Decompression Planning

[davisj]

I have an advanced open water certification, with basic NITROX to 40%. I am in no manner an intructor or a guru. I post this info based upon what I have learned, and would like to have an open dialog.

My first point in planning this dive would be to figure the "best mix" for the dive, assuming that NITROX is the only gas used, and that only one dive is planned.

To mimimize nitrogen exposure, which will reduced decompression obligation and also the effects of nitrogen narcosis, I will want to maximize the oxygen content of my breathing gas, as long as I stay withing the oxygen exposure limits.

For this dive, I have chosen 28% O2 for my best mix. At a depth of 130 ft., my PO2 should be about 1.4. This should give me a single dive limit of about 150 minutes, which should be plenty to complete the dive.

Running this dive plan on my PC shows a 2 min stop at 30ft, 3 min stop at 20. and a final stop at 15 ft fot 25 minutes, for a total dive time of 64 minutes. With a working SAC of 0.70, and a DECO SAC of 0.50, this equates to a gas consumption of 127cuft.... If using the "Rule of Thirds", you couldn't find cylinders large enough to complete this dive. What have I figured wrong ????

Accepting all coments.....

JDavis