Getting the most out of your O2 tank

Abbo · 21st May 2007, 11:00

There seems to be a huge range of O2 consumption rates in polls on Rebreather World. What tricks have you found most efficient in reducing your oxygen consumption? Since my switch to CCR I have been forced back into the shallows with divers who have short-duration sawtooth profiles. I tend to be away for weekend trips without opportunities for oxygen fills, so it's a pressing problem - but it's also a strong stimulus to hone those skills.

Cheers,
Nicholas

Hanssing · 21st May 2007, 11:13

Quote: (Originally Posted by Abbo)

There seems to be a huge range of O2 consumption rates in polls on Rebreather World. What tricks have you found most efficient in reducing your oxygen consumption? Since my switch to CCR I have been forced back into the shallows with divers who have short-duration sawtooth profiles. I tend to be away for weekend trips without opportunities for oxygen fills, so it's a pressing problem - but it's also a strong stimulus to hone those skills.

Cheers,
Nicholas

Hi Nicholas,

Please be aware, that I'm talking out of my ass here, as I'm not yet a Rebreather-diver.
But concerning your question the following seems to apply:

1. If possible avoid changes in depth.

2. Minimum CL-volume at all times. This helps keep the amount of gas that needs to be replenished low, and reduces your overall consumption of Dil and O2. It helps keep boyancy, and reduces amount of weight needed.

3. When ascenting, Dr. Richard Pyle, mentions that he keeps the PPO2-setpoint low (0.5-0.7bar'ish) to avoid releasing a lot of unused O2 to the water (You can find the article in the library i think).

4. My own conclusion, avoid running with optimal PPO2 whenever depth-changes are about to happen: When descending you'll sometimes have to dil-flush to keep PPO down (if using rich DIL), and when ascending you'll just release it into the water. Your Rebreather should keep up with the OC-divers deco-profile even if you run a setpoints away from the optimal, while chaging depths.

OBS: Read my first disclaimer - I could be wrong.....

Nicolai

Abbo · 21st May 2007, 11:40

Mr. Hanssing, these are all very fair points, but all points covered in Mod 1 - at least in principle. The devil seems to be in the execution. In the oxygen consumption poll on
http://www.rebreatherworld.com/gener...er-minute.html
plenty of trained ranks appear to be running consumption rates of 2 litres/ min, while some claim to be below 1. I would be willing to bet that they are all aware of the points you make and attempt to implement them. What do people who use less than 1 litre think they do differently?

**PhilSiswick** · 21st May 2007, 11:55

Quote: (Originally Posted by Abbo)

Mr. Hanssing, these are all very fair points, but all points covered in Mod 1 - at least in principle. The devil seems to be in the execution. In the oxygen consumption poll on
http://www.rebreatherworld.com/gener...er-minute.html
plenty of trained ranks appear to be running consumption rates of 2 litres/ min, while some claim to be below 1. I would be willing to bet that they are all aware of the points you make and attempt to implement them. What do people who use less than 1 litre think they do differently?

I wonder whether the variation you see in the polls is a) the difference between what people actually breathe and what they use for planning (i.e. a difference in reporting, rather than usage) or b) simply down to physiological differences between people. Just as RMV varies across experienced OC divers, would not O2 consumption vary depending on similar factors?

You shouldn't give up trying to improve on gas consumption but, immediate mitigations could include a) bigger cylinders, b) more cylinders (i.e spares on the boat for later dives) or c) finding Rebreather divers to dive with. Any of these (or all three) would give you time to get your consumption down without being under pressure to do it. My experience from OC indicates that, the more pressure there is, the less likely you are to achieve optimal gas consumption....

Cheers,

Phil

Hanssing · 21st May 2007, 12:33

Quote: (Originally Posted by Abbo)

Mr. Hanssing, these are all very fair points, but all points covered in Mod 1 - at least in principle. The devil seems to be in the execution. In the oxygen consumption poll on
http://www.rebreatherworld.com/gener...er-minute.html
plenty of trained ranks appear to be running consumption rates of 2 litres/ min, while some claim to be below 1. I would be willing to bet that they are all aware of the points you make and attempt to implement them. What do people who use less than 1 litre think they do differently?

The poll you reference, concerns actual usage and not metabolic rate. But assuming metabolic rates are more or less in the same range [0.75-1.1 l/min] for average divers, then the rest is down to how much gas you let bubble away OC.

Quote: (Originally Posted by Andy_Del)

I've found about 2 litres per minute based on 50m dives for around 70 minutes. This includes flushes, is my bailout O2 reg working tests and the like.

So methods for reducing this amount, includes the topic I mentioned before, and keeping OC/loop flushes to a safe minimum. The longer dives you perform the less waste pr. dive-minute, and therefor you get a better O2-rate.... But that does not give you any ideas for your type of dive-profiles, which we can assume are fixed.

So to lower you wasted gas, follow you MOD1-training, get perfect at these skills. Especially during ascent.
To lower metabolic rate - go to sleep/into trance/hit your Zen/loose your muscles

Regards
Nicolai

Ps: So easy to write on computer - so hard in real life. Looking forward to see my own consuption

Nick uk. · 21st May 2007, 12:40

Quote: (Originally Posted by Abbo)

There seems to be a huge range of O2 consumption rates in polls on Rebreather World. What tricks have you found most efficient in reducing your oxygen consumption? Since my switch to CCR I have been forced back into the shallows with divers who have short-duration sawtooth profiles. I tend to be away for weekend trips without opportunities for oxygen fills, so it's a pressing problem - but it's also a strong stimulus to hone those skills.

Cheers,
Nicholas

Buy yourself another set of O2 and dill tanks!!!

**wedivebc** · 21st May 2007, 16:39

Quote: (Originally Posted by Abbo)

Mr. Hanssing, these are all very fair points, but all points covered in Mod 1 - at least in principle. The devil seems to be in the execution. In the oxygen consumption poll on
http://www.rebreatherworld.com/gener...er-minute.html
plenty of trained ranks appear to be running consumption rates of 2 litres/ min, while some claim to be below 1. I would be willing to bet that they are all aware of the points you make and attempt to implement them. What do people who use less than 1 litre think they do differently?

Yes the information is covered in theory during MOD1. There are no special techniques that I am aware of other than to practice these methods by logging lots of time on the unit. Be aware of every bubble that leaves you and heads for the surface. They are all wasted gas and they all add up. Minimum loop volume, optimal weighting, and slow ascents are the main gas miser techniques. I am not sure I agree with the low setpoint during the ascent idea but slow ascents accomplish the same function.

Hanssing · 21st May 2007, 17:18

Quote: (Originally Posted by wedivebc)

I am not sure I agree with the low setpoint during the ascent idea but slow ascents accomplish the same function.

Well, not quite.

If you keep PPO2 of 1.3, then what ever gas vents during ascent has a PPO2 of that setpoint (breathe out used gas, then app. 0.05 bar lower).
But if you keep a PPO2 of 0.5 then, you have saved 0.8bar O2 x Volume vented.

So you save O2 on ascent (Assuming your not shooting directly for the surface).

But you increase Deco-loading and yore using your safety marging while ascending, so it should be done only when youre in control. If possible keep PPO2 at a level, where gas when expanded to surfacepressure is still breatheable, ie. PPO2 at least as high as air, at the same depth.
Breakeven occurs when deco-obligation due to described technique increases by more minutes x metabolic rate, than liters of O2 saved during ascent....

Again I could be confused....

Nicolai

SimonK · 21st May 2007, 17:20

pre-emptive dumping of gas and manual O2 injection during ascent works for me.

and as Nick said, get another set of tanks.

Simon

Hanssing · 21st May 2007, 18:00

Quote: (Originally Posted by Hanssing)

So you save O2 on ascent (Assuming your not shooting directly for the surface).

Again I could be confused....

Just did a simplified calculation of an ascent from 40m to 3m, at CL-volume of 5l. Using a setpoint of ppo 0.5bar instead of ppo=1.2bar only saves app. 5l. of O2, and is off course directly proportional to CL-volume!
5l. is so little, I wouldnt bother my self.

Apparently I am confused, and think I know it all - I will shut up now

Nicolai

21st May 2007, 11:00	#1 (permalink)
Abbo Going down on Meg Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: Tokyo Posts: 389	Getting the most out of your O2 tank There seems to be a huge range of O2 consumption rates in polls on Rebreather World. What tricks have you found most efficient in reducing your oxygen consumption? Since my switch to CCR I have been forced back into the shallows with divers who have short-duration sawtooth profiles. I tend to be away for weekend trips without opportunities for oxygen fills, so it's a pressing problem - but it's also a strong stimulus to hone those skills. Cheers, Nicholas
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21st May 2007, 11:13	#2 (permalink)
Hanssing flap-flop ..... flap-flop Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Denmark Posts: 351	Re: Getting the most out of your O2 tank Quote: (Originally Posted by Abbo) There seems to be a huge range of O2 consumption rates in polls on Rebreather World. What tricks have you found most efficient in reducing your oxygen consumption? Since my switch to CCR I have been forced back into the shallows with divers who have short-duration sawtooth profiles. I tend to be away for weekend trips without opportunities for oxygen fills, so it's a pressing problem - but it's also a strong stimulus to hone those skills. Cheers, Nicholas Hi Nicholas, Please be aware, that I'm talking out of my ass here, as I'm not yet a Rebreather-diver. But concerning your question the following seems to apply: 1. If possible avoid changes in depth. 2. Minimum CL-volume at all times. This helps keep the amount of gas that needs to be replenished low, and reduces your overall consumption of Dil and O2. It helps keep boyancy, and reduces amount of weight needed. 3. When ascenting, Dr. Richard Pyle, mentions that he keeps the PPO2-setpoint low (0.5-0.7bar'ish) to avoid releasing a lot of unused O2 to the water (You can find the article in the library i think). 4. My own conclusion, avoid running with optimal PPO2 whenever depth-changes are about to happen: When descending you'll sometimes have to dil-flush to keep PPO down (if using rich DIL), and when ascending you'll just release it into the water. Your Rebreather should keep up with the OC-divers deco-profile even if you run a setpoints away from the optimal, while chaging depths. OBS: Read my first disclaimer - I could be wrong..... Nicolai __________________ Woohooo - I can change my rEvo! Its going to be bitchin' tricked out piece of gear
(Online)

21st May 2007, 11:40	#3 (permalink)
Abbo Going down on Meg Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: Tokyo Posts: 389	Re: Getting the most out of your O2 tank Mr. Hanssing, these are all very fair points, but all points covered in Mod 1 - at least in principle. The devil seems to be in the execution. In the oxygen consumption poll on http://www.rebreatherworld.com/gener...er-minute.html plenty of trained ranks appear to be running consumption rates of 2 litres/ min, while some claim to be below 1. I would be willing to bet that they are all aware of the points you make and attempt to implement them. What do people who use less than 1 litre think they do differently?
(Offline)

21st May 2007, 11:55	#4 (permalink)
PhilSiswick WSKD 0001 Current Rebreather/s: Evolution Other Rebreather/s: Inspiration Vision Join Date: Apr 2006 Location: Oxford, UK Posts: 884	Re: Getting the most out of your O2 tank Quote: (Originally Posted by Abbo) Mr. Hanssing, these are all very fair points, but all points covered in Mod 1 - at least in principle. The devil seems to be in the execution. In the oxygen consumption poll on http://www.rebreatherworld.com/gener...er-minute.html plenty of trained ranks appear to be running consumption rates of 2 litres/ min, while some claim to be below 1. I would be willing to bet that they are all aware of the points you make and attempt to implement them. What do people who use less than 1 litre think they do differently? I wonder whether the variation you see in the polls is a) the difference between what people actually breathe and what they use for planning (i.e. a difference in reporting, rather than usage) or b) simply down to physiological differences between people. Just as RMV varies across experienced OC divers, would not O2 consumption vary depending on similar factors? You shouldn't give up trying to improve on gas consumption but, immediate mitigations could include a) bigger cylinders, b) more cylinders (i.e spares on the boat for later dives) or c) finding Rebreather divers to dive with. Any of these (or all three) would give you time to get your consumption down without being under pressure to do it. My experience from OC indicates that, the more pressure there is, the less likely you are to achieve optimal gas consumption.... Cheers, Phil __________________ Phil No comment on open circuit... it's an evolutionary dead end not really worth discussing here. Dave Sutton, 2007 I have always felt that the dive I am on is not nearly important as the dives I plan to be on the rest of my life. Tom Rose, 2007 www.hugsac.org.uk
(Offline)

21st May 2007, 12:33	#5 (permalink)
Hanssing flap-flop ..... flap-flop Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Denmark Posts: 351	Re: Getting the most out of your O2 tank Quote: (Originally Posted by Abbo) Mr. Hanssing, these are all very fair points, but all points covered in Mod 1 - at least in principle. The devil seems to be in the execution. In the oxygen consumption poll on http://www.rebreatherworld.com/gener...er-minute.html plenty of trained ranks appear to be running consumption rates of 2 litres/ min, while some claim to be below 1. I would be willing to bet that they are all aware of the points you make and attempt to implement them. What do people who use less than 1 litre think they do differently? The poll you reference, concerns actual usage and not metabolic rate. But assuming metabolic rates are more or less in the same range [0.75-1.1 l/min] for average divers, then the rest is down to how much gas you let bubble away OC. Quote: (Originally Posted by Andy_Del) I've found about 2 litres per minute based on 50m dives for around 70 minutes. This includes flushes, is my bailout O2 reg working tests and the like. So methods for reducing this amount, includes the topic I mentioned before, and keeping OC/loop flushes to a safe minimum. The longer dives you perform the less waste pr. dive-minute, and therefor you get a better O2-rate.... But that does not give you any ideas for your type of dive-profiles, which we can assume are fixed. So to lower you wasted gas, follow you MOD1-training, get perfect at these skills. Especially during ascent. To lower metabolic rate - go to sleep/into trance/hit your Zen/loose your muscles Regards Nicolai Ps: So easy to write on computer - so hard in real life. Looking forward to see my own consuption __________________ Woohooo - I can change my rEvo! Its going to be bitchin' tricked out piece of gear
(Online)

21st May 2007, 12:40	#6 (permalink)
Nick uk. Made in England. Current Rebreather/s: Inspiration Classic Azimuth Other Rebreather/s: Azimuth Join Date: Nov 2005 Location: Viale C.Colombo 75 Marina di Carrara. MS 54036 Italy Posts: 579	Re: Getting the most out of your O2 tank Quote: (Originally Posted by Abbo) There seems to be a huge range of O2 consumption rates in polls on Rebreather World. What tricks have you found most efficient in reducing your oxygen consumption? Since my switch to CCR I have been forced back into the shallows with divers who have short-duration sawtooth profiles. I tend to be away for weekend trips without opportunities for oxygen fills, so it's a pressing problem - but it's also a strong stimulus to hone those skills. Cheers, Nicholas Buy yourself another set of O2 and dill tanks!!! __________________ If it aint broke....don't fix it, and if it is.............well......get another one! divechief2000@hotmail.com
(Offline)

21st May 2007, 16:39	#7 (permalink)
wedivebc FIGJAM Current Rebreather/s: Megalodon Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Other CCR Join Date: Feb 2005 Location: Vancouver Island BC Canada Posts: 1,358	Re: Getting the most out of your O2 tank Quote: (Originally Posted by Abbo) Mr. Hanssing, these are all very fair points, but all points covered in Mod 1 - at least in principle. The devil seems to be in the execution. In the oxygen consumption poll on http://www.rebreatherworld.com/gener...er-minute.html plenty of trained ranks appear to be running consumption rates of 2 litres/ min, while some claim to be below 1. I would be willing to bet that they are all aware of the points you make and attempt to implement them. What do people who use less than 1 litre think they do differently? Yes the information is covered in theory during MOD1. There are no special techniques that I am aware of other than to practice these methods by logging lots of time on the unit. Be aware of every bubble that leaves you and heads for the surface. They are all wasted gas and they all add up. Minimum loop volume, optimal weighting, and slow ascents are the main gas miser techniques. I am not sure I agree with the low setpoint during the ascent idea but slow ascents accomplish the same function. __________________ Cheers, Dave.... Man is the only animal burdened with the knowledge he will eventually die
(Offline)

21st May 2007, 17:18	#8 (permalink)
Hanssing flap-flop ..... flap-flop Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Denmark Posts: 351	Re: Getting the most out of your O2 tank Quote: (Originally Posted by wedivebc) I am not sure I agree with the low setpoint during the ascent idea but slow ascents accomplish the same function. Well, not quite. If you keep PPO2 of 1.3, then what ever gas vents during ascent has a PPO2 of that setpoint (breathe out used gas, then app. 0.05 bar lower). But if you keep a PPO2 of 0.5 then, you have saved 0.8bar O2 x Volume vented. So you save O2 on ascent (Assuming your not shooting directly for the surface). But you increase Deco-loading and yore using your safety marging while ascending, so it should be done only when youre in control. If possible keep PPO2 at a level, where gas when expanded to surfacepressure is still breatheable, ie. PPO2 at least as high as air, at the same depth. Breakeven occurs when deco-obligation due to described technique increases by more minutes x metabolic rate, than liters of O2 saved during ascent.... Again I could be confused.... Nicolai __________________ Woohooo - I can change my rEvo! Its going to be bitchin' tricked out piece of gear
(Online)

21st May 2007, 17:20	#9 (permalink)
SimonK Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Oct 2005 Location: Cumbria UK Posts: 231	Re: Getting the most out of your O2 tank pre-emptive dumping of gas and manual O2 injection during ascent works for me. and as Nick said, get another set of tanks. Simon
(Online)

21st May 2007, 18:00	#10 (permalink)
Hanssing flap-flop ..... flap-flop Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Denmark Posts: 351	Re: Getting the most out of your O2 tank Quote: (Originally Posted by Hanssing) So you save O2 on ascent (Assuming your not shooting directly for the surface). Again I could be confused.... Just did a simplified calculation of an ascent from 40m to 3m, at CL-volume of 5l. Using a setpoint of ppo 0.5bar instead of ppo=1.2bar only saves app. 5l. of O2, and is off course directly proportional to CL-volume! 5l. is so little, I wouldnt bother my self. Apparently I am confused, and think I know it all - I will shut up now Nicolai __________________ Woohooo - I can change my rEvo! Its going to be bitchin' tricked out piece of gear
(Online)

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