Posted by Steve on August 09, 2001 at 21:14:05:
In Reply to: Re: what about price, Mike? posted by MHK on August 09, 2001 at 17:25:49:
"Take that logic and apply it out over a 4 dive day or a 5 day liveaboard and then can you honestly offer your theory that you aren't safer on Nitrox????"
Maybe, however you may be paying for that extra BT by compromising somewhat your enzyme system from the higher PPO2. Consider this statement from Dan Volker. Which is the healthier or safer way to dive: all nitrox, no nitrox or nitrox in moderation????
Dan Volker wrote:
What I really had in mind related more to 100 to 120 foot deep diving, where I see Nitrox badly misued. I see the real problem is with Nitrogen, and adding oxygen to the entire dive has been the cheap fix for all depths up to 150 feet deep or so.
I like Oxygen for creating a large gradient to remove nitrogen, but I like to keep my exposure to high levels of O2 to shorter durations. While I don't have definitive scientific studies "I" can cite on this right now, my concern is that high PO2 is harmful, and while short durations are easily handled by your body ( repair), purposely diving hot nitrox mixes for 3 to 6 dives in a day will be very unhealthy. I expect it to cause much more prevalence of random oxidative metabolism, which will create very high levels of free radicals....,it is bad for many enzyme reactions, and as we all know, when oxygen is inspired for way too long at a given depth--even 70 feet, your enzyme systems will shut down, and you will tox. Everyone likes to ignore the middle part---where you are not shutting down, but clearly, your system is adversely effected. Bottom line, if I go tech diving I will need to use 50/50 for deco from 70 feet on up to the surface, but only for the duration of the deco, which will generally be less than 40 minutes. For the dive previous to the deco, my PO2 will rarely be much over 1.2 or 1.3, and the goal is to keep it as close to 1.0 as is feasible, particularly for any significant duration. In tech diving, we "do" expose our bodies to risks and effects unacceptable to recreational diving standards ( or what they should be). Gas choices, smart profiles, and extreme fitness levels will help minimize the damage ( and it appears that "small damage" will be repaired by the highly fit diver).
When I do recreational dives to 60 or 70 feet, there is no need to push PO2 levels to "harmful levels". Personally, if I "had" to do 4 or 5 dives in one day in this depth range, rather than use Nitrox, I would be more apt to spend 20 minutes breathing O2 after the 3rd dive--on the surface, and then right after the last dive if I was feeling tired ( what usually happens to recreational divers after 5 or 6 dives--sub-clinical DCS will typically mean you feel tired). But normally I would just use air for this, and do very slow ascents to aid prevent large bubble formation---and this would be with a totally flat/horizontal body position during the entire ascent, to maximizze the bubble filter effect of the lungs.
Regards,
Dan Volker