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RE: Dry vs. Immersed Oxygen Limits
NOAA (and the USN) very definitely differentiate between "wet" and "dry"
oxygen limits.
Actually, probably a single more important differentiator is exercise or
rest.
The 3rd Edition of the NOAA Manual (4th due out this month - but I don't
expect changes) has time/pO2 limit tables for oxygen exposure for
working divers as follows:
SINGLE EXPOSURE Maximums:
PPO2 ATA Minutes
1.6 45
1.5 120
1.4 150
1.3 180
1.2 210
(i.e., if your underwater time is planned for 125 minutes, the max. you
can breathe at any point in the dive is 1.4).
In a dry chamber - AT REST - pO2 up to 3.0 (100% O2 at 3 ATA or 50/50
Nitrox at 6 ATA) are permitted.
But in a chamber, an oxygen seizure is not much more than a nuisance
(stop O2, wait for seizure to stop, air break, restart O2).
An oxygen seizure in a diver usually equates to a drowning.
Please note that the chamber should have an inside tender breathing air
to come to the assistance of the patient.
Even in a dry chamber, a WORKING tender wouldn't be permitted to
approach a pO2 of 3.0.
--
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