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   Gas Choices


   First, while we can get used to the effects of narcotic mixes, we can not 
operate any better on them. We are still impaired.

   To set the depth, it is ammazing how well the old PADI 130 foot mark seems
to 
be the demarcation line for the onset of hidden impairment. Keep in mind that 
ten feet is more narcotic that the surface, and that oxygen is also narcotic.

    A 130 AED with reduced oxygen is likely to be less narctoic than air at 130.

    Also keep in mind that the mere presence of helium in a mix alters the way 
nitrogen effects the rigidity of red blood cells, and reduces or eliminates the 
mircrocirculatory damaged associated therewith.

    Moving on, we set the oxygen to a maximum of 1.4 PPO2 simply because that
it 
the level at or below which commercial diving operations have found that
seizure 
is no longer to be expected in normal individuals. 

     From the 1.4 (MAXIMUM/1.6 deco MAX) we reduce the PPO2 for the longer 
exposures for both whole body, CNS, and pulmonary toxicity reasons. The longer 
the exposure, the lower the PPO2.For a saturation, a mix may have to be 
ridiculously low in oxygen just to accomplish this.

     Once establishing the bottom mix, the legth of deco will dictate the use
of 
the decompression gasses. Keeping them standardized is a good idea, and marking 
them for depth is the way to go, but two primary points must be considered: do 
not spike the oxygen after a long bottom exposure, so maybe move your gas 
switches up a step or two, and figure where to begin taking air or bottom gas 
breaks. 

     Taking breaks at a regular interval, including 20 minute "cleanup" breaks 
will greatly reduce the risk of seizure on the one hand, and greatly reduce the 
pulmonary damage on the other. We break every twenty for five, but do not alter 
the deco schedule for it.

      This is a good starting point for discussion, but let's leave out the 
"good deep on air" bullshit, since we are talking technical diving here.

  G     

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