgassing slows down how your loop contents stop dropping as rapidly. I think that was the oddest revelation for me going from OC to CC

 

[tbone1004]

That's basically what I do as well. When I first started diving trimix on the unit I was really annoyed because I was too stupid to realize that during the initial part of deco it was ridiculously hard to keep a high p02 due to offgassing helium so rapidly. When it finally dawned on me what was happening deco became alot less annoying. It's really odd to see as offgassing slows down how your loop contents stop dropping as rapidly. I think that was the oddest revelation for me going from OC to CC

it's a neat trick to know when deco is actually done as well. If the loop is still dropping rapidly then you probably shouldn't head up yet...

 

[rddvet]

it's a neat trick to know when deco is actually done as well. If the loop is still dropping rapidly then you probably shouldn't head up yet...

Yep that revelation came along with the helium one.