Open circuit at first sign of trouble?

***caveseeker7*** · 8th April 2005, 20:56

Ken, I don't remember where Dr.Mike's post is, but the most thorough and gut-wrenching account of a very seriously CO2 hit is JasonM.'s at Dive-Oz .
His total inability to bailout from the loop gas is alarming if not terrifying.

decoweenie · 8th April 2005, 21:02

Quote: (Originally Posted by caveseeker7)

...but the most thorough and gut-wrenching account of a very seriously CO2 hit is JasonM.'s at Dive-Oz ....

Perfect example of a case of "Get the money back from the instructor and sell the unit on e-Bay"...

***caveseeker7*** · 8th April 2005, 21:20

Well, that or complacency. For the issue at hand it doesn't really matter.
If anything it's a nice wake-up call for those that are about to doze off.

***schford*** · 8th April 2005, 21:30

Quote: (Originally Posted by decoweenie)

If you do actually dive MLV, there is one breath (plus a tiny bit). So I could and do teach people to completely empty the loop volume with one breath out. No need to do any "cross your arm, squeeze your CL" bit. It is that simple to breath out thru the nose (or what you guys call Open Loop). I could trigger the ADV if I exaggerate the exhalation breath

I dive the Insp as well which isn't much different than the Meg. And I could do the same with MLV.

The problem is people think they are diving MLV and they are not if they have to squeeze gas out from the CL to empty the loop.

Thanks for sharing this information Phi - it might be my lack of knowledge around squeezing the CLs - the reason might be to ensure a full flush of the loop as the adv is on exhale side.

As for MLV - I would have though that even with empty CLs when you have a breath there would still be a fairly significant volume of gas in the system - in the Meg ther must easily be a few litres with the hoses, head and space in the can around the scrubber unit and the 10cm or so under the scrubber.

Stuart

***caveseeker7*** · 8th April 2005, 21:37

There are several liters in the loop, but only the bags (and to a lesser extend the hoses) are compressable.
If they are empty the gas in the loop won't move much as you're unlikely to be able to suck a vacuum into the solid parts. That's why we need bags in the first place.

decoweenie · 8th April 2005, 21:38

Quote: (Originally Posted by schford)

... the reason might be to ensure a full flush of the loop as the adv is on exhale side...

Stuart,

It is just my observation that when you are drawing from the loop, gas comes from the CLs first (first to react). When the CLs are flat (empty), I could feel the ADV on the Insp triggers so I don't think you could draw much more from the loop even though the hoses are not "collapsed".

***schford*** · 8th April 2005, 21:42

ok ok I am getting this - then it would make sense to manually compress / crush your counter lungs to ensure that when you fire the ADV or manual add valve that the CLs wont inflate so the gas that comes in pushes the old contaminated gas in the loop can etc around and then out of the valve?

***caveseeker7*** · 8th April 2005, 22:18

Another thought I want to throw in, and maybe DaveT. can help out here, is this:
Breathing resistance on 'open loop' is quite a bit higher than on open circuit.
Higher breathing resistance, from what I understand, leads to higher CO2 generation in the body.
So if the problem is high CO2 in the loop, breathing 'open loop' might be counterproductive, or at least less productive than open circuit ... .

Anyone, anyone? Bueller?

narked at 90 · 8th April 2005, 22:34

this for me is hitting on a very good piont, for some off us with back mounted cl and with out o/c dsv's, going to open loop has a very very high WOB to maintain for more than a few breaths and in an already stressed situation can just make a problem worse,

so with my rig i would prefer to go o/c get it together then go back if i think it's possible.
i have just brought a new o/c dsv after my co2 hit........which failed on me at 30m but thats anouther story!!!!
john routley

Quote: (Originally Posted by caveseeker7)

Flying a CCR as an SCR means dumping every 4th to 5th breath, depending on who you ask.
Open loop refers to dumping every breath, you basically turn the ADV into your 2nd stage (or refill the loop manually).

ROB DAVIE · 9th April 2005, 02:27

Folks,

This is the easiest way to get a breath of fresh air, so to speak, if you have a problem with your box.

You reach up, and with two fingers, turn the lever 90 degrees. Instantly, you have closed off the loop, and turned on your OC gas supply. Two or three healthy breaths should clear your head. NOW you can use your carbon-based life-form-unit logic circuits to analyze the problem, solve it (if it can be solved), and return to your magic box if it is safe to do so!

There is almost no thought involved, and almost no monkey-motion. The lever moves very smoothly, and with only two fingers. Very nice!

Rob Davie

8th April 2005, 20:56	#41 (permalink)
*caveseeker7* Who loves ya, baby Current Rebreather/s: Sport Kiss Other Rebreather/s: Prism Topaz Join Date: Jan 2005 Location: Too far from Neverland Posts: 5,555	Ken, I don't remember where Dr.Mike's post is, but the most thorough and gut-wrenching account of a very seriously CO2 hit is JasonM.'s at Dive-Oz . His total inability to bailout from the loop gas is alarming if not terrifying. __________________ Cheers Stefan "Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"
(Offline)

8th April 2005, 21:02	#42 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,487	Quote: (Originally Posted by caveseeker7) ...but the most thorough and gut-wrenching account of a very seriously CO2 hit is JasonM.'s at Dive-Oz .... Perfect example of a case of "Get the money back from the instructor and sell the unit on e-Bay"...
(Offline)

8th April 2005, 21:20	#43 (permalink)
*caveseeker7* Who loves ya, baby Current Rebreather/s: Sport Kiss Other Rebreather/s: Prism Topaz Join Date: Jan 2005 Location: Too far from Neverland Posts: 5,555	Well, that or complacency. For the issue at hand it doesn't really matter. If anything it's a nice wake-up call for those that are about to doze off. __________________ Cheers Stefan "Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"
(Offline)

8th April 2005, 21:30	#44 (permalink)
*schford* RBW Founder Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: UK Posts: 3,564	Quote: (Originally Posted by decoweenie) If you do actually dive MLV, there is one breath (plus a tiny bit). So I could and do teach people to completely empty the loop volume with one breath out. No need to do any "cross your arm, squeeze your CL" bit. It is that simple to breath out thru the nose (or what you guys call Open Loop). I could trigger the ADV if I exaggerate the exhalation breath I dive the Insp as well which isn't much different than the Meg. And I could do the same with MLV. The problem is people think they are diving MLV and they are not if they have to squeeze gas out from the CL to empty the loop. Thanks for sharing this information Phi - it might be my lack of knowledge around squeezing the CLs - the reason might be to ensure a full flush of the loop as the adv is on exhale side. As for MLV - I would have though that even with empty CLs when you have a breath there would still be a fairly significant volume of gas in the system - in the Meg ther must easily be a few litres with the hoses, head and space in the can around the scrubber unit and the 10cm or so under the scrubber. Stuart
(Offline)

8th April 2005, 21:37	#45 (permalink)
*caveseeker7* Who loves ya, baby Current Rebreather/s: Sport Kiss Other Rebreather/s: Prism Topaz Join Date: Jan 2005 Location: Too far from Neverland Posts: 5,555	There are several liters in the loop, but only the bags (and to a lesser extend the hoses) are compressable. If they are empty the gas in the loop won't move much as you're unlikely to be able to suck a vacuum into the solid parts. That's why we need bags in the first place. __________________ Cheers Stefan "Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"
(Offline)

8th April 2005, 21:38	#46 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,487	Quote: (Originally Posted by schford) ... the reason might be to ensure a full flush of the loop as the adv is on exhale side... Stuart, It is just my observation that when you are drawing from the loop, gas comes from the CLs first (first to react). When the CLs are flat (empty), I could feel the ADV on the Insp triggers so I don't think you could draw much more from the loop even though the hoses are not "collapsed".
(Offline)

8th April 2005, 21:42	#47 (permalink)
*schford* RBW Founder Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: UK Posts: 3,564	ok ok I am getting this - then it would make sense to manually compress / crush your counter lungs to ensure that when you fire the ADV or manual add valve that the CLs wont inflate so the gas that comes in pushes the old contaminated gas in the loop can etc around and then out of the valve?
(Offline)

8th April 2005, 22:18	#48 (permalink)
*caveseeker7* Who loves ya, baby Current Rebreather/s: Sport Kiss Other Rebreather/s: Prism Topaz Join Date: Jan 2005 Location: Too far from Neverland Posts: 5,555	Another thought I want to throw in, and maybe DaveT. can help out here, is this: Breathing resistance on 'open loop' is quite a bit higher than on open circuit. Higher breathing resistance, from what I understand, leads to higher CO2 generation in the body. So if the problem is high CO2 in the loop, breathing 'open loop' might be counterproductive, or at least less productive than open circuit ... . Anyone, anyone? Bueller? __________________ Cheers Stefan "Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"
(Offline)

8th April 2005, 22:34	#49 (permalink)
narked at 90 John Routley Current Rebreather/s: Inspiration Classic Other CCR Dolphin Home Build Other Rebreather/s: Other CCR Dolphin Home Build Join Date: Feb 2005 Location: middlands uk Posts: 1,073	this for me is hitting on a very good piont, for some off us with back mounted cl and with out o/c dsv's, going to open loop has a very very high WOB to maintain for more than a few breaths and in an already stressed situation can just make a problem worse, so with my rig i would prefer to go o/c get it together then go back if i think it's possible. i have just brought a new o/c dsv after my co2 hit........which failed on me at 30m but thats anouther story!!!! john routley Quote: (Originally Posted by caveseeker7) Flying a CCR as an SCR means dumping every 4th to 5th breath, depending on who you ask. Open loop refers to dumping every breath, you basically turn the ADV into your 2nd stage (or refill the loop manually).
(Online)

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