Video about oxygen shutoffs on Sidewinder

[rjack321]

I don't wish to be trite, but isn't Rebreather 101's slogan "always know your PPO2"?

Meaning you monitor this with your HUD / Nerd and notice if the PPO2 drops as alarms go off. As it's a manual CCR you'll be well aware of monitoring everything.

(Happy if I'm wrong with this assumption)

Sadly instead of reassessing the concept of adding an O2 shutoff to the sidewinder after a fatality which is directly linked to shutoff usage (combined with the ability to order a sidewinder without a HUD or NERD) - some instructors are doubling down that there "couldn't possibly be" any fault of the unit, it's configuration, or their training course/materials.

The deceased isn't here to defend themselves. "Diver error" after a CCR fatality is the cop out response instead of recognizing that all divers make mistakes. The more that you can engineer out opportunities for those mistakes to happen, or at least make it so when you do make a mistake you land softly instead of go unconscious and die - Then the safer the unit will be.

 

[rddvet]

fter a fatality which is directly linked to shutoff usage (combined with the ability to order a sidewinder without a HUD or NERD) - some instructors are doubling down that there "couldn't possibly be" any fault of the unit, it's configuration, or their training course/materials.

This is exactly the thought the video put in my head, combined with the stories I've been hearing.
I was in the room being part of/listening to a conversation about the loops popping off of the towers a few years back and got to hear the whole diatribe about it had to be the divers, the unit would never be at fault, from a sw instructor. There was never a thought that it could actually been a problem, just they don't know how to setup and dive the unit.

 

[Jack Hammer]

So I watched the video. Yeah, I get it it, staying at a constant depth your PO2 won't suddenly plummet if your O2 gets shut off. That doesn't address the fact that PO2 drops much more quickly, even with the O2 on, while ascending. A lot of caves have ups and downs and you are not at a constant depth. I'm not implying that using an inlineO2 shutoff is a death sentence, just that I believe that generally speaking the potential downsides outweigh the limited benefits of the upside. Regardless of what people choose to do they should understand the pros & cons and strive to make solid decisions.

 

[davehicks]

Yes you can.
Swim at 30ft with air dil and O2 off. After about the 2nd or 3rd ADV injection you'll be going hypoxic quick.

As i stated, it is not a realistic scenario. The video showed it taking 10 minutes to drop from 1.2 to .7 at which point the adv was was needed to add volume. If a ccr diver does not check their PPO2 after the 10-20 minutes and multiple ADV injections they are beyond careless, likely suicidal.

 

[Wibble]

(Numpty "intermediate experienced" CCR diver opinion...)

One of the key reasons people choose to dive with manual rebreathers is the simplicity of them. Aside from monitoring, they're purely mechanical and require the diver's brain to fly them. The simplicity means that less can go wrong as happens with complex systems with many interrelated systems. This tends to suit the attitude of the caving community.

Adding secondary shutoffs seems to be against the simplicity concept as you can shut off your oxygen and diluent at the valves should you need it. (From what I understand there's many people who dive with certain popular CCRs who use diluent shutoffs for things like the ADV which, being external, can fail.)

As a general engineering point, simple systems are far easier to design and build as there's fewer components to manufacture. From all walks of engineering, failures frequently happen in the backup and auxiliary systems which causes the failure of the whole system. These backup systems are often put in place to compensate for the underlying system's poor design and implementation -- Boeing's ridiculous recent problems are a perfect example (add bigger engines; which changes trim, etc.; add compensatory monitoring system; non-sentient flawed monitoring system kills everyone)

Humans are born fallible. This is compensated for by training and practice. Any rebreather diver knows this very well. Diving a CCR is a progression which slowly increases depth and complexity to gain the all-important experience which will save your life.

And then there's complacency; the biggest killer?

 

[tbone1004]

@Wibble
what isn't mentioned though is that eCCR's can actually sustain consciousness where an mCCR can't. They also have the advantage of stopping the flow of O2 when it isn't needed *i.e. on descents with rich dil mixes*. There are pros and cons to many systems but if I could put a solenoid in my primary unit I would in a heartbeat.

The shutoff didn't kill that diver in Ginnie, the lack of a HUD didn't kill that diver in Ginnie. They probably were a slice in the Swiss Cheese Model, but there certainly weren't the only two slices that day.

 

[Wibble]

what isn't mentioned though is that eCCR's can actually sustain consciousness where an mCCR can't. They also have the advantage of stopping the flow of O2 when it isn't needed *i.e. on descents with rich dil mixes*. There are pros and cons to many systems but if I could put a solenoid in my primary unit I would in a heartbeat.

The shutoff didn't kill that diver in Ginnie, the lack of a HUD didn't kill that diver in Ginnie. They probably were a slice in the Swiss Cheese Model, but there certainly weren't the only two slices that day.

Definitely. Rarely is it one thing that is the single cause; at the very least there's the failure to detect and mitigate the problem (am talking generally).

Can't avoid it: I love my Revo as it's a "hCCR"(hybrid CCR) -- developed from a manual CCR but with electronic control as a backup. Whenever I hear the hiss from the solenoid it's like a kick up the jacksie because I've not monitored my PPO2 correctly (I set it to 1.2 and run it manually at 1.3).

"No HUD"? It does seem a bit amiss to not have a HUD backup to the main computer.

 

[tbone1004]

Definitely. Rarely is it one thing that is the single cause; at the very least there's the failure to detect and mitigate the problem (am talking generally).

Can't avoid it: I love my Revo as it's a "hCCR"(hybrid CCR) -- developed from a manual CCR but with electronic control as a backup. Whenever I hear the hiss from the solenoid it's like a kick up the jacksie because I've not monitored my PPO2 correctly (I set it to 1.2 and run it manually at 1.3).

"No HUD"? It does seem a bit amiss to not have a HUD backup to the main computer.

On my Meg I leave it in low setpoint at 0.7 and just run it manual. As shown in the video I do not find that the leaky valve adds enough to warrant the hassles with leaky valves. The ppO2 just doesn't drop that fast, especially when you're deep.
I did just buy one of the experimental KISS needle valves and I like that it clicks as well as has the dual orifice so I can run an unblocked first stage. It still has clog potential, but it would easily replace an O2 MAV from a bmcl rig with no other modifications which is nifty.