Quote: (Originally Posted by
PCDiver)
Karl,
If a controller insists on doing a cell validation at a higher PPO2 (in the water), then I will not buy it since it is not practical on negative entry dives. Most of the reef dives we did in Egypt were negative entry dives from ribs. You just don't have the time for these kind of checks. If you don't go down like bomb, you will not find the reef.
The same goes for our North Sea wreck dives. You don't wan't to block the shot line too long. If you do the guys behind you crawl over you to get to the wreck.
But a warning message from the controller would be OK.
Why not insist?
You can run a 0.9 even if it insists, since you can validate a 1.0 on the surface.
Its if you want to run a 1.2 or 1.4 that you need to prove hyperbaric PO2 readings first.
Going in negative is something I do on a somewhat-regular basis here too - but you don't need to validate every dive.
If the controller insists on a weekly validation your first dive after a week's layoff is going to be at a 0.9. When you reach 20' on the ascent you can validate with the O2 flush and now you've got hyperbaric capability back.
If you can maintain dilligence with some sort of surface testing regime (e.g. in a pressure pot) then that's cool too, but engineering prudence says you do not trust a sensor until you have proven that it can read
beyond the range you want it to measure.
Current designs violate this maxim every day, and it simply isn't safe.