CCR Cave - O2 shutoffs and HUDs

[BlueTrin]

Which video is it?

 

[lostsheep]

Which video is it?

Presumably this one:

 

[Superlyte27]

Agree in principle, but you can’t see the NERD2 in a proper whiteout AND it doesn’t vibrate. Combined with the case design and thus depth sensor issues, it’s not ideal. Vibrating Petrel3 or vibrating Freedom and a Fathom or DiveCAN etc HUD > NERD2 by a mile.

Actually, you can. Sorta. You can see the glow of red or green.

 

[kierentec]

It’d be nice if a training agency or some other higher power could force these guys to issue a retraction for that video. The content is downright dangerous and illustrates a real lack of understanding of how a rebreather works. In 11 minutes he breathed the PO2 down by .6. He says the PO2 of the victim’s dil was around .45. The SW has a super small lung, all you need to do is clear your mask hard or vent the loop for any other reason and it will flush the loop down significantly. With a .45 PO2 dil, I’d say it’d drop from a 1.2 down to about .7. Do it again and it’ll be almost a complete flush, so down to that .45 range.

So about 7-8 minutes until lights out. Yes, the ADV will fire or you will need to manually add dil, but with a very hypoxic dil, it won’t drive the PO2 back up very much. So you’re maybe looking at about 10-15 minutes till hypoxic depending on the divers workload and metabolic rate. If a diver is seriously task loaded, and fairly inexperienced, they may not notice and out like a light.

I say should issue a retraction and say “sorry, we are the ones that should have known better than that, I guess this guy and many others have actually gone hypoxic at depth and it’s not some big conspiracy against inline shutoffs and rebreathers without HUDs.

 

[Capt Jim Wyatt]

the ADV will fire

Maybe and only if the online shutoff for the ADV has not been closed.

 

[kierentec]

Maybe and only if the online shutoff for the ADV has not been closed.

Yup, which is why I also said “or you will need to manually add dil”. If not, you eventually won’t be able to breathe.

 

[rjack321]

It’d be nice if a training agency or some other higher power could force these guys to issue a retraction for that video. The content is downright dangerous and illustrates a real lack of understanding of how a rebreather works. In 11 minutes he breathed the PO2 down by .6. He says the PO2 of the victim’s dil was around .45. The SW has a super small lung, all you need to do is clear your mask hard or vent the loop for any other reason and it will flush the loop down significantly. With a .45 PO2 dil, I’d say it’d drop from a 1.2 down to about .7. Do it again and it’ll be almost a complete flush, so down to that .45 range.

So about 7-8 minutes until lights out. Yes, the ADV will fire or you will need to manually add dil, but with a very hypoxic dil, it won’t drive the PO2 back up very much. So you’re maybe looking at about 10-15 minutes till hypoxic depending on the divers workload and metabolic rate. If a diver is seriously task loaded, and fairly inexperienced, they may not notice and out like a light.

I say should issue a retraction and say “sorry, we are the ones that should have known better than that, I guess this guy and many others have actually gone hypoxic at depth and it’s not some big conspiracy against inline shutoffs and rebreathers without HUDs.

I remember back when Andrew G. released his fully manual UTD CCR (the first iteration of which was based on a Meg). He did the same stunt about how you "can't go hypoxic" with it cause loop volume will save you. He got absolutely crucified on TDS and WallyWorld (RBW) at the time.

There are vastly more circumstances where you will pass out and die than those where loop volume, if the depth & dil stars align just right, will save you.

I actually have a shutoff on my SW when I am using my needle valve. But I don't use it underwater. It's for very specific circumstances where I am walking in water (sometimes for an hour plus) and don't want my O2 dumping into my loop nor my first stage knocking loose and flooding.

 

[Cio]

I just did this exercise in training.
50 ft depth, 1.2 PPO2 O2 shut off.
12 minutes to get to a PPO2 of 0.7.
ADV fired 6 times to make up the loop volume.

I agree there is no need for an inline shut off.
I also agree that it seems far fetched someone would die from hypoxia if their O2 accidently shut off. PPO2 monitor and and ADV firing would have to be ignored for a prolonged period of time. 50 feet is not deep, there is way more mass of O2 in the loop at greater depths, making this take even longer.

 

[evandroairton]

I am SW certified, but, after a fatality report (O2 shutt followed by ascent - no hud) i started to get annoyed, when i was studying general rebreather theory, and operation, to get prep for become an inspiration instructor, i've realized some flaws on the SW design, when compared with more usual loop concepts, and sold mine right after (using a nerd as redundancy on my inspo)
I do agree that the SW main concept is great for cave diving, but i've lost confidence, and at least for me wasn't worthy keeping using something i can't trust anymore.
Probably will get an chestmount ccr on a near future.
But, again, is a personal matter, and will not bash those who uses the SW

 

[inquis]

50 feet is not deep, there is way more mass of O2 in the loop at greater depths, making this take even longer.

The mass of O2 is the same regardless of depth, assuming the same loop volume and PO2. While the total molecule count does increase at greater depth, the fraction of O2 decreases by the same proportion (since the same PO2 is present). As such, it wouldn't take longer. If anything, it could take a little less time, due simply to the choice of a diluent with lower O2 fraction (and less O2 added when restoring loop volume) on a deeper dive.