PPO2's and rules for conditions

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Posted by Maddiver on November 19, 2001 at 00:26:28:

In Reply to: Re: More thoughts on NitrOx posted by Karl S. on November 18, 2001 at 17:55:48:


Below I snipped out your quote on PO2's and limits for dive exposures. I commend you for attention to detail in acknowledging the necessity of decreased PPO2's when dealing with increased workloads, cold etc. However as you get further into technical diving you will begin to see the merit of reducing PPO2's even further for the 'working' or "Bottom Mix" portion of the dive. 1.4 may even be too much (I tend to use as abosolute max for warm water drift dives *personal note) and back off accordingly on cold, current dives or where dives require increased deco loads. In essence you do yourself several 'favors' by reducing the PPO2 deep:

1) Reduce the overall CNS %
2) Above being stated you allow more CNS% to be available at the deco stops ie your O2 1.6 level stops (see what I mean by cutting tables on any deco software out there) running lower bottom gas ie 1.3 or 1.2 can actually get you out of the water safer and faster.
3) On multiday or massive deco dives you leave room with a decreased PPO2 for the OTU tables (especially when it applies to recompression after a DCS incident and can be the difference between suffering a reduction in Vital Lung Capacity or walking away normal)

4) Everyone knows dive planning doesn't always go as we plan it (see ms blucow's dcs case for pertinent example) What if you plan to dive your 1.4 PPO2 mix at a site that has sand at 109 ft but the boat deviates to a site that is 120 ft deep to really 'do the dive'. A better choice in my opinion is to mix lighter ie 1.2 or 1.3 and give yourself some room. Will you get hammered doing it your way....probably not. Food for thought and possibly it may save a dive that you would have to sit out on otherwise.

>Here on the West Coast, as you know, we are encouraged to set our MOD based on a PO2 of 1.4 since the water is very cold. An MOD based on a PO2 of 1.6 would be perfectly acceptible if the water was warmer here and the workload was comparatively light at depth, such as floating around inflating and deflating your B/C with only light fin kicking.

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