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--_=_=_=IMA.BOUNDARY.HTML_4998384=_=_=_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Susan, gas switches on a FFM are a nightmare. Either you use a gas switch block, which is a death sentence, or you physically switch the mask which is a pain in the ass, and in cold water is at best uncomfortable and at worst dangerous due to the risk of skin bends in your face from poor perfusion, and the possibility of a laryngospasm. I thought this discussion was about decompression, but John seems to lack a very basic understanding of the principles involved, despite claims of having read the applicable literature. How much time you are spending in the water is not the key issue, although it's nice to get out ASAP, especially in cold water. Probably the most compelling reasons to use oxygen are the benefits it provides in emergency situations, such as minimizing the damage done if I need to omit deco and surface for whatever reason, or for IWR (the real use for the FFM). John was right about one thing: that the real risk in diving is not DCS, but oxtox. Proper management of oxygen exposure includes keeping the bottom PPO2 reasonable (I usually mix for 1.2), using the correct deco gases to maximize gas exchange and effectively provide a break from oxygen before switching to the next gas, and incorporating breaks to the lowest breathable PPO2 gas when on the oxygen stop, according to exposure. John thinks that a PPO2 of 1.606 on oxygen at 20 fsw is dangerous, but using 80/20 for a PPO2 of 1.527 at 30 fsw is safe. Fine. I can use oxygen at 17.4 feet for the same lower PPO2, while still getting the decompression benefit of the wide open oxygen window, and get out of the water in time for Christmas. This is nuts. -Sean --Original Message Text--- From: LouisianaLegal@ao*.co* Date: Fri, 20 Jul 2001 11:40:00 EDT John, Use whatever gas you select and whatever equipment you select on your dives. Sean has calmly explained his use of O2 and why. You've read his reasons and the "Baker's Dozen" and are apparently unconvinced. If you don't want to use it - so be it. The beauty of it is this is it's a free country, at least as far as gear selection. You can choose your own buddies and boat too. You'll just be in the water longer on 80% or in the water longer fooling around switching from a FFM to back gas and then back again to the FFM. Try it a couple of times and I'll bet you'll do what's necessary to use O2 without a FFM and no one likes to be the last one on the boat from deco. FFM would be safer but unless you are in a bell they are a pain to switch to back gas and carry during a dive, particularly a wreck penetration dive. I am not saying don't do it if you want. That's your decision. I think everyone else on the list has got this point and has made their own choices. I am sure techdiver archives has many posts on use of O2 versus 80%. Susan --_=_=_=IMA.BOUNDARY.HTML_4998384=_=_=_ Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: 7bit <HTML> <FONT FACE="MS Sans Serif" DEFAULT="FACE"><FONT SIZE="1" POINTSIZE="8" DEFAULT="SIZE">Susan, gas switches on a FFM are a nightmare. Either you use a gas switch block, which is a death sentence, or you physically switch the mask which is a pain in the ass, and in cold water is at best uncomfortable and at worst dangerous due to the risk of skin bends in your face from poor perfusion, and the possibility of a laryngospasm.<BR> <BR> I thought this discussion was about decompression, but John seems to lack a very basic understanding of the principles involved, despite claims of having read the applicable literature.<BR> <BR> How much time you are spending in the water is not the key issue, although it's nice to get out ASAP, especially in cold water. Probably the most compelling reasons to use oxygen are the benefits it provides in emergency situations, such as minimizing the damage done if I need to omit deco and surface for whatever reason, or for IWR (the real use for the FFM).<BR> <BR> John was right about one thing: that the real risk in diving is not DCS, but oxtox. Proper management of oxygen exposure includes keeping the bottom PPO2 reasonable (I usually mix for 1.2), using the correct deco gases to maximize gas exchange and effectively provide a break from oxygen before switching to the next gas, and incorporating breaks to the lowest breathable PPO2 gas when on the oxygen stop, according to exposure.<BR> <BR> John thinks that a PPO2 of 1.606 on oxygen at 20 fsw is dangerous, but using 80/20 for a PPO2 of 1.527 at 30 fsw is safe. Fine. I can use oxygen at 17.4 feet for the same lower PPO2, while still getting the decompression benefit of the wide open oxygen window, and get out of the water in time for Christmas.<BR> <BR> This is nuts.<BR> <BR> -Sean<BR> <BR> <BR> <BR> --Original Message Text---<BR> <B>From:</B> LouisianaLegal@ao*.co*<BR> <B>Date:</B> Fri, 20 Jul 2001 11:40:00 EDT<BR> <BR> <FONT FACE="arial"><FONT SIZE="2" POINTSIZE="10">John, <BR> <BR> Use whatever gas you select and whatever equipment you select on your dives. <BR> Sean has calmly explained his use of O2 and why. You've read his reasons and <BR> the "Baker's Dozen" and are apparently unconvinced. If you don't want to use <BR> it - so be it. The beauty of it is this is it's a free country, at least as <BR> far as gear selection. You can choose your own buddies and boat too. <BR> <BR> You'll just be in the water longer on 80% or in the water longer fooling <BR> around switching from a FFM to back gas and then back again to the FFM. Try <BR> it a couple of times and I'll bet you'll do what's necessary to use O2 <BR> without a FFM and no one likes to be the last one on the boat from deco. <BR> <BR> FFM would be safer but unless you are in a bell they are a pain to switch to <BR> back gas and carry during a dive, particularly a wreck penetration dive. I am <BR> not saying don't do it if you want. That's your decision. <BR> <BR> I think everyone else on the list has got this point and has made their own <BR> choices. I am sure techdiver archives has many posts on use of O2 versus 80%. <BR> <BR> Susan <BR> <FONT SIZE="1" POINTSIZE="8" DEFAULT="SIZE"><BR> </HTML> --_=_=_=IMA.BOUNDARY.HTML_4998384=_=_=_-- -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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