Gas switch using air

Peter L said:
I could plug 100% O2 in on my DIL on that program, it makes as much sense and impact.
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rather than inventing some random way of fudging the deco obligation.
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Well I never said it was a good idea. But I do think it a better idea than flushing. If you had access to the algorithm you could tweak the M-values..but as we don't all that is left it deco-voodoo.

The other technique I've seen used CCR for early get out is what I call MLV-watching. When you're off gassing volume is not a problem, falling PO2 is. When you're done it switches; PO2 stabilises but volume becomes a problem (to see it find MLV and reduce SP to 0.7). This for some means time to get out...I'd try it if I had to (I have practised it), shaves about the same as 1.5 from the bottom does.

Matt.
 
paul t said:
Matt, are you talking about flushing the loop to add a new dill, or flushing to refresh the loop during deco?

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This thread is about flushing the loop with a new gas primarily to reduce the PHe as most computers still think He the devil.

I'm suggesting you never flush as it is a) potentially ICD contraindicated and b) it makes me feel shit (especially the 3 I tried; Air @ 42m, 20/30 @ 42m, 20/30 @ 60m).

My later posts suggest that flushing is so bad that it's probably safer to skip the flush and just lie to the computer. I'm being picked up for that. But people do and they are not all dead so perhaps it too has legs (for emergency planning, for example).

Matt.
 
Cheers matt

I've been reading through and got what it was about

I think there is a huge grey area when it comes to off gassing on a RB. I have not been able to find any information regarding scientific study of the loop contents (inert gases) throughout the decompression phase

Matt, do you switch to pure o2 at 6mts?

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JukkaO said:
If I rip my suit I might still survive if my deco oblication allows early surfacing.
Jukka
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I've done a couple of hours deco with a flooded suit. Ripped left shin, and felt the water creeping up to my nadgers (brrr!) then down the other leg. I have a heated vest now.

To me - I can't see why switching dils gives you less deco - the IBCD makes things worse and means you need to stay longer in the water.

If I need to get out of the water quickly then I'll cut back on the deco (using higher GF in Bulhman, or lower conservatism in VPM) and accept I'm more likely to get a hit.

Janos
 
paul t said:
Cheers matt

I've been reading through and got what it was about

I think there is a huge grey area when it comes to off gassing on a RB. I have not been able to find any information regarding scientific study of the loop contents (inert gases) throughout the decompression phase

Matt, do you switch to pure o2 at 6mts?

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I think your right, no one knows. If they do and there is a study please someone post it! Messing with loop-gas cannot be compared to OC switches IMHO as a) exhale is recycled, b) depth of CCR dives is routinely deeper, c) total time is typically longer. My OC dives were to 80m but for a total time of 90 mins. Here I'm only talking about CCR dives with deco times over 200 minutes.

I do not flush O2 at 6m; I am lazy and I let the unit do the work - I just keep MLV. Depending on the parameters I either run 1.3 all the way or 1.5 from the bottom. For the long times I take the extra CNS and I do not back-switch.

Matt.
 
We have now done the dive why I started discussing here about dil switch.
The dive includes three parts as the deep part starts from an air chamber:
0 – 32 - 0m
0 – 132 – 0m, Diluent switch 9/65 -> 10/55 between 116…111m
0 – 32 – 0m
Our strategy has always been to do all the deco and move over the air chamber without any delay.
The whole dive time was 6 h. Water temperature 5 degrees.
During the deep dive cells were quite ok for the first four hours but the rest of the dive was continuous beeping. Cell warning and oxygen exposure warning of the Vision. Classic is better for long dives as it does not complain about the oxy exposure and it is also possible to switch off during shallow deco to make it silent and save batteries for the later parts of the dive.

Any constructive comments about the diluent switch? We did it deep as that one study suggested it is not as bad as a bit shallower ones. We feel cutting deco obligation is really important for safety.

Plura Cave Deep Exploration 2012, depth 132m on Vimeo

Jukka
 
Hello Jukka,

Nice video! Pity about the comments on the bottom - first come first served in my books.

Anyhow I have no comment on your gas choices, nice achievement!

How much gas did you have with you deeper than 80m?

Cold lips!

Cheers
Matt.
 
I had 12x250bar + 12x230bar and she had (10+10)x230bar.
We use scooters and keep very relaxed all the time... thinking we would not need extra big amounts of gas for fast breathing.

Jukka
 
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