Wreck diver killed by leaking computer - UK

[BlueTrin]

Relying on the O2 in your diluent for your metabolism is called "semi-closed". Basically flushing the loop every X breaths to replenish the fO2 in there. How many breaths depends on the diluent, the depth, and your workload. But no matter what the dil was, at 6m with no O2 injected or regular loop flushes, the loop will go hypoxic and you will gradually fall asleep, drown, and die.

So I have been taught that we breath air which is roughly 20% O2 and exhale gas with 15% O2.

Does that mean that at 10m, because the pressure is 2 bar, you exhale gas with roughly 17.5% if you inhale air ?
i.e. is the quantity of O2 you metabolise roughly depth independent ?

So I agree with your statement you would go hypoxic really quickly without O2 being injected at 6m because you would be at 1.6bar and.

 

[Jack Hammer]

So I have been taught that we breath air which is roughly 20% O2 and exhale gas with 15% O2.

Does that mean that at 10m, because the pressure is 2 bar, you exhale gas with roughly 17.5% if you inhale air ?
i.e. is the quantity of O2 you metabolise roughly depth independent ?

So I agree with your statement you would go hypoxic really quickly without O2 being injected at 6m because you would be at 1.6bar and.

PO2 and metabolism are completely different things. How much O2 you metabolize is related to how hard you are working or how stressed you are and is not depth dependent. So you will metabolize the same amount of O2 at 200'/60m as you will at 20'/6m. PO2 on the other hand will drop or spike as you ascend or descend. You still need to keep PO2 in a safe and appropriate range. What is safe on OC is not necessarily safe on CCR.

 

[kelemvor]

Imagine a self driving car that has two computers. One breaks and says "turn left" the other one is saying "turn right". You cant just have a backup takeover, as there is no way to know which is correct.

Two is one and one is none. You need 3 and some sort of voting communication between them.. or is that also not a thing?

 

[JonG1]

The incident for me does highlight 2 obvious points for discussion, teamwork and the corollary how to deal with a situation when the team breaks down for whatever reason or was never an entity (e.g. solo), and why there is such a focus on staying on the loop even in the face of failures that could be compromising the unit.

That said we can't know whether it was a separate unrelated issue that was the actual proximate cause of death.

I have had 4 issues which could be termed unit failures, 3 of which I managed on the loop and 1, I bailed off.

With hindsight I believe I would have been better off bailing in each instance, not because anything bad happened as a result of my decision, more that it didn't and a false sense of security in managing issues whilst still using the loop can be engendered.

I had the gas and that was what it was there for.

Maybe its time for agencies and RB culture generally to start gradually moving more towards to a situation where bailing is more emphasised, there is almost a feeling of an under swell of intellectual superiority for the diver that can manage issues and preserve the gas in their tins.

Very few of us are diving at a level where having all the clever stuff that is technically feasible with a RB is actually warranted in the face of a problem that may or may not deteriorate further, because the profiles and exposures can be covered with sufficient bailout provision.

Teamwork/solo is a whole other ballgame, that may have been discussed a few times before!

 

[doctormike]

Two is one and one is none. You need 3 and some sort of voting communication between them.. or is that also not a thing?

Are you talking about sensors or controllers?

 

[DiveTucson]

Found in a FB forum. Posting here as it adds some details that may be useful the ongoing discussion.

“I did the forensic equipment examination for the Devon & Cornwall Police Dive Team for this incident. It was a JJ. The oxygen controller on that version of the product is in the handset. It intermittently failed, due to a flooded handset, and when it did fail and then start again you can see the PO2 drop. (this was done by Shearwater overlaying the data from a stand alone dive computer, the known dive profile, with the available data from the handset). On restart this controller defaults back to 0.7 set point. The oxygen controller worked for some of the ascent but it failed for the last time when the diver reached his 6m stop. As his deco ceiling cleared he descended to the bottom. The assumption is he went unconscious and let go of his SMB line. The chance of it being hyperoxia is minuscule as we know what the PO2 was for virtually all of the dive except for the deco stop and for that stop we know what the maximum PO2 could have been. Hypoxia fits the known facts. Either he didn’t look at his HUD or didn’t believe what it was telling him. As you go more hypoxic you do lose the ability to think clearly. Why didn’t he bailout, he had plenty of gas? Why didn’t he add lots of oxygen while at the stop? There’s only one person that knows the answers I’m afraid. I suspect that he was under the impression that his unit would keep going in the background, like a few other other makes would do, AP Visions and 2020s and the newer Megaldons for instance. Why else would he blindly continue knowing full well that he had a handset display that wasn’t working? At the start of his 6m stop the PO2 was okay, so no hypoxia issues then. The really annoying bit is ...the “super safe” GFs he used...he didn’t need to do that deco stop. When things aren’t going right, use 95-98 GF high then if everything is back under control add extra shallow stop time yourself but if things are desperate, get out and accept the very very slight increased risk of DCS. You can do this by using a 2nd dive computer set up with quicker GFs (90/98 for air diluent, 60/98 for Tx). You then have the means to get out quickly if you need to but can add safety by extending the last stop if everything is going okay.”

 

[JonG1]

Which forum is this from please DiveTucson?

 

[DiveTucson]

Which forum is this from please DiveTucson?

It was in a FB group called “Technical Divers”

 

[doctormike]

Found in a FB forum. Posting here as it adds some details that may be useful the ongoing discussion.

“I did the forensic equipment examination for the Devon & Cornwall Police Dive Team for this incident. It was a JJ. The oxygen controller on that version of the product is in the handset. It intermittently failed, due to a flooded handset, and when it did fail and then start again you can see the PO2 drop. (this was done by Shearwater overlaying the data from a stand alone dive computer, the known dive profile, with the available data from the handset). On restart this controller defaults back to 0.7 set point. The oxygen controller worked for some of the ascent but it failed for the last time when the diver reached his 6m stop. As his deco ceiling cleared he descended to the bottom. The assumption is he went unconscious and let go of his SMB line. The chance of it being hyperoxia is minuscule as we know what the PO2 was for virtually all of the dive except for the deco stop and for that stop we know what the maximum PO2 could have been. Hypoxia fits the known facts. Either he didn’t look at his HUD or didn’t believe what it was telling him. As you go more hypoxic you do lose the ability to think clearly. Why didn’t he bailout, he had plenty of gas? Why didn’t he add lots of oxygen while at the stop? There’s only one person that knows the answers I’m afraid. I suspect that he was under the impression that his unit would keep going in the background, like a few other other makes would do, AP Visions and 2020s and the newer Megaldons for instance. Why else would he blindly continue knowing full well that he had a handset display that wasn’t working? At the start of his 6m stop the PO2 was okay, so no hypoxia issues then. The really annoying bit is ...the “super safe” GFs he used...he didn’t need to do that deco stop. When things aren’t going right, use 95-98 GF high then if everything is back under control add extra shallow stop time yourself but if things are desperate, get out and accept the very very slight increased risk of DCS. You can do this by using a 2nd dive computer set up with quicker GFs (90/98 for air diluent, 60/98 for Tx). You then have the means to get out quickly if you need to but can add safety by extending the last stop if everything is going okay.”

Thanks so much for this.

I know that this isn't your post, but it seems that the main question - given that he apparently elected to stay on the loop - was why he didn't maintain his PO2 manually. With a dead controller, hard to imagine anyone just assuming that somehow the backup in the head (defaulting to 0.7) would be fine and not watching PO2.

I guess there is no internal log of the OBOE board that runs the HUD? That would tell you what the PO2 in the loop was for the whole dive...

 

[EireDiver606]

You would never do a 70m dive without deco gas on your person.

As was said in post #41 some of them do carry, but not enough deco gas.

This is the issue.

There needs to be a more integrated safety culture in diving especially for rebreather diving. Leave the ego and pride on the surface, your family will thank you. You might even thank yourself, maybe not as a study has showed that people will choose the survival of their ego over the survival of their life...