YD Scuba Diving Forums banner

1 - 11 of 11 Posts

·
Registered
Joined
·
23 Posts
Discussion Starter · #1 ·
Imported post

Theres no doubt that RB's are the future of diving but I won't be getting one until they start making them with CO2 sensors, I cant understand with the technology to hand why this critical component is still not part of design when it's of equal importance as PPO2.  So why are'nt they ?  Please discuss (no less than 100 words please, to be handed in on return to school)
 

·
Grumbler-chief in Residence
Joined
·
1,969 Posts
Imported post

Simple, it is not easy to do, the solution they have come up with is to monitor the temp of the scrubber, trouble with this is, by the time you get a real warning it is already half way to being too late. The solution is to replace the material at or within the recomended limits and to pack it properly in the first place.

Andrew
 

·
A short fat well off crap cave diver. Likes wrecks
Joined
·
15,343 Posts
Imported post

[b said:
Quote[/b] (karl_winrow @ Dec. 21 2003,20:54)]Theres no doubt that RB's are the future of diving but I won't be getting one until they start making them with CO2 sensors, I cant understand with the technology to hand why this critical component is still not part of design when it's of equal importance as PPO2.  So why are'nt they ?  Please discuss (no less than 100 words please, to be handed in on return to school)
As I understand it the existing technology on CO2 sensors is so advanced that it will now inform you of a problem only 3 mins after your dead. Much better than the old sensor which didn’t react until at least 5 mins after your dead.


Funny but also sadly true

Mark Chase
 

·
Banned
Joined
·
1,389 Posts
Imported post

Further to Andy's reply - it's actually incredibly difficult to do.  Existing monitors check the temperature of the stack as the 'reaction wavefront' makes its way from the bottom of the stack to the top.  Not enough of a solution, for the simple reason that they can't detect if you've not packed the scrubber properly or left a critical o-ring out.
There are a number of guys working on a proper CO2 monitor, but the whole physics of the thing (remember I've got to keep it below 100 words) is proving to be a bit of a bastid.
Push comes to shove, CO2 problems are avoidable.  Proper preparation, packing, pre-breathing, not taking the p1ss etc will obviate the problem.
There are thousands of people all over the world diving the hell out of these things, be they Inspirations, Megs, Cis-Lunar, MK15s, KISSs, Drager, what have you. CO2 incidents, whilst rare, are a worry -  if you look after your kit it'll look after you. If you don't you're in all sorts of trouble.
To sum up:  If you're going to wait till a 'safe' CO2 monitor's available before making the switch, you've got a long wait coming.  And they're not the future of diving, as long as they cost as much as they do.
Went over the 100 words I reckon, hope I get a credit on your 'F'
 

·
Registered
Joined
·
23 Posts
Discussion Starter · #5 ·
Imported post

Rob the prices have already fallen if you look at what they cost a few years ago, they will drop as demand rises it's simple economics. As for the sensors taking 3 minuites to react have a look at PASCO's site, they have a realtime monitor that updates every second, admit it would be hard to adapt to the harsh environment we throw ourselves in but its only a matter of time.  

As regards looking after your kit I totally agree however my concern was for the unforseen occasions, eg scrubber has an small leak and before you know it CO2 through the roof and game over.  Does the temp sensor react quickly enough to warn of this ?
 

·
Banned
Joined
·
1,389 Posts
Imported post

The trouble is that existing CO2 detectors only detect a level of CO2 which, if it hasn't already killed you, is rapidly on its way to doing just that.  It only takes a very small amount of CO2 in the inhalation side to seriously impair your functions. You're perfectly right about the harsh environment though - the lid of the scrubber (where you would put them) generally sits at 100% humidity but that can vary significantly, compounding the difficulty.

The temperature sensors measure where the reaction front of a properly functioning scrubber is, ie from the bottom working its way to the top (to use the Evolution as an example).  What they won't pick up is CO2 sneaking through the gaps in a badly packed or settled scrubber, nor CO2 that's bypassed the scrubber stack altogether in the case of a missing lid O-ring, nor a seriously 'overbreathed' scrubber.
I personally don't have a lot of time for the temp sensors.  Call me an old luddite, but there are strict guidelines set down by APD about the life of the scrubber under various conditions - if you follow them & chuck it out when you're supposed to then you can't go far wrong. A bar graph that tells you you're 3/4 of the way through the scrubber when the manufacturer's limit has already passed is IMHO going to encourage nitwits to push the scrubber life.   Sofnolime's cheap, funerals ain't


As regards cost.  I for one would love to see them get cheaper, but the Insp is still the thick end of £4k + training after 6 yrs of manufacture & all the major CCRs similar money. The KISS is cheaper (and many would argue better) by virtue of its simplicity but it's still a ton of cash compared to what 99% of the world's population will pay for their diving kit.  Dont even ASK what an RB80 costs, then again they're not really aimed at the recreational (sic) market.
It'd be good to see them become more mainstream, but to really take off they'll need to be much cheaper, simpler, more robust, reliable, easier to look after and -dare I say it- less lethal when improperly used. I'm sure we've all seen manky old rental regs being used by first-time try divers, OW students & 7 dives-per-year-types at holiday resorts around the world. Treat a CCR with the same lack of respect & it'll bump you off.

As years go by, you're certainly going to see loads more around the place - the major mfrs are selling all they can build - but I reckon it'll be a good long while before they're as accessible as regular SCUBA.
 

·
Banned
Joined
·
1,389 Posts
Imported post

PS - Wanna know how a scrubber works?  A nice man wrote a document so dopes like me could get their heads around it..  Reproduced with kind permission of MadMole and Gordon Henderson (when I get round to asking them)


<FX: TwilightZone music...>

Here on Zorg, we abducted some humans to test your resistance to CO2 and the efficiency of our patented CO2 grabbing demon chamber.

We took a human and connected a hose to them. The hose supplies gas and has one-way valves. The exit of the hose goes into a box. Inside this box are 1000s of little demons. These demons adore CO2. They will grab a passing molecule of CO2 and hang onto it for the rest of their lives. They can only hold one each. After the CO2 demon box there is another box with different demons inside - these count the number of O2 molecules you have used and replaces them.

We observed that humans when in a steady state consume the same amount of O2 per breath, regardless of the pressure we subjected them to. When given 100 molecules of our gas, they would use 4 molecules of our oxygen and turn this into 3 molecules of CO2 and 1 molecule of water vapour.

So in the test, with 100 molecules of gas in the loop. The human push/pulled this through the box with the CO2 demons in it. Every breath, 3 lucky demons grab a CO2 molecule each and are happy for the rest of their lives. We repeated this for many of your earth hours, pushing 100 molecules of gas through the CO2 box at a nice steady rate - the happy demon front line progressed linearly through the CO2 demon box until eventually they are all happy. At that point, the loop gas has some CO2 in it and we observed that the humans started to show signs of unease, panic and general ill-feeling. They eventually died a rather uncomfortable death.

To continue our experiments, we abducted more humans and carried on, this time we subjected them to a pressure of 2 bar. This is the same as being under 10 metres of your water. There is now 200 molecules of gas in the loop, but the human still only uses 4 molecules of O2 and turnes these into 3 molecules of CO2 and 1 water vapour. Each breathe pushes 200 molecules through the CO2 demon chamber, so the demons have to work faster to grab the CO2 molecules and die happy. Sometimes a front-line demon misses, but the 2nd line catches it OK. This carries on and eventually all the demons are happy, then as above, the human dies painfully and horribly from CO2 poisoning.

We needed to do more experiments, so we continued with our abduction programme. Now we're testing to 90m. There are now 1000 molecules of gas in the loop, but as observed before, then humans still only take 4 molecules of O2 out and metabolises these into 3 of CO2 and one of water with each breath, However, the poor CO2 demons now have 1000 molecules of gas going through their chamber like a hurricane, and in those 1000 molecules there are still only 3 molecules of CO2! It's now very hard for the demons to catch a CO2 molecule and hang on to it! The front-line demons have a real hard time catching the CO2 molecules and a lot more pass further down the line to be caught by the latter ones. Eventually, the front-line demons are full, but still the latter ones need to work to catch the CO2 and there will come a stage where there aren't enough latter ones who can catch the CO2 fast enough, so some will get through. Eventually so many will get through that the human starts to notice it and dies horribly as before - even when there are still some unhappy and empty CO2 demons left.

Continuing our experiments with more abducted humans, we test again at 90m, but then we decide to ascend the human to some depth where the number of molecules in the loop is much less, so each breath the CO2 demons have more of a chance to catch the CO2 molecules left.

Eventually, after 100's of trials, killing a great many humans every time, (And you should have seen our abduction budget! Off the scale!) we have come up with some rules for keeping humans alive and maximising the happiness of the CO2 demons. Our rules are many, long and complex but to simplify them for you humans we have reduced them to 3 simple rules..

Rule 1: You have 3 hours maximum.

Rule 2: For subsequent dives deeper than 20m: You must leave the bottom when the _total time_ breathed through the system reaches 140 minutes.

Rule 3: For subsequent dives deeper than 50m: You must leave the bottom when the _total time_ breathed from the system reaches 100 minutes.
 

·
Registered
Joined
·
23 Posts
Discussion Starter · #8 ·
Imported post

Thanks for that Rob, I didn't need the lesson but found that very funny anyway, credit to the guys who wrote it, probably with crayon


I may take the plunge later on next year if funds allow, I was very tempted earlier this year by the Azimuth SCR by the simplicity and its use of common parts, but for now I'll have to make do with a try dive next time Andy (Dales divers) arranges one.

Merry xmas everyone.
 

·
Banned
Joined
·
1,389 Posts
Imported post

It did make me chuckle the first time I read it, sums it all up beautifully though eh?

Dunno why, but the Azi really hasn't ever struck me as that great a unit compared to the alternatives.  Must get a grip on an Azi diver & find out what it's all about. Perhaps Andy could add a bit to the debate.

FWIW I do rate the KISS.  CE rating aside (not a massive issue as far as I'm concerned) it's a very tidy unit, cheap and flexible. No less a luminary than Dave Thompson owns one, which is a turn-up for the books


The very best of the season to you & all the other browsers out there..
 

·
Registered
Joined
·
16,363 Posts
Imported post

<font color='#000080'>I found the Azimuth didn't feel right, and ade some funny noises when diving that the inspiration just didn't. OK, the inspiration is a wardrobe, but it's much better made from what I can see and how it felt.

I'm not trained in all this business, but I know what I like. And I really wasn't keen on the Azimuth.
 

·
Registered
Joined
·
1 Posts
Imported post

Short arms - Deep Pockets, we'll get them eventually but only when other fields have a requirement.  Those wonderful ppO2 sensors are used in many other applications (and if you need replacements hospital equipment suppliers list them for use in 'iron lungs' at very sensible prices), in a Lab, optical method to track CO/CO2 concentration is by measuring light absorbed at certain wavelength (Infra Red) more CO = less light transmitted but kit too big to take underwater....

Did see a 'flue gas analyser' that measures CO and CO2 (on screwfix site £280) though don't know how 'convertable' something like that would be......
 
1 - 11 of 11 Posts
Top