It finally happened - my CCR tried to kill me

[wedivebc]

Can you explain this in more detail? I've not heard of using the sensors to monitor pos/neg during check out.

If you look at the mv when drawing a vacuum in your loop it will drop proportially. If there is a leak the mv reading will increase as the PPO2 increases in the loop.

 

[grantctobin]

I flipped my BOV to BO and breathed from that for the few seconds it took to pull out my OC BO reg and switch over to that...


But, my ppO2 was good and my rMS showed that my scrubber was still working off the top basket...

The first will get overlooked, but these are my two areas of concern:

1) Onboard 2L? 3L? Plugged into a BOV is nigh on worthless. If you use a BOV, plug it offboard.
2) You’re worried about the integrity of your loop (or something just doesn’t feel right”...same thing) and you’re trusting a part of this same loop.

Kudos for having the willingness to write all of this out. Especially in an open water environment (you’re 10 minutes from your 20’ stop, not an hour swim or scooter), I’d have stayed off the loop and had different bailout gas. Even a 40 of air and 40 of O2 or 50% would have been appropriate for this dive.

How many hours are you up to on the loop?

Tbone’s point about pressure sensors is spot on. I watch lots of poorly trained divers suck a negative, then fill the unit with O2 to do a positive and calibrate or verify calibration. They fail to realize pressurizing the unit above ambient changes the mV reading of their cells.

 

[KDAD]

Electrochemical sensors actually measure the partial pressure, not the percentage, of oxygen in the gas stream they are exposed to. So the output of the 5 sensors while under either a positive or negative pressure should remain constant unless there is a leak.

 

[rjack321]

Especially in an open water environment (you’re 10 minutes from your 20’ stop, not an hour swim or scooter), I’d have stayed off the loop and had different bailout gas. Even a 40 of air and 40 of O2 or 50% would have been appropriate for this dive.

Ditto...
Probably used an air AL80 as deep BO, or possibly 28% if available (either down to 130ft-ish) and as suit gas. This would have lasted a long weekend for me and gone back to the shop at the end of my 6 dive trip with 2300psi, the rest having been in my drysuit. Would need to be below 130ft before I would switch to the 18/45 BO for a warm OW wreck dive like this. But then I'm stuck with needing a suit bottle which I would prefer to skip for a 125ft dive. And I am basically never using trimix BO without a deco gas for the exact problem you realized - the deco penalty is unfriendly.

al40 of 50% for deco is good for wreck profiles
O2 would also have been fine and rides nice in the ocean with only 2000psi. But an al30 of O2 would have been fine too.

Onboard dil would have been 18/45 or 21/35.

Carry enough of the right mixes as BO. Never go back to a compromised loop unless you are positive you can fix it. In this case it worked out, but as you learned after the fact - you were one head tilt away from an absolute disaster and had no idea how close to the cliff you actually were.

 

[Jack Hammer]

A lot of people perform pos/negative tests that only last 1 minute each. This may not be long enough to catch smaller leaks. We perform 5 minute each pos/neg pressure tests. This has caught a few leaks that were still passing at the 3 minute mark. As mentioned, noting the mv/PO2 will also show something is leaking.

 

[rjack321]

A lot of people perform pos/negative tests that only last 1 minute each. This may not be long enough to catch smaller leaks. We perform 5 minute each pos/neg pressure tests. This has caught a few leaks that were still passing at the 3 minute mark. As mentioned, noting the mv/PO2 will also show something is leaking.

I'm in the 3 to 5 min camp. But I have still had a couple of leaks which were not detectable at all on the surface (pO2 was stable but flickers plus minus a few hundredths as it sometimes does) and then they showed up via a bubble check.

 

[Dusty123]

My instructor instilled in me to feel under the cover (no jokes please) to make sure its sitting flat. I also dont add cylinders until after installing the cover. I make sure the battery box is free to wiggle. Its really the battery box that screws up the cover going on. Might be a cool mod to mount the box permanently

 

[Heat Miser]

\

 

[AdamSa]

I usually leave a negative test going overnight and until I actually get to the dive site. If you have a very small leak, this will detect it over several hours - much more effective compared to a 5 minute test.

 

[Wibble]

Electrochemical sensors actually measure the partial pressure, not the percentage, of oxygen in the gas stream they are exposed to. So the output of the 5 sensors while under either a positive or negative pressure should remain constant unless there is a leak.

To give examples, when running the build and closed checklists you pump in O2 to reach (nearly) 100%. If you put this under pressure, before the OPV triggers, you can see the cells read over 1.00 PPO2, therefore they’re reading the partial pressure and not relative gas ratios/percentage. Which is why a descent will show the PPO2 go well over 1.00