How Far Do You Push Your Scrubber?

RichClark

Take what I say with a pinch of salt, as I don't actually own a Rebreather yet - i collect in March.

I can understand running a scrubber a past it's duration on a long single dive, especially considering that the majority of the dive will be spent on deco (i.e shallow and at rest) but i just don't understand why people push their scrubber on multiple dives.

Why do it, is it to save a few ££?

Cheers

Rich

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Tom F.

Yep

RichClark

As I said, I don't own my Rebreather yet so it's possible that I'll change my mind - but i doubt it.

Diving isn't a cheap sport, we all accept that when we enter it, we accepted it when we bought our first bits of kit all the way through to Trimix and then Rebreather's. Saving £8 is insignificant when you consider the total cost of a dive.

I think it's all about having the right tools for the job, this includes a fresh scrubber, or a scrubber that has sufficient remaining life for the dive. If you don't have the right tools then I believe that you should't be doing the dive.

I try and apply the same principle to all my diving... I wouldn't penetrate a single tank, just as I don't dive deep air, nor do I cave dive without training etc...

I guess life is one big risk assessment, and we each personally decide on our own level of acceptable risk.

Just my 2p's worth.

Cheers

Rich

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Louby Lou

Graham

Why do you so "urgently" (so it appears) need to know how far people push their scrubber? It is more often than not down to individual preference and I think your poll will show the same.

Would you jump off a cliff if I told you too?
Same principles apply

DrMike's words are very true and I personally would take heed of what he says. Scrubber duration is not based solely on manufacturer's spec but also YOU, your body and your diving practices. The duration specified by people such as AP are there for YOUR safety! Not because they want to do you out of a couple of ££'s.

Just one thing to consider... life insurance... how much is your life valued at?

Now compare that to the cost of a fill...

At the end of the day, is your life worth the cost of a fill of lime???

I very much doubt it!


Thanks

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Drmike

Who was it that said 'what works - works'

If it works for you then great!

If it doesnt you will most likely only be dead or crippled (or kill or cripple your buddy) - but hey at least you will know for sure what your scrubber duration actually is




I look at it this way;

Replacement value of gear I take with me on a typical dive in USD;

Rebreather 12K
Scooter 3.5K
HID Light 2K
2xVR3S 3K
Drysuit 2K
Stages 0.5K
Regs 1K
Rest 1K

Total USD 24.5K!!!!


.....and how much cost of lime do I save by extending the scrubber usage to the absolute max/dive? 10 bucks??



Personaly, especially on a deep dive I find it reassuring to know I have a good scrubber - there is enough to worry about as it is without this niggling worry in the back of my head.

If I was diving with a buddy I wouldnt appreciate him pushing the limits either as that might endanger me - just so he can save a few bucks!

If you really want to get more bottom time from your scrubber go OC on O2 at the last stops on those deep dives.

In the same way as we dive OC to 3rds I think its best to keep some reserve in the scrubber for unexpected problems such as currents picking up, getting lost/trapped, especially at depth, ect ect. if you always dive it to the limit or beyond you might get caught out one day should something nasty happen - and that wouldnt be a good time to have a CO2 hit.

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LS_DK

I think the way the question is asked is wrong.
When you ask "the scrubber duration question" like this, you get people to write what they do in the most extreme scenario (from a scrubber duration perspective).

My extreme scrubber duration scenario would occur on a shore/shallow dive.
Never in a planned deep dive scenario.

Many on this list (incl myself) have tried a Co2 hit, and all agree it is not very pleasant (at the least). It is not a nice feeling when you loose control of your breathing at depth, and it can, and have, led to worse things than discomfort.

Cheers,
Lasse

01RMB

Take the case of a car and a tank of petrol (gas if you drive on the wrong side of the road!!).

Now imagine the car manufacturer hasn’t invented a fuel gauge yet so the manufacturer rates how long between when you have to fill the car up based on time. They estimated in the worse case scenario (ie. Up a very steep hill towing a heavily loaded caravan) using lab experiments that you can drive for 3 hours before you need to put more petrol in the car.

The other problem I didn’t mention is that to fill up you must first dump whatever petrol is left in the tank because you can’t mix new petrol with old petrol.

We know that if you are not driving up a steep high with a heavily loaded caravan that you can get more than 3 hours before you have to fill up again so without the caravan and on the flat you ‘push’ it a little further.

Would you ‘push’ the time between fills if you were very confident that you hadn’t done any hard driving and that the next petrol station was close? How long you go is a guess your confidence based on previous experience to bend the rules a little.

You would save money and some effort which over the long run could be very significant – you all know how expensive petrol is getting! True you want to be hanging onto some reasonable reserve just in case and don’t want to push it to the limit since there are many places where you just don’t want to be left on the side of the road.

Once the car manufacturer has invented and fitted the fuel gauge you can be more confident of how much longer we can go before we need to dump the petrol and fill up again.

Granted the petrol gauge is not a perfect solution because you may have to drive up a steep hill or travel a bit further than you thought to get to the next petrol station so you shouldn’t push it too far but the gauge is still a pretty good guide.

You can pull this analogy apart pretty easy but as a simple example this gives some idea to what is being talked about.

A stop watch isn’t a good tool for measuring scrubber life unless you are very conservative. The big trouble at this stage in rebreather development is that the tests that manufacturers use to define how long a scrubber should last are not consistent and are probably not achievable in the real world sense anyway. The inspo, evo, meg, kiss, prism and Mk15 are not measured using the same ruler so comparisons are a little fraught with danger. People likewise are all different and the environment will have a huge impact on the achievable times.

APD have done some good work with their scrubber monitor which to my mind only makes diving a rebreather safer (something like using a stick and seeing how wet it is when you stick it in the tank). But you can’t just pull your rebreather over to the side of the road when you run out of scrubber (if you actually knew you had run out!) so you must take a lot more care with how you dive.

Each to their own, but for me, I like having the Evolution with the temp stik to give me a guide to the time left on the scrubber. I for one am happy with the system and have a cautious belief that the tests by APD on the temp stik means that I am not going to suddenly stop living as soon as the dive time gets to 2 hours. Although I know that sustained depth, high work rate and cold water etc will reduce the times I am currently getting back closer to the 2 hour number – a bit like the steep hill and caravan.
It is not about saving a few dollars but about being efficient in the use of it. I will always leave enough scrubber time for the bad current or extended deco requirement. I am not going to jump in to do a 3 hour dive to 100m with old scrubber after already done a deep dive - but on the same hand why change scrubber for a doodle at 20m after only having done 2 hours at 6m and the scrubber monitor is showing plenty of reserves left.

How far can you push the scrubber? That is up to you, the diving you have done, the diving you have got planned, the contingency you wish to add, the risks you want to take and the technology you are using to measure the scrubber performance. Me - I am happy to use the scrubber in my Evo for more than the 2 hours quoted figure for the diving that I am currently doing.

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Cheers
Rod

CCR900

May I ask if you tried this on yuor course, and if so did it in someway help you become a better CCR diver . The reason I ask is I am very much against students being forced/aked to do this during a course. I believe that one doesn't need to run into a brick wall to know it will hurt.

Fil

CCR900

01RMB

In your scenario does the car cause you to convulse/panic or become unconcious and drown when you run out of fuel or does it stop working and you get out and walk?

Fil

decoweenie

I know you didn't ask me, but I actually did do the hypercapnia exercise in the pool during my PVR-BASC course in 1998.

Did it help ? Yes and no.

Yes, I think it did. I got to experience some of the hypercapnic symptoms which was the main idea behind the exercise.

No, I have on occasions over-breathed the unit when having to work very hard, and noticed that the symptoms were not always the same.

BTW, the walk-into-the-wall analogy isn't quite right. Drinking and hang-over is more like it, different feeling each time but always unpleasant. And not repeatable perfectly...

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