Clogged orifice vs stuck solenoid

[grantctobin]

It seems to me that most ccr accidents involved a lack of o2 rather than too much.
I was taught to bail out straight away when the o2 in the loop is over 1.6. Than flush and see if I can go back on the loop. Would you stay on the loop and try to fix it while your cells show more than 1.6? Unless it's just a 2 second spike or so.

Who taught your CCR class?

 

[lostsheep]

The Kiss orifice is .0035mm according yo the manual.

Are your units correct? That’s terrifyingly small and beyond most people’s ability to fab.

 

[broncobowsher]

Pretty sure it is 0.0035" and the small one (for higher fixed IP) is 0.0030"

 

[grantctobin]

The Kiss orifice is .0035mm according yo the manual.

You sure?

 

[lostsheep]

I found it in the manual. They don’t include units which is a major pet peeve of mine.

That said, I believe that is .0035” , which makes a lot more sense

 

[berndo]

Who taught your CCR class?

Danish guy. Why? What's wrong?

 

[Wibble]

I don't have a ccr yet, but I think eventually (in 5 years maybe) I will get one.
So right now I am reading about them for general education purposes.

Until today, I was sure that if I go the ccr route, it will be some manual machine as opposed to an electronic one. But now I am doubting myself a little because I read numerous mentions of a clogged orifice, meanwhile I didnt see a single case of a stuck (open or closed) solenoid. Which brings some questions:

1) Is a clogged orifice a higher frequency failure when compared to a stuck solenoid?
2) Is a clogged orifice something that every mccr user is expected to go through at some point or another (say over the course of 10-15 years)?
3) If the ccr is used for cave diving with avg depths of 20-30m, what would you rather have: a clogged orifice or a stuck solenoid (i.e which one is less dangerous)?
4) Anything else I should have asked but didn't?

A very major part of CCR training is going through the very long list of failures that could happen and getting you to think about what you'd do if it all went horribly wrong. It's not about scaring the bejesus out of the student, it's just being prepared for things to go wrong.

With any luck things will never go wrong and you can get on with enjoying your diving.

However, relying on "good luck" is like keeping Baldrick's bullet in your pocket ("There's a bullet with your name on it, mine's kept in my pocket" -- Black Adder Goes Fourth).

To mitigate bad luck, you train for things to go wrong. Then there's no surprises.

So what can go wrong. Everything and anything. Basically every component of your rebreather could fail at some time or other. The reality is that they are pretty reliable, although you do come across people who are really "unlucky". Often they're the ones who fiddle with things, don't do the maintenance, are cheapskates, or just unaware of what's going on around them. OK, there's stupid people too: those who let their gas get really low, dive beyond their abilities or who just push things beyond limits -- just get one more dive out of my used scrubber.




Answering your specifics... Actually a lot depends upon the machine you're thinking of.

1) I have both orifice and solenoid on my Revo. Neither have failed. Yet.
The mitigation is always know your PPO2: you'll notice it drop or spike. Deal with it.

2) Don't know, see 1.
The mitigation is always know your PPO2: you'll notice it drop or spike. Deal with it.

3) Stuck solenoid.
If stuck open, that's not good. Need to shut down your oxygen ASAP and control the loop PPO2. Depending on your bailout supplies, you could connect offboard high % oxygen and run it manually to get you out. Could run it as SCR (semi-closed rebreather using diluent/bailout). Alternatively bail out. Pretty serious.

If stuck closed, then run the unit manually on the way out.

The mitigation is always know your PPO2: you'll notice it drop or spike. Deal with it.

4) Anything else.
Everything and loads.

• CO2 hit. Lots of reasons not following correct procedures when building your kit or pushing scrubbers beyond their limits.
• High PPO2
• Low PPO2
• Unexpected changes in PPO2
• Cell failures. Lots of different failure modes.
• Loop flood and leaks (root cause of my full bailout last year -- coupled with the chimp brain on the creature using the unit)
• Run out of diluent (which also feeds the wing).
• Run out of oxygen.
• Run out of drysuit inflation gas.
• Scrubber failure; pretty much means a CO2 hit as that's its job.
• Leaks (bubbles). Hoses do fail.
• Bailout failure, bailout leaks.
• Water in the loop (royal PITA on some rebreathers).
• ADV (auto diluent valve) failure.
• Manual add valve failures.
• Computer failures.
• Battery failures for solenoid.
• Wing/buoyancy failure including valves.
• Drysuit failure and leaks
• Heated undersuit failure (not fun being cold with loads of deco)
• ... and so on; this list isn't exhaustive ...

Many of the above can be handled with an immediate bailout (switching to open circuit) and abort of the dive; some may need a temporary bailout to resolve the problem; some can be fixed and the dive continued; and some are minor requiring adjustments.

Which is why you train. Why you practice. Why you hone your skills. Why you do a slow progression to extend your diving.

 

[rjack321]

Pretty sure it is 0.0035" and the small one (for higher fixed IP) is 0.0030"

You can also get 0.0025" but those have fallen out of favor for needle valves.

 

[rjack321]

I don't have a ccr yet, but I think eventually (in 5 years maybe) I will get one.
So right now I am reading about them for general education purposes.

Until today, I was sure that if I go the ccr route, it will be some manual machine as opposed to an electronic one. But now I am doubting myself a little because I read numerous mentions of a clogged orifice, meanwhile I didnt see a single case of a stuck (open or closed) solenoid. Which brings some questions:

1) Is a clogged orifice a higher frequency failure when compared to a stuck solenoid?
2) Is a clogged orifice something that every mccr user is expected to go through at some point or another (say over the course of 10-15 years)?
3) If the ccr is used for cave diving with avg depths of 20-30m, what would you rather have: a clogged orifice or a stuck solenoid (i.e which one is less dangerous)?
4) Anything else I should have asked but didn't?

I've seen far more clogged orifices in the last couple years (2) than stuck solenoids (either on or off = 0). But really neither are problems you should base buying decisions on. The number of failed cells is legions higher than orifice or solenoid issues. Plus there are plenty of other failure points in any CCR, flooding, ripped hose, battery failure, cord/wiring issue, HP seat failure, Orings galor, flapper valves sticking, ADV sticking, OPV leaking the list goes on and on.

 

[macado]

It seems to me that most ccr accidents involved a lack of o2 rather than too much.
I was taught to bail out straight away when the o2 in the loop is over 1.6. Than flush and see if I can go back on the loop. Would you stay on the loop and try to fix it while your cells show more than 1.6? Unless it's just a 2 second spike or so.

There have been quite a few CCR deaths involving O2 toxicity. How many? I dont know the exact numbers or enough to say if one is more common.

The difference is hypoxia is considered a "silent killer". You pass out and drown. Some will argue you might notice decreased loop volume but I dont buy that argument.

O2 toxity (hyperoxia) may or may not have warn signs associated with Central Nervous System oxygen (CNS) toxicity such as visual changes (especially tunnel vision), tinnitus , nausea, twitching (especially of the face), and dizziness.

You may remember hearing VENTID which is used to remember the symptoms of Oxygen Toxicity. Visual disturbances, Ear ringing, Nausea, Twitching, Irritability, and Dizziness.

In both scenarios without a loop or regulator in your mouth you pass out and drown. The result is usually the same, death. Both could be survivable provided you don't drown. e.g., gag strap on loop, regulator in your mouth.

Both circle back back to the rebreather matra of "always know your ppO2." Monitoring a handset and HUD to alert you to either impending hypoxia or hyperoxia.

It is my understanding that the most recent death in Roaring River, MI was likely the result of an O2 tox / seizure. Not because of any particular equipment failure but because of a diluent that had too high ppO2 / gas density / narcotic effect for the depth involved.

https://nsscds.org/wp-content/uploads/2023/01/Roaring-River-2022.10.14.pdf

This is probably a whole other discussion and I'm sure people will disagree with me but I won't immediately bailout at ~1.6 ppO2 but it's certainly going to get my undivided and immediate attention.

Hyperoxia caused by breathing oxygen at elevated partial pressures usually has a bunch of different variables, including actual ppO2, time and length of dosage, workload, gas density, individual tolerances to oxygen, etc.

For example: NOAA's maximum CNS recommendation is exposure of 1.6 ppO2 for 45 minutes. We probably all know people who have ended dives way over 100% CNS but I am just using that as an example.

Being at ppO2 1.6 (or even 1.7) is not an instant death sentence but it should damn well get your full attention. If I looked down at my handset and suddenly saw my ppO2 at 2.0 then I'd probably immediately bailout and go into troubleshooting mode. My brain would have some questions. How long have I been at 2.0? Why didnt I notice it sooner? What's my loop / counterlung volume? What's my pressure in my 3L bottle of O2?