CO2 Monitoring

schford

With Rebreathers becoming increasingly mainstream and a decent volume building up - I can not but help consider that the economics in producing a CO2 sensor for the loop will become increasingly attractive.

Does any one have any thoughts on what the price / volume break point will be and when we could expect to see such a thing?

Stuart

Nad

The problem with CO2 monitors is not just the price, for what I know (not that much, really) it also a moisture problem.

Nad

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onetime

Not sure what the limitations are but would sure love to hear peoples' thoughts. What's the hold up in such a development? I've heard it's about sensor response time and/or cost.

What are the response times that people are aware of? What pieces are available to develop one?

As far as price points go, I'd say the $1000 to $1500 mark is probably an easy target since the HSE and VR3 computers play in that range and a lot of Rebreather divers have ponied up for them.

caveseeker7

HSM has a complete setpoint controller system that includes CO2 monitoring capabilities with a CO2 sensor. Response time and accuracy are quite good, but the price is prohibitive for the recreational market.

I'll let Iain fill you in on the details as he has done so in the past, and will be most current with the info.

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Padowan

If you ask me, CO2 monitoring of the loop could be considered a bit pointless. Surely you want to know before you have CO2, not when it's already there? The predictive nature of the temp stick in the Evo seems much more preventitive to me.

If you want a reactive indicator that you have CO2 breakthrough, I heard of cunning ideas like having a little transparent tube of colour change lime spliced into the inhale hose, so you have almost like a CO2 HUD!

I suppose that the idea of a sensor is that it would be sensitive enough to detect a really small amount of CO2, but does that mean that the stack is shot? Maybe you're just exerting a bit at depth? I had breakthrough recently caused by this.

Just throwing ideas out there, but another possibility is 2 sensors, one before and one after the stack to measure perhaps the efficiency of the scubber. Or in something like the Sport KISS with it's twin chamber scrubber, what about a sensor in between the 2 compartments, so that you know when half the scrubber is shot, at least that's making it a pre-emptive warning, kind of like a "reserve fuel" light!

Looking at it from a cost no-object perspective, I would think that something that is monitoring the activity of the whole stack would be best. The central temp stick of OK, but will not notify you of channeling around the sides.

What about the development of "channel proof" scrubber materials?

Bit of a ramble, but sometimes my mind just works like that...

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onetime

Lots of good stuff in there. IMO, the idea of the sensor is to see the creep up of CO2 levels. It's just a bit more information than you have now. Is the stack shot? If you see the rate increase significantly in a short period (or exceed an "acceptable" range then be safe and bailout.

I like the idea of measuring the change from before and after the scrubber but the cost would likely be really prohibitive as you'd need two independent sensors. I don't think the idea on the Sport Kiss would work as there really don't seem to be two independent stacks since there's a crossover in there I believe.

Channel proof scrubbers I think are interesting and possible with a bit more engineering focus. At a minimum a series of smaller scrubbers may minimize the odds that a channel could form.

The see through slime tube is also interesting. Maybe we could put a little parakeet in the tube like the miners used to do? PETA, if you're watching, I'm joking.

schford

My understanding is that you want to know when CO2 starts to be come present in the loop and this will then slowly build up - potentially giving you plenty of warning to finish the dive or bail.

Temp stick is interesting, but can not cope with channeling etc and just encourages one to over run the scrubber IMHO.

Stuart

Mark Chase

I think every one knows that the scrubber figures are wildly conservative. Unfortunately we progress and start pushing the scrubber and suddenly were comfortable with 4 hours and 5 hours is like running your set down to 20bar in the old days. The blokes running 9 -10 hours we all think are mad but we secretly think wellllllll 6 hours must be OK then. In truth it varies dive to dive dependent on temp work load how well the scrubber was packed minimum loop volumes, time spent at depth etc etc.

The temp stick is a nice simple way to monitor the scrubber. Apparently channelling will produce cold spots in the scrubber that will show up on the screen. The temp stick will also identifie crap sorb that’s been frozen solid in the shad over the winter, as it will stay cold. As I understand it the warning signal on the temp stick goes off with a fair margin of error.

Using the stick and deliberately pushing the scrubber to see what would happen a friend got four and a half hours out of an Evo when the warning finally went off on a 50m dive. Apparently it cleared as he ascended for deco.

Personally I think the stick to sort out a dodgy fill is a good thing but apart from that I just don’t quibble at throwing away the lime in the UK and on the warm blue stuff I fix a limit of 4 hours and call it quits at that.

ATB

Mark Chase

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Kevin Juergensen 16/11/08
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Padowan

The hit I had recently was out in the warm blue stuff. The "rules" of Lime were being followed; ie <50m after 100min, <20m after 140min etc... The can had done 2x 1 hour dives down to about 50m. It was on it's 3rd dive, in only 12m of water. After about 30 mins, swimming into a hard current I felt it build up, and it required lung flushes to relieve the symptoms, I went back to the shot line and back to the boat, all on the loop. It *could* have been a dodgy pack (it was coarse grade lime) it also could have been a duff batch, or an old batch, as I know it was close to the printed expiry date.....

Alternatively it could have just been one of those things, that even whe you do everything right you still get bitten in the ass!

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Mark Chase

Interesting, obvously the heavy work load on the last dive is a bad thing but its not exactly extreem diving.

I dont know what lime you were using but i was told to reduce the scrubber time by 25% for Spherasorb and Dragersorb.

In cyprus we were only diving to 40m with 35m average dive depth in 18c water but I did 4-5 hours on each scrubber no problem with three dives in each fill and 80 to 105min run times on each dive. Work load was minamal on most of the dives.

ATB

Mark Chase

__________________
See my "Doing It Chasey" video where I'm locked into a padded room, naked, with two ball bearings and within an Hour, I manage to lose one and break the other!!!

Kevin Juergensen 16/11/08
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