A guide about setpoint selection for deep dives

divetheworld · 18th April 2006, 15:09

Quote: (Originally Posted by Genesis)

You will have to be actively involved by doing a partial diluent flush; this, and the buoyancy shift, mean that it has to be prompted and not automatic.

Perhaps a simple annunciator would suffice?

Genesis · 18th April 2006, 15:17

It could just switch but I'm not sure people would like that due to the shift in buoyancy that will come along with the changeover.

Also, since dropping the PO2 takes quite some time if you just breathe it down it would seem to be better to prompt for it and request the diver to do at least one or two "nose-exhale" flushes of the loop and replacement with DIL to help things along once the change has been confirmed.

divetheworld · 18th April 2006, 16:01

Quote: (Originally Posted by Genesis)

It could just switch but I'm not sure people would like that due to the shift in buoyancy that will come along with the changeover.

Also, since dropping the PO2 takes quite some time if you just breathe it down it would seem to be better to prompt for it and request the diver to do at least one or two "nose-exhale" flushes of the loop and replacement with DIL to help things along once the change has been confirmed.

No, I meant prompt. As in "Air break Y/N"
Then let the user decide.
Grammar is shite today, sorry.

Brent

AD_ward9 · 18th April 2006, 16:48

Quote: (Originally Posted by dave t)

how will you get the loop down on the airbreak? bearing in mind it a four min break. If I am running 1.3 at my stop and I switch to low setpoint (0.7) it takes me 7-8 mins to breathe it there!

What is the problem with that?

Just breathing it down, you get credit for whatever the PPO2 is. It stays there until you have 5% CNS margin, then puts you back up. This way you always stay off the limit.

By limit, I refer to the accelerated CNS limit caused by the PPO2 margin in the calculation, not the normal CNS limit, 75% of which would cause around 1% of divers to have hits.

Alex

dave t · 18th April 2006, 17:00

theres nothing wrong with that, it just wont fit the 12/4 airbreak schedule Genesis was talking about

**UWSojourner** · 18th April 2006, 17:57

Good article. Thanks for the effort.

Just for perspective ...

A 33 minute dive to 300ft @ setpoint of 1.2 - RGBM has you surface at 178 minutes.

However, a 30 minute dive to 300ft @ setpoint of 1.0 with switch to 1.2 at 100ft results in a runtime of 177 minutes. Looking at it this way, you only lose 3 minutes (of bottom time) to implement the strategy.

Seems like it might be worth the additional safety margin to me. If someone insisted on the full bottom time, then it would be interesting to consider whether it would be safer to run a lower PO2 and decrease the safety factor in the deco schedule. Moving from a +1 conservatism setting to a +0 setting wipes out the time difference. Tradeoffs ...

GAP RGBM run at 10/50 on +1 conservatism.

AD_ward9 · 18th April 2006, 18:22

Quote: (Originally Posted by dave t)

theres nothing wrong with that, it just wont fit the 12/4 airbreak schedule Genesis was talking about

Ah, OK. But, if the system did it automatically Genesis's idea would work. For example, going to 90% of an accelerated CNS limit, then the system stops injecting O2 and tells the user it is an "air break", until the PPO2 is down to 0.4 or the CNS limit is down to 85%.

Alex

Mdemon · 18th April 2006, 18:29

1.3 seems to have been used quite happily up until now.
The Manufacturer recommends 1.3 on the Inspo.
Keeping the O2 lower on the deep dives means the He is increased, so you have less margin for error on your stops.

IIRC, the NOAA limits were "guesstimates", so OC/CC is irrelevant - 1.3/4 was chosen as a suitable PO2 for a working dive, 1.6 for deco, so where is the need to drop that still further to 1.0/1? How can little old ladies merrily endure PO2s of 2.4/8 in the chamber without bouncing off the walls? And divers treated for 7.5 hours on 50/50 heliox to the same PO2, likewise? Mainly because they're told to sit still and therefore the CO2 is kept low.

Not convinced.

***ScubaDadMiami*** · 18th April 2006, 18:36

Quote: (Originally Posted by Mdemon)

1.3 seems to have been used quite happily up until now.
The Manufacturer recommends 1.3 on the Inspo.
Keeping the O2 lower on the deep dives means the He is increased, so you have less margin for error on your stops.

IIRC, the NOAA limits were "guesstimates", so OC/CC is irrelevant - 1.3/4 was chosen as a suitable PO2 for a working dive, 1.6 for deco, so where is the need to drop that still further to 1.0/1? How can little old ladies merrily endure PO2s of 2.4/8 in the chamber without bouncing off the walls? And divers treated for 7.5 hours on 50/50 heliox to the same PO2, likewise? Mainly because they're told to sit still and therefore the CO2 is kept low.

Not convinced.

Though it's not fully understood, there is a difference between being wet and dry even if the subject is relaxed under both circumstances.

We don't know everything there is to know. So, since we don't, I don't see why erring on the side of being somewhat overly cautious is a problem. If we are too aggressive, the down side to that is a lot worse than spending a few extra minutes doing deco.

Drmike · 18th April 2006, 18:47

Quote: (Originally Posted by dave t)

yes, as we all know there are a couple of phases of the convulsion, the first is to spasm the muscles including the ones in the throat which will probably close off the airways trapping gas in the divers lung. If you were to lift the diver at this stage the likelyhood of a burst lung is certain.
I had to wait until the second phase where the diver relaxes before I could take him to the surface. Now this all happens very quickly and the only indication I got of the second phase was to see gas escaping from the divers mouth, I held his head in a sort of neck exstension and waited (a few seconds) had the diver been wearing a FFM I would not have been able to see the gas and tell when it was safe to lift him. Sure he wouldnt drown, he would just die of an embolism. On the surface it was nesacary to give AV a FFM may have hindered the need for very quick acsess to oral/nasal passages. Anyone who thinks that the convusion is over quickly is mistaken, once back on the boat the diver took at least 45mins before beginning to regain consiousnes.

I was scared to hell,missed 35mins of deco but it all turned out ok, I didnt get bent he made a full recovery

Dave I think this is very dodgy and potentialy dangerous advice.

Anyone wearing a ffm with a Rebreather should have a BOV fitted to it. Not to doesnt make any sense at all.

If they convulse you just wait until they stop then turn the BOV to OC.
You will see bubbles from the OC exhaust when/if they start breathing.

Letting someone drown as a way to tell there airway is open enough to allow a 'safe' ascent is lunacy IMO. FFM+BOV.

18th April 2006, 15:09	#41 (permalink)
divetheworld Dive porn pimp Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Classic Kiss Other CCR Join Date: Mar 2005 Location: Leeds, England Posts: 1,586	Re: A guide about setpoint selection for deep dives Quote: (Originally Posted by Genesis) You will have to be actively involved by doing a partial diluent flush; this, and the buoyancy shift, mean that it has to be prompted and not automatic. Perhaps a simple annunciator would suffice? __________________ Attitude and self praise is no reccomendation. Dont try to be a great man, just be a man and let history be the judge of you. CHECK OUT OUR INTERWEBS FOR CUSTOM REBREATHER UPGRADES *WWW.NARKEDAT90.CO.UK* *http://www.grpservices.com/pursuit/* Supporting Shearwater Research Products in Europe
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18th April 2006, 15:17	#42 (permalink)
Genesis Bubbless Box of Death Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Oct 2005 Location: Sunny Florida Posts: 1,395	Re: A guide about setpoint selection for deep dives It could just switch but I'm not sure people would like that due to the shift in buoyancy that will come along with the changeover. Also, since dropping the PO2 takes quite some time if you just breathe it down it would seem to be better to prompt for it and request the diver to do at least one or two "nose-exhale" flushes of the loop and replacement with DIL to help things along once the change has been confirmed. __________________ "A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American." http://www.denninger.net http://www.diversunion.org/liability.htm - Fix the Diving Cert racket
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18th April 2006, 16:01	#43 (permalink)
divetheworld Dive porn pimp Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Classic Kiss Other CCR Join Date: Mar 2005 Location: Leeds, England Posts: 1,586	Re: A guide about setpoint selection for deep dives Quote: (Originally Posted by Genesis) It could just switch but I'm not sure people would like that due to the shift in buoyancy that will come along with the changeover. Also, since dropping the PO2 takes quite some time if you just breathe it down it would seem to be better to prompt for it and request the diver to do at least one or two "nose-exhale" flushes of the loop and replacement with DIL to help things along once the change has been confirmed. No, I meant prompt. As in "Air break Y/N" Then let the user decide. Grammar is shite today, sorry. Brent __________________ Attitude and self praise is no reccomendation. Dont try to be a great man, just be a man and let history be the judge of you. CHECK OUT OUR INTERWEBS FOR CUSTOM REBREATHER UPGRADES *WWW.NARKEDAT90.CO.UK* *http://www.grpservices.com/pursuit/* Supporting Shearwater Research Products in Europe
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18th April 2006, 16:48	#44 (permalink)
AD_ward9 So much more to learn Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 1,862	Re: A guide about setpoint selection for deep dives Quote: (Originally Posted by dave t) how will you get the loop down on the airbreak? bearing in mind it a four min break. If I am running 1.3 at my stop and I switch to low setpoint (0.7) it takes me 7-8 mins to breathe it there! What is the problem with that? Just breathing it down, you get credit for whatever the PPO2 is. It stays there until you have 5% CNS margin, then puts you back up. This way you always stay off the limit. By limit, I refer to the accelerated CNS limit caused by the PPO2 margin in the calculation, not the normal CNS limit, 75% of which would cause around 1% of divers to have hits. Alex
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18th April 2006, 17:00	#45 (permalink)
dave t Custom Title Allowed! Current Rebreather/s: Inspiration Classic Inspiration Vision Evolution Sport Kiss Classic Kiss Dolphin Ray Azimuth Home Build Other Rebreather/s: Dolphin Ray Azimuth Home Build Join Date: May 2005 Location: UK Posts: 654	Re: A guide about setpoint selection for deep dives theres nothing wrong with that, it just wont fit the 12/4 airbreak schedule Genesis was talking about
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18th April 2006, 17:57	#46 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 556	Re: A guide about setpoint selection for deep dives Good article. Thanks for the effort. Just for perspective ... A 33 minute dive to 300ft @ setpoint of 1.2 - RGBM has you surface at 178 minutes. However, a 30 minute dive to 300ft @ setpoint of 1.0 with switch to 1.2 at 100ft results in a runtime of 177 minutes. Looking at it this way, *you only lose 3 minutes* (of bottom time) to implement the strategy. Seems like it might be worth the additional safety margin to me. If someone insisted on the full bottom time, then it would be interesting to consider whether it would be safer to run a lower PO2 and decrease the safety factor in the deco schedule. Moving from a +1 conservatism setting to a +0 setting wipes out the time difference. Tradeoffs ... GAP RGBM run at 10/50 on +1 conservatism.
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18th April 2006, 18:22	#47 (permalink)
AD_ward9 So much more to learn Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 1,862	Re: A guide about setpoint selection for deep dives Quote: (Originally Posted by dave t) theres nothing wrong with that, it just wont fit the 12/4 airbreak schedule Genesis was talking about Ah, OK. But, if the system did it automatically Genesis's idea would work. For example, going to 90% of an accelerated CNS limit, then the system stops injecting O2 and tells the user it is an "air break", until the PPO2 is down to 0.4 or the CNS limit is down to 85%. Alex
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18th April 2006, 18:29	#48 (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: 1,927	Re: A guide about setpoint selection for deep dives 1.3 seems to have been used quite happily up until now. The Manufacturer recommends 1.3 on the Inspo. Keeping the O2 lower on the deep dives means the He is increased, so you have less margin for error on your stops. IIRC, the NOAA limits were "guesstimates", so OC/CC is irrelevant - 1.3/4 was chosen as a suitable PO2 for a working dive, 1.6 for deco, so where is the need to drop that still further to 1.0/1? How can little old ladies merrily endure PO2s of 2.4/8 in the chamber without bouncing off the walls? And divers treated for 7.5 hours on 50/50 heliox to the same PO2, likewise? Mainly because they're told to sit still and therefore the CO2 is kept low. Not convinced. __________________ 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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18th April 2006, 18:36	#49 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 2,130	Re: A guide about setpoint selection for deep dives Quote: (Originally Posted by Mdemon) 1.3 seems to have been used quite happily up until now. The Manufacturer recommends 1.3 on the Inspo. Keeping the O2 lower on the deep dives means the He is increased, so you have less margin for error on your stops. IIRC, the NOAA limits were "guesstimates", so OC/CC is irrelevant - 1.3/4 was chosen as a suitable PO2 for a working dive, 1.6 for deco, so where is the need to drop that still further to 1.0/1? How can little old ladies merrily endure PO2s of 2.4/8 in the chamber without bouncing off the walls? And divers treated for 7.5 hours on 50/50 heliox to the same PO2, likewise? Mainly because they're told to sit still and therefore the CO2 is kept low. Not convinced. Though it's not fully understood, there is a difference between being wet and dry even if the subject is relaxed under both circumstances. We don't know everything there is to know. So, since we don't, I don't see why erring on the side of being somewhat overly cautious is a problem. If we are too aggressive, the down side to that is a lot worse than spending a few extra minutes doing deco. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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18th April 2006, 18:47	#50 (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: 3,323	Re: A guide about setpoint selection for deep dives Quote: (Originally Posted by dave t) yes, as we all know there are a couple of phases of the convulsion, the first is to spasm the muscles including the ones in the throat which will probably close off the airways trapping gas in the divers lung. If you were to lift the diver at this stage the likelyhood of a burst lung is certain. I had to wait until the second phase where the diver relaxes before I could take him to the surface. Now this all happens very quickly and the only indication I got of the second phase was to see gas escaping from the divers mouth, I held his head in a sort of neck exstension and waited (a few seconds) had the diver been wearing a FFM I would not have been able to see the gas and tell when it was safe to lift him. Sure he wouldnt drown, he would just die of an embolism. On the surface it was nesacary to give AV a FFM may have hindered the need for very quick acsess to oral/nasal passages. Anyone who thinks that the convusion is over quickly is mistaken, once back on the boat the diver took at least 45mins before beginning to regain consiousnes. I was scared to hell,missed 35mins of deco but it all turned out ok, I didnt get bent he made a full recovery Dave I think this is very dodgy and potentialy dangerous advice. Anyone wearing a ffm with a Rebreather should have a BOV fitted to it. Not to doesnt make any sense at all. If they convulse you just wait until they stop then turn the BOV to OC. You will see bubbles from the OC exhaust when/if they start breathing. Letting someone drown as a way to tell there airway is open enough to allow a 'safe' ascent is lunacy IMO. FFM+BOV. __________________ 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
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