Passive Scr Superiority?

robertfondren

By virtue of the "fact" that passive addition SCRS require little or no monitoring of loop PO2, and still manage to enhance gas utilization by an engineer-defined ratio (1/7) or greater, are they not at least theoretically the safest form of rebreather?

GKAM

They do have a prety safe track record, but as with all designs they have their weaknesses. There is no such thing as the perfect Rebreather

My regular dive buddy dives a Recy'01 (RB80 clone). It is a very robust and forgiving rig but it has an Achillea's heel - a particular one way valve.

/GKAM

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nigelh

"Safest" cannot be determined theoretically and even when you start counting incidents Passive SCRs are so rare and only used under certain conditions so comparing like with like is virtually impossible.

My personal view is that safety on a rebreather is largely down to attitude.

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nigelh

lizardland

A Rebreather is only as good as the user. Change depth with the wrong gas or not forcing an injection and it's lights out.

I nearly bought a PSCR until I tried one. It might be safer from an engineering point of view as a system but it all comes down to reality in the water. There were just as many "design features" as supposedly unsafe CCR that would get you. You still need to be just as aware. Add to that they breathe like pigs (I found the one I tried more tiring than OC), I wouldn't want to be in a stressful situation with one.

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gtzavelas

First of all when doing such comparisons we have to assume that the competency level of divers is similar – one can’t suggest that on average mCCR and pSCR divers are more competent than eCCR divers or that their training is better.Or that the "worse" track record of eCCR is only due to "diver error" or to bad or unsafe divers.



My experience in RBs is very limited as I have been diving a pSCR for less than a year. So I cant claim to be an expert but here is my 2 (euro)cents:
Before buying my unit though I did a lot of reading / searching.

Comparing the main 3 categories (pSCR, mCCR, eCCR) my conclusion was that the “worst” safety record of all categories goes with eCCR and especially some specific brands.
The number of accidents seemed unnaturally high…compared to the other types or even as a statistic compared to the number of units sold.

During the last few months that my experience is (slowly) increasing and after discovering and reading through all of Rebreather World I have confirmed to myself that eCCRs (and specially some specific brands) have an increased risk versus other units and versus mCCR and pSCR.

The last couple of days reading http://www.rebreatherworld.com/rebreather-accidents-incidents/7374-always-know-your-ppo2.html and the responses of INSPO divers it is seems to me that a large part of accidents with the specific units has been related to Design Error, Not enough safety checks and Unit malfunctions (that now seem to be fixed???)

On the other hand pSCR have serious limitations but like mCCR have an excellent safety record. And you can’t say that they are “rare” because in specific applications (long and deep cave explorations) they have a great record (GUE single RB80 WKPP exlporations , EKPP dual RB80 explorations, Casati dual RECY01 dive at -184m cave dive etc etc…)

Finally I think that eCCRs are improving rapidly (improving the designs/fixing faults, new units) and in the long run will dominate the market.

As an electrical engineer in the industrial controls area (up to SIL 3) I have come to trust electronics – but only the electronics that have had a LOT of money in design and R&D a couple of years of testing and large number of installed base so all possible bugs have been identified. And we still find bugs after many-many years of “normal and good” operation…

lizardland

As everyone knows, the best rebreather is the one that you have shelled out a couple of grand at least on.

I think the biggest thing that is clear from Rebreather World and Rebreather divers is that most people defend quite fervently whatever RB we happen to own.

It's how you use it that counts and your ability to stay alive. I agree with Nigel, attitude is by far the overwheleming factor in whether or not your rebreather is safe. That and having a reliable indication of your ppO2.

Is a PSCR better than a CCR?

Are apples better than coconuts?

Would Spiderman kick Superman's arse?

If you are alive on your rebreather by the time you decide to retire from diving then it was probably the safest rebreather for you.

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Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you?

www.westons-cider.co.uk

Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler

Marc T

[quote=lizardland;72928]Is a PSCR better than a CCR?

Are apples better than coconuts?

Would Spiderman kick Superman's arse?

quote]

That wasnt the question I think.
Its an evidence that a life support must be idiot proof.
Even an" underwater - idiot" can slowly and carrefuly prepare his dive before ( correct gaz etc ) but even a genius or a professional pilot can do a mistake with or without any stress.
I dived a pSCR for enough time to appreciate that the only thing to do underwater was to listen to the regular flow of bubbles on inhale time.
The less you have to do underwater the less mistake you can do.
If your Rebreather is complex or possible known issue then its just a matter of time.

gtzavelas

well for sure pSCR is worse than both eCCr and mCCR in terms of:
- Efficiency
- Deco obligations
- Gas planning
- WOB

But I think the question raised was not related to the point better/worse but instead safer/less safe.

Maybe the only correct way to evaluate is to consider the number of units is to define the number of units of each type, the number of accidents with each type and find out the percentage of accidents for each type.

any one has any numbers available?

AD_ward9

There are a lot of things not fixed on popular rebreathers: critical failure points that are likely to cause fatalities. If any manufacturer wants the list for their unit, see me at DEMA. I will see if I can pack in a few tools to demo the failures in a quiet room off the exhibition.

Alex

Dutchy

Is that all you do? Your dives must be one long dull experience. Try looking at fish or wrecks some time. You might like it

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