Fiona Sharp death in Bonaire

[RainPilot]

I understand that part. But adding 100% oxygen to make up the losses from metabolism would not helping in reducing the PPO2 in the loop, would it?

No, but it wouldn't increase the issue either, as the machine just wouldn't add any until it reached its set point, then on the ascent it would add O2 as needed to keep the SP (usually 1.2-1.3) If she lost gas at depth (mask clear, etc) then if the machine added diluent it would spike the PO2 and then she would need to breathe it down again till the machine could keep it constant.

 

[KenGordon]

Let me rephrase.
Could she have breathe the O2 level down at 91m-then ascended to 24m without adding any more air into the loop?

Yes, the normal thing is to be adding o2 to the loop to make up for the drop in ppo2. If you do nothing you will end up hypoxic. The computer/solenoid/o2 supply on an eCCR, such as the APD she was using, will do that without user intervention. The user does have to dump the expanding gas in their own lungs and the loop, just as an OC diver has to dump the BCD, or they become very positive. From 90 to 24 that will be many litres. That suggests to me that she was in control back to 24m, unless the trip from 90 to 24 involved bouncing off the surface.

Honestly, I think the 90m thing is a red herring.

 

[markmud]

Read Scuba diving fatalities - Wikipedia, "Human Factors"

Hi Popgun Pete,

Thanks for that link. I enjoyed reading it.

In an extreme situation, my most basic take away from your link is drop your weight belt or weight system no matter how your sinkers are configured. Or, drop your BCD if it is entangled. Drowning is permanent, the bends can be survived. Exhale as you ascend so you don't embolize. You know, basic stuff.

Or, better yet, have a good dive plan, and dive with a qualified buddy if doing dives that are beyond benign.

I witnessed a raccoon drown last summer. It was ghastly. Drowning is a crappy way to die. I would rather die in a chamber.

I have no idea how Fiona Sharp died. I would love to read a forensic analysis by a qualified scientist or team.

Sorry for her family's loss.

markm

 

[wedivebc]

I understand that part. But adding 100% oxygen to make up the losses from metabolism would not helping in reducing the PPO2 in the loop, would it?

Not adding anything to the loop would help reduce the po2. Adding either gas would increase it, one to a lesser degree. If she flushed with diluent at her target depth her po2 would spike to 2.0 . Not a good idea.

 

[wedivebc]

To my understanding, every time you exhale you will lose 4-5% of the gas volume as some of the oxygen is metabolized and converted to carbon dioxide, which is further absorbed by scrubber. To keep from generating vacuum in the loop, a diluent gas must be added. If you used helium as the diluent gas or trimix with low oxygen concentration, then you can slowly reduce the oxygen concentration in the loop. She used air for the diluent gas, from what I read. So there is no way that she could bring the oxygen concentration down.

The 5 % you're referring to applies at 1 at a the proportion of gas metabolized is much less at depth. Regardless of the o2 content if you continue to only replace lost o2 with an inert/oxygen mix like air the inert volume will eventually build up displacing the oxygen .remove the co2 and the diver will have no sensation of low o2 until it's too late.

 

[Couv]

So, to become hypoxic, she'd need to breath the 17% O2 down to 5% O2.
is this the kind of thing you mean?

Yes. Similar to shallow water blackout...but while on CC.

Yes, the normal thing is to be adding o2 to the loop to make up for the drop in ppo2. If you do nothing you will end up hypoxic.

^^^This is what I was wondering about...thank you.

The computer/solenoid/o2 supply on an eCCR, such as the APD she was using, will do that without user intervention.

That makes perfect sense else one would be have to deal with it manually throughout every dive. But let's say a diver overrides the automatic function for good reason (to lower the level of O2 so as not to exceed the PP limit at depth) will the computer/solenoid supply valve reactivate on it's own?

 

[JohnnyC]

Anything's possible but 24 msw on the reef is maybe 30 m from shore at Buddy's, possibly closer. 90 msw is 300 m out and the current is normally at right angle to required drift direction.

Absolutely. I'm just pointing out that we can't necessarily discount tox'ing simply based on the fact that she was found at 24m. She could just as easily tox there as at 90m. Or maybe she didn't tox at all, went hypoxic, lost the loop, and drowned. Could be any number of things.

Really, without seeing the actual profile and data from the computer, it's hard to prescribe a cause.

 

[The Chairman]

A reminder, Ms Sharp was not recovered in the high danger zone for hypoxia which is shallower than 20fsw. PPO2 decreases due to ascent @ 90fsw are easily mitigated by your bleed valve and/or a solenoid. In fact, this would normally be handled without human intervention, unless something went wrong mechanically. You still need to be vigilant, but personal intervention is not that common below 60 fsw.

On ascent, I turn off my ADV @ 30fsw, and will do an oxygen flush right at 20 fsw.

 

[fsardone]

On ascent, I turn off my ADV @ 30fsw, and will do an oxygen flush right at 20 fsw.

+1 I also switch setpoint to low to make sure I have total control of buoyancy so if she did the same the solenoid could have stopped firing util the loop came down to .7 (default low setpoint for APD inspiration) and so negating a possible buoyancy addition ...

 

[KenGordon]

That makes perfect sense else one would be have to deal with it manually throughout every dive. But let's say a diver overrides the automatic function for good reason (to lower the level of O2 so as not to exceed the PP limit at depth) will the computer/solenoid supply valve reactivate on it's own?

Electronic CCRs have a target ppo2. Typically 0.7 in the shallows, 1.3 at depth. While the ppo2 is above that it doesn’t add o2.

Some CCRs are manual, it is agued that you cannot fail to pay attention to a manual one as you are soon dead, whereas with an electronic one you can get away with not paying attention for years, until there is a failure you don’t notice.

The dumping as you ascend is of course manual, as per wing, drysuit etc. Sometimes you manually preempt the computer control, for example bumping up the ppo2 before an ascent, or dropping the setpoint so the computer doesn’t add o2 as you ascend to avoid causing more of a buoyancy problem. Also on stops you might have the setpoint at 0.7 but try to keep the loop 100% o2.