Wreck diver killed by leaking computer - UK

[BlueTrin]

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...

It may be the issue for other people but this guy has bailout apparently

 

[rjack321]

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.

Your metabolism is only related to your workload/effort and is completely independent of depth.
e.g. you consume X molecules of O2 per minute for a given workload.

You will go hypoxic at 6m far faster than at 60m because you're at 7ata in the latter - there's more O2 molecules in the gas all smushed together. If you only put air in at 6m you have about ~10 breaths before the loop is no longer supporting life. The exact number depends in the counterlung size and how hard you're breathing.

 

[rjack321]

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 emphasized, 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!

Thank you for this. Especially the purple bit which is what I have been trying (with so so effectiveness) to communicate.

 

[Nirvana]

You will go hypoxic at 6m far faster than at 60m because you're at 7ata in the latter - there's more O2 molecules in the gas all smushed together. If you only put air in at 6m you have about ~10 breaths before the loop is no longer supporting life. The exact number depends in the counterlung size and how hard you're breathing.

Perhaps I am missing something, but I don’t see that being true. If we calculate the number of oxygen molecules in the loop using the ideal gas law and Dalton’s law, we arrive at a number independent of ambient pressure.

Dalton’s law:
(1) ppO2 = fO2*P
or
(2) fO2 = ppO2/P
Where ‘fO2’ is the mole fraction of O2 in the mix and ‘P’ is the total pressure (pressure in the loop, equal to ambient pressure).

As noted, 'fO2' is the mole fraction of O2, that is, 'n' being the total number of gas molecules and 'nO2' being the number of oxygen molecules:
(3) fO2 = nO2/n

From (2) and (3), we get:
(4) nO2/n = ppO2/P
(5) nO2 = n*ppO2/P

Ideal gas law:
(6) P*V = n*R*T
Where ‘P’ is the pressure of the gas mix (pressure in the loop), ‘V’ is the volume (in this case, total loop volume), ‘n’ the total number of gas molecules, ‘R’ is a constant, and ‘T’ is the temperature.

Solving (6) for ‘n’:
(7) n = P*V/(R*T)

Now, combining (5) and (7):
(8) nO2 = ppO2*V/(R*T)

Therefore, for a given loop volume (‘V’) and temperature (‘T), the number of O2 molecules in the loop should depend solely on ‘ppO2’.

 

[BlueTrin]

Perhaps I am missing something, but I don’t see that being true. If we calculate the number of oxygen molecules in the loop using the ideal gas law and Dalton’s law, we arrive at a number independent of ambient pressure.

Dalton’s law:
(1) ppO2 = fO2*P
or
(2) fO2 = ppO2/P
Where ‘fO2’ is the mole fraction of O2 in the mix and ‘P’ is the total pressure (pressure in the loop, equal to ambient pressure).

As noted, 'fO2' is the mole fraction of O2, that is, 'n' being the total number of gas molecules and 'nO2' being the number of oxygen molecules:
(3) fO2 = nO2/n

From (2) and (3), we get:
(4) nO2/n = ppO2/P
(5) nO2 = n*ppO2/P

Ideal gas law:
(6) P*V = n*R*T
Where ‘P’ is the pressure of the gas mix (pressure in the loop), ‘V’ is the volume (in this case, total loop volume), ‘n’ the total number of gas molecules, ‘R’ is a constant, and ‘T’ is the temperature.

Solving (6) for ‘n’:
(7) n = P*V/(R*T)

Now, combining (5) and (7):
(8) nO2 = ppO2*V/(R*T)

Therefore, for a given loop volume (‘V’) and temperature (‘T), the number of O2 molecules in the loop should depend solely on ‘ppO2’.

I didn’t read but look, if you are at 7ATA. Air is compressed 7x times, so in one litre you have the equivalent of 7 litres of molecules at 1ATA, so there is 7x more molecules of everything including O2

 

[Nirvana]

I didn’t read but look, if you are at 7ATA. Air is compressed 7x times, so in one litre you have the equivalent of 7 litres of molecules at 1ATA, so there is 7x more molecules of everything including O2

In your example, you are taking the same mix at different total pressures. The partial pressure of O2 would not stay constant.


Edit:

To illustrate my point above, take a cylinder and fill it to 2atm with pure O2. In this case, ppO2 = P = 2atm.

Now, start adding nitrogen to the cylinder (keeping the oxygen in, just to be clear). No matter how much N2 you add, ppO2 will remain constant (at 2atm in this example), as will the number of O2 molecules. What will change is the total pressure.

 

[BlueTrin]

In your example, you are taking the same mix at different total pressures. The partial pressure of O2 would not stay constant.

I do not know much about CCRs but I replied in the context of this post so maybe there is some confusion.

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.

 

[rjack321]

Sorry I worded my post above incorrectly trying to respond to the "just breath air dil" idea that was mentioned.

The ppO2 drop (ignore the fO2 as its not relevant and I was not thinking clearly) is much faster as you ascend and especially for small changes in depth near the surface vs at depth. That's partly why there are far more hypoxic events at or near the surface. Just going from 10m to the surface drops the ppO2 in half which is a much larger drop than when the deceased went from 70m up to 60m.

 

[broncobowsher]

It was in a FB group called “Technical Divers”

Ben, I'll have to read up on that once I get home. There were too many details missing here and I was hoping they would come out somewhere.

 

[dmaziuk]

Are you talking about sensors or controllers?

Yes. Whatever you have more than one of.

It's a well known problem in Comp.Sci., google for raft consensus or look here: Raft for the darling du jour solution if interested. (It's a cute visualization, to a computer geek anyway.)

(Another Comp.Sci. darling is mathematical induction: if "two is one, one is none", it follows that two is none. As well as any other number.)