Cave diving on CC is safer than on OC?

[rjack321]

Damnit. You're reminding me one of my favorite cave sections in mexico is much harder to get to nowadays. Do it from the other end every once in a while, but I miss grand cenote. IMO one of the most underrated mexican caves along with Taj Maha because people think they're training or tourist caves

I was only using the excessively dismissive "tourist cave" verbage because that's how the OP phrased the question. Despite far more people diving & dying in seemingly "easy" OC divable caves.

I still think the whole question is flawed. You can't just do simple 2 number arithmetic to derive a death rate nor can you isolate one type of gear from another. Pretty soon we'll be dissecting the death rates for LED vs HID lights.

 

[formernuke]

Do you dive CCR @berndo ?

He likes causing trouble

 

[Underwater Tourist]

I think the question was designed to cause a row, or just plain silly.

It was not. I think its pretty obvious the thought experiment I wanted to discuss.

I will paraphrase it in a new way as we are getting to caught up on what's "an easy" dive.

Universe A: only nitrox dives with anywhere from 2-4 tanks area allowed, no CC allowed, no solo allowed.
Universe B: the exact same dives are done on CC, no OC allowed (ofc bailout doesnt count), no solo allowed.

Which universe you think will have more accidents?

Now I admit that after a thread like "Is cave diving safer than Open Water" generated 200+ responses I probably shouldn't have posted in the first place, but I hey, I was interested if there is consensus on the topic.

 

[rddvet]

I was only using the excessively dismissive "tourist cave" verbage because that's how the OP phrased the question.

Sorry, that wasn't directed at you.

 

[rjack321]

It was not. I think its pretty obvious the thought experiment I wanted to discuss.

I will paraphrase it in a new way as we are getting to caught up on what's "an easy" dive.

Universe A: only nitrox dives with anywhere from 2-4 tanks area allowed, no CC allowed, no solo allowed.
Universe B: the exact same dives are done on CC, no OC allowed (ofc bailout doesnt count), no solo allowed.

Which universe you think will have more accidents?

Now I admit that after a thread like "Is cave diving safer than Open Water" generated 200+ responses I probably shouldn't have posted in the first place, but I hey, I was interested if there is consensus on the topic.

If you examine the Riviera Maya alone, then perhaps surprisingly, A has more accidents. There are plenty of CCR and SCR divers being done in that area of the world and I can't recall a single fatality. Vs ample OC fatalities.

If you look at someplace the USA, then we've had more far accidents and fatalities on CCR then on OC. Two accidents in Roaring River last year, the double Eagle's fatality plus plenty more.

It "depends" and there is no universal answer in part because the world ain't that simple. It's a different pool of divers, with different experience and complacancy levels, doing different types of dives, and their equipment is generally a tertiary factor in the whole incident chain anyway.

 

[Underwater Tourist]

I think that dichotomy is because in MX a major contributing factor is navigation error, which is exactly when you would want to be on a ccr

 

[Celt]

It was not. I think its pretty obvious the thought experiment I wanted to discuss.

I will paraphrase it in a new way as we are getting to caught up on what's "an easy" dive.

Universe A: only nitrox dives with anywhere from 2-4 tanks area allowed, no CC allowed, no solo allowed.
Universe B: the exact same dives are done on CC, no OC allowed (ofc bailout doesnt count), no solo allowed.

Which universe you think will have more accidents?

Now I admit that after a thread like "Is cave diving safer than Open Water" generated 200+ responses I probably shouldn't have posted in the first place, but I hey, I was interested if there is consensus on the topic.

The question is hypothetical, you need to ask, who’s making the dives and what are the personal risks for them. I can only speak for myself, a perfect candidate for a rebreather accident. Years and years of OC diving used to dealing with narcosis and once I’m getting gas I’m safe. A lethal mistake on a rebreather. You can’t take the diver out of the accident and just ask about gear. That’s what happens in diving accident investigations people don’t like to criticise the dead, especially their friends.

 

[Wibble]

The issue with CCR is not that the CCR system is intrinsically unsafe (the system comes with bailout), but that CCR naturally encourages divers to go far beyond their natural limits.

OC diving means you've an absolute maximum time as measured by your gas limits (min gas) with the max time to surface. You know these because you've planned it in advance. These hard limits mean people will tend to not exceed the limits -- idiots aside.

CCR doesn't have those hard limits. Ignoring bailout, the difference between a 20m/60ft dive and a 90m/300ft dive is only the diluent gas mix used (helium for narcosis prevention, less oxygen). You could dive a 90m/300ft mix at 20m/60ft on CCR without issues. On Open Circuit this would require masses more gas for the greater pressure, a mix that's optimised for that specific depth, plus all the decompression gasses, e.g. a bottom stage and three deco stages -- that would not be acceptable for a shallower dive, even ignoring the excruciating costs. Similarly for overhead, a CCR is measured on absolute time on the loop, whereas open circuit is all about gas consumption.

CCR doesn't have a hard min gas limit, "many hours" of gas is available. The problematic main limit to CCR is the amount of bailout gas available. This is hard to plan and very easy to exceed. Bailout planning is very much a finger in the air guess of what the peril is, with the worst case being a CO2 hit. However, for other bailouts (flood, caustic, or temporary bailout), then it's much easier to plan around the TTS required. The good news is CO2 hits are very rare.

The real challenge with bailout is exceeding its limits, especially for deep dives or long penetrations. You could do 1000 dives, all exceeding the bailout limits... then one day you discover your limits.

Arguably CCR is safer than Open Circuit. There's more options and CCR divers should be fully trained, know the risks AND practice frequently. Especially in the first 200 hours or more.

 

[PfcAJ]

The issue with CCR is not that the CCR system is intrinsically unsafe (the system comes with bailout), but that CCR naturally encourages divers to go far beyond their natural limits.

OC diving means you've an absolute maximum time as measured by your gas limits (min gas) with the max time to surface. You know these because you've planned it in advance. These hard limits mean people will tend to not exceed the limits -- idiots aside.

CCR doesn't have those hard limits. Ignoring bailout, the difference between a 20m/60ft dive and a 90m/300ft dive is only the diluent gas mix used (helium for narcosis prevention, less oxygen). You could dive a 90m/300ft mix at 20m/60ft on CCR without issues. On Open Circuit this would require masses more gas for the greater pressure, a mix that's optimised for that specific depth, plus all the decompression gasses, e.g. a bottom stage and three deco stages -- that would not be acceptable for a shallower dive, even ignoring the excruciating costs. Similarly for overhead, a CCR is measured on absolute time on the loop, whereas open circuit is all about gas consumption.

CCR doesn't have a hard min gas limit, "many hours" of gas is available. The problematic main limit to CCR is the amount of bailout gas available. This is hard to plan and very easy to exceed. Bailout planning is very much a finger in the air guess of what the peril is, with the worst case being a CO2 hit. However, for other bailouts (flood, caustic, or temporary bailout), then it's much easier to plan around the TTS required. The good news is CO2 hits are very rare.

The real challenge with bailout is exceeding its limits, especially for deep dives or long penetrations. You could do 1000 dives, all exceeding the bailout limits... then one day you discover your limits.

Arguably CCR is safer than Open Circuit. There's more options and CCR divers should be fully trained, know the risks AND practice frequently. Especially in the first 200 hours or more.

Lack of bailout isn’t what’s killing ccr divers. It’s hypoxia and hyperoxia, and hypercarbia, three things that are much easier to experience on a rebreather.

 

[kensuf]

I can think of one in recent years that was an unverified traverse attempt.

Two. One from Catfish to Manatee, one from Friedman's to Catfish.

Edited to add, both were partially trained but not fully trained.