One dead, one missing (since found), 300 foot dive - Lake Michigan

[cathal]

Per the manual there is a quite significant change in WOB from 2.45J/L to 2.75J/L give or take in going from horizontal to vertical on a mixed gas dive

Its a 11% difference in WOB. But as we do not know the Diluent mix for the dive in question, this point is moot for this incident.

The WOB on ‘a’ CCR doesn’t need to be higher than OC. Granted on some CCRs it is. Dependent on the specific pitch, depth, gas and workload and test criteria 'a' CCRs WOB can be lower, see http://www.deeplife.co.uk/or_files/DV_OR_WOB_Respiratory_C1_101111.pdf
Unlike scrubber duration, WOB is also independent of temperature. Though for CE purposes its testing is done at 4’C or roughly the water temp of this dive.

Again Diluent mix is a factor that will heavily impact the WOB of both CC and O.C regardless of unit type. Gas Density plays a significant role in WOB at depth as Mitchell et al recent paper demonstrated:

"One of the most important influences on work of breathing in diving is the increase in density of respired gas that occurs as depth increases. Since any underwater breathing apparatus will supply gas at ambient pressure, the density of the respired gas increases in direct proportion to depth. Increases in gas density result in a parallel increase in the resistance to flow of the gas through the diver's own airways, and in rebreather diving there is also the extra effort of moving dense gas through the hoses, connectors and CO2 scrubber of the unit. Under these circumstances, the associated increase in the work of breathing can be substantial."

"QinetiQ is a UBA testing house located near Portsmouth in the UK. Over some 20 years hundreds of manned test dives have been undertaken utilising ethics committee approved protocols which incorporate graded levels of underwater work for evaluating performance of a range open-circuit, semi-closed, and closed-circuit UBA. These dives have been conducted over depths ranging from 4 to 80 m (13 to 262 ft), using a range of gases including oxygen, air, nitrox and heliox. Throughout these tests a standard set of endpoints have been used to define 'dive failure' including: (any of) equipment or monitoring failure, diver unable or unwilling to continue because of dyspnoea (shortness of breath) or exhaustion, and an end-tidal CO2 >8.5 kPa (64 mm Hg) over five consecutive breaths. The latter is indicative of significant CO2 retention to a level associated with sudden incapacitation in the diving setting (Warkander et al. 1990)."

"there is a clear signal that near a respired gas density of 6.0 g·L-1 there is an upward inflection in the risk of dangerous CO2 retention during working rebreather dives. A similar analysis of dive failures in open-circuit underwater breathing apparatus trials produced a virtually identical result."

"For the purposes of planning rebreather dives and in the current absence of more definitive or contradictory data, it seems prudent to recommend an ideal maximum gas density of 5.2 g·L-1 and an absolute maximum of 6.2 g·L-1."

I understand that the ALVBOV significantly lowers the rEvo WOB when substituted for the stock DSV and has the same right to left gas flow as default. And a gag strap. While I know one wasn’t being used in this case, the option to fit ALVBOVs to rEvos and therein lower their WOB, has been an option that the manufacturer has known about for a considerable period.
http://www.deeplife.co.uk/or_files/DV_DL_ALVBOV_Breathing_Params_A3_100318.pdf https://www.opensafety.eu/datasheets/ALVBOV_40m_75lpm_air_081014.pdf
Open Safety Equipment Ltd

[FONT=Open Sans, Helvetica, Arial, sans[/COLOR]
Can you share with us who tested this particular BOV, which I struggle to find for sale anywhere?

 

[Brad_Horn]

Its a 11% difference in WOB. But as we do not know the Diluent mix for the dive in question, this point is moot for this incident.

No it’s not moot because when the diver goes vertical - from the horizontal we both would have to assume they were in whilst scootering - as if could occur when they stop after noticing a problem and look at ascending. Their WOB automatically worsens. Exasperating any issue and making it harder to resolve. This is by design BUT a known, so I’d assume has been covered in their training.

Granted an increase of 0.3J/L irrelevant of the gas density is not a lot but it is a fixed increase. And potentially half the total WOB on an alternative CCR on heliox at 100m at 75lpm. I’m sure someone more clever than I can work out what that functional difference in He% works out as by reverse engineering the gas density variation at 100m.

Again Diluent mix is a factor that will heavily impact the WOB of both CC and O.C regardless of unit type. Gas Density plays a significant role in WOB at depth as Mitchell et al recent paper demonstrated:

Agreed but note that they also state

All underwater breathing apparatus, including rebreathers, should be designed with the goal of reducing their external breathing resistance as much as is practicable. Other than choosing a device with good related design and testing characteristics there is little that divers can do in this regard.

which is being commonly ‘misinterpreted’ by others as there being little to no WOB difference between CCRs. Which is a little white lie at best and a severe fallacy at worse.

Equipment differences are typically small, and divers tend to manage other relevant factors before they enter the water, leaving divers to contend with gas density as a primary modifier of WOB in many situations and a focal point for hyperbaric researchers.

So if in this instance the manufacturer had designed their rebreather with the gaol of reducing their current external breathing resistance as much as is practicable it’s going to be in the order of 0.65J/L at 100m on Heliox at 75lpm. Per http://www.deeplife.co.uk/or_files/DV_OR_WOB_Respiratory_C1_101111.pdf per tests 28 & 30 tabled page 190 proving it quite possible and practicable.

And you’d think they would certainly be below the NEDU Heliox Diving acceptable levels of Work of Breathing per Table 4-3 http://archive.rubicon-foundation.o...0662/NEDU_TM_15-01_7_July_2015.pdf?sequence=1

Something that I can’t find listed in the above gas density paper is the upper and lower limits of the WOB for the rebreathers that the QinetiQ got their data from. But considering the WOB of a 30yr old Mk16 is 1.85J/L at 100m on Heliox http://archive.rubicon-foundation.org/xmlui/bitstream/handle/123456789/9902/a550047.pdf?sequence=1 and one would assume QinetiQ tests better performing kit now, it would be interesting if the data was rerun using higher WOB equipment. As was dived in this instance by recreational divers.

Now the rEvo could have better WOB than 2.75J/L when vertical at 100m on Heliox but I can’t find that documented?
[FONT=Open Sans, Helvetica, Arial, sans[/COLOR]

Can you share with us who tested this particular BOV, which I struggle to find for sale anywhere?

Well the test data is published by Deep-Life as you know,
but I think it’s no secret that it has also been tested by Micropore, QinetiQ, TechnipFMC and rEvo rebreathers with this openly documented. Quite a few others to boot. You’ll note that no other rebreather manufacturer who tests their rebreathers has disputed the documented testing and low WOB of the ALVBOV….

As to availability, its only been readily pursuable from OSEL for the past decade or so Open Safety Equipment Ltd
OSEL isn’t forcing anyone to dive a lower WOB rebreather. Just giving you the option to do so! And at a lower cost than a number of higher WOB or untested BOVs. And with more integrated safety features.

 

[Kay Dee]

First, condolences to family and friends.

With regards this incident, its rare (actually this is the first I know about) to hear of two deaths whilst diving a CCR - or SCR - on the same dive (be it on a so-called 'technical' dive or otherwise), but what makes it rarer still is that they are family members, and even rarer still to have been diving on the same make of rebreather.

Does anyone know any other CCR incidents that cover even one of the above points? (I know of a couple of OC incidents on 'techincal' dives - and regular dives - but not whilst on a rebreather.)

 

[Marie13]

I’d be careful calling these “CCR deaths” as that implies the rebreathers were the cause of death. We don’t know that now and may never know that.

 

[Kay Dee]

I’d be careful calling these “CCR deaths” as that implies the rebreathers were the cause of death. We don’t know that now and may never know that.

Have edited accordingly. It was not my intent to imply that the CCR's caused the deaths. But they were deaths while diving on CCR's.

 

[Celt]

Generally speaking, I’m not talking about the people who lost their lives in this accident, I think the differences in scuba equipment design is small compared to the difference in fitness levels of the people using it, I could walk out of an old folks home with half a lung and buy and use all the diving gear I want.

 

[cerich]

First, condolences to family and friends.

With regards this incident, its rare (actually this is the first I know about) to hear of two deaths whilst diving a CCR - or SCR - on the same dive (be it on a so-called 'technical' dive or otherwise), but what makes it rarer still is that they are family members, and even rarer still to have been diving on the same make of rebreather.

Does anyone know any other CCR incidents that cover even one of the above points? (I know of a couple of OC incidents on 'techincal' dives - and regular dives - but not whilst on a rebreather.)

Without even thinking hard I can recall two others with multiple fatalities where the divers were on CCR.

One of which really had nada to do with the fact they were on CCR except it allowed them to make a dive they REALLY should not have been making.

The other one, IMHO, while they had a cascade of issues in a very demanding dive for a host of reasons, there were multiple deaths in part (there were other contributing factors, it went horribly pear shaped and the divers managed it until they couldn't) due to team bailout.

The dive in question, I "suspect" one diver had issues of some type(I am not saying with CCR) and the other died as a result of trying to help. Hopefully eventually there will be a clear picture.

 

[Kay Dee]

Without even thinking hard I can recall two others with multiple fatalities where the divers were on CCR.

How right you are, and just goes to show how posting "off the cuff" and the falablity of relying on (my) memory alone is. I assume one that you refer to is the cave incident in Norway that happened to a Finnish diver group, but the other you allude to still escapes me.

How many of my 'criteria' did they fulfill, one or two (same dive / make of CCR?), or the one that alludes me, all three even? If I had of thought harder, I expect I would have eventually realised it was more the same family members / same make of rebreather that I cant really recall offhand.

 

[Nirvana]

How right you are, and just goes to show how posting "off the cuff" and the falablity of relying on (my) memory alone is. I assume one that you refer to is the cave incident in Norway that happened to a Finnish diver group, but the other you allude to still escapes me.

How many of my 'criteria' did they fulfill, one or two (same dive / make of CCR?), or the one that alludes me, all three even? If I had of thought harder, I expect I would have eventually realised it was more the same family members / same make of rebreather that I cant really recall offhand.

I suspect the other incident he was referring to was a double fatality at Eagle's Nest: Diving incident at Eagles Nest Sink

The two deceased divers were on the same model of rebreather, for what I've read. As far as I know, the divers were not related.

 

[cerich]

How many of my 'criteria' did they fulfill, one or two (same dive / make of CCR?), or the one that alludes me, all three even? If I had of thought harder, I expect I would have eventually realised it was more the same family members / same make of rebreather that I cant really recall offhand.

your criteria, you decide what they meet, I wasn't aware it was a test.