O2 slug

Guilhem

NEDIVER, my point was that the Meg is not the only unit that does inject O2 in the inhale side. Your question was about if this type of design, as encountered in the Meg, may lead to a situation where one inhales a pure slug of O2, as you put it. I've tried to help by pointing out another manufacturer's answer to the question, which, as I was saying, is lacking hard numbers as supporting evidence - as your quick math shows. They basically say: "it's a non-issue, believe us" . This seemed relevant to the question.

NEDIVER

I do appreciate your comments and feedback, have some green.

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mountain diver

you are right.





all the best.

tibby

I've read a lot about the potential hazards of having the O2 bypass valve on the inhale side and the "theory" behind it but... has anyone validated this theory in any way? Have there been any recorded close calls or incidents of oxtox that were or could have been related to having the manual O2 valve on the inhale side?
Since it's not nice to reply with a question here's what I do. I dive my Meg with "the theory" in mind and being a bit paranoid about this issue I force myself to always take a deep breath before I manually inject O2 and push the button on an exhale cycle hoping I force some of the slug through the loop to give it a chance to dilute. I haven't bought into the connecting the O2 to the exhale CL yet for reasons previously mentioned in this thread or other posts. Keep in mind though that the deepest I've been on the Meg (while manually holding a setpoint) is 140ft so I don't know if this is acceptable for deeper stuff.
Regards,
Tibby

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Hk101gr

Hi andy,
I believe that an oxtox from a single breath of pure O2 even at considerable depth is highly unlikely. One breath just isn't enough for the gas to diffuse into your body in sufficient quantities. I agree it can't be good though.

Consider also that when flying manualy at depth (i've never flown manually to the depth you mention) you need a very slight push of the button to add a sufficient quantity of O2, i don't think it's anywhere close to a lungfull or even half.

Dive safe
Dimitris

Lancer4545

I had a lot of trouble with the 4th cell/VR3 option when manual adding in the inhale CL. That is because the cell is in very close proximity to the manual add valve. The continual O2 spiking on the VR3 led me to simply remove the O2 hose from the inhale CL and connect it to the exhale CL (MGBP)

It kept the PO2 aligned a lot better and also gave the O2 more time to homogenize with the gas in the loop and pass the cells in the head before being inhaled therefore giving a more accurate reading of the inspired gas. This at the time seemed to be the best solution.

Then I got to thinking why Leon had put it where it is........and that is, in the event that the diver finds the loop has become hypoxic and needs O2 fast it's right there. The other reason for putting it back was that if anything were ever to happen to me and another diver was to rescue me and wanted to manually add O2 into my loop he would have to work out where the hell the manual addition was.

I fly my unit manually 99% of the time and only rely on the electronics as a backup in the event I get distracted or my workload is higher than normal. It's really very easy...The deeper you go the less time you need to hold the valve open. I haven't had any issues shallow or at depth and your batteries last heaps longer.

Regards,

Lance

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mempilot

I bet that really shortened the perceived deco obligation by the VR3 and is probably the best the reason I've read for moving the O2 hose to the exhale side.

I think for Megs without the 4th cell, moving it alleviates a small hazard, but creates a bigger one. ie. hypoxia vs hyperoxia and how quickly the diver succombs to them and how quick the response needs to be

Thank you for the insight on the 4th cell. It may be in the future for my rig.

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Lancer4545

Hi Eric,

It was such a concern I took the 4th cell out of the system altogether and it now resides in my spares kit and I dive with 2 VR3s.

Let me know when you want one

Lance

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jkaterenchuk

I have posted a seperate thread to poll how many Meg owners have moved the O2 injection.

John

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