Canister Insulation

[tbone1004]

following up on what @DA Aquamaster said, the problem with the CO2 sensors is not really any different than the reason we don't have commercially available optical O2 sensors. The technology exists, but it does not function properly in the environment of the loop *mainly the humidity*. Several units have CO2 sensors on them, but they don't work all that well....

 

[wedivebc]

following up on what @DA Aquamaster said, the problem with the CO2 sensors is not really any different than the reason we don't have commercially available optical O2 sensors. The technology exists, but it does not function properly in the environment of the loop *mainly the humidity*. Several units have CO2 sensors on them, but they don't work all that well....

The other big concern is where to put the sensor in the circuit. Putting it in the scrubber outlet will only detect CO2 from scrubber failure. There are other failures that a scrubber sensor would fail to detect even massive amounts of CO2 caused by various bypass scenarios. Failed mushroom valve for example.

 

[tbone1004]

The other big concern is where to put the sensor in the circuit. Putting it in the scrubber outlet will only detect CO2 from scrubber failure. There are other failures that a scrubber sensor would fail to detect even massive amounts of CO2 caused by various bypass scenarios. Failed mushroom valve for example.

inhale t-piece or canister outlet is about the only spot that makes sense. T-piece is problematic because you have to have extra cables going into and out of the head

 

[wedivebc]

inhale t-piece or canister outlet is about the only spot that makes sense. T-piece is problematic because you have to have extra cables going into and out of the head

Problem with that is if there is a problem with exhale mushroom valve path of least resistance would be though exhale hose where CO2 would be undetected by inhale hose monitor. This is a real problem as I have seen this on two different rebreathers.

 

[KevinNM]

inhale t-piece or canister outlet is about the only spot that makes sense. T-piece is problematic because you have to have extra cables going into and out of the head

You want end tidal co2. May not get it, but that’s what you want. Increased exhaled co2 is bad news no matter why.

 

[rjack321]

You want end tidal co2. May not get it, but that’s what you want. Increased exhaled co2 is bad news no matter why.

exhaled CO2 is variable based on workload and O2 consumption.

 

[KevinNM]

exhaled CO2 is variable based on workload and O2 consumption.

And when you drift outside the normal range it either means you are working too hard or have a breakthrough. Either way you want to know. It seems to be fairly well established what is a safe level for the density, so knowing you are drifting outside that would seem pretty useful.

 

[kensuf]

inhale t-piece or canister outlet is about the only spot that makes sense. T-piece is problematic because you have to have extra cables going into and out of the head

Not all rigs have T-pieces. I'm certified on two that don't. It also won't solve the mushroom valve problem, the only CO2 hit I've seen first hand was caused by duckweed in a DSV.

 

[doctormike]

exhaled CO2 is variable based on workload and O2 consumption.

Right, but it's the relevant measurement when you are concerned about the effect of hypercapnea on the diver. That's why in anesthesia (using a machine which is essentially a rebreather with a drug port), they follow end tidal CO2, because it's the closest thing that you can get to actually measuring arterial CO2 in real time.

In anesthesia circuits the ETCO2 is sampled from near where the endotracheal tube comes out of the patient, so I guess the most accurate sampling spot on a rebreather would be the mouthpiece. Sampling the canister outlet would be simpler and would let you detect scrubber failure but would miss a problem with the mushroom valves where you were rebreathing the same gas without it going through the scrubber at all....

 

[tbone1004]

Not all rigs have T-pieces. I'm certified on two that don't. It also won't solve the mushroom valve problem, the only CO2 hit I've seen first hand was caused by duckweed in a DSV.

correct, and arguably some of the most popular ones at least for 2017 don't, and the O2ptima just deleted theirs. Inhale t-piece is just a bit more convenient than canister outlet because it offers some more real estate, especially on something like the SF2 where there isn't a whole lot of room left in the head to stick another sensor.

So the question is if you put it on the inhale side, you are checking for any CO2, ergo big alarms going off if there is any CO2 detected, or do you put it on the exhale side where you need to have to have the diver monitor the CO2 levels and watch for any sudden rise because of the roughly 4% CO2 in exhaled gas