TOTAL ELECTRONIC FAILURE…well… nearly...

pchanning · 21st March 2005, 17:36

What a cracker of a weekend we had in Plymouth. Not a hint of fog (unlike the rest of the country

) just clear warm skies as I slipped into one of Plymouths’ best Shore Dives; Devils Point. Had a hugely enjoyable descent freefalling off the wall on the edge of the viz just loving it. Its dives like this that postpone holiday urges. That is until my breather decides to play-up...

At 43m after a good birthday night-out and whilst studying a nudibrach of a type that I hadn’t seen before, I was soberly informed of a double-beep and a flickering blank display. I switched to the other to see it had become the master and I promptly did a dil flush to satisfy myself of the readings. The dysfunctional handset didn’t have enough juice to even turn itself on as the Slave. That is until after about 5 minutes, which was curious.

Rattled, but not overly concerned, as the conditions were nice and easy, I carried on and finished a lovely dive.
Here comes the twist… apon surfacing I was gasping a load of o2 in preparation for the ‘Iron Man’ walk back up over an intimidating hill (I love post-piss-up dives

) where I was surprised to learn that the supposedly good handset displayed Low-Battery..!! Which, for the benefit of non-Inspiration divers, is not supposed to happen, at least for a long time yet. Normally after what should be plenty of notification beeps the other handset will take over… but not in this case..!!

I had 12 hours on the clock and I changed the batteries together. I acknowledge that inserting two new ‘duff’ batteries could well lead to this sort of situation but that is likely to be in the first dive – (ie: two totally stuffed batteries) as the operational current drain of Master and Slave is something like 75/25% IIRC. So extended use on one (ie: one dive) would render the other to be fit for another like dive. I’ve read that some divers check they’re batteries either operationally or with a multimeter before undergoing a dive that figures extended deco but who really does that… anyone…??

As I said the conditions were excellent so it wouldn’t have been so bad to lose both handsets in such a situation. I had a full Dil cylinder that would have comfortably carried me semi-closed for the rest of the dive back up to o2 rebreather depth. However, I can imagine that performing the same whilst coming up an SMB in black mid-water with a large deco penalty would make for a very different experience.
Consequently, I’m thinking of running my usual dives and manually maintaining both volume and the high setpoint - for educational purposes. It certainly wont hurt and my buddy will be stressed for the whole dive

.

Funnily enough I did a manual setpoint ascent the day before which served as a learning experience (namely that I really like the benefits of an electronically controlled CCR) but also it was surprising to learn about the extent and duration of a quick o2 squirt and how it was affected by depth.

Has something similar happened to anyone in this forum? What do other people think of this and what skills/knowledge have you sought to attain. Is it a MOD 3 task to conduct a manual o2 ascent to get an appreciation of the ability of extending a semiclosed bailout..?? (in the shallows only). Obviously one should never need to, but for the sake of argument lets assume one might need to do it “blind”… or just because it serves to heighten the appreciation of what is a very variable tool.

What I’m saying is a squirt or two at say <20ish metres and dumping every 8th or 12th breath (I haven’t tested the numbers yet – but would be interested to learn of others experience).

BTW if I wanted a flaming I would have put this on the Inspiration List

Mdemon · 21st March 2005, 17:44

Sounds like you had some fun there!

Glad you made it out in one piece. Had a low bat alarm yesterday but it worked as it should have.

Your post makes me think that some "blind" ascent practice might be a good idea...

Devils is a great dive - what are the tides like this week? Might be up for a night dive...

pchanning · 21st March 2005, 18:08

[quote=Mdemon] ...your post makes me think that some "blind" ascent practice might be a good idea...

errr... thats not quite what I meant. A "blind" ascent is definately a bad idea... even for a Crash Test Dummy

Only joking.

Careful how you quote things m8, some people might think youre nuts

cheers

paul

Mdemon · 21st March 2005, 20:19

LOL! I meant doing it as if blind but buddy/me keeping an eye on the handsets...

[quote=Mr. Greekbird]

Quote: (Originally Posted by Mdemon)

...your post makes me think that some "blind" ascent practice might be a good idea...

errr... thats not quite what I meant. A "blind" ascent is definately a bad idea... even for a Crash Test Dummy

Only joking.

Careful how you quote things m8, some people might think youre nuts

cheers

paul

Mark Chase · 22nd March 2005, 08:43

Strangely I got back after a weeks diving in Egypt and I did a full kit check. Turned on the master and its battery was so low it couldn’t click the solenoid. Turned on the slave and it said low battery no dive??

I had put in two brand new batteries before the trip and there was no low bat warning on the last dive.

My conclusion was its better to use the slave to master and fresh batteries in the slave system rather than swap them both at the same time. This helps avoid the duff batteries issues and ensures that the slave will have plenty more than the master.

ATB

Mark Chase

pchanning · 22nd March 2005, 14:06

Quote: (Originally Posted by Mark Chase)

Strangely I got back after a weeks diving in Egypt and I did a full kit check. Turned on the master and its battery was so low it couldn’t click the solenoid. Turned on the slave and it said low battery no dive??

I had put in two brand new batteries before the trip and there was no low bat warning on the last dive.

My conclusion was its better to use the slave to master and fresh batteries in the slave system rather than swap them both at the same time. This helps avoid the duff batteries issues and ensures that the slave will have plenty more than the master.

ATB

Mark Chase

thanks mark,

I still dont understand how when one uses the same handset as master all the time one should learn that the slave hasn't got any juice (considering the 75/25 power split deal).

Maybe my head needs a service, though it was done in August. Maybe, I left a handset on after a dive, Maybe I just had a duff battery, I'll check the List archives I seem to remember losts of banter on the subject. Who knows, and how can I check..??

Anyway, what do people think about a semi-closed ascent / o2 top-up..??

I've got mixed responses so far. Some say:

" Oooohh, its not in the MOD 3 training, so it cant be a good idea... can it..??"

...

I'm not so sure,( someone please correct me if i'm wrong ), but a slow ascent with stops say every 3m (V-Planner etc) and flushing every so often will not lower the ppo2 sufficiently on an air Dil to go hypoxic. Figure a little to progressively more o2 top-up in the shallows (test drills with handsets required - john

) and the math appears to be fine. I haven't tried it but it doesn't appear to be that difficult..?? After all, theres no more task loading than descending without an ADV and having to clear ears, sort the suit, watch handsets, wheres my buddy, bump into something, turn on the torch, switch to high setpoint, etc, etc..

So whats all the fuss about, have I missed something (apart from the sphincter factor of course

)

I fact, within sports limits (40m) so long as you know you had at least 1 bar ppo2 in the loop one could surface without breaching a normoxic loop, let alone hypoxic..!!

I'd be grateful for any thoughts.

cheers

paul

Mdemon · 22nd March 2005, 15:02

In the absence of anyone else posting, I seem to remember DrMike putting up a trip report where his instructor made him run the unit (Mk15?) blind for over an hour IIRC.

I also think Padowan has done some work on SCR for the Inspo. Might be worth PMing him for his results.

At the end of the day, if you can justify the need for the technique (e.g. to cope with handset failure and a problem with full OC bailout) then it's worth investigating further...

Andy M · 22nd March 2005, 15:15

Quote: (Originally Posted by Mr. Greekbird)

Anyway, what do people think about a semi-closed ascent / o2 top-up..??

I've got mixed responses so far. Some say:

" Oooohh, its not in the MOD 3 training, so it cant be a good idea... can it..??"

...

Umm, this was covered in my Mod 1 course and practiced in the water!

In the event of total electronics failure, you should make your way back to the shot, by using minimum loop volume technique as you feel the CL getting smaller while O2 is consumed, you squirt more O2 into the CL. I pretended total electronics failure and kiss valve freeflow i.e. hold kiss valve open and twiddle O2 supply knob to add O2 manually. It was difficult but not impossible. pO2 went up to 1.55 at the most on the first go (if you overshoot you can dil flush). I did this for 10 mins and will be practising it more.

When reaching bottom of shot, ascend, breathing out through your nose every fourth breath (i.e. SCR mode ascent). This was practised and it worked fine.

When reaching 6m, do O2 flush, any stops necessary and ascend to surface.

Padowan · 22nd March 2005, 17:31

Quote: (Originally Posted by Mdemon)

In the absence of anyone else posting, I seem to remember DrMike putting up a trip report where his instructor made him run the unit (Mk15?) blind for over an hour IIRC.

I also think Padowan has done some work on SCR for the Inspo. Might be worth PMing him for his results.

At the end of the day, if you can justify the need for the technique (e.g. to cope with handset failure and a problem with full OC bailout) then it's worth investigating further...

I've done some theoretical modelling of a unit in SCR operation, and also practiced the skills in the water to compare, and the results correlate pretty well. I've got a spreadsheet where you can pump in your loop volume, tidal breathing volume, diluent gas, breathe recycle strategy and depth and it'll graph the (theoretical) PO2 drop off over time and show you approximately the PO2 that the unit will stabilise at.

You mention, Mr G.B. about a 8:1 or 12:1 breath strategy, and yeah, you can do this, and maintain a breathable PO2, from a certain depth, assuming a certain %O2 in the dil, but the downside, it that if you cut the SCR operation to the line and work out how you can maximise the duration you can get out of the gas, breathing it down to perhaps a 0.2bar PO2 you may get ages out of the gas, but you're gonna be in the water a long time due to the deco you'll incurr breathing such a crap mix. So at the end of the day it's a bit of a trade off between what mix you want to be breathing and how long you need to spend in the water, more of one = less of the other, and vice versa.

If anyone wants the spreadsheet, PM me and I'll send it on.... (unless there's a documents posting section on the forum I don't know about....)

The model I've got is a steady state model, so it's for constant depth. Doing SCR ascents mean you need to constantly be adjusting your breath recycle strategy in order to maintain a breathable gas... for example at 10m, if you do a 8:1 strategy using air dil, you'll probably pass out after about 10 minutes, assuming you started with the loop at 1.3bar. The lower the FO2 of the dil, the more dramatic it gets - if you've got 16/25 which is not quite hypoxic on the surface, will become hypoxic if you do more than about 4:1 at 10m....

Best thing is to practice this stuff in benign conditions, using the handsets to cross check your predictions (and I would advocate predicting the behaviour first, because if you can work out the mechanics of what's happening before hand, you are more empowered in the water to apply this knowledge during a culsterf*ck)

Worked out I can add an attachment - my model is attached for your use, entertainment and

flaming. By the way, I do get out and dive too, I'm not just a key-tapper - that's just my day job, and writing Rebreather models is a lot more fun than what I should be doing!!!!!

pchanning · 22nd March 2005, 19:14

Quote: (Originally Posted by Padowan)

I've done some theoretical modelling of a unit in SCR operation, and also practiced the skills in the water to compare, and the results correlate pretty well. I've got a spreadsheet where you can pump in your loop volume, tidal breathing volume, diluent gas, breathe recycle strategy and depth and it'll graph the (theoretical) PO2 drop off over time and show you approximately the PO2 that the unit will stabilise at.

You mention, Mr G.B. about a 8:1 or 12:1 breath strategy, and yeah, you can do this, and maintain a breathable PO2, from a certain depth, assuming a certain %O2 in the dil, but the downside, it that if you cut the SCR operation to the line and work out how you can maximise the duration you can get out of the gas, breathing it down to perhaps a 0.2bar PO2 you may get ages out of the gas, but you're gonna be in the water a long time due to the deco you'll incurr breathing such a crap mix. So at the end of the day it's a bit of a trade off between what mix you want to be breathing and how long you need to spend in the water, more of one = less of the other, and vice versa.

Too be honest what i'm thinking off is a little more modest. Simply being able to utilise a 3litre as a 12 or more to get me back up to my exit point (which in the case on Sunday was a considerable distance from where the handset died) whilst continuing the dive, ie: not terminating it and ascending open circuit as my Training Agency would have it. (I wont tell you who they are as Mrs. Padowan will start....

) But thanks to her I know all about current limiting

Anyway, the "enough open circuit gas at all times" (or at least for the diving i'm doing) principle is fine, but the problem I have is the shore dives I haunt here in Plymouth can lead one quite a way away from the exit point. Which means surfacing in a shipping channel that can have frigates, ferries, subs and god knows what bounding up and down it, not to mention a current which, in certain places, I would defy anyone in full kit to swim against.
So the "all yeah, a pony is enough to get you up" is fine and that maybe so, its the getting back that is the problem. and with characters in the diving community round here being what they are, i'd get ripped to bits: "...look-out here comes breakwater paul..." etc.

Nah, youre alright m8.
The dives also entail one hell of a walk when wrapped up in a dry bag and having to carry 70kg. I dont wanna sound lazy, just realistic.

So, if I know whats going on from practicing, i'm gonna be better equipped to chase the bottom and ascend back up semi-closed.

If anyone wants the spreadsheet, PM me and I'll send it on.... (unless there's a documents posting section on the forum I don't know about....)

The model I've got is a steady state model, so it's for constant depth. Doing SCR ascents mean you need to constantly be adjusting your breath recycle strategy in order to maintain a breathable gas... for example at 10m, if you do a 8:1 strategy using air dil, you'll probably pass out after about 10 minutes...

Why would you last 10 minutes..?? The gas is either hypoxic or not. Would the onset be as protracted as that? I'm assuming that you would flush the loop as best you could (depressing the counterlungs and all)

I was talking about giving it a little squirt of o2 for say... every cycle (at this depth), to make-up the metabolic consumption and put the gas pressure in the safety zone. How does that figure with you..??

Having lowered the pp02 for the ascent I appreciate ones deco might then be a bit shit, but the pp02 will be better than air. Which is what I'm talking about carrying as it needs to be breathable at 50m and I dont fancy a hot mix when I'm sphinctered-up..!!

As i'm running a Vytec at the mo, accelerated deco is still poss and i'd just keep it on air for the ascent. (i've got CC and accelerated OC tables on the back of the handsets as well). What do you think..??

...assuming you started with the loop at 1.3bar. The lower the FO2 of the dil, the more dramatic it gets - if you've got 16/25 which is not quite hypoxic on the surface, will become hypoxic if you do more than about 4:1 at 10m....

Best thing is to practice this stuff in benign conditions, using the handsets to cross check your predictions (and I would advocate predicting the behaviour first, because if you can work out the mechanics of what's happening before hand, you are more empowered in the water to apply this knowledge during a culsterf*ck)

Also, it would be interesting to see how ones predictions bared-up for real. I can imagine that in the shallows it would be harder to control the ppo2 - as at depth its not going to vary too much in 4, 8 or maybe even 12 breaths due to the density. And of course above 6m would be easy. I'm thinking that between 20 and 6m would be the tricky/dangerous part. Would youre findings concurr with that..?? I know, i'll shut up and play with your programme, cheers

Worked out I can add an attachment - my model is attached for your use, entertainment and

flaming. By the way, I do get out and dive too, I'm not just a key-tapper - that's just my day job, and writing Rebreather models is a lot more fun than what I should be doing!!!!!

damn...you beat me too it

Quote: (Originally Posted by Andy M)

"

Quote: (Originally Posted by Andy M)

When reaching bottom of shot, ascend, breathing out through your nose every fourth breath (i.e. SCR mode ascent). This was practised and it worked fine.

When reaching 6m, do O2 flush, any stops necessary and ascend to surface.

Quote: (Originally Posted by Andy M)

!!!!!

Exactly

Do any Inspiration Training Agencies teach this, or is it just a KISS thing..??

Wheres Ammers..??

cheers

paul

21st March 2005, 17:36	#1 (permalink)
pchanning PFO free :) Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: fixed! Posts: 454	TOTAL ELECTRONIC FAILURE…well… nearly... What a cracker of a weekend we had in Plymouth. Not a hint of fog (unlike the rest of the country ) just clear warm skies as I slipped into one of Plymouths’ best Shore Dives; Devils Point. Had a hugely enjoyable descent freefalling off the wall on the edge of the viz just loving it. Its dives like this that postpone holiday urges. That is until my breather decides to play-up... At 43m after a good birthday night-out and whilst studying a nudibrach of a type that I hadn’t seen before, I was soberly informed of a double-beep and a flickering blank display. I switched to the other to see it had become the master and I promptly did a dil flush to satisfy myself of the readings. The dysfunctional handset didn’t have enough juice to even turn itself on as the Slave. That is until after about 5 minutes, which was curious. Rattled, but not overly concerned, as the conditions were nice and easy, I carried on and finished a lovely dive. Here comes the twist… apon surfacing I was gasping a load of o2 in preparation for the ‘Iron Man’ walk back up over an intimidating hill (I love post-piss-up dives ) where I was surprised to learn that the supposedly good handset displayed Low-Battery..!! Which, for the benefit of non-Inspiration divers, is not supposed to happen, at least for a long time yet. Normally after what should be plenty of notification beeps the other handset will take over… but not in this case..!! I had 12 hours on the clock and I changed the batteries together. I acknowledge that inserting two new ‘duff’ batteries could well lead to this sort of situation but that is likely to be in the first dive – (ie: two totally stuffed batteries) as the operational current drain of Master and Slave is something like 75/25% IIRC. So extended use on one (ie: one dive) would render the other to be fit for another like dive. I’ve read that some divers check they’re batteries either operationally or with a multimeter before undergoing a dive that figures extended deco but who really does that… anyone…?? As I said the conditions were excellent so it wouldn’t have been so bad to lose both handsets in such a situation. I had a full Dil cylinder that would have comfortably carried me semi-closed for the rest of the dive back up to o2 rebreather depth. However, I can imagine that performing the same whilst coming up an SMB in black mid-water with a large deco penalty would make for a very different experience. Consequently, I’m thinking of running my usual dives and manually maintaining both volume and the high setpoint - for educational purposes. It certainly wont hurt and my buddy will be stressed for the whole dive . Funnily enough I did a manual setpoint ascent the day before which served as a learning experience (namely that I really like the benefits of an electronically controlled CCR) but also it was surprising to learn about the extent and duration of a quick o2 squirt and how it was affected by depth. Has something similar happened to anyone in this forum? What do other people think of this and what skills/knowledge have you sought to attain. Is it a MOD 3 task to conduct a manual o2 ascent to get an appreciation of the ability of extending a semiclosed bailout..?? (in the shallows only). Obviously one should never need to, but for the sake of argument lets assume one might need to do it “blind”… or just because it serves to heighten the appreciation of what is a very variable tool. What I’m saying is a squirt or two at say <20ish metres and dumping every 8th or 12th breath (I haven’t tested the numbers yet – but would be interested to learn of others experience). BTW if I wanted a flaming I would have put this on the Inspiration List
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21st March 2005, 17:44	#2 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,946	Sounds like you had some fun there! Glad you made it out in one piece. Had a low bat alarm yesterday but it worked as it should have. Your post makes me think that some "blind" ascent practice might be a good idea... Devils is a great dive - what are the tides like this week? Might be up for a night dive... __________________ www.southwestmafia.com "small minds talk about people, Average Minds Talk About Events, GREAT MINDS TALK ABOUT IDEAS!" The WRONG Attitude will get you killed. "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"
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21st March 2005, 18:08	#3 (permalink)
pchanning PFO free :) Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: fixed! Posts: 454	[quote=Mdemon] ...your post makes me think that some "blind" ascent practice might be a good idea... errr... thats not quite what I meant. A "blind" ascent is definately a bad idea... even for a Crash Test Dummy Only joking. Careful how you quote things m8, some people might think youre nuts cheers paul
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21st March 2005, 20:19	#4 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,946	LOL! I meant doing it as if blind but buddy/me keeping an eye on the handsets... [quote=Mr. Greekbird] Quote: (Originally Posted by Mdemon) ...your post makes me think that some "blind" ascent practice might be a good idea... errr... thats not quite what I meant. A "blind" ascent is definately a bad idea... even for a Crash Test Dummy Only joking. Careful how you quote things m8, some people might think youre nuts cheers paul __________________ www.southwestmafia.com "small minds talk about people, Average Minds Talk About Events, GREAT MINDS TALK ABOUT IDEAS!" The WRONG Attitude will get you killed. "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"
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22nd March 2005, 08:43	#5 (permalink)
Mark Chase RBW Member Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,868	Strangely I got back after a weeks diving in Egypt and I did a full kit check. Turned on the master and its battery was so low it couldn’t click the solenoid. Turned on the slave and it said low battery no dive?? I had put in two brand new batteries before the trip and there was no low bat warning on the last dive. My conclusion was its better to use the slave to master and fresh batteries in the slave system rather than swap them both at the same time. This helps avoid the duff batteries issues and ensures that the slave will have plenty more than the master. ATB Mark Chase __________________ See my "Doing It Chasey" video where I'm locked into a padded room, naked, with two ball bearings and within an Hour, I manage to lose one and break the other!!! Kevin Juergensen 16/11/08 [/quote]
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22nd March 2005, 14:06	#6 (permalink)
pchanning PFO free :) Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: fixed! Posts: 454	Quote: (Originally Posted by Mark Chase) Strangely I got back after a weeks diving in Egypt and I did a full kit check. Turned on the master and its battery was so low it couldn’t click the solenoid. Turned on the slave and it said low battery no dive?? I had put in two brand new batteries before the trip and there was no low bat warning on the last dive. My conclusion was its better to use the slave to master and fresh batteries in the slave system rather than swap them both at the same time. This helps avoid the duff batteries issues and ensures that the slave will have plenty more than the master. ATB Mark Chase thanks mark, I still dont understand how when one uses the same handset as master all the time one should learn that the slave hasn't got any juice (considering the 75/25 power split deal). Maybe my head needs a service, though it was done in August. Maybe, I left a handset on after a dive, Maybe I just had a duff battery, I'll check the List archives I seem to remember losts of banter on the subject. Who knows, and how can I check..?? Anyway, what do people think about a semi-closed ascent / o2 top-up..?? I've got mixed responses so far. Some say: " Oooohh, its not in the MOD 3 training, so it cant be a good idea... can it..??" ... I'm not so sure,( someone please correct me if i'm wrong ), but a slow ascent with stops say every 3m (V-Planner etc) and flushing every so often will not lower the ppo2 sufficiently on an air Dil to go hypoxic. Figure a little to progressively more o2 top-up in the shallows (test drills with handsets required - john ) and the math appears to be fine. I haven't tried it but it doesn't appear to be that difficult..?? After all, theres no more task loading than descending without an ADV and having to clear ears, sort the suit, watch handsets, wheres my buddy, bump into something, turn on the torch, switch to high setpoint, etc, etc.. So whats all the fuss about, have I missed something (apart from the sphincter factor of course ) I fact, within sports limits (40m) so long as you know you had at least 1 bar ppo2 in the loop one could surface without breaching a normoxic loop, let alone hypoxic..!! I'd be grateful for any thoughts. cheers paul
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22nd March 2005, 15:02	#7 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,946	Anyone seen my helmet? It's got a nice black and yellow pattern on it... ;) In the absence of anyone else posting, I seem to remember DrMike putting up a trip report where his instructor made him run the unit (Mk15?) blind for over an hour IIRC. I also think Padowan has done some work on SCR for the Inspo. Might be worth PMing him for his results. At the end of the day, if you can justify the need for the technique (e.g. to cope with handset failure and a problem with full OC bailout) then it's worth investigating further... __________________ www.southwestmafia.com "small minds talk about people, Average Minds Talk About Events, GREAT MINDS TALK ABOUT IDEAS!" The WRONG Attitude will get you killed. "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"
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22nd March 2005, 15:15	#8 (permalink)
Andy M Dude Current Rebreather/s: Home Build Other Rebreather/s: Sport Kiss Home Build Join Date: Mar 2005 Location: Cambridge, UK Posts: 428	Quote: (Originally Posted by Mr. Greekbird) Anyway, what do people think about a semi-closed ascent / o2 top-up..?? I've got mixed responses so far. Some say: " Oooohh, its not in the MOD 3 training, so it cant be a good idea... can it..??" ... Umm, this was covered in my Mod 1 course and practiced in the water! In the event of total electronics failure, you should make your way back to the shot, by using minimum loop volume technique as you feel the CL getting smaller while O2 is consumed, you squirt more O2 into the CL. I pretended total electronics failure and kiss valve freeflow i.e. hold kiss valve open and twiddle O2 supply knob to add O2 manually. It was difficult but not impossible. pO2 went up to 1.55 at the most on the first go (if you overshoot you can dil flush). I did this for 10 mins and will be practising it more. When reaching bottom of shot, ascend, breathing out through your nose every fourth breath (i.e. SCR mode ascent). This was practised and it worked fine. When reaching 6m, do O2 flush, any stops necessary and ascend to surface.
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22nd March 2005, 19:14	#10 (permalink)
pchanning PFO free :) Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: fixed! Posts: 454	Quote: (Originally Posted by Padowan) I've done some theoretical modelling of a unit in SCR operation, and also practiced the skills in the water to compare, and the results correlate pretty well. I've got a spreadsheet where you can pump in your loop volume, tidal breathing volume, diluent gas, breathe recycle strategy and depth and it'll graph the (theoretical) PO2 drop off over time and show you approximately the PO2 that the unit will stabilise at. You mention, Mr G.B. about a 8:1 or 12:1 breath strategy, and yeah, you can do this, and maintain a breathable PO2, from a certain depth, assuming a certain %O2 in the dil, but the downside, it that if you cut the SCR operation to the line and work out how you can maximise the duration you can get out of the gas, breathing it down to perhaps a 0.2bar PO2 you may get ages out of the gas, but you're gonna be in the water a long time due to the deco you'll incurr breathing such a crap mix. So at the end of the day it's a bit of a trade off between what mix you want to be breathing and how long you need to spend in the water, more of one = less of the other, and vice versa. Too be honest what i'm thinking off is a little more modest. Simply being able to utilise a 3litre as a 12 or more to get me back up to my exit point (which in the case on Sunday was a considerable distance from where the handset died) whilst continuing the dive, ie: not terminating it and ascending open circuit as my Training Agency would have it. (I wont tell you who they are as Mrs. Padowan will start.... ) But thanks to her I know all about current limiting Anyway, the "enough open circuit gas at all times" (or at least for the diving i'm doing) principle is fine, but the problem I have is the shore dives I haunt here in Plymouth can lead one quite a way away from the exit point. Which means surfacing in a shipping channel that can have frigates, ferries, subs and god knows what bounding up and down it, not to mention a current which, in certain places, I would defy anyone in full kit to swim against. So the "all yeah, a pony is enough to get you up" is fine and that maybe so, its the getting back that is the problem. and with characters in the diving community round here being what they are, i'd get ripped to bits: "...look-out here comes breakwater paul..." etc. Nah, youre alright m8. The dives also entail one hell of a walk when wrapped up in a dry bag and having to carry 70kg. I dont wanna sound lazy, just realistic. So, if I know whats going on from practicing, i'm gonna be better equipped to chase the bottom and ascend back up semi-closed. If anyone wants the spreadsheet, PM me and I'll send it on.... (unless there's a documents posting section on the forum I don't know about....) The model I've got is a steady state model, so it's for constant depth. Doing SCR ascents mean you need to constantly be adjusting your breath recycle strategy in order to maintain a breathable gas... for example at 10m, if you do a 8:1 strategy using air dil, you'll probably pass out after about 10 minutes... Why would you last 10 minutes..?? The gas is either hypoxic or not. Would the onset be as protracted as that? I'm assuming that you would flush the loop as best you could (depressing the counterlungs and all) I was talking about giving it a little squirt of o2 for say... every cycle (at this depth), to make-up the metabolic consumption and put the gas pressure in the safety zone. How does that figure with you..?? Having lowered the pp02 for the ascent I appreciate ones deco might then be a bit shit, but the pp02 will be better than air. Which is what I'm talking about carrying as it needs to be breathable at 50m and I dont fancy a hot mix when I'm sphinctered-up..!! As i'm running a Vytec at the mo, accelerated deco is still poss and i'd just keep it on air for the ascent. (i've got CC and accelerated OC tables on the back of the handsets as well). What do you think..?? ...assuming you started with the loop at 1.3bar. The lower the FO2 of the dil, the more dramatic it gets - if you've got 16/25 which is not quite hypoxic on the surface, will become hypoxic if you do more than about 4:1 at 10m.... Best thing is to practice this stuff in benign conditions, using the handsets to cross check your predictions (and I would advocate predicting the behaviour first, because if you can work out the mechanics of what's happening before hand, you are more empowered in the water to apply this knowledge during a culsterfck) Also, it would be interesting to see how ones predictions bared-up for real. I can imagine that in the shallows it would be harder to control the ppo2 - as at depth its not going to vary too much in 4, 8 or maybe even 12 breaths due to the density. And of course above 6m would be easy. I'm thinking that between 20 and 6m would be the tricky/dangerous part. Would youre findings concurr with that..?? I know, i'll shut up and play with your programme, cheers Worked out I can add an attachment - my model is attached for your use, entertainment and flaming. By the way, I do get out and dive too, I'm not just a key-tapper - that's just my day job, and writing Rebreather models is a lot more fun than what I should be doing!!!!! damn...you beat me too it Quote:* (Originally Posted by Andy M) " Quote: (Originally Posted by Andy M) When reaching bottom of shot, ascend, breathing out through your nose every fourth breath (i.e. SCR mode ascent). This was practised and it worked fine. When reaching 6m, do O2 flush, any stops necessary and ascend to surface. Quote: (Originally Posted by Andy M) !!!!! Exactly Do any Inspiration Training Agencies teach this, or is it just a KISS thing..?? Wheres Ammers..?? cheers paul
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