mCCR and zero viz exit

jkaterenchuk · 3rd April 2008, 21:27

Quote: (Originally Posted by Gill Envy)

Great idea, and why even limit the drill to cave diving... it could happen anywhere in deep dark water, given the low light and crap viz we deal with routinely up here in the north west.

No reason to limit it. I only mentioned it because I finished a CCR cave course a few months ago and we did the black out mask, touch contact emergency exit drill. I must admit I was a little uncomfortable not being able to monitor my PO2 myself and leaving it in the hands of the instructor to keep watch. Would also be useful for a Technical CCR Wreck course.

Maybe you could market some little bags of pea soup that happen to fit perfectly into dive masks.

John

Drmike · 4th April 2008, 07:34

Quote: (Originally Posted by mattmexico)

yo

Particular to mCCR I had an incident a couple of month ago that had a ccr cave diver student in a high stress and work load situation on a mCCR doing a zero viz exit out of a cave ... and it could have been out of a wreck too .... and had me on my toes.

While doing a high stress, high work load, high breathing zero viz exit out of a cave a mCCR diver exeeded his active O2 injection rate of his mCCR. While I was told by the diver upon inquiry how he is going to deal with the situation ahead of time and prior to the dive I was told he is gonna count to 120 and then inject some O2.

In the heat of battle so to speak I had to abort the drill as I realized the diver was at at a normoxic Po2 level and was about to exit the cave in the final stage, means coming up shallow and going back to the entrance - surface.

I amin my opinion confident that the diver would have suffered a hypoxic event even when only coming from about 40 feet - 12 meters ... but again he was at .21 when at depth.

My point here is not so much to point fingers or make a big fuzz, it just got me thinking about mCCR in zero viz situations, especially when under high stress and work load.

Just wanted to let the forum know about this potential issue that was prevented and how to overcome it in future procedure.

greetings
Matt

appologies if this has been mentioned already but im half way up a mountain so dont have good connection to read all posts -

in zero vis if using mccr i either do nothing as far as o2 inject is converned if the duration of zero viz is short as you wont breathe down loop ppo2 much at all - or run it semiclosed during longer zero vis time. --this is usually not a problem as the zero vis time is short if its due to diver traffic. or If theres min change in depth I run manual o2 inject on min loop volume.

usually its the latter. I dump some loop vol or flush to min loop as soon as i enter zero viz then manual inject o2 when I have metabolised o2 to be bello min loop vol. at depth you can ascend quite some way without a huge change in ppo2 and normally duration of zero vis is short so no effect on deco. Exit sra keow sees several hours in zero vis ascending from 55m to surface so used clear plastic block between facemask and ppo2 display running boris manually off secondary 8no electrics9. plastic block made display readable no matter how crap the vis

Drmike · 4th April 2008, 07:49

Quote: (Originally Posted by Meng_Tze)

Supposing you can not read a HUD in zero vis, having a bailout table is also useless? Anything requiring visual reference is useless.......

There would be a physical obstruction between your eyes and the outside world for one not to see anything (true zero vis). Not even the glow of the HUD/lights and such would be seen. This I do not think is a realistic scenario.

even in true darkness -no light at all cave -you dont need to see anything to know for sure what your breathing - just go semiclosed - and if wish run min loop too.

you plug in each subsequent bail gas as needed to change dil then run each [new] dil semiclosed or better still min loop o2 manual inject. Should be able to do whole deco using bail and deco gas dil and min loop without much change to original deco schedule

Hanssing · 4th April 2008, 08:03

Quote: (Originally Posted by Drmike)

in zero vis if using mccr i either run it semiclosed during zero vis time. --this is usually not a problem as the zero vis time is short if its due to diver traffic. or If theres min change in depth I run manual o2 inject on min loop volume.

usually its the latter.

HI Mike,

As a know-it-all-newbie I pointed out to my Mod1-instructor that mCCR Min-loop+O2 becomes harder at depth....
We never really reached an agreemment

Still being the know-it-all-newbie, I would say this is still true!
As you dive very deep, I'd like to know at wich depth you are "comfortable" to run mCCR based on loop-volume alone?

Regards
Nicolai

Drmike · 4th April 2008, 08:09

Quote: (Originally Posted by Hanssing)

HI Mike,

As a know-it-all-newbie I pointed out to my Mod1-instructor that mCCR Min-loop+O2 becomes harder at depth....
We never really reached an agreemment

Still being the know-it-all-newbie, I would say this is still true!
As you dive very deep, I'd like to know at wich depth you are "comfortable" to run mCCR based on loop-volume alone?

Regards
Nicolai

why do you feel it becomes harder?

if anything i think its easier as your dil ppo2 is closer to your assumed ccr setpoint the deeper you are. so on deep dives where bottom ppo2 is not so critical to deco then you can get away with just running dil semiclosed and not even need to worry about o2 injections and still have a good ppo2. just flush loop every few mins. although personally id run min loop on horizontal sections or during stopso or deep section of ascents

to answer your second part - im happy at any depth as the variation of ppoo2 is really quite small if done correctly and if not up and down profile or ascending. the deeper you are the less important the actual po2 is to your deco so deeper is better if your going to run just semiclosed. on ascent you switch dils and flush with deco gas at gas switch depths and run min loop during stops

ive done quite a few dives this way as a practice. its well worth practicing if for no other reason than you can see the effect of what you do on your display and develop a good understanding of effect of depth/semiclosed freq etc on ppo2...if you follow basic method you will be surprised how easy it is to maintain a reasonable ppo2

Hanssing · 4th April 2008, 08:23

Quote: (Originally Posted by Drmike)

why do you feel it becomes harder?

The relative change in loop-volume when O2 is metabolised is inversely porportional to absolute pressure.
Ie. the loop-volume changes becomes smaller when depth increases, and I would therefor think it would be increasingly harder to use this method?

It probably just my chasing a theoretical point, with no relevance to practical diving - I have a tendency to do just that.
Drove my instructor to the brink of madness

I'm asking as a newbie because I have not yet tried to experiment with this method at depth.

Regards
Nicolai

Hanssing · 4th April 2008, 08:33

Opps, you edited your post while I answered...

Quote: (Originally Posted by Drmike)

ive done quite a few dives this way as a practice. its well worth practicing if for no other reason than you can see the effect of what you do on your display and develop a good understanding of effect of depth/semiclosed freq etc on ppo2...if you follow basic method you will be surprised how easy it is to maintain a reasonable ppo2

There was an interresting (and long) thread about SCR last year. Suffice to say I'll be practicing this when I have off-board diluent-conections on my rEvo.

Work in progress - work in progress.

Nicolai

Drmike · 4th April 2008, 08:36

Quote: (Originally Posted by Hanssing)

The relative change in loop-volume when O2 is metabolised is inversely porportional to absolute pressure.
Ie. the loop-volume changes becomes smaller when depth increases, and I would therefor think it would be increasingly harder to use this method?

It probably just my chasing a theoretical point, with no relevance to practical diving - I have a tendency to do just that.
Drove my instructor to the brink of madness

I'm asking as a newbie because I have not yet tried to experiment with this method at depth.

Regards
Nicolai

yes the deeper you are the less finger on button time you need so easier it is to overshoot ppo2. however as long as your not adding dil and as long as your injecting when you feel min loop your average ppo2 will not change only the magnitude of its variation

we are concerned with average ppo2.

easiest way to manage the degree of overshoot is to inject several little squirts of o2 to make up loop vol by feel in stages rather than try to do it in one bigger inject at one go

so it may be like;-

sub min loop feel, squirt, still sub min loop feel, squirt, min loop feels ok - go

Drmike · 4th April 2008, 08:54

Quote: (Originally Posted by mattmexico)

diver exeeded his active O2 injection rate of his mCCR.

in this situation where hes exceeding his mccr o2 feedrate in zero viz due to workload would he be safer adding dil instead of O2 to make up that extra small metabolised loop volume?

this i assume would be better than running semiclosed as hes still getting benefit of most of his o2 needs from kiss valve so his loop ppo2 will only drop by the difference in adding say 21 instead of 100 for the extra o2 vol metablised over kiss setting so shouldnt be much - thoughts?

Hanssing · 4th April 2008, 08:57

Quote: (Originally Posted by Drmike)

yes the deeper you are the less finger on button time you need so easier it is to overshoot ppo2. however as long as your not adding dil and as long as your injecting when you feel min loop your average ppo2 will not change only the magnitude of its variation

Its not the addition I'm wondering about.
Its the divers skill/sensitivity to detect that O2 should be added.
Either by change in boyancy, and by the CL starting to bottom out.

I guess my arguments only affects at depth so great its not relevant.

Nicolai

3rd April 2008, 21:27	#111 (permalink)
jkaterenchuk . Current Rebreather/s: Inspiration Classic Megalodon Classic Kiss Other Rebreather/s: Join Date: May 2006 Location: Lititz, PA Posts: 750	Re: mCCR and zero viz exit Quote: (Originally Posted by Gill Envy) Great idea, and why even limit the drill to cave diving... it could happen anywhere in deep dark water, given the low light and crap viz we deal with routinely up here in the north west. No reason to limit it. I only mentioned it because I finished a CCR cave course a few months ago and we did the black out mask, touch contact emergency exit drill. I must admit I was a little uncomfortable not being able to monitor my PO2 myself and leaving it in the hands of the instructor to keep watch. Would also be useful for a Technical CCR Wreck course. Maybe you could market some little bags of pea soup that happen to fit perfectly into dive masks. John
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4th April 2008, 07:34	#112 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,165	Re: mCCR and zero viz exit Quote: (Originally Posted by mattmexico) yo Particular to mCCR I had an incident a couple of month ago that had a ccr cave diver student in a high stress and work load situation on a mCCR doing a zero viz exit out of a cave ... and it could have been out of a wreck too .... and had me on my toes. While doing a high stress, high work load, high breathing zero viz exit out of a cave a mCCR diver exeeded his active O2 injection rate of his mCCR. While I was told by the diver upon inquiry how he is going to deal with the situation ahead of time and prior to the dive I was told he is gonna count to 120 and then inject some O2. In the heat of battle so to speak I had to abort the drill as I realized the diver was at at a normoxic Po2 level and was about to exit the cave in the final stage, means coming up shallow and going back to the entrance - surface. I amin my opinion confident that the diver would have suffered a hypoxic event even when only coming from about 40 feet - 12 meters ... but again he was at .21 when at depth. My point here is not so much to point fingers or make a big fuzz, it just got me thinking about mCCR in zero viz situations, especially when under high stress and work load. Just wanted to let the forum know about this potential issue that was prevented and how to overcome it in future procedure. greetings Matt appologies if this has been mentioned already but im half way up a mountain so dont have good connection to read all posts - in zero vis if using mccr i either do nothing as far as o2 inject is converned if the duration of zero viz is short as you wont breathe down loop ppo2 much at all - or run it semiclosed during longer zero vis time. --this is usually not a problem as the zero vis time is short if its due to diver traffic. or If theres min change in depth I run manual o2 inject on min loop volume. usually its the latter. I dump some loop vol or flush to min loop as soon as i enter zero viz then manual inject o2 when I have metabolised o2 to be bello min loop vol. at depth you can ascend quite some way without a huge change in ppo2 and normally duration of zero vis is short so no effect on deco. Exit sra keow sees several hours in zero vis ascending from 55m to surface so used clear plastic block between facemask and ppo2 display running boris manually off secondary 8no electrics9. plastic block made display readable no matter how crap the vis __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by Drmike : 4th April 2008 at 08:49.
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4th April 2008, 07:49	#113 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,165	Re: mCCR and zero viz exit Quote: (Originally Posted by Meng_Tze) Supposing you can not read a HUD in zero vis, having a bailout table is also useless? Anything requiring visual reference is useless....... There would be a physical obstruction between your eyes and the outside world for one not to see anything (true zero vis). Not even the glow of the HUD/lights and such would be seen. This I do not think is a realistic scenario. even in true darkness -no light at all cave -you dont need to see anything to know for sure what your breathing - just go semiclosed - and if wish run min loop too. you plug in each subsequent bail gas as needed to change dil then run each [new] dil semiclosed or better still min loop o2 manual inject. Should be able to do whole deco using bail and deco gas dil and min loop without much change to original deco schedule __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment
(Offline)

4th April 2008, 08:03	#114 (permalink)
Hanssing flap-flop ..... flap-flop Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Denmark Posts: 378	Re: mCCR and zero viz exit Quote: (Originally Posted by Drmike) in zero vis if using mccr i either run it semiclosed during zero vis time. --this is usually not a problem as the zero vis time is short if its due to diver traffic. or If theres min change in depth I run manual o2 inject on min loop volume. usually its the latter. HI Mike, As a know-it-all-newbie I pointed out to my Mod1-instructor that mCCR Min-loop+O2 becomes harder at depth.... We never really reached an agreemment Still being the know-it-all-newbie, I would say this is still true! As you dive very deep, I'd like to know at wich depth you are "comfortable" to run mCCR based on loop-volume alone? Regards Nicolai __________________ Woohooo - I can change my rEvo! Its going to be bitchin' tricked out piece of gear Last edited by Hanssing : 4th April 2008 at 08:05. Reason: Clarification?
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4th April 2008, 08:09	#115 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,165	Re: mCCR and zero viz exit Quote: (Originally Posted by Hanssing) HI Mike, As a know-it-all-newbie I pointed out to my Mod1-instructor that mCCR Min-loop+O2 becomes harder at depth.... We never really reached an agreemment Still being the know-it-all-newbie, I would say this is still true! As you dive very deep, I'd like to know at wich depth you are "comfortable" to run mCCR based on loop-volume alone? Regards Nicolai why do you feel it becomes harder? if anything i think its easier as your dil ppo2 is closer to your assumed ccr setpoint the deeper you are. so on deep dives where bottom ppo2 is not so critical to deco then you can get away with just running dil semiclosed and not even need to worry about o2 injections and still have a good ppo2. just flush loop every few mins. although personally id run min loop on horizontal sections or during stopso or deep section of ascents to answer your second part - im happy at any depth as the variation of ppoo2 is really quite small if done correctly and if not up and down profile or ascending. the deeper you are the less important the actual po2 is to your deco so deeper is better if your going to run just semiclosed. on ascent you switch dils and flush with deco gas at gas switch depths and run min loop during stops ive done quite a few dives this way as a practice. its well worth practicing if for no other reason than you can see the effect of what you do on your display and develop a good understanding of effect of depth/semiclosed freq etc on ppo2...if you follow basic method you will be surprised how easy it is to maintain a reasonable ppo2 __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by Drmike : 4th April 2008 at 08:22.
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4th April 2008, 08:23	#116 (permalink)
Hanssing flap-flop ..... flap-flop Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Denmark Posts: 378	Re: mCCR and zero viz exit Quote: (Originally Posted by Drmike) why do you feel it becomes harder? The relative change in loop-volume when O2 is metabolised is inversely porportional to absolute pressure. Ie. the loop-volume changes becomes smaller when depth increases, and I would therefor think it would be increasingly harder to use this method? It probably just my chasing a theoretical point, with no relevance to practical diving - I have a tendency to do just that. Drove my instructor to the brink of madness I'm asking as a newbie because I have not yet tried to experiment with this method at depth. Regards Nicolai __________________ Woohooo - I can change my rEvo! Its going to be bitchin' tricked out piece of gear
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4th April 2008, 08:33	#117 (permalink)
Hanssing flap-flop ..... flap-flop Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Denmark Posts: 378	Re: mCCR and zero viz exit Opps, you edited your post while I answered... Quote: (Originally Posted by Drmike) ive done quite a few dives this way as a practice. its well worth practicing if for no other reason than you can see the effect of what you do on your display and develop a good understanding of effect of depth/semiclosed freq etc on ppo2...if you follow basic method you will be surprised how easy it is to maintain a reasonable ppo2 There was an interresting (and long) thread about SCR last year. Suffice to say I'll be practicing this when I have off-board diluent-conections on my rEvo. Work in progress - work in progress. Nicolai __________________ Woohooo - I can change my rEvo! Its going to be bitchin' tricked out piece of gear
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4th April 2008, 08:36	#118 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,165	Re: mCCR and zero viz exit Quote: (Originally Posted by Hanssing) The relative change in loop-volume when O2 is metabolised is inversely porportional to absolute pressure. Ie. the loop-volume changes becomes smaller when depth increases, and I would therefor think it would be increasingly harder to use this method? It probably just my chasing a theoretical point, with no relevance to practical diving - I have a tendency to do just that. Drove my instructor to the brink of madness I'm asking as a newbie because I have not yet tried to experiment with this method at depth. Regards Nicolai yes the deeper you are the less finger on button time you need so easier it is to overshoot ppo2. however as long as your not adding dil and as long as your injecting when you feel min loop your average ppo2 will not change only the magnitude of its variation we are concerned with average ppo2. easiest way to manage the degree of overshoot is to inject several little squirts of o2 to make up loop vol by feel in stages rather than try to do it in one bigger inject at one go so it may be like;- sub min loop feel, squirt, still sub min loop feel, squirt, min loop feels ok - go __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by Drmike : 4th April 2008 at 08:39.
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4th April 2008, 08:54	#119 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,165	Re: mCCR and zero viz exit Quote: (Originally Posted by mattmexico) diver exeeded his active O2 injection rate of his mCCR. in this situation where hes exceeding his mccr o2 feedrate in zero viz due to workload would he be safer adding dil instead of O2 to make up that extra small metabolised loop volume? this i assume would be better than running semiclosed as hes still getting benefit of most of his o2 needs from kiss valve so his loop ppo2 will only drop by the difference in adding say 21 instead of 100 for the extra o2 vol metablised over kiss setting so shouldnt be much - thoughts? __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by Drmike : 4th April 2008 at 08:58.
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4th April 2008, 08:57	#120 (permalink)
Hanssing flap-flop ..... flap-flop Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Denmark Posts: 378	Re: mCCR and zero viz exit Quote: (Originally Posted by Drmike) yes the deeper you are the less finger on button time you need so easier it is to overshoot ppo2. however as long as your not adding dil and as long as your injecting when you feel min loop your average ppo2 will not change only the magnitude of its variation Its not the addition I'm wondering about. Its the divers skill/sensitivity to detect that O2 should be added. Either by change in boyancy, and by the CL starting to bottom out. I guess my arguments only affects at depth so great its not relevant. Nicolai __________________ Woohooo - I can change my rEvo! Its going to be bitchin' tricked out piece of gear
(Offline)

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