Quote: (Originally Posted by
gtzavelas)
Interesting discussion, as everything in life you have to balance the pros/cons of the 2 alternatives.
I will try to detail my thinking about the 2 risks discussed:
RISK A: Hypoxia
possibility: extremely low , must arrive to 0,16 from the 1, 1 I usually use. I must really mess up as monitoring my PO2 is usually number priority #1
action : turn your BOV to OC (preferred for me , take 2-3 breaths from BOV and deal with the problem at the same time)or inject diluent (not so good) or inject O2 (this will have a slower response if plugged at the exhalation )
So moving the O2 to the exhalation lung will slow the response time of 1 of the 3 solutions to resolve a low PO2 situation
RISK B: Hyperoxia
Manual addition button sticking ON at great depth [ or alternatively much less risk to eject more O2 than planned by pressing the O2 addition longer (again at great depth)]
Possibility: low but out of control of diver (the manual button sticking ON)
Action: if O2 is stuck ON, remove O2 hose (or close O2 tank) and at the same time bail out or flash with diluent. Task loading will be very high as buoyancy will change fast and diver becomes buoyant
By plugging O2 to exhalation you minimize risk of Hyperoxia
risk B seems to me to be higher and because of high task loading seems worse
so by plugging the O2 to exhalation you mizimize the worst of the two risks
To say that the risk of Hypoxia is extremely low is VERY WRONG. If you look at the majority of rebreather incidents it's very clear the most dangerous part of the dive is at or near the surface and from Hypoxia......
There are a few different options to fix the situation if you're able.........But that's where the trouble seems to be. You're here one minute and off in noddy land the next........Dropped the DSV or BOV had a big drink and flooded your unit and on the express elevator.....DOWN!!!
There have been many arguments about stuck manual addition valves but when you hit the button and it sticks on you DO HAVE TIME to fix the situation and you have the ability to fix it. The manual addition valves don't allow a high flow rate like the ADV. Just how long will it take for you to disconnect the hose and stop the flow.......Not very long if you have been practicing and know your way around your unit. Then flush the loop and swap the hose to the other valve......Not really a big deal!!!
And don't forget if you change the hose to the exhale CL there is the issue with accidentally firing the ADV.
Knowing the buttons are in the std configuration is a big help if someone has to rescue you and they can go straight to the right one and activate it.......more so when every second could make a big difference to the outcome.....
Regards,
Lance