Quote: (Originally Posted by
O.C.Diver)
While this thread has been quite interesting, Dave I feel you have overlooked a couple of points:
The Navy is prepared to accept losses, such is the nature of their business, most of our families are not!
While I am not a proponent of a 10% FO2 Dil, suggesting that a 1.8 PO2 is nothing to worry about on a loop flush for your average overweight, out of shape, 50+ diver who has no idea at what PO2 he really toxes at, is irresponsible. If you choose to do it, that's your decision. To tell others that they categorically won't have a problem regardless of their age, health, and tolerance to high POs, is totally different.
Personally I prefer an FO2 of 16%. Breathable for short periods on the surface, normoxic at 10', and not toxic for 99% of the dives most of us do.
Ted
First, as a pilot flying with Naval Aviation, I can tell you that your first statement is dead wrong... (pun intended).
Second, for the *time durations* am a discussing, there is no posssibility for any tox issue. Re-Read *again* the time durations we are talking about.... a few minutes when *accepted limits* for that same exposure is set forth in *hours*.
I know what I am writing may seem counterintuitive, but it's proven, and is well within any sensible limit. It's been done for years. And not to push the Navy, but within published Mark-15 depth limits, either air (21% obviously) or 80/20 Heliox are the only diluents that the military has *ever* used. The Mark-15's manual basically states that when the diver bottoms out, the high alarm will be illuminated. After a period of some minutes, the 02 will be consumed from the loop and the setpoint will be reached, upon which time the solenoid will begin to function. The manual basically states that you will REACH THE BOTTOM HOT and then will METABOLIZE THE 02 IN A FEW MINUTES and that this is NORMAL AND EXPECTED. Go read the book. They don't say more than that in the manuals because *no further discussion is warranted* because *the duration of exposure is so short as to be irrelevant*. And don't think for a minute that all Navy divers are fit and youthful. When these limits were established and tested, the average Chief Petty Officer/Master Diver was a 50 year old out of shape guy who had his right hand permanently deformed into a hook because it was rarely separated from his coffee cup. I grew up in the Navy, and spent a lot of time at EDU when I was working in the Ocean Simulation Facility. Trust me on this.... the research "subjects" weren't supermen. They were "Fleet Average". The Navy PT program has gotten lots better, but when the limites were established, the debate regarding smoking and a diver was "filtered or unfiltered" with Camel's being the divers choice as a smoke....
I REALLY appreciate your experience, and your excellent reputation, but I VERY respectfully believe that you are in the generation of "non-military trained, non commerical-diver trained" mixed gas divers who are of a group that was incorrectly taught (due to no fault other than that of their instructors) to fear *transient* (not sustained) PP02 spikes as though they were as dangerous as low PP02 conditions. Just ain't so. I think it' time for the industry to revisit this and to teach people the more complex "fuzzy" regarding high PP02 transition states as opposed to the "dumbed down" versions of simply avoiding them at all costs.
16% 02 is not going to help that overweight out of shape diver kick the last 20 feet to the ladder on the surface in a current after letting go of the tag-line and then to huff and puff his way up the ladder with all that crap he carries. It's the air/sea interface where divers struggle and sweat, and I'm gonna make sure my divers have GOOD GAS there. If I have a guy on a BOV kicking hard trying to make it to the back of my boat, breathing his diluent straight outta the bottle, I want that mix to be GOOD, not feeble.
And overweight, out of shape divers? They ought not to be doing technical rebreather diving anyhow... the best way for them to not tox is to take up riding the excercise bike for an hour a day...... no sympathy otherwise....
At least we agree that 10% is not best... ;-)
Dave