Accident in Finland

[dmainou]

1. The JJ ADV could be moved from the t-piece in the inhale counterlung, to the t-piece in the exhale counterlung, such that any hypoxic leak is further away from the mouth and upstream of the O2 Sensors.

The counter to that is that it would be harder to flush the unit and lower a high PPO2. So it's a no win here. It's better on some instances and not on others but reversing the position simply reverses the problem. It's harder to flush for example.

2. The JJ Controller could default on start-up at 0.7 with no lower than that being made available in any Menu.

It does, you need to manually change it to 0.21 and you need to be mad to jump into the water with the whole screen flashing red 0.21 and the HUD flashing non stop in red

I can manage, but I'd be much happier if the ISC APECS Controller in my Meg had only 3 Setpoints: 0.7, 1.0, and 1.2 (less button pushes and less chance of a user error). The Meg has the ADV as standard on the exhale counterlung (safe side!).

With the predator you can modify it on the fly to whatever you want.

From a moral/ethical standpoint, if a rebreather has a Probability of Failure on Demand of greater than 1 in 10,000, then you'd have to inform the user and obtain his/her informed consent before selling it, and if it is safer than that, you could fetch a higher price.

You keep going around this but still don't know who's going to test this. They are risky accept it, don't use them or write a pdf. Yes, rebreathers will change over time but it will be a small gradual change at a time. Pretty sure that both the unit manual and the training manual have plenty of disclaimers. To the point that one of the first disclaimers in the training manual is the risk of explosion. So I think that's pretty much covered. Further to this, open the predator's manual... no illusions that you are using a potentially buggy system.

"DANGER"

"You really are risking your life with this activity"

"WARNING

This computer has bugs. Although we haven't found them all yet, they are there. It is certain that there are things that this computer does that either we didn't think about, or planned for it to do something different. Never risk your life on only one source of information. Use a second computer or tables. If you choose to make riskier dives, obtain the proper training and work up to them slowly to gain experience.

This computer will fail.It is not whether it will fail but when it will fail. Do not depend on it. Always have a plan on how to handle failures. Automatic systems are no substitute for knowledge and training.

No technology will keep you alive. Knowledge, skill, and practiced procedures are your best defense. (Except for not doing the dive, of course)"




my 2c

 

[Mike Ferguson]

It does, you need to manually change it to 0.21 and you need to be mad to jump into the water with the whole screen flashing red 0.21 and the HUD flashing non stop in red

yes you would, but the issue here is that just because your setpoint is 0.19 doesn't mean your whole screen is flashing red, if it did it would be less of an issue. The problem with 0.19 setpoint not being immediately obvious is that you can get distracted at a critical point in your pre-dive checks then look at your handsets, see a figure of 0.68, 0.67, 0.68 and the whole screen a steady green and think near enough I'm good to go, and then jump in only to have your ppO2 crash to a dangerous level before you even reach the shot when working hard.

this is not a hypothetical situation. It happened to me and I posted an incident report to highlight my own stupidity in not paying sufficient attention to pre-dive checks and to stress the importance of giving those checks 100% attention and restarting from step 1 if you get distracted.

Subsequent to that post it was quite interesting to hear other people say 'I've done that as well'.

harking back to earlier posts in this thread it's may be better to remove the risk of hypoxic dil in the loop altogether by running pure O2 above 6m.

 

[gianaameri]

yes you would, but the issue here is that just because your setpoint is 0.19 doesn't mean your whole screen is flashing red, if it did it would be less of an issue. The problem with 0.19 setpoint not being immediately obvious is that you can get distracted at a critical point in your pre-dive checks then look at your handsets, see a figure of 0.68, 0.67, 0.68 and the whole screen a steady green and think near enough I'm good to go, and then jump in only to have your ppO2 crash to a dangerous level before you even reach the shot when working hard.

this is not a hypothetical situation. It happened to me and I posted an incident report to highlight my own stupidity in not paying sufficient attention to pre-dive checks and to stress the importance of giving those checks 100% attention and restarting from step 1 if you get distracted.

Subsequent to that post it was quite interesting to hear other people say 'I've done that as well'.

harking back to earlier posts in this thread it's may be better to remove the risk of hypoxic dil in the loop altogether by running pure O2 above 6m.

Running 100% O2 6 meters and shallower (including surface) would not be enough if in error you have set 0.21 (i.e. MAN) as Setpoint for example on the Meg (or if the JJ controller fails to auto-switch to say 0.7 when the depth sensor kicks in).

Much better to remove alltogether unsafe Setpoints from any part of the Menu to reduce the risk of User Error.

 

[GLOC]

And before this thread disappears down a rabbit hole of stats/probabilities of occurrence, can you take that discussion to another thread...

<<Bugger too late! I'll move it to another thread when home>>

Regards


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[Janos]

Stats posts moved to their own thread here: www.ccrexplorers.com/showthread.php?t=15190

Janos

 

[Baron015]

Bit tricky on a Sentinel (and possibly Poseidon Mk6) as the surface set-point is 0.4. It only raises to 0.7 once below the "splash" zone.

FYI - I was led to understand that pre-breathing on a lower set-point meant you where more likely to feel any CO2 effects (that's masked by higher set-points)

I seem to remember from when I owned a Sentinel that you could change the low set point value from the factory default of 0.4 to higher value, say 0.7.

I didn't do this and other Sentinel divers I met we're also running low SP at 0.4.

I never thought about why, until now. Still don't have an answer. I guess 0.4 always seemed high enough for surface SP.

Tb.

 

[Michael Thornton]

I seem to remember from when I owned a Sentinel that you could change the low set point value from the factory default of 0.4 to higher value, say 0.7.

I didn't do this and other Sentinel divers I met we're also running low SP at 0.4.

I never thought about why, until now. Still don't have an answer. I guess 0.4 always seemed high enough for surface SP.

Tb.

I like a .4 Low because it is easier to maintain on surface/boat in Altitude. For me it is high enough. Before I get in water I switch to .7

 

[MeRodent]

yes you would, but the issue here is that just because your setpoint is 0.19 doesn't mean your whole screen is flashing red, if it did it would be less of an issue. The problem with 0.19 setpoint not being immediately obvious is that you can get distracted at a critical point in your pre-dive checks then look at your handsets, see a figure of 0.68, 0.67, 0.68 and the whole screen a steady green and think near enough I'm good to go, and then jump in only to have your ppO2 crash to a dangerous level before you even reach the shot when working hard.

this is not a hypothetical situation. It happened to me and I posted an incident report to highlight my own stupidity in not paying sufficient attention to pre-dive checks and to stress the importance of giving those checks 100% attention and restarting from step 1 if you get distracted.

Subsequent to that post it was quite interesting to hear other people say 'I've done that as well'.

harking back to earlier posts in this thread it's may be better to remove the risk of hypoxic dil in the loop altogether by running pure O2 above 6m.

I realise I dive a rEvo rather than JJ (both of which use the shearwater) so the may be some differences but the pre-jump checklist involves changing to low set point (0.7) prior to adding O2. Therefore you shouldn't be in a position where O2 can drop to 0.19 if you follow the checklist, or even if you get interrupted during the check.

The critical point is going to the checklist before you start any dive. On my course we had another CCR diver onboard who agreed to help recover an anchor in about 10m for a boater as we returned from the dive site. Given that it was expected to be a quick dive (they were sitting on top of the lost anchor) he didn't do a pre-dive and realised after entering that he'd forgotten to turn on his gasses. Great reminder to the two of us doing the course that there's no excuse to shortcut your pre-dive regardless how long or insignificant the dive will be.

 

[Igor]

I realise I dive a rEvo rather than JJ (both of which use the shearwater) so the may be some differences but the pre-jump checklist involves changing to low set point (0.7) prior to adding O2. Therefore you shouldn't be in a position where O2 can drop to 0.19 if you follow the checklist, or even if you get interrupted during the check.

The critical point is going to the checklist before you start any dive. On my course we had another CCR diver onboard who agreed to help recover an anchor in about 10m for a boater as we returned from the dive site. Given that it was expected to be a quick dive (they were sitting on top of the lost anchor) he didn't do a pre-dive and realised after entering that he'd forgotten to turn on his gasses. Great reminder to the two of us doing the course that there's no excuse to shortcut your pre-dive regardless how long or insignificant the dive will be.

Obviously if you do a pre-dive breath as you should you will spot the the 0.19 setting right away. I don´t understand why you would use the 0.19 for anything else then dive log uploads and firmware updates though. The only reason i have herd so far is it will help identify a problem with the solonoid. That is a rather weak argument i think. In my view better avoid the 0,19 setting unless needed.

To get back to the topic. I do not think that this fatality was caused by a 0.19 setting or being drowned by the ADV. Although it has been interesting to follow the discussions and this shows that we can actually learn something from speculation to. I have had several PM´s indicating that the O2 bottle was turned off, that being said it might not be correct but everything points to this direction.

Unfortunate circumstances such as the mine was not allowed to dive in may have lead to the divers ignoring their normal routine. The sad fact is that the diver died setting up his deco bottles at 6m depth before a dive to 140m depth. He did not die at 140m, he died at 6m preparing for the dive.

This tells me something as numerous other accidents before this. Even the most routine dives on rebreathers are dangerous, in fact probably even more dangerous then the advanced ones. These are the times where you will not keep attention. Also in rebreather accidents it seems a large percentage of the casualties are very experienced, complacency killed them. Hypoxia is sneaky and very deadly indeed. Low o2 will not trigger a breathing response only co2 does, in many cases the divers just passes out with not much warning if any at all. Remember we are breathing in and out of a frigging bag. Back in the days when i ran a dive shop i amused myself by breathing pure helium between customers. I was young and stupid. I found that taking 3-4 full breaths made the voice optimal donald duck. It floored me though, convulsing on the floor. Just 3 frigging breaths! This illustrates both the ADV problem and the hypoxia problem. Both real risks.

Rebreather design is important and can help reduce risk. More important is proper training and strict procedures in my opinion. There is really no room for personal preference here! Strict protocols needs to be thought with out any compromise what so ever. Almost 270 CCR divers have died so far.

 

[Jude]

In both JJ cases there has been discussoion that CPR was not successfull perhaps as the whole body has become too hypoxic after some minutes of breathing of hypoxic gas. Would be interesting to get an experts opinion about that.
In the earlier case there was effective O2 treatment few minutes after unconsciousness but still no success.

Jukka

Comments to above question? Is there any way to revive diver from hypoxic?

 

[Garth]

Gian, Don't be obtuse.

0.19 is the substitute for SOLENOID OFF.

.

It's USED exactly like MAN on a Meg.

IsCAN on Meg Pathfinder has this at 0.20

It is designed as a soft "solenoid off" mode for rig servicing in air or for taking control of the rig manually in the water.



Dave

.

I might a correction or two here but I think the Hammerhead accomplishes by allowing a user to select open circuit on their handsets. The solenoid is turned off however if the PPO2 drops below .19 the solenoid will engage.

Sound about right?

If the above is correct it would seem like a greater safety factor than selecting a .19 setpoint.

 

[Bruce Partridge]

To clarify:

On the Shearwater controller you can not select a .19 setpoint or turn off the solenoid in any way during a dive.

As a convenience to the diver, the setpoint can be set to .19 on the surface to support maintenance. It was originally added at users' request due to the controller turning on on wet boats in the North Sea. The controller would activate due to the wet contacts and either empty the O2 tank if it happened to be on, or drain the solenoid battery. Over time, people also started to use it when they were doing firmware updates, downloads, or maintenance when the loop was open and setpoint could not be maintained. I use it to quickly stop and restart the solenoid during my build checklist to allow me to confirm the correct operation of my CMF valve and solenoid separately. I do this checklist any time I open my rebreather for maintenance.

It should never be used for diving, and the electronics will automatically override the setting if the controller enters dive mode.

The controller will never select .19 setpoint on its own. It must be selected explicitly by the user and is at the bottom of the menu. It cannot be selected in dive mode since it does not appear on the menu.

The Shearwater controller is state-aware and only provides menu options or asks questions that are appropriate for the current operating state.

As others have stated several times, the available information surrounding this accident points to the oxygen tank not being turned on.

If there is any value to be gained from this thread, it is that divers that enter the water without first confirming that their system is functioning correctly are SIGNIFICANTLY increasing their probability of dying on a rebreather.

It's fun for some to bash rebreather X, Y, or Z, but lets not lose sight of the fact that our friends are dying out there, and it is important that we also consider the real causes of these accidents. The overwhelming evidence, in my opinion, is that rebreather fatalities could be reduced substantially by following a very short list of operational behaviors. Using a checklist (in any form) to confirm the correct operation of your unit before diving is one. Having a reasonable cell replacement strategy is another.

We are always going to have some deaths that are more personal than diving related like heart disease and substance abuse.

If we as a community can persevere in getting root cause analysis of more accidents, I'm also sure that some causes will be mitigated better as technology improves. This goal is still severely hindered by the paucity of reliable and comprehensive accident data. We need to solve the right problems.

But, for now, we CAN improve our operational behavior and we CAN reduce fatalities if we accept the hard truth that most of these problems are human factors issues that can be best mitigated by changes in behavior.

Bruce

 

[Robert Månsson]

I might a correction or two here but I think the Hammerhead accomplishes by allowing a user to select open circuit on their handsets. The solenoid is turned off however if the PPO2 drops below .19 the solenoid will engage.

Sound about right?

If the above is correct it would seem like a greater safety factor than selecting a .19 setpoint.

And why would that be better, why would it be easier to remember to switch form OC rather then change set point.

I think the discussion about the set point is bit out of the track! (or how to say in English) - it's the whole time back to one thing - the diver don't follow the checklist, and do the pre-dive breath.

I also don't understand the thing with the shout-of valve on the dil. If you have a small leak you notice it on the countervolume, and the work of the solenoid - and close the DIL-tank.
I the ADV free-flow - well that you notice and close the DIL-tank.
Well that was the drill I learn on my Mod 1 and 2.

My thoughts
Robert

 

[Simon Mitchell]

Comments to above question? Is there any way to revive diver from hypoxic?

Hello Jude,

A diver who has become unconscious because of hypoxia can be resuscitated... in theory. However, the outcomes are frequently poor in any attempt at resuscitation in the community, even without the added challenges of retrieving a diver to the surface, removing them from the water, and running a resuscitation protocol in the cramped space of a boat. Not to mention that in diving the pathophysiology is frequently complicated by other problems such as aspiration of water, and decompression sickness.

Speed, and protecting the airway from water ingress are important ingredients to success. Speed is important because there is a variable interlude between the onset of respiratory arrest (accompanied by unconsciousness), and progression to cardiac arrest. If rescue breaths can be delivered during this interlude to restore oxygenation prior to cardiac arrest, then there is a fighting chance of a successful outcome. If cardiac arrest occurs, then the chances of resuscitating a diver in the field are slim to none (unfortunately). This is why the Diving Committee of the UHMS supports the concept of in water rescue breaths if it is possible to deliver them after arriving at the surface with an unconscious diver. These matters are covered in detail in their latest guidelines on rescue of an unresponsive diver from depth:

MITCHELL SJ, BENNETT MH, BIRD N, DOOLETTE DJ, HOBBS GW, KAY E, MOON RE, NEUMAN TS, VANN RD, WALKER R, WYATT HA. Recommendations for rescue of a submerged unconscious compressed gas diver. Undersea Hyperbaric Med 39, 1099-1108, 2012

Simon M

 

[Lancer4545]

Hello Jude,

A diver who has become unconscious because of hypoxia can be resuscitated... in theory. However, the outcomes are frequently poor in any attempt at resuscitation in the community, even without the added challenges of retrieving a diver to the surface, removing them from the water, and running a resuscitation protocol in the cramped space of a boat. Not to mention that in diving the pathophysiology is frequently complicated by other problems such as aspiration of water, and decompression sickness.

Speed, and protecting the airway from water ingress are important ingredients to success. Speed is important because there is a variable interlude between the onset of respiratory arrest (accompanied by unconsciousness), and progression to cardiac arrest. If rescue breaths can be delivered during this interlude to restore oxygenation prior to cardiac arrest, then there is a fighting chance of a successful outcome. If cardiac arrest occurs, then the chances of resuscitating a diver in the field are slim to none (unfortunately). This is why the Diving Committee of the UHMS supports the concept of in water rescue breaths if it is possible to deliver them after arriving at the surface with an unconscious diver. These matters are covered in detail in their latest guidelines on rescue of an unresponsive diver from depth:

MITCHELL SJ, BENNETT MH, BIRD N, DOOLETTE DJ, HOBBS GW, KAY E, MOON RE, NEUMAN TS, VANN RD, WALKER R, WYATT HA. Recommendations for rescue of a submerged unconscious compressed gas diver. Undersea Hyperbaric Med 39, 1099-1108, 2012

Simon M

Should the same diver who suffered the CNS event be wearing a FFM the possibility of a positive outcome is greatly increased given that there is now almost no possibility of him inspiring water.

Add a BOV to the FFM and the rescuer can now safely switch the diver to OC bailout gas and see if he is actually breathing or not. Knowing if the diver is breathing will allow the rescuer to chose the appropriate next course of action he would not otherwise know.

And finally have you ever rescued a diver from depth and had to try and hold his DSV or OC second stage in place........With a FFM strapped to his face he cannot drop the mouthpiece allowing the rescuer to concentrate on the rescue and not having to focus on keeping water out of his airway.

Diving with a FFM might seem like a PITA to some but when it comes down to it, the benefits far outweigh any negatives......

Regards,

Lance

 

[kwinter]

Going a bit further than Lance, after the rescuer switches the diver's BOV, he can use the BOV's purge button to ventilate. Tip the victim's head back to open the airway and the tight seal of the FFM makes it like using a rescue mask.

And don't forget about the added safety being able to use comms with FFM. (Insert nasty comeback from Lance here)

 

[Lancer4545]

Going a bit further than Lance, after the rescuer switches the diver's BOV, he can use the BOV's purge button to ventilate. Tip the victim's head back to open the airway and the tight seal of the FFM makes it like using a rescue mask.

And don't forget about the added safety being able to use comms with FFM. (Insert nasty comeback from Lance here)

Come on Ken........Comms are great but as you know you'll need to spit out the mouthpiece to speak

You can certainly press the purge button to get some "Fresh Gas" to the diver but I doubt you'll be able to actually able to ventilate him unless you have him upside down as the hydrostatic pressure will be too great to drive the gas into his lungs and will simply open the exhaust valve. But there is some merit in doing it maybe once.

Regards,

Lance

 

[bazSXD]

I have some strong reservations about FFM's on CCR units, the jury for me is still out on this matter.

Apart from the fact of the added failure points .... Keep it simple works for me. I also think you need to consider the following:

The gas that causes the problem is now fixed in place and if you pass out you will continue breathing that very same problem gas .... and you will fit until the gas runs out. So you cook your brain and then suffocate, maybe Simon M can comment on this ??

If you pass out the chances are very very good that you will sink and if like most of us we dive the "in the same ocean" approach with our buddy then you will sink downwards all alone. In this case the same applies as above ... a lonely death. The PPO2 will increase as you sink and thus will increase the already fatal problem, if thats possible.

Having had a hit I know for a fact that going to bail out is pointless and the only way you survive is head for the surface very very fast. If you are loaded with high O2 then breathing air will do Jack Sh*t. Once the beginnings of a CNS hit starts to appear you have very little if no chance of stopping it. My advice is reduce the PPO2 by going up, lots of free air up there and don't need to worry about deco, you've been on pure O2.

In the case of a rescue the FFM makes it more complicated for the rescuer. You are also dead weight and that is heavy and difficult to handle, again trust me I know. Most serious attempts to bring a person up from a deep dive end in the victim being uncontrollable from about the 35m mark upwards and normally results in either both divers having an uncontrolled ascent or the victim breaking or being set free and hitting the surface alone.

A FFM is not a self help item it depends on buddy action which makes it a poor second choice in my book. Self help rules.

The question goes back to risk assessment and should/would you help others and risk yourself. One death is better than two.

Just my two bobs worth .... comments ??? (sensible comments Lance if you can please).

regards BAz

 

[kwinter]

I'm a little confused, Baz. Haven't you been using an AGA mask with your rebreather for many years? Or have I mistaken you for someone else?

 

[dmainou]

Baz lives in Sydney.... not sure it's the same bloke.

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