Filmmaker Rob Stewart dies off Alligator Reef

[Diver0001]

I have never experienced that either, and I teach also.

I have actually seen divers sign "OK" to problems.

One example I clearly remember from a number of years ago was a student in the OW checkout dives. We were descending along a line to 6 or 7 meters and she gave me a "stop" sign. I stopped. I helped her stabilize her depth and then gave her the "OK?" sign. She signed back OK. I made eye contact with her and she seemed calm so I proposed continuing with the descent (descend sign) to which she replied OK again. I went down another meter and signed OK to her and she signed OK and then started swimming up.

At this point I knew that there was definitely something wrong so I went to her and we went back to the surface.

What it turned out to be is that she couldn't clear her ears. She managed to reach a depth of 3 meters or something before she decided to take matters into her own hands and swim back up.

In OW I teach that OK was is a question and that it needs to be answered with OK or NOT-OK. She got confused, apparently, and kept signing OK to me when it was NOT OK.

..... And just to point out that it isn't only a problem for OW students .....

During a check out dive in my Trimix course one of the divers -- who was an instructor in training -- suddenly broke with the group and started swimming away.

I looked at the instructor. He gave me palms up (don't know). I assumed it was a test of some kind so I signed to the instructor that I wanted to go after him. He approved and away I went. I caught up with him as he was still swimming away from the group in the direction of the shore. I stopped him. Signed OK to which he responded NOT OK and then turned and started swimming again. I tackled him a second time and pressed my regulator up to his ear and shouted "how can I help you". He then gave me "OK" "swim" "line" "ok" and started swimming again. That was two OK's in one chain of signs for something that I knew was not ok. He wasn't trying to make it clear, he was just trying to get back to the shallows as quick as he could and everything I did at that point seemed to be holding him up..... I concluded that he was hell bent on following the line back to the shallows, although I wasn't sure why and I needed to go do some stops and decided to leave him and rejoin the others. If I had had a computer I may have gone with him but I was diving on tables and I was locked into a deco schedule that involved swimming back mid-water so I couldn't have accompanied him over the bottom like that..... so I had to leave him. (and yes, there was a lot of learning done on that dive but that's for another post).

The instructor signed for where is my buddy.... I signed back "don't know" and the direction of the shore. He shook his head and at that point I still thought it was a scenario and that I had failed.

As it turned out it wasn't a test at all, it was a total cluster fk that was precipitated by the diver who left the group. His problem, it turned out after the fact, was that he was experiencing vertigo and decided to bail. There's a hand sign for vertigo but instead he gave me OK .... twice!

R..

 

[cathal]

Hello,

The most (and perhaps only) significant fact to come out of the MEs report (as represented in the attachment) is that the oxygen cylinder was empty. But before commenting further on this someone will have to remind me whether the rebreather Rob was diving had a leaky valve or not. It if did, then the oxygen cylinder being empty is difficult to interpret.

Simon M

Hi Simon
Yes the rEvo comes configured with a leaky valve. The O2 reg is capped and it therefore delivers a fixed I.P regardless of depth. The leaky valve is known as CMF (continuous mass flow) that delivers O2 at approximately .8lpm. This can be adjusted via the I.P of the O2 reg. The unit is called a HCCR in this operational mode as it is using both a leaky valve and a solenoid.
However the leaky valve can be plugged (the O2 reg has to be uncapped) for deeper dives i.e. depths greater than the I.P of the O2 reg. But in this particular instance there would have been no need to have plugged the leaky valve as it is reported the depth was 70M approx, so the I.P of the O2 reg would easily supply O2 at that depth.

Cathal (rEvo diver!)

 

[fsardone]

Hi Simon
Yes the rEvo comes configured with a leaky valve. The O2 reg is capped and it therefore delivers a fixed I.P regardless of depth. The leaky valve is known as CMF (continuous mass flow) that delivers O2 at approximately .8lpm. This can be adjusted via the I.P of the O2 reg. The unit is called a HCCR in this operational mode as it is using both a leaky valve and a solenoid.
However the leaky valve can be plugged (the O2 reg has to be uncapped) for deeper dives i.e. depths greater than the I.P of the O2 reg. But in this particular instance there would have been no need to have plugged the leaky valve as it is reported the depth was 70M approx, so the I.P of the O2 reg would easily supply O2 at that depth.

Cathal (rEvo diver!)

I believe this not to be completely correct.

A constant flow orifice works by establishing a shock wave into the orifice which makes the speed of gas capped at the speed of sound (this would be function of absolute temp but rather constant in the rango of temp we dive).

In order for the shock wave to establish the pressure on the high pressure side has to be at least twice of the pressure on the low side. Any increase of pressure will not increase the speed of the gas only its upstream density hence will change the mass flow.

Uncapping the reg will keep a 10 (or whatever the IP of the reg is set to) above ambient and therefore you will have an increasing with depth mass flow. Also you might even lose the shock wave if the IP is set at 10 bar at 90 meters (the equation to discover where you loose the shock wave is x+10=2x, where x is the ATA at which the high side is twice the low side and 10 is the reg IP).

So if the reg was capped, in order to maintain CMF at 70 meters (8 bar) the IP had to be at least 16 bars ... if uncapped at least 7 bar differential.

In this latter case the mass flow would be depth dependant and decreasing with shallower depths.

Cheers

 

[NAND]

Hey@all,

I am following this case with high interest, as an IANTD rEvo diver myself this accident is hard to swallow.

Reading trough this entire topic up and down and with the coroners report now available, there are still open questions to me which in my eyes are left to be clearified.

(I am in no way associated with IANTD, rEvo nor Addhelium except for being a customer, below are just my thoughts)

To first follow up on the 'leaky valve', yes- the rEvo units utilize CMF (Constant Mass Flow) which ideally is adjusted to the metabolism of the diver or slightly below. This may explain why such unit will be recovered with empty O2 tank. (Exactly as Cathal explained)

To wonder about the question of hypoxia, the rEvo's use Shearwater Computers as setpoint controllers. One feature on all versions (Petrel2 or NERD) is the fact that the PPO2 is logged equally to all other dive parameters such as depth and water temperature. The Coroners Report concludes with hypoxia at dive end as the main accident-mechanism triggering the drowning.

This makes a lot of sense spite the loop-PPO2 drop during ascent is a physical phenomenon. Diving with strap on the Dräger-made mouthpiece may not (in my opinion) save you from drowning- the mouth nose airway may still allow the counterlung to deflate. Further the gaspressure may just bypass your lips. It could therefore be established that RS failed to create positive boyancy.

It however seems weird to me that the PPO2-data of the controller were not mentioned in the report. Further, IANTD typically insists on O2-flush at the end of any ccr-dive (at least in my training records).

Q: If such was conducted, how can someone possibly become hypoxic surfacing?
Q: Is information on the Computer logfiles available?

The report further mentiones a computer gradient factor of 90/90 and fHe set to 20% instead of 50% being analysed in cylinder and liftbag. This in my eyes can not be easily explained.

Q: What reason may have caused both divers to falsify their settings? Was the problem perhaps a wrong gas being boosted into the CCR cylinders?

I am unsure if it is just me wondering, but the report raises more questions than answers.

 

[PfcAJ]

The report further mentiones a computer gradient factor of 90/90 and fHe set to 20% instead of 50% being analysed in cylinder and liftbag. This in my eyes can not be easily explained.

Q: What reason may have caused both divers to falsify their settings? Was the problem perhaps a wrong gas being boosted into the CCR cylinders?

That one is fairly straight forward. Game the computer to reduce deco time by lowering the inputted helium content relative to the actual mix. 90/90 is fairly aggressive (as is their whole diving style, apparently), so fibbing to the computer to reduce the deco time it outputs falls right in line.

 

[cathal]

I believe this not to be completely correct.

A constant flow orifice works by establishing a shock wave into the orifice which makes the speed of gas capped at the speed of sound (this would be function of absolute temp but rather constant in the rango of temp we dive).

In order for the shock wave to establish the pressure on the high pressure side has to be at least twice of the pressure on the low side. Any increase of pressure will not increase the speed of the gas only its upstream density hence will change the mass flow.

Uncapping the reg will keep a 10 (or whatever the IP of the reg is set to) above ambient and therefore you will have an increasing with depth mass flow. Also you might even lose the shock wave if the IP is set at 10 bar at 90 meters (the equation to discover where you loose the shock wave is x+10=2x, where x is the ATA at which the high side is twice the low side and 10 is the reg IP).

So if the reg was capped, in order to maintain CMF at 70 meters (8 bar) the IP had to be at least 16 bars ... if uncapped at least 7 bar differential.

In this latter case the mass flow would be depth dependant and decreasing with shallower depths.

Cheers

Apologies if I have not explained cmf correctly, in this instance I will defer to Mr Raymaekers in his explanatory paper on CMF here: http://www.revo-rebreathers.com/wp-content/uploads/2016/02/Understanding_Constant_Mass_Flow.pdf

I hope this clarifies any confusion

Cathal

 

[fsardone]

Apologies if I have not explained cmf correctly, in this instance I will defer to Mr Raymaekers in his explanatory paper on CMF here: http://www.revo-rebreathers.com/wp-content/uploads/2016/02/Understanding_Constant_Mass_Flow.pdf

I hope this clarifies any confusion

Cathal

I was not clear myself ... but the paper you linked is, thank you!
I was only concerned that people missed the issue of increasing density since the constant speed orifice has a mass flow depending on the upstream pressure hence gas density.

Cheers

 

[uwxplorer]

For whatever reasons, uploaded documents from the case discussed in this thread: Filmmaker Rob Stewart's family files wrongful death lawsuit have disappeared, together with the original posts (presumably infringing some of the forum rules).
For those of us who had a chance to take a look at them, the computer logs cleared up some of the questions raised in the present thread, namely the hypoxia hypothesis.
Indeed, the log clearly showed a pO2 of ~1 during the whole time the diver was at the surface, and above the maximum recordable value after that for the next 5 hours (after which the pO2 seems to have reached diluent level, suggesting they had swapped their O2 bottle just before jumping back in the water).
The noticeable fact on the log is the ascent rate on the last bounce dive: something like 200 ft to 20 ft in about 2 min, possibly less (they came back up faster than they went down). This is after a 25 min SI following three deep dives (including the last bounce dive, lasting roughly 3 min at the bottom depth).
I could see some serious fizzling occurring at the surface, with both divers equally hit...

 

[Wookie]

For whatever reasons, uploaded documents from the case discussed in this thread: Filmmaker Rob Stewart's family files wrongful death lawsuit have disappeared, together with the original posts (presumably infringing some of the forum rules).
For those of us who had a chance to take a look at them, the computer logs cleared up some of the questions raised in the present thread, namely the hypoxia hypothesis.
Indeed, the log clearly showed a pO2 of ~1 during the whole time the diver was at the surface, and above the maximum recordable value after that for the next 5 hours (after which the pO2 seems to have reached diluent level, suggesting they had swapped their O2 bottle just before jumping back in the water).
The noticeable fact on the log is the ascent rate on the last bounce dive: something like 200 ft to 20 ft in about 2 min, possibly less (they came back up faster than they went down). This is after a 25 min SI following three deep dives (including the last bounce dive, lasting roughly 3 min at the bottom depth).
I could see some serious fizzling occurring at the surface, with both divers equally hit...

The documents are still posted here: Horizon Dive Adventures Complaint Filed in Federal Court

 

[uwxplorer]

The documents are still posted here: Horizon Dive Adventures Complaint Filed in Federal Court

Thanks for the correction.