Which do you think is less dangerous at 160ft? Open-circuit air or CCR trimix?

[flymolo]

But that’s what I’m saying, with equal levels of training a CCR is more dangerous than OC ( with a CCR there’s more chance of a mechanical failure)

an unfixable mechanical failure on ccr would just drop you right back onto OC

 

[inquis]

But that’s what I’m saying, with equal levels of training a CCR is more dangerous than OC ( with a CCR there’s more chance of a mechanical failure)

Risk encompasses likelihood of a failure AND severity of consequence. You're correct that there are more things that could go wrong (equipment-wise), but you seem to be missing the fact there are far more options to handle failures if they do. In OC terms, it's like comparing manifolded doubles vs single tank: yes, doubles increases the probability of equipment failure, but the reduction in severity of consequence vastly outweighs that.

Risk also includes the diver, not just equipment. While you may be able to function adequately while narced, that's not the norm. (I also believe even you would handle issues better/more quickly at 60 ft vs 160 ft, lessening the chance of a cascade/spiral of issues.) The self-awareness goes down on deep-air, and the likelihood of (non-equipment) problems goes up. The severity of consequence goes up. That means risk goes up and safety goes down.

 

[Celt]

Risk encompasses likelihood of a failure AND severity of consequence. You're correct that there are more things that could go wrong (equipment-wise), but you seem to be missing the fact there are far more options to handle failures if they do. In OC terms, it's like comparing manifolded doubles vs single tank: yes, doubles increases the probability of equipment failure, but the reduction in severity of consequence vastly outweighs that.

Risk also includes the diver, not just equipment. While you may be able to function adequately while narced, that's not the norm. (I also believe even you would handle issues better/more quickly at 60 ft vs 160 ft, lessening the chance of a cascade/spiral of issues.) The self-awareness goes down on deep-air, and the likelihood of (non-equipment) problems goes up. The severity of consequence goes up. That means risk goes up and safety goes down.

Proper training is what’s needed to reduce human error whether OC or CCR. But a mistake on CCR has proven a lot more fatal.

 

[Celt]

an unfixable mechanical failure on ccr would just drop you right back onto OC

Is that a post in favour of OC

 

[flymolo]

Is that a post in favour of OC

no just means that a failure of the ccr is a nonissue as long as you have adequate bailout

 

[broncobowsher]

So if the post was...
If I have no training on CCR and a fair bit on OC, which is more dangerous on a random deep cave dive that isn't properly trained for?
That sounds more like the real question.

 

[flymolo]

So if the post was...
If I have no training on CCR and a fair bit on OC, which is more dangerous on a random deep cave dive that isn't properly trained for?
That sounds more like the real question.

haha it kinda sounds like this thread isn't really asking hypothetical question and maybe someone is just looking for justification to do something dumb?

 

[Wibble]

CCR is a great tool for caves and other overheads... if you can get in to that location with the CCR you use (e.g. if there's a backmount "filter"/restriction on the entrance where you need sidemount to get through)

The great thing about CCR is it effectively removes gas and time limits, allows diving with the right gases for narcosis and density, CCR is cheap and much more pleasant to dive in overheads. All things being equal, why on earth would anyone choose to use Open Circuit when CCR is an available option???

A dive to 50m/165ft is a trimix deco dive. When blowing bubbles your time is just ebbing away with every breath. With CCR there's no reason for the dive to not complete on the unit; only should it fail do you revert to OC and you're getting the heck out of Dodge.

 

[PEDiver]

someone is just looking for justification to do something dumb?

Unfortunately, all too common at the dive site that I believe OP is referring to. Known to many locals as the "stroke pit" due to the number of divers doing sketchy dives here on the regular. We had a double fatality recently with two single tank divers on air going down to 140' or so in the no-light zone and running out of air.

 

[Snusmumrik]

mistake on CCR has proven a lot more fatal.

Mistake on OC due to nitrogen narcosis is more likely to kill you.
Messed mix switch, O2 taken deep enough, a lot of it.