Rebreather error!

[Okeanos]

We had planned a dive to 60m on H.S. Rewa on either Saturday or Sunday or both, but as we got closer to the weekend the forecast wasn't looking so keen so we waited until the day.

Saturday morning came and we were still unsure. Did we want to travel 26 miles on a RHIB in rough conditions and then have the dive cut short? Not really. I had planned 45 minutes at the bottom and relied on surface support in case of CCR failure, if it turned out rough I couldn't rely on surface support finding me quick enough if I didn't return to the shot line. So the safest bet was to wait until a flat day. Not wanting to miss the tides we ended up back on the old favourite, the Sphene.

We arrived on site on slack water, but there was going to be loads of time so there was no rush. I switched on the rebreather and set it to calibrate, 'Low Oxygen', I checked valve and it was on. I pressed the manual oxygen addition and that worked, the solenoid wasn't firing! I then pressed the manual oxygen button until the unit calibrated, I could run it manually, it was a shallow dive and would be good practice. I did note that it calibrated rather quickly but assumed that was down to the amount of oxygen entering through the manual button rather than the small amount through the solenoid. We kitted up and rolled in.

When I reached the bottom I added enough oxygen to get my PPO2 up to 1.3 and started to swim around. For some reason the VR3 wasn't giving me a lot of no deco time so I looked at it's PPO2, it was 1.0. I looked back at the handsets, they were 1.3! Something wasn't right, the VR3 always reads higher that the handsets. I decided that I was going to trust the VR3 and it's lower reading, if I pumped oxygen in to get it to 1.3 the handsets would beep 'High Oxygen', so I would keep the VR3 to 1.0. Any sane person would have aborted the dive, I was just thinking to myself, lucky it wasn't at 60m on the Rewa and only 27m on the Sphene. If it was a 60m dive I wouldn't have even entered the water.

At the end of the dive I released the anchor and made my ascent. At 6m I pumped in oxygen to do the VR3's 2 minutes of deco, I was going to add another 5 minutes to be on the safe side. The handsets went crazy, 1.7+ PPO, that was impossible at 6m! I trusted the right piece of equipment, the VR3. The VR3 always tries to get me out of the water too quickly so I added my 5 minutes on oxygen and exited the water safely.

Later I dismantled the rebreather and looked at the solenoid first, a wire was off. I then checked the unit to see if it would calibrate, it said cell 3 failure! I then restarted the unit and added oxygen, it calibrated when the readings hit about 0.6 PPO, THAT SHOULDN'T HAPPEN. It then read 1.0 PPO!!

I now have to change the cell and make sure it calibrates properly again, I'll do that when it has dried totally and post the result.

So the moral is, if it doesn't feel right, it probably isn't.

[David]

which breather were you on ?
who did the soldering :-)

glad your ok

David

[Okeanos]

Originally Posted by David

which breather were you on ? Classic Inspo
who did the soldering :-) 2nd hand unit, so I can't tell!

glad your ok

David

I could have aborted the dive, but with plenty of bailout and knowing that planning deco on the lowest PPO reading was safe and I always add a little extra to the VR3's deco depending on the dive, I wasn't concerned.

What did concern me was, if the solenoid was working I wouldn't have realised it had calibrated so quickly. I might then have been more concerned about trusting the VR3, I would have taken the lowest PPO reading for deco, but what if I didn't have a VR3 plumbed in?

If I didn't have a VR3 plumbed in I would have done a much longer dive trusting the handsets, the deco would have been totally wrong, I would be in the chamber right now. I know I should watch the handsets as they calibrate, but who does?

[Mal Bridgeman]

Hi Mark

I'm glad it turned out to be a non-incident but it's not clear to me what you "Learned about diving".
I read with great interest Depth Junkie's rationale for diving alpine and was impressed with his "if it ain't right, don't dive it" approach.

Yet, repeatedly we get reports, like this, of RB divers who dive with known faults. I have never had RB training but is there anything in the training which gives assurances over diving with faulty readings? I could understand it being explained how to complete a dive if the failure occured during a dive but to start a dive with these types of faults seems unnecessarily risky.
Mal

[NotDeadYet]

A dil flush would've shown quite clearly which cell(s) were out. I do a double check at 6m, drop on O2 to spike the cells, if they read 1.55-1.6 then I do a dil flush. If the cells then read what they are supposed to read depending on what the dil is and the O2 spike has been OK then I keep descending. It's difficult to get an ambiguous reading after that.

Any time I get a cell reading something it shouldn't a dil flush is my first instinct. It's better than choosing arbitrarily which cell to trust.

[SoggyFox]

Originally Posted by Mal Bridgeman

Yet, repeatedly we get reports, like this, of RB divers who dive with known faults. I have never had RB training but is there anything in the training which gives assurances over diving with faulty readings? I could understand it being explained how to complete a dive if the failure occured during a dive but to start a dive with these types of faults seems unnecessarily risky.

ask yourself if you'd drive a car on a motorway at 70mph with a known fault. you just wouldn't, better safe than sorry and feeling annoyed on the boat.

[Scuttler]

Originally Posted by SoggyFox

ask yourself if you'd drive a car on a motorway at 70mph with a known fault. you just wouldn't, better safe than sorry and feeling annoyed on the boat.

Poor analogy....I have and probably still would do because most faults would simply mean pulling onto the hard shoulder and waiting for the RAC/AA/etc to sort it out rather than almost certain death ot personal injury

[Okeanos]

Originally Posted by Mal Bridgeman

I'm glad it turned out to be a non-incident but it's not clear to me what you "Learned about diving".

I learned that I should not have dived the unit with a fault, no matter how much you want Lobster for tea.

The solenoid alone isn't a major concern, there are many manual rebreathers out there. I should have tried re-calibrating the unit on the surface when I thought it calibrated too quickly, I would then have seen that it was calibrating incorrectly before getting in the water.

A simple dil flush would have told me what was the correct reading, I should have done that too, but once again I was too keen to trust my feelings rather than think about the situation.

[David]

Originally Posted by Mal Bridgeman

Hi Mark

I'm glad it turned out to be a non-incident but it's not clear to me what you "Learned about diving".

its very easy to ask.. but is the information for other divers more important than the clinical right wrong to dive point your making.

I have seen tec divers in action what happens on a boat is so far from what is taught its a joke.

[Okeanos]

Originally Posted by SoggyFox

ask yourself if you'd drive a car on a motorway at 70mph with a known fault. you just wouldn't, better safe than sorry and feeling annoyed on the boat.

My car has many faults, but none are unsafe, a dodgy alternator for one.

A faulty solenoid, I class as safe for shallow depths.