Clogged orifice vs stuck solenoid

[Heat Miser]

It comes down to allways knowing your PP02 and acting accordingly.

The advantage of an HCCR when learning rebreathers, is you can run it with a lower setpoint (say at 1.0) versus a target PP02 ( of say at 1.2 or 1.3) and get used to manually having to read/maintain the PP02 at the target. After a many dives you will get to the stage that you reflexively check PP02, make O2 additions and dilutions.

Im yet to experience a solenoid stuck open, I have had solenoid stuck closed twice, I have had a clogged CMF, which I noticed in the build once. Ive had one cell fail (get limited) which led to the other two firing the solenoid to spike O2 to level where the third was voted out and I have to compare to a fourth cell in the HUD. These are all thing to train for and contend with from good lessons and drills from good instructors.

 

[rjack321]

Same on the JJ. Haven't had a spike over 1.6 though.

That would depend on your starting ppO2, and still probably be a big burst of O2. I have transitory spikes about 0.25-0.3 ppO2 units above whatever it started at. Eg if its at 1.0 and I want it up to 1.2 my first injection will go up to 1.25ish then settle back around 1.1, second squirt will bump up to 1.35ish and settle back to 1.2 Assuming no depth changes.

 

[nadwidny]

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

You don't. You are there, then you are not. No notice.

 

[Wibble]

You don't. You are there, then you are not. No notice.

Some interesting videos of pilot training where they have to determine if they are suffering from hypoxia. Many fail to recognise this and just pass out. The brain needs oxygen to function, even to recognise the effects of hypoxia.

 

[lermontov]

You're ascending, PPO2's dropping, you manually inject some O2 which hits the sensors as a "bubble" of oxygen. Sensors may do a jump to 1.6/whatever, then come down on the next breath as that bubble of oxygen's diluted. Need to tell the difference between a "bubble" and a general high PPO2.

Damn annoying if just after injecting the O2, you then over-dump your wing/suit/loop and the ascent stops.

Cant say Ive noticed a 'bubble' that you speak of on ascent -is this only for manual ?

the only 'bubble" im aware of is if you have had a BO and your on OC then go back on the loop and you switch the BOV back to cc. The orifice has been leaking 02 and suddenly youve got a small vacuum that causes the gas to rush through at a higher pressure than the inhale chamber . Is that a similar principle that ascending is doing your creating a small vacuum ? not sure of the physics on this

 

[Brad_Horn]

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.

Out of curiosity I went and looked it up. Based on analysis of best available data, which itself is limited by lack of reporting, only about 9-12% or 60-75odd fatalities likely involved Hyperoxia..... so just a fraction of the 600+ that are known.

Looks like about a 1 to 4 ratio compared with those who most likely succumbed to Hypoxia being roughly 40% of rebreather fatalities.

Separate to Hyperoxia a further 3% are tagged CNS O2 toxicity but I'd hazard a guess that the dividing line might be opaque without more detailed accident reporting published.

Deep Life Design Team: databases and analysis of rebreather accident data

Rebreather Accident Data, a source to improve safety

deeplife.co.uk

 

[GF99/99]

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.

I own an eCCR and mCCR and as @rjack321 has pointed out the rare chance of having a clogged orifice or stuck solenoid should not be your deciding factor between an eCCR or mCCR.

Honestly I would never even use this in my deciding criteria between rebreathers. Plus the solution to both problems is the same (even for cave diving avg. depth of 20-30m) on either a eCCR or mCCR putting even more emphasis on the fact that this should not be a decided factor between units. If your orifice is clogged you fly your unit manually, if your solenoid is stuck you fly your unit manually (yeah yeah some may tell you if its stuck open you can feather the valve but honestly I would find it much easier to just fly off the MAV)

But to answer you questions I would say clogged orifice is more common that suck solenoid but then again I would say dead battery is more common than clogged orifice. But all of these are service neglect so if you keep your equipment fully serviced you can pretty much avoid these. i.e. have an inline filter, regularly service your CMF, keep your O2 tanks, valve, regs O2 clean, check your batteries or just have a set interval when you change them regardless.

 

[berndo]

That would depend on your starting ppO2, and still probably be a big burst of O2. I have transitory spikes about 0.25-0.3 ppO2 units above whatever it started at. Eg if its at 1.0 and I want it up to 1.2 my first injection will go up to 1.25ish then settle back around 1.1, second squirt will bump up to 1.35ish and settle back to 1.2 Assuming no depth changes.

I only ever ran the JJ manually and in class. I added too much o2 and than didn't wait long enough in class soemtimes and also after the class a few times. I was aiming for 1.2-1.4 and ended up at1.6. Probably just takes practice to hit the ppO2 you want.

 

[berndo]

You don't. You are there, then you are not. No notice.

You said in another thread that there is a report about what happened to you. Can we find that online somewhere?

 

[Underwater Tourist]

You don't. You are there, then you are not. No notice.

I always thought that hypoxia is something that you could, in principle, sense coming, while o2 toxicity is something that just happens without warning.

Turns out its the exact opposite

__

Thank you everyone for your replies.