Going to back gas while switching stages?

[onepointfivethumbs]

Trying to learn more about tech techniques I came across the ISE deco stage switching procedure


It looks like the hoses on his stage tanks are either white or clear and the doubles regs are black, with three bottles I'm assuming one is travel mix, one is nitrox and the last is O2, which would mean his back gas is bottom mix.

When he goes to switch stages (bottom to travel, travel to nitrox, nitrox to O2) he goes onto his back gas on the long hose while tidying up the stages, if the bottom mix is hypoxic trimix wouldn't he black out especially at O2 depth? Or am I not seeing something?

 

[SandyRobinson]

Someone check my math but if the trimix had 13% O2, at 20 feet(1.6 atmospheres) where the switch occurs, the PO2 would be .13*1.6 = 20.8 or .1% less than we are breathing now. He would OK.

 

[Searcaigh]

When I dive with a back gas mix of 15/40 I usually descend on my 50% deco gas until I'm at 15-20m and change to back gas.

I was not taught to go to back gas between deco gas changes though.

with three bottles I'm assuming one is travel mix, one is nitrox and the last is O2, which would mean his back gas is bottom mix.

His third tank is a bottom mix.

 

[Wibble]

Hypoxic mixes, generally lower than 18% oxygen, have too little oxygen to breathe on the surface especially if you’re "working" hard, such as carrying yourself and your cylinders across a boat. Thus special hypoxic procedures are used where you breathe from the deepest normoxic (18 to 22%) mix you’re carrying.

For a dive with 13% oxygen, this would be a maximum of 1.4 PPO2 at depth,
Max operating depth (MOD) = dose over mix = 1.4 / 0.13 = 10.7 = 97 metres (318')

In reality few people would ever dive to this depth on open circuit nowadays, they'd use a rebreather.

 

[Wibble]

When switching between deco gasses, you’d do that from one to another, not via the backgas.

If your richest deco gas is 100%, you’d need to take "oxygen breaks" every 30 mins or so to give your lungs a rest. This may mean you switch to back gas or an intermediate normoxic mix.

 

[GF99/99]

Trying to learn more about tech techniques I came across the ISE deco stage switching procedure


It looks like the hoses on his stage tanks are either white or clear and the doubles regs are black, with three bottles I'm assuming one is travel mix, one is nitrox and the last is O2, which would mean his back gas is bottom mix.

When he goes to switch stages (bottom to travel, travel to nitrox, nitrox to O2) he goes onto his back gas on the long hose while tidying up the stages, if the bottom mix is hypoxic trimix wouldn't he black out especially at O2 depth? Or am I not seeing something?

All I can say about this video is Wow...

I am really not to sure what is being taught in this video? I guess that's what you get with an ISE video.

First off the supposed "bottom mix" looks like it only has an MOD of 45m (not much of a bottom mix for Open water diving) so this would make us assume his back gas is a travel gas??? or more of the same bottom mix???
Next it does not appear that he is switching his computers to reflect the gas he is breathing
Next I have no clue why he switched to his back gas to transition from the 50% to O2. There is zero benefit from this all it does is makes is decompression less effective. And in reality if you require 3 stage for an open water dive then your probably doing something deep alot more that 45m so you would have a pretty high helium mix back gas so there is no way you would switch from your 50% to back gas then to O2 sounds like an ICD nightmare

 

[Frogman82]

Not sure if it still is, but this was standard GUE procedure for gas switches. ISE is a dir oriented organization so it would make sense to them.
Printed from DIR-diver.com ⓒ 2002-2014 Peter Steinhoff

 

[lermontov]

All I can say about this video is Wow...

I am really not to sure what is being taught in this video? I guess that's what you get with an ISE video.

First off the supposed "bottom mix" looks like it only has an MOD of 45m (not much of a bottom mix for Open water diving) so this would make us assume his back gas is a travel gas??? or more of the same bottom mix???
Next it does not appear that he is switching his computers to reflect the gas he is breathing
Next I have no clue why he switched to his back gas to transition from the 50% to O2. There is zero benefit from this all it does is makes is decompression less effective. And in reality if you require 3 stage for an open water dive then your probably doing something deep alot more that 45m so you would have a pretty high helium mix back gas so there is no way you would switch from your 50% to back gas then to O2 sounds like an ICD nightmare

its simply a video demonstrating a gas switching system by ISE - his 'bottom gas' is on his back and the 45m is his first switch - unlikely he'd be using a single cylinder to do a bottom part of a deep dive as a failure at depth would be problematic - computer switches are missed - would have been better to have them - anyone who has done similar diving will know that so i guess from an instructional video its a little tardy.

 

[GF99/99]

its simply a video demonstrating a gas switching system by ISE - his 'bottom gas' is on his back and the 45m is his first switch - unlikely he'd be using a single cylinder to do a bottom part of a deep dive as a failure at depth would be problematic - computer switches are missed - would have been better to have them - anyone who has done similar diving will know that so i guess from an instructional video its a little tardy.

Yes I can see this is an educational video but it should show proper techniques. Not trying to attack anyone but I am just say this video is clearly meant for newer divers and I don't fully understand why this is the instructions that would be shown

If his back gas is his bottom gas why in the video does is show him breathing off the 45m mix and then its clearly says "bottom stage empty - time to go" and then he signals to his buddy he is switching to his back gas. Yes I am aware that it is unlikely he'd be using a single cylinder for bottom gas as I would never do that but if this is an educational video then the audience it most likely new divers and this is not educating them very well.

Lets give the video the benefit of the doubt and say the bottom gas is actually his back gas and he is breathing off the travel 45m mix. So why would he switch to the back gas again then?? the whole point of a travel is to get you up to your 50% gas switch. And then why from the 50% to 100% does he go to his back gas again.

I have not done much OC deep diving (that's what the rebreather is for) with 3 stages so sorry in advance if I am wrong but the 100m OC dives I have done I would never and was never taught to go to my back gas between stage switching. I was actually taught never to do this only in an emergency situation would you ever do this. Lets say you have 12/60 back gas, 20/30 travel, 50%, and O2 (and realistically 3 stages is really pushing the limit for a 100m dive). So your at 100m breathing your back gas 12/60 you ascend up to 50m switch to your travel 20/30. Now normally I would just follow both computers/plan up to 21m switch directly from travel to the 50% continue following computers/plan up to 6m switch directly from 50% to O2 (and in reality I would probably use an 80% not 100% run it through Multideco you will only a couple more minuets of deco but your CNS will be significantly lower) I would never do any of this funny switching to back gas be for gas switches. Also if this is an educational video how does that even work do you switch to back gas at the previous stop be for?? or do you ascend on the back gas?? or ascend up to 21m on the travel then switch to back gas then quickly switch to the 50%?? seem like a lot of regulator switching and just complicating a simply process. Lastly try going on a 100m dive and during your deco when you get to the 50% switch on your 12/60 back gas then switch to the 50% tell me how that works out for you ICD wise. And in the reverse tell me how that works out for switching from the 50% to the 12/60 back gas. I would never be showing this technique to potential new technical divers. This is very bad practice and could potentially be dangerous. Like I said maybe I am wrong and I apologies if I am, I guess that's why we have forums like this to learn from others but IMO this video could be teaching new divers some very poor techniques.

 

[happy-diver]