What's the lowest percentage "O2" you would use?

JonnyB · 27th February 2006, 06:40

Quote: (Originally Posted by tdvanniekerk)

The problem is not 92 or 94% O2, the problem is what is in the remaining 6 or 8%.

If you go to the gas supply companies you will find that they have many grades of O2, all classified as "Medical" grade. You should also check for the CO content and then decide if it is going to be a factor in the depth you are going to dive. I have no idea at what percentage CO will have negative physcological affect, but if you are going to drop standards, then at least do it with knowledge. Remember at a 90m dive the pressure is 10 ata. If you have 2% CO in the mix it will be ppCO 20 at 90m, with a setpoint of 1.2 you will be breathing the equivalent of 2% CO. (Not sure if my calcs are correct, need to check it for yourself). Maybe some expert out there will know if 2% CO will be bad for you.

A lower O2% will also be a factor when calibrating the O2 cells in rebreathers. If you think you have 100% O2 but only have 92% it can affect your actual setpoint. Off course if you know you only have 94% O2 you can set the rebreather to calibrate on 94% (at least you can on the Inspiration).

TD

If i remember correctly the CO is calculated in ppm (parts per million) and not percentage. I will check this though this afternoon when i come home, what the limits are, but i belive the limits are WAY below 2%. But i do agree that the problem is what is the other X% of gas in the mixture.

/Jonny

jaap · 27th February 2006, 09:59

Quote: (Originally Posted by JonnyB)

If i remember correctly the CO is calculated in ppm (parts per million) and not percentage. I will check this though this afternoon when i come home, what the limits are, but i belive the limits are WAY below 2%. But i do agree that the problem is what is the other X% of gas in the mixture.

/Jonny

Yes having as high a CO as 2% surface equivalent conc of CO would be extremely dangerous. But not very likely.

CO is much much more dangerous than CO2. If i recall correctly a few hundred ppm of CO is lethal at the surface. So having 2% CO would be about 20 000 ppm CO!

27th February 2006, 06:40	#21 (permalink)
JonnyB Johnny The Hatch Current Rebreather/s: MK 15.X Titan Other CCR Other SCR Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Megalodon Sport Kiss Classic Kiss Other CCR Other SCR Home Build Join Date: Jan 2005 Location: Sweden (Stockholm)/Cyprus(Ayia Napa) Posts: 975	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by tdvanniekerk) The problem is not 92 or 94% O2, the problem is what is in the remaining 6 or 8%. If you go to the gas supply companies you will find that they have many grades of O2, all classified as "Medical" grade. You should also check for the CO content and then decide if it is going to be a factor in the depth you are going to dive. I have no idea at what percentage CO will have negative physcological affect, but if you are going to drop standards, then at least do it with knowledge. Remember at a 90m dive the pressure is 10 ata. If you have 2% CO in the mix it will be ppCO 20 at 90m, with a setpoint of 1.2 you will be breathing the equivalent of 2% CO. (Not sure if my calcs are correct, need to check it for yourself). Maybe some expert out there will know if 2% CO will be bad for you. A lower O2% will also be a factor when calibrating the O2 cells in rebreathers. If you think you have 100% O2 but only have 92% it can affect your actual setpoint. Off course if you know you only have 94% O2 you can set the rebreather to calibrate on 94% (at least you can on the Inspiration). TD If i remember correctly the CO is calculated in ppm (parts per million) and not percentage. I will check this though this afternoon when i come home, what the limits are, but i belive the limits are WAY below 2%. But i do agree that the problem is what is the other X% of gas in the mixture. /Jonny __________________ A quote from Crazyduck - In remembering our own Rob Davies. "Outbound flight 777 heavy you are cleared for flight Due west into that warm red Texas sunset You have angels on your wings and divers memories on your six." Rest In Peace http://www.divetekcyprus.com http://www.diveccr.com
(Online)

27th February 2006, 09:59	#22 (permalink)
jaap Normal people worry me Current Rebreather/s: Classic Kiss Other CCR RB80 / Clone Ray Other SCR Home Build Other Rebreather/s: Other CCR RB80 / Clone Ray Other SCR Home Build Join Date: Jun 2005 Location: Stockholm Sweden Posts: 451	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by JonnyB) If i remember correctly the CO is calculated in ppm (parts per million) and not percentage. I will check this though this afternoon when i come home, what the limits are, but i belive the limits are WAY below 2%. But i do agree that the problem is what is the other X% of gas in the mixture. /Jonny Yes having as high a CO as 2% surface equivalent conc of CO would be extremely dangerous. But not very likely. CO is much much more dangerous than CO2. If i recall correctly a few hundred ppm of CO is lethal at the surface. So having 2% CO would be about 20 000 ppm CO!
(Offline)

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode