My hypoxic incident

[beldridg]

I said I would someday get this out there so here it is. I'm putting it here in the RB forum and not the near misses forum as it is more for RB people to learn from than the general diving community.

Thanks, very useful. It can happen so quickly when shallow.

Regards,

- brett

 

[nadwidny]

Just a quick clarification. There are two types of rEvo MAVs and two different methods used to implement a constant mass flow (CMF).

1) The orifice is included in the MAV. I think this is the type that rjack321 is referring to above. This is known as the "R217C" type and you can see the indication of the orifice at .0035" on the MAV shunting between the O2 input and the output Picture below:

View attachment 780613

2) There is a different MAV that my unit has that does NOT have the orifice included in it. These are R217A and R217B (the difference being the type of connector on the output side. See picture below:


View attachment 780614

My MAV is like the first one. I got it early on (2009ish) from a guy in Washington. I think this was before they were known as the "Revo MAV". After the event I was able to take it apart to get to the orifice.

 

[MinimalMayhem]

Have you

Have you ever triggered the alarm yet (unintentionally)?

I have triggered mine (at 0.4) and it is awesome. I had to go SCR a couple of days ago and it was nice to get that unmistakeable vibration alert when the po2 dropped and I had taken a couple too many breaths before flushing.
In fact, it was 'seeing', well, hearing the vibration alert on a buddy's petrel 3 that prompted me to replace my petrel 2 with one...not a super cheap swap but I'm very happy I did it.

 

[berndo]

I had to go SCR a couple of days ago

Why is that?

 

[MinimalMayhem]

Why is that?

This feels a bit OT, but I had loss of O2 due to the DIN insert came unscrewed...not sure why it got loose, I imagine it took a knock on the boat after my checks or had already worked loose but was tight enough to pass pre-dive checks. I depressurised after the checks then turned on again before getting ready to jump in, I imagine it was leaking then but not loud enough to hear.

 

[kensuf]

I’m familiar with tiny drills. Last time we had to make ~.004” hole in acrylic we gave up on the drills and just spun up a guage pin to about 60K and melted through it. WRT actual tiny drills, in my experience, they better be high quality drills and they better be running dead nuts or don’t even bother.

You can buy a new orifice for around $40. Sometimes it's just quicker, simpler, and easier to do that.

 

[lostsheep]

You can buy a new orifice for around $40. Sometimes it's just quicker, simpler, and easier to do that.

Understood and agree. I don’t dive an MCCR and am fairly new to ccr; I didn’t know they were that cheap.

 

[bubblemonkey2]

Wow, scary & lucky story, amazing response by your buddies!

Was there any sign in previous ppO2 logs that could have hinted that the ppO2 and O2 flow were becoming limited during ascents? Something we could be monitoring in ppO2 data, for those who synch and review their profiles?

What was your normal target ppO2 during ascents and the end of dives?

If a diver at ppO2 of 1.3 surfaced instantaneously from 24m (~79ft) with no O2 flow, the result should be just short of ~0.4, ignoring metabolism. There would be say ~3 liters of O2 left in the loop, only ~1.5 liters of which could be consumed before the loop becomes hypoxic. So about 1 to 2 minutes including ascent to notice a problem before passing out? Not very long.

Great reminder to watch ppO2 even more closely during ascents/exits, and immediately stop the ascent if it drops oddly. Another one of those "this could kill you someday"

Do you practice O2 MAV ascents, manually maintaining your 'high' ppO2 target of 1.3 or whatever + minimum loop volume while ascending? It was drilled a lot in trainings and really reinforces things, so I like to practice it every few dives.

 

[mr_v]

Thanks for sharing - very informative. Glad all it worked out in your favor.

 

[beldridg]

Do you practice O2 MAV ascents, manually maintaining your 'high' ppO2 target of 1.3 or whatever + minimum loop volume while ascending? It was drilled a lot in trainings and really reinforces things, so I like to practice it every few dives.

I can't remember the last time I didn't run the unit manually on ascent/deco. It might be because I tend to dive wrecks with a square profile and almost every dive involves deco on a line in open ocean.

My "typical" dive is that I start with a low set-point, turn off my ADV (a lot of times my diluent is really hypoxic and I like knowing that the only way it gets into the loop on the surface is if I add it) and add diluent manually on descent (unless I know it is going to be a ****-fast descent and I won't have time to fuss with my MAV), change to high set point when I hit the bottom, do my dive, then change to low set point and do my ascent / deco and run the unit manually.

I find it more enjoyable (easier?) to add O2 when I know I'm going to need it (moving up stops, etc.) and not letting the unit do it.

The only time the solenoid fires is on the bottom section of the bottom. It doesn't mean I don't monitor the PO2. Sometimes, if I'm in a wreck that I know involves a lot of up-and-down, I'll leave it on the low set point and run it manually the whole dive.

Regards,

- brett