Overbreathing the scrubber

[wedivebc]

wedivebc,

You mentioned that you were using medical sorb during the dive that you had your co2 incident. Is that an inferior sorb compared to other products? What's the difference between different sorb products? (I'm not an rb diver. I have a very basic understanding of rebreathers, but that's about it.)

Medical sorb is great for medical use. Divers grade sorb is designed (I'm not a chemist) to be faster acting. This causes it to react faster to sudden increases in CO2 production. There are other differences such as moisture content and granule size. I also believe the granule size contributed to my problem since radial scrubbers tend to like a finer grain due to the shorter path the gas takes compared to axial. I was very surprised at how quickly the medical sorb had changed colour after only <3 hours.

 

[amascuba]

Medical sorb is great for medical use. Divers grade sorb is designed (I'm not a chemist) to be faster acting. This causes it to react faster to sudden increases in CO2 production. There are other differences such as moisture content and granule size. I also believe the granule size contributed to my problem since radial scrubbers tend to like a finer grain due to the shorter path the gas takes compared to axial. I was very surprised at how quickly the medical sorb had changed colour after only <3 hours.

The sorb changing into a purple color basically means that the sorb has been spent of it's co2 scrubbing properties, correct?

 

[Cave Diver]

Color change is an indicator of where the reactivity is occurring. Basically as the sorb is "spent" it changes to a purple color. It is not however, a definitive indicator of sorb life left. Another thing to note, is that the color change is not permanent. Once you quit breathing it, the purple will eventually fade, so unless you look at the cannister immediately after a dive, you will have a false sense of scrubber usage.

 

[Cave Diver]

As a side note, I was taught to monitor/log the time on my sorb. Variables will affect how much time each individual will get out of a cannister. When we empty a cannister, our instructor had us "dig" through the spent sorb, to note how it felt, moist, warm, clumping, etc. to determine how much of it had actually been used up already. Tracking this sort of information under variety of conditions gives us real world experiences of what sort of life we can expect from a scrubber.

 

[wedivebc]

The sorb changing into a purple color basically means that the sorb has been spent of it's co2 scrubbing properties, correct?

Usually, there are some indicators that turn from pink to white, or purple to white, or no idicator. Most diver sodalime products I have seen use white to purple inicator meaning it starts white and when the sorb is saturated (ie. lower Ph) it turns purple.

 

[Tienuts]

Any idea what caused it?

Long story - Here's the cliff notes:

The unit was new, and post dive inspection of showed some machined delrin shavings were caught in between an o-ring on the canister. (It passed a positive and a negative both pre AND post dive) It caused me to leak loop volume during the dive. Video of the dive, showed an intermittent stream of bubbles coming from my head area. The instructor didn't think too much of it since I had trouble not venting our of my mask. I was aware I was venting dil, as I kept bottoming out the CL's. The ADV was turned off at depth, and I was manually adding dil via the manual add button (the bypass valve for you meg guys)

I was at the opposite side of the wreck from the anchor line at 140 feet. I decided to make my way back, and was caught in a huge current. Fighting the current caused me to 1) over-breath, and 2) forget to add dil into the depleting loop. I ended up breathing very shallow and built up a huge amount of CO2. You can see me on the video swimming hard, and as I do, my technique gets sloppier and sloppier.

 

[Tienuts]

No need to apologize for the discussion becoming wider ranging. I'm finding it fascinating. I know very little about rebreathers, and the more I read, the more convinced I become that they aren't for me. The complexity sounds incredibly scary.

It's not as complex as you think.

If there is a rebreather "demo day" in your area you should think about going for just the lecture portion. Living in Meg country, I'm sure you could find one. Even if you have no desire to ever go CCR - I bet it would be informative and help dispel some of the mystery behind the curtain.

Here in So Florida, CCR is more and more popular, and finding yourself on a dive boat with a CCR diver is quite likely.

 

[mtrotterjr]

Thanks for all the info everyone. Think i will stick with OC a little longer before i make that jump. It seems that there is a lot more risk with RB.
Thanks again.

 

[TSandM]

Oh, if they ever have a rebreather experience day when I'm here in town, I will definitely attend it. I don't think you can ever learn enough in this diving world. I'm not anti-rebreather at all; I just don't see the risk-benefit-complexity ratio working out for me and my diving. Maybe someday, when I just can't drag all those stages into a cave . . .

 

[Cave Diver]

Oh, if they ever have a rebreather experience day when I'm here in town, I will definitely attend it.

And the dark side beckons...