Scrubber times

wagger

What is the general opinion about recommended scrubber durations set by the experts/manufacturers. I was told yesterday when at a UK inland site that I could easily do 5 hours on my inspo and the bloke saying this could do 3 hours plus on his evolution. My personal feeling is to stay inside the set scrubber times and have done so for my 63 hours on my inspo with no signs of any problems, although he also recommends getting a co2 hit just so I know what it is like. I'd prefer to avoid that myself!

So, is this the general thought throughout Rebreather divers or just another plonker with too much money?

Paul

dave t

The times laid down by most manufacturers are based on worst case scientific testing, example the inspo was tested at 40lpm rmv with a throughput of 1.6lpm co2 in 4degrees of water temp. anything inside that is going to give you possible longer times, the problem is you dont know by how much. What starts as a gentle bimble on a half used scrubber could turn rapidly into a hard work dive for lots of reasons, if you have allready overrun your time it could breakthrough. There are lots of "experts" who will tell you this and that but only the manufacturers paid lots and lots of money to fix their figures. If you dive a vision with the temp stick, then you may have a better idea as to what is happening but if you dont stick to the stated figures, your life is worth more than a few quids worth of sorb.

As for the "getting a co2 hit to see what its like" you might want to try putting gun to your head and pulling the trigger to see if it will hurt. End result will probably be the same!!!

Dave

wagger

Yep, my feelings as well. The tempsticks give an indication that there is no channeling etc but I belive it gives no indication of the life of the sorb. My mod 1 instructor spoke about ignoring the recommended times and the divers who do it. In all my diving be oc or closed I don't tend to ignore limits, advenurous dosn't have to be leathal! Interesting to find out how far people are willing to push things though, don't you think?

Ben Field

Dare I suggest the person you spoke to is a complete plonker.

There are more productive ways to kill brain cells than faking a CO2 hit.

This has been discussed endlessly, lots of threads on here about it, try a search... not that we can't discuss it again of course....

Short story- Scrubber is Cheap, Life is Valuable.
Do the hours, bin the kitty litter and repeat.

I've always figured pushing slime time leaves you with very little reserve if something else fails, even 3hours into a fill there is probably some reserve for climbing out of the incident pit, 4 or 5hours in that might not be an option. (IMVHO of course)

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Abbo

Three rebreather divers died this week. Don't become another one - of course for your sake but also for the sake of everyone who knows you. I can understand taking risks to do something or see something nobody has done before, but pushing scrubber duration serves absolutely no useful purpose: the stuff isn't even particularly expensive.

There was a case reported on Rebreather World where a diver died trying to give himself experience of a CO2 hit. Clearly it isn't always possible to recognise the effects and react in time. Even in laboratory conditions, scrubber life appears to be pretty unpredictable, even taking out the obvious variable of how well it was packed. Then there is the large variability of CO2 production in your body, with work rate, stress and mood. On OC we dived 'rule of thirds', so it is no surprise that scrubbers can at least last half as long again as the published number. The effects of hypercapnia seem to come on too fast, which is why BOVs are getting the attention they are: the reports on this site say that just closing the loop and pulling out a reg is really tough in a CO2 hit. CO2 is of the order 175x as narcotic as nitrogen, so you won't be thinking clearly. Even when one day we have reliable CO2 sensors, this seems one thing there's no sense screwing with. There have got to be better places to channel your thirst for adventure.

OceanOpportunity

there are way too many variables to predict scrubber duration. Read up on the calcs in life Support System Design & Development by Nuckols, et al if you want to get to the meat of this. In general, I agree with Dave, play the mfg recommendations relatively conservatively. That's bout as good as you can do til we have a good CO2 monitor out there.

good luck
ML

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Oceans of Opportunity
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Elected Director, Society for Human Performance in Extreme Environments

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Project Manager, Diving a Dream

decoweenie

Having done it personally as part of the original Rebreather course on the PVR-BASC in 1998, I recommend NOT to do it. It wasn't fun...

And it was done in a controlled environment as in on the side of the shallow end of the pool with 2 supporting divers on either side. I still would not have made it on my own.

narked at 90

dont push your scrubber below is some thing i posted a wile back
and like decoweenie a number of us have experimented with co2 hits and now i see how stupied i was as it did not help when i took a real hit.
kind regards john routley

i have changed my mind in the hope you dont make the same mistakes as my friend we put to rest last friday after getting him self killed on his home build rebreather and don't think because you have a commercial unit it will be different
you can not handle co2 and sorb is cheap so why do you want to push it?
#now don't get me wrong because those that know me know my history with rebreathers and the things i have done with them over the years to see what are the limits, and some of the things like giving my self a dry hit to see if i would recognise the onset of co2 before it takes hold underwater....i have had 2 co2 hits for real and i can tell you the dry hit dose not help in any way.
the 2 hits i have had have been different from each other and with different on sets.
my friend was a very capable diver much more so than most of the internet warriors on these boards but it would appear that was no help to him when the rebreather killed him,
i have been told my friend was pushing his scrubber to the limit and i know he thought he could tell the onset of co2....he was wrong......
please don't be the next person to find out the hard way about co2 and what it is capable of doing because you can not handle it...run away from it and stay as far away from the limit as you can, there are no second chances

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Barjumpa

Morning all.

I am new to rebreathers and as such I am still wallowing around happlily in the 20metre range practicing drills and just getting used to my Inspiration Vision.

However my personal problem or concern is that I dont feel that the scrubber is working as well as it should. Having dived on the weekend the scrubber was up to 3hrs and 15 minutes. The Temp Stick was in the middle of the range. set point was at 1.3 and only using air as dil. Water here in Sydney is about 18C BUT... I dont feel as though my breath is being quenched. I certainly am not working hard.

Last month I ran the unit and the scrubber time got up to 5hrs and 10 min and again the temp stick still showed that the scrubber had ample life. 25 minutes into a dive however I recognised the obvious signs of a CO2 hit instigated a series of loop flushes and returned to the boat to live and dive another day. That little gem gave me a migrane until Monday Night...! But regardless of the calibration of the temp stick I have set a marker to replace sorb at or just after 3 hours from now on.

I have never run the scruber to the temp stick warning and so my question is how reliable are these temp sticks as an indicator of scrubber life? and is 3 hours being a little too conservative?

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doug allen

One thing my instructor told me time and time again about CCR diving....don't do it on the cheap!!! When the scrubber life is over.....it is over.

I remember reading info about Olympic quality cyclists successfully getting 5 or 6 hours useful operation out of them....but I've also been told that they are pretty much like a light switch...either on or off.....If it turns off while underwater, that may present a problem.

From my own experience, diving an Optima, I had to(elected to) violate the stack time on my scrubber waiting on a dive buddy that decided to venture deeper and with a fresh scrubber. The diver knew that I had about 60 mins scrubber life remaining at the start of the dive. In any event, I overstayed my stack time waiting for him and at 70 fsw the mouth piece starting vibrating....that was it, enough....for sure it got my attention. All kinds of things were going thru my mind....do I bail out to OC? Do I stay on the loop and believe the info I read on the internet about the extended life of scrubbers? (the underlying thought is that the manufacturer must have a built in safety margin). Fear and the task loading of the HUD flashing red and the vibrating mouth piece did make me ascend, but I didn't bail out....but should have.

My future dives on CCR will fall within the safety parameters of the gear I've been trained on. That was a good lesson for me. Perhaps these types of shared experiences will be helpful.