In-water cell check ?

[Alex]

Hi

I heard a lot about non-linear and current-limited cells, and that it is advisable to do a cell check in the beginning of the dive. How to do it? It seems to be difficult to do a proper oxygen flush at 6 m on descent- you need to flush the loop quite a few times in order to achive high PPO2.

And another (related) question. Doing oxygen flush at 6 m (on ascent), I can get only about 1.5. And then, when ascending, the PPO2 stays approximately 0.1 below the ambient pressure, showing about 0.9 on the surface. It does not seem to be related to bad cells because they do show 1.0 when properly flushed on the surface.

Any explanation?

Thanks a lot
Alex

[colinicky]

High Alex have you thought of posting this on Rebreather World - Rebreathers for Scuba Diving - the next step
Were there are a lot more rebreather divers of all levels ?
HTH
Colin

[Depth-junkie]

Originally Posted by Alex

Hi

I heard a lot about non-linear and current-limited cells, and that it is advisable to do a cell check in the beginning of the dive. How to do it? It seems to be difficult to do a proper oxygen flush at 6 m on descent- you need to flush the loop quite a few times in order to achive high PPO2.

And another (related) question. Doing oxygen flush at 6 m (on ascent), I can get only about 1.5. And then, when ascending, the PPO2 stays approximately 0.1 below the ambient pressure, showing about 0.9 on the surface. It does not seem to be related to bad cells because they do show 1.0 when properly flushed on the surface.

Any explanation?

Thanks a lot
Alex

1.5 @ 6m is a good flush as you are off gassing into the loop as well as motabalising 02 at the same time so a true 1.6 @ 6m is very hard to get to.

So i am more than happy when my cells get to 1.45-1.5pp02 @ 6m. You can get 1.6 @ 6m but you will have to do quite a few big flushes to acheive this, in turn burning through your 02 very quickly.

as for the descent i just tend to spike the PP02 to 1.4ish by not drawing through the ADV for the 1st few meters after i have swithed to HSP (which is usualy at about 15-18m), this is enough to ensure myself that the cells are not current limited to setpoint or below.

So during the dive if my cells were constantly showing above setpoint of 1.3 i would know something was wrong with the 02 content in the loop (I.E high). So long as i can verify the cells can read above and below setpoint, thats more than enough for me.


ATB
Gareth

[Janos]

The important thing is that they can read over your setpoint, as Garth says. Your c'lung doesn't have to be pure O2 though, you can just inject O2 manually instead of dil through the ADV to bring them to a level your happy with.

Also, 1.5 at 6m is normal. My theory is this is because the loop is 100% humid at the end of a dive, so cells will underread by 5%.

Janos

[Alex]

Thanks guys

Originally Posted by Depth-junkie

1.5 @ 6m is a good flush as you are off gassing into the loop as well as motabalising 02 at the same time so a true 1.6 @ 6m is very hard to get to.

Does it mean then that the deco at 6 m on the loop is less effective than on OC oxygen?

Originally Posted by Janos

Also, 1.5 at 6m is normal. My theory is this is because the loop is 100% humid at the end of a dive, so cells will underread by 5%.

Janos

I'll try to do it in the beginning of the dive next time

[nigelH]

Originally Posted by Alex

Does it mean then that the deco at 6 m on the loop is less effective than on OC oxygen?

No. 100% oxygen is not the requirement. 0% inert gases is the trick. The fact that you breath wet rather than dry air also makes it more comfortable. Warm is an addd bonus.

Frankly I was suprised, the first time I went back to OC after moving to the CCR, just how unpleasant breathing cold, noisy, dry OC gas is. I suspect that when I started the whole novelty of actually breathing underwater pushed it from my mind and after that it was just what I was used too.

[Mark Chase]

[quote]

Originally Posted by Alex

Hi

I heard a lot about non-linear and current-limited cells, and that it is advisable to do a cell check in the beginning of the dive. How to do it? It seems to be difficult to do a proper oxygen flush at 6 m on descent- you need to flush the loop quite a few times in order to achieve high PPO2.

At 6m i do a bubble check then I jack up the 02 manually and monitor it for mty decent down to 10m. If I can spike the 02 past 1.6 I am happy and I exhale through my nose and suck in dill via the ADV for the rest of my decent. I do this on the move.

Once at max depth I will do a life check on gas reserves on all tanks and then suck down the lungs to inject dill and watch the reaction from the cells. They should drop to dill ppo2 and quickly recover to set point. i do this IMMEDIATELY after an injection from the solenoid to give it a couple of seconds to work.

If my HUD is flickering or not acting as i feel it should i may repeat this during the dive or switch to low set point and do a dill flush. I may also decide to squirt in some 02 and manually jack the PP02 to 1.6 at max depth just to check the cells if I feel they are acting up.

And another (related) question. Doing oxygen flush at 6 m (on ascent), I can get only about 1.5. And then, when ascending, the PPO2 stays approximately 0.1 below the ambient pressure, showing about 0.9 on the surface. It does not seem to be related to bad cells because they do show 1.0 when properly flushed on the surface.

Any explanation?

Thanks a lot
Alex

At the end of the dive the humidity inside the loop has built up considerably so the gas is water vapor and 02. The cells are now analyzing 02 in humid conditions so check out your Analox chart for humidity compensation.

When you calibrated it it was on a bench dry just assembled.


ATB

Mark Chase

[Alex]

Originally Posted by Mark Chase

Once at max depth I will do a life check on gas reserves on all tanks and then suck down the lungs to inject dill and watch the reaction from the cells. They should drop to dill ppo2 and quickly recover to set point. i do this IMMEDIATELY after an injection from the solenoid to give it a couple of seconds to work.

This sounds complicated. Will a single injection of dill drop the ppo2 in the loop to the dill ppo2 ? And why do you need to do this second check? You have checked the reaction of cells to low ppo2 on dry land... Why could they react differently at depth?

Cheers
Alex