Redundant Octos & 2nd Stages Unable to Deliver Air?

[SlugLife]

Disclaimer: This is an advanced thread, I do not advocate beginner-to-intermediate divers ditching their octo.

In a thread about pony-bottles, the topic of whether or not to ditch your octo came up. Specifically, someone mentioned being unable to access your larger air supply, if you use a pony and ditch your octo. That brings up 2 interesting questions:

1. Has anyone heard about or experienced an incident where a 2nd stage is able to deliver air?
2. When does an octo become "ditchable?"

 

[SlugLife]

1) 2nd Stage Unable to Deliver Air

When I was a beginner diver, I assumed a major reason for the octo was intended to handle your primary-regulator failing to deliver air. However, now I'm wondering how that's even "possible".

Just speculating:

• Mouthpiece is knocked off, or bitten off. I've heard of this happening, afterall, they're usually held on by zip-ties. Would it still be usable, just a giant pain? Obviously, you can breathe off the bubbles and purge button, but perhaps you could still directly breathe off it? (If it wasn't so cold, I'd try it. Maybe later....)
• Frozen regulator - I'd think the 1st stage would freeze long before the 2nd. I don't dive in areas cold enough to have a regulator freeze.
• Extreme Impact - A very strong impact could potentially break an internal component of the regulator. Though you might also be missing a few teeth. It seems more likely you'd cause a free-flow than break it in a way which prevents air-delivery.
• Unusable at beginning of dive - In the context of considering ditching your octo, it would be difficult to miss your primary/only 2nd stage not working at all while top-side.

I'm also speculating here, but perhaps at the time Octos became standard practice, 2nd stage failures (to deliver air) were more common, but a few minor chances to the design of 2nd stages have made those failures "impossible." I'd be curious if any of the regulator-gurus know anything about that?

2) When does an octo become nearly pointless?

The typical Sidemount configuration has 2 tanks, 2 first-stages, 2 second-stages, and no octo. This is generally more than adequate for air-share and redundancy.

What about a properly used pony-bottle? For air-share, either the main-regulator or pony-regulator could be shared. There is some risk you might end up in a buddy-breathing scenario though if the pony isn't big enough for the other diver, or big enough to handle the extra air-consumption for yourself rescuing another diver.

For a solo-diver, so long as the pony is adequately sized, (IMO) the octo just become another hose to manage. Theoretically, if you "need" air from your primary-tank, your pony wasn't big enough. Assuming your pony works at the beginning of the dive, and regulators weren't run-over by a semi-truck, the chances of your pony failing during your ascent are probably much less than winning the lottery.

 

[rx7diver]

When I was a beginner diver, I assumed a major reason for the octo was intended to handle your primary-regulator failing to deliver air. However, now I'm wondering how that's even "possible". ...

A quick comment: My open water course (YMCA/NAUI) was in 1986. Our training with single-hose regulators involved a no-octopus single-hose regulator. We were trained to buddy-breathe. So, buddy diving and buddy-breathing.

We were taught that an octopus reg is for facilitating air-sharing--especially when sharing air with someone who isn't competent buddy-breathing.

rx7diver

 

[rick00001967]

it is interesting that i have never been taught to ever switch to my own back up 2nd stage (other than when discussing "passing the primary" during shared air drills in single tank bm) and yet i can think of two scenarios when it could have been useful. once for me and once for a friend.

i once had my primary delivering more water than air. i did not know it at the time but i had gotten sand in the check valves during a beach shore dive. switching to the back up would have saved me a lot of grief. it is a long story.

i had a friend many years ago who was diving fairly deep in lake superior in very cold conditions. (cant remember the details). her primary froze and would not deliver air. she was able to share with her buddy but it was a tense situation that may have been handled easier of she had switched to her back up. i am quite sure it never even occurred to her as it never occurred to me either.

i cannot recall ever hearing of someone trying to use their back up and it failed to deliver. but i was on a cavern dive once when one of the divers in the group had to share with the guide due to her primary not delivering air. tank had about half the gas left. people said that was impossible. i never did find out what the result of that one was.

i certainly have heard a few solo divers say the do not bother carrying a back up.

as you pointed out, double tank sm would not typically use any more than one 2nd stage on each tank.

but i did know a guy who used to dive bm twins that had two 2nd stages on each tank.

 

[SlugLife]

i once had my primary delivering more water than air. i did not know it at the time but i had gotten sand in the check valves during a beach shore dive. switching to the back up would have saved me a lot of grief. it is a long story.

A good example, where an octo may be useful. Was it wet-breathing the entire dive? Debris/sand could get stuck in a regulator mid-dive.

For example, where I dive is very muddy/silty, sometimes zero-vis. It wouldn't be that shocking for a bunch of mud to get in my regulator. I always dive with redundant air, so it's not my biggest concern, but it would be a way my 2nd stage could fail.

i had a friend many years ago who was diving fairly deep in lake superior in very cold conditions. (cant remember the details). her primary froze and would not deliver air. she was able to share with her buddy but it was a tense situation that may have been handled easier of she had switched to her back up. i am quite sure it never even occurred to her as it never occurred to me either.

Do you know if the 1st or 2nd stage froze? If the 1st stage froze, the octo would have not been usable.

i was on a cavern dive once when one of the divers in the group had to share with the guide due to her primary not delivering air. tank had about half the gas left. people said that was impossible. i never did find out what the result of that one was.

That would be interesting to know more about. There are multiple potential things which could cause that. Debris in the tank, 1st stage failure, kinked/clogged hose, 2nd stage, or even tank-valve closed (perhaps by bumping into ceiling/wall/floor).

 

[happy-diver]

The only times I've seen when second stages on anything on any diver anywhere, wasn't able to deliver



is when the diver has overexerted is out of breath or subsequently panicked so nothing to do with regs



Hundreds and hundreds and hundreds of divers, over decades!



Maybe even thousands and thousands of divers, over decades!



Ever!



Not bad!

 

[Wibble]

Seen a kinked flow at 70m/230ft during a bailout drill. Took a little time to work out why if would only give one breath — hindsight is always 20/20, but not the first time you see it.

Freeflowing regulators are surprisingly violent and very swift at emptying tanks.

 

[rick00001967]

A good example, where an octo may be useful. Was it wet-breathing the entire dive? Debris/sand could get stuck in a regulator mid-dive.

Not sure. Doesnt really matter. Not a fun experience. Long story that i dont wanna get into

Do you know if the 1st or 2nd stage froze? If the 1st stage froze, the octo would have not been usable.

Primary 2nd stage

 

[Tracy]

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.

 

[MidOH]

One tank, one 2nd stage.

I only run a necklace octo on my single tank rig, because I didn't put in the effort to remove it.

But that's with an Al40 pony/stage.