My hypoxic incident

[justinthedeeps]

I guess this and other recent incidents expose a seldom-admitted weakness of passive flow systems.

One one hand, it is celebrated as 'simpler and less prone to failure'
On the other hand, it can not correct a rapid significant drop in ppO2 (e.g. on ascent), whereas a solenoid aka auto-MAV can. And subtle flow issues can go unnoticed.

The passive flow is supposed to keep the diver alive (otherwise why even have an orifice at all?) But a reliance on this assumption sounds dangerous.

So it sounds pretty similar to a solenoid stuck closed. We should probably all assume that our orifices or solenoids are going to block at some point. We just don't know when. [Begin drill...]

 

[davehicks]

I guess this and other recent incidents expose a seldom-admitted weakness of passive flow systems.

One one hand, it is celebrated as 'simpler and less prone to failure'
On the other hand, it can not correct a rapid significant drop in ppO2 (e.g. on ascent), whereas a solenoid aka auto-MAV can. And subtle flow issues can go unnoticed.

The passive flow is supposed to keep the diver alive (otherwise why even have an orifice at all?) But a reliance on this assumption sounds dangerous.

So it sounds pretty similar to a solenoid stuck closed. We should probably all assume that our orifices or solenoids are going to block at some point. We just don't know when. [Begin drill...]

This scenario can be largely avoided by servicing and cleaning orifice at least once per year and measuring the flow rate. The MAV should also have a separate filter upstream to prevent particles from blocking it.

 

[nadwidny]

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?

Nothing but as I said I'm normally injecting O2 on my way up for deco.

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

1.4 to 1.6

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.

That's pretty much standard practice on almost all my dives, just not this one as it wasn't a deco dive. Plus loop flushes with O2, etc..

 

[billgraham]

Well, I'm super happy you are OK, nadwidny. I'm not currently diving my CCR because I'm just getting back into cave diving and don't need it, but I spent a lot of time doing photography on closed circuit in the caves and the ocean. I have carefully read through the responses and while it's obviously important to focus on the CCR and was it set up/functioning correctly, nobody has mentioned the camera. When you are doing photography, you've got one hand at best, and maybe half a brain. A friend who is a very well known photographer used to have someone watch her and make sure everything was right with her rig while she was shooting for this reason. The danger is greatest in shallow water.

 

[nadwidny]

Well, I'm super happy you are OK, nadwidny. I'm not currently diving my CCR because I'm just getting back into cave diving and don't need it, but I spent a lot of time doing photography on closed circuit in the caves and the ocean. I have carefully read through the responses and while it's obviously important to focus on the CCR and was it set up/functioning correctly, nobody has mentioned the camera. When you are doing photography, you've got one hand at best, and maybe half a brain. A friend who is a very well known photographer used to have someone watch her and make sure everything was right with her rig while she was shooting for this reason. The danger is greatest in shallow water.

Good point. At the time I wasn't shooting but I was packing up (folding lights in, etc) getting ready to storm the beach. If I didn't have the camera there is a very good chance that I would have been more attentive to my PO2.

I agree that a huge danger on a CCR is shallow.

 

[John C. Ratliff]

I just received this from Garth Lock, who has a Facebook page about ”The Human Diver,” looking at safety from a human factors perspective in diving. He just wrote:

The risks that exist in diving are irreducible. The adventures that are out there mean that those hazards are sometimes encountered.
RIP Axel.

 

[berndo]

Third in seven days? Where was the third?

 

[Whitrzac]

Third in seven days? Where was the third?

My question too

 

[grantctobin]

Third in seven days? Where was the third?

Axel there, Strelnik in JB, and these one Dykare saknas i Gullmarsfjorden

Edit: I’m wrong.

 

[berndo]

Axel there, Strelnik in JB, and these one Dykare saknas i Gullmarsfjorden

The one in Sweden was last year. Two in one dive.