Redundant Octos & 2nd Stages Unable to Deliver Air?

[Fibonacci]

That's the problem with the egg-shell-thin wall thickness on modern second stages these days!
Poor DFMEA... harrumph.

What Is DFMEA? Design Failure Mode and Effect Analysis

Design failure mode and effect analysis (DFMEA) is a process that helps engineers understand the impact of potential risks associated with a design.

www.ansys.com

Back in the day Sea Hornet Command Air regs were designed to survive repeated impacts from a falling tank

 

[Tracy]

That's the problem with the egg-shell-thin wall thickness on modern second stages these days!
Poor DFMEA... harrumph.

What Is DFMEA? Design Failure Mode and Effect Analysis

Design failure mode and effect analysis (DFMEA) is a process that helps engineers understand the impact of potential risks associated with a design.

www.ansys.com

Back in the day Sea Hornet Command Air regs were designed to survive repeated impacts from a falling tank
View attachment 818048

I won't knock it. It is probably 20-30 years old and works. Most of my stage regs are just junk that nobody wants to buy,

 

[SlugLife]

You have collected a wide variety of ways a second stage can fail.

I wasn't expecting this many responses about actual failures (and not just theoretical ones), but this thread has been very educational. That's why I create these threads.

Failure to assemble the second stage and or hose properly is not that unusual.

I was more focused on mid-dive incidents, with the idea being the main 2nd stage is useless, while the octo is useful. However my own incident (where the hose came loose) is an example of improper assembly causing an incident.

I frequently dive with a few people who dive solo, with no redundancy, no octopus and below recreational depths, it makes me nervous to watch it. Hopefully they know how to breath from a purged and broken regulator and/or how to suck off the bc inflator.

I dive with redundancy on ALL dives myself, even the 20 to 30ft dives. CESA is always an option that depth, but if you don't notice or react quickly enough, or react improperly, even OOA at that depth can be risky.

 

[SlugLife]

I won't knock it. It is probably 20-30 years old and works. Most of my stage regs are just junk that nobody wants to buy,

For pony-bottles, I've advocated that it's fine to start out with just any regulators including ebay/craigslist acquisitions that breathe consistently, and don't leak or free-flow constantly. If on a budget, it's better to get some redundant air, than to worry about getting the perfect setup. If your pony has a problem, no big deal, just surface. You're still safer than the majority of divers who don't have redundant air.

I still have a pile of Mk10s & G250s that I barely use but know how to service myself. To me, I can't tell the difference between those and my Mk25 and S600 regulators.

 

[Tracy]

For pony-bottles, I've advocated that it's fine to start out with just any regulators including ebay/craigslist acquisitions that breathe consistently, and don't leak or free-flow constantly. If on a budget, it's better to get some redundant air, than to worry about getting the perfect setup. If your pony has a problem, no big deal, just surface. You're still safer than the majority of divers who don't have redundant air.

I still have a pile of Mk10s & G250s that I barely use but know how to service myself. To me, I can't tell the difference between those and my Mk25 and S600 regulators.

A stage bottle isn't a pony bottle. Not even in the same plane of thought.

 

[Sea_Jay]

A torn diaphragm or failed exhaust valve makes a second stage useless. Not something that would likely occur in the middle of a dive, but either one would do it.

The issue of a torn diaphragm is a very real risk, and I personally believe the risk is underestimated by 90% of divers. When you are topside, preparing for a dive, you "purge" the 2nd stage on your octo, and as long as it is delivering air --- you continue on with your gear check. You can breathe off of it & it seems to be working fine....because you are topside.

Now introduce an emergency with your buddy @ depth.....You remove & donate the primary and switch to your octo, only to get a mouthful of water. Now you are in a bad situation, and panic is a very real possibility. Things can snowball quickly and take a fatal turn.

I only realized this risk when I was introducing my girlfriend to "buddy breathing" in 1m of water. I was using the underwater metal detector in Lake Boca and she wanted to breathe off of the octo, just to see how it felt. We went to waist-deep water and I had a hold of her.....let her insert the octo and we just dipped our heads underwater. She immediately had trouble so I told her to wait a moment while I checked the gear. Tried breathing off of the octo underwater and got a swift mouthful of seawater. Aborted the treasure-hunting immediately and disassembled the 2nd stage octo. Look what I found:

 

[rx7diver]

... I only realized this risk when I was introducing my girlfriend to "buddy breathing" in 1m of water. I was using the underwater metal detector in Lake Boca and she wanted to breathe off of the octo, just to see how it felt. We went to waist-deep water and I had a hold of her.....let her insert the octo and we just dipped our heads underwater. ...

@Sea-Jay, what you describe is not "buddy breathing" (two divers passing a single 2nd stage back and forth). You and your GF were air/gas-sharing (but not "buddy breathing").

Also, when you're going through your gear check when you're setting up your gear prior to a dive, you can check for things like a torn 2nd stage diaphragm or torn/folded 2nd stage exhaust valve. Check both your primary 2nd stage and your back-up 2nd stage or AIR 2-like device.

rx7diver

 

[Sea_Jay]

@Sea-Jay, what you describe is not "buddy breathing" (two divers passing a single 2nd stage back and forth). You and your GF were air/gas-sharing (but not "buddy breathing").

Also, when you're going through your gear check when you're setting up your gear prior to a dive, you can check for things like a torn 2nd stage diaphragm or torn/folded 2nd stage exhaust valve. Check both your primary 2nd stage and your back-up 2nd stage or AIR 2-like device.

rx7diver

Sorry for the semantics lol -- she is not a diver and we were not actively diving together. She wanted to try breathing off of the octo.

How do you figure that you can inspect the diaphragm without disassembling the 2nd stage? Or are you advocating disassembly?

...If I am diving off of my own boat, I would consider disassembly but is STILL not all that practical. On a crowded cattle boat that's listing all over the place? Forget about it.

 

[SlugLife]

How do you figure that you can inspect the diaphragm without disassembling the 2nd stage?

I think the procedure is to (when depressurized) blow out, and then breathe in through the regulator, and then you get no air if there is no leak. I keep forgetting about that procedure myself.

 

[Sea_Jay]

I think the procedure is to (when depressurized) blow out, and then breathe in through the regulator, and then you get no air if there is no leak. I keep forgetting about that procedure myself.

This sounds great, I'll give it a try! Appreciate the info.