Hi JK, not to imply that I'm quoting you directly but...
Quote: (Originally Posted by
jkaterenchuk)
Direct from the source....
Hi John,
This is a fairly common question, at first glance injecting oxygen on the inhale side would seem counter intuitive. However, CNS is not a condition that "strikes" with a breath of pure O2, it is a combination of time and level of PO2. If your operating envelope is anywhere near normal PO2 range a CNS hit is not an issue from a an occasional injection of O2.
What about running the unit manually at say, 70 meters? Even 1 breath of pure O2 at a PO2 of nearly 8.0 can't be good for you, and this is what would happen each time you injected at depth. I'm no doctor, but I'd guess that 1 breath at some very high PPO2, an O2 tox would be near to instant.
Quote: (Originally Posted by
jkaterenchuk)
On the other side of the envelope if your PO2 had dropped to dangerously low levels and you were on the edge of Hypoxia you may not have the 3 or 4 breaths left to pull O2 from the exhale side, through the loop to your lips before you pass out.
The only time I can see this scenario playing out is with a very hypoxic single digit O2 % dil, no O2 injects for a while and a rapid ascent from shallower than 20 meters, which seems an unlikely combination. The times I have run my ECCR manually during an ascent, I was very concious of my falling PO2 and injected frequently. On dives requiring hypoxic dil, I was doubly paranoid and extra vigilant of my PO2 during ascent. And when manually injecting O2, I have never needed more than 1 breath to see my sensors start to rise.
If I'm understanding the Meg loop properly, given that the O2 is in the inhale CL, does that mean that the dil addition is in the exhale CL? If that is true and given the more common problem of ADVs not working right and the possibility of CO2 retention during periods of high workload, I would much rather have my dil addition in the inhale lung and have fresh gas near to my inhale hose that is breathable for the majority, if not all of my dive. Maybe I'm missing something.
Quote: (Originally Posted by
jkaterenchuk)
The overall design of the Meg is based on crictical controls being assessable to either hand and the ability of a diver on the edge of unconsciousness from whatever cause to have the best chance of self rescue.
Is there any OTS CL unit out there that doesn't allow access to the manual dil and O2 addition with both hands? Isn't that one of the benefits of OTS CLs, easy access to manual addition buttons?-Andy