toxing while on ffm/gag strap

serpentara said:
Maybe it is limited to us back mount counter lung guys (rEvo here) who cant adjust their OPV.

Was your instructor Robin Jacoway?
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In my Meg class we did the same (toss loop over head). Its rather hard to flood it even with the loop floating overhead but seems like a silly approach for hard overhead/cave diving so I have since switched to pulling it down. I don't put either the gag strap or my mask strap under my hood here and losing my mask at that exact moment would only add to the excitement.
 
I can very much see why it would be beneficial to tuck it in a cave diving/overhead environment. I have seen some of the restrictions that cave divers wiggle through. I have a great deal of respect for cave divers but for lack of a better phrase, y'all are crazy! ;) Maybe one day...
 
rjack said:
I have found the buckles on the drager gags to be pretty iffy. They are very hard to adjust with gloves on beforehand (to snug up the strap) and then hard to loosen if you want the loop to hang lower in a bailout scenario. This is definitely a product which could be improved upon by a competitor, both price and function.
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They can be a bit hard to get the hang of tightening up with thick gloves
but the strap should be worn high on the crown of your head. It is simple
to slip it down to the back of your neck and leaves it easy to remove the
DSV/ADV from your mouth and tuck under your chin.
No loosening required.
 
Not all units have the same protocols for loop position when bailing out. Some units when using a BOV are more difficult to stow the loop over your head when bailing out. Part of the reason for having individual unit specific training! :)
 
bazSXD said:
"Simon's talk was interesting at Oztek where he mentioned that a O2 convulsion can be delayed. E.g you've come off the high ppo2 and on to a lower O2 gas and you'll still tox. "

Having survived an O2 hit I would say that you cannot delay a hit. I felt it coming on and switched to air but it still hit me twice on the way up. You can only get rid of O2 by metabolism, so once the O2 is high it is high and unless you get it very very early on you will get a hit .... trust me I know. If you keep pumping more gas into you ( using a FFM ) then you will fit and fit and fit. What does that do - cook the brain maybe ???

I guess we need Simon to cover this for a firm answer ... me I'm just a bush lawyer or doctor in this case so its only theory and bull ... regards Baz
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Hello,

I think there is some misunderstanding at play here. Indeed, I think both of you are saying the same thing. I think that "delay" in the original post was intended to mean that a convulsion could still occur even after a diver stopped breathing a high PO2, basically because the epileptogenic stimulus had reached a point where it was going to happen no matter what the diver did. Baz is effectively saying the same thing.

In answer to this:

"Any stats on how many people have survived an Ox TOx, verus fatalities?"

Not for the general diving population. However, there were some stunning data published by the French Navy in the journal "Military Medicine" in 2011. They reported a series of ~50 loss of consciousness events during diving by French Navy divers, and only two of these resulted in fatalities (IIRC). To those of us accustomed to hearing of such events and learning their outcomes this seemed like a very low rate of fatalities. There may be a number of contributing factors, but one of them (almost certainly) is that all the divers were wearing mouthpiece retaining straps. This is the best data of relevance to this issue we are ever likely to have, and I think it makes a powerful argument for using of these straps.

Simon M
 
Here is the paper

http://publications.amsus.org/doi/pdf/10.7205/MILMED-D-10-00420

ABSTRACT Introduction: Rebreathers are routinely used by military divers, which lead to specific diving injuries. At present, there are no published epidemiologic data in this field of study. Methods: Diving disorders with rebreathers used in the French army were retrospectively analyzed since 1979 using military and medical reports. Results: One hun- dred and fifty-three accidents have been reported, with an estimated incidence rate of 1 event per 3,500 to 4,000 dives. Gas toxicities were the main disorders (68%). Loss of consciousness was present in 54 cases, but only 3 lethal drowning were recorded. Decompression sicknesses (13%) were exclusively observed using 30 and 40% nitrox mixtures for depth greater than 35 msw. Eleven cases of immersion pulmonary edema were also noted. Conclusion: Gas toxicities are fre- quently encountered by French military divers using rebreathers, but the very low incidence of fatalities over 30 years can be explained by the strict application of safety diving procedures.
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GLOC said:
Here is the paper

http://publications.amsus.org/doi/pdf/10.7205/MILMED-D-10-00420
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I think that the critical factor in this French study that gets a mention at the very end of the paper is that the dive buddy's are tethered together when diving:

"However, the diving procedures imposed by military regulations (mouthpiece strap, buddy team with link, and diving instructor with open circuit to lend assistance if necessary during training) have greatly limited life-threatening complications, ie, drowning, which are too often recorded in recreational
technical diving."

i.e. if a buddy goes unconscious he is tethered to his buddy who will be alerted immediately and can then render assistance straight away. I do not believe that the fatality rate would be as low without this tether.

All the best

Cathal
 
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Simon Mitchell said:
Hello,

I think there is some misunderstanding at play here. Indeed, I think both of you are saying the same thing. I think that "delay" in the original post was intended to mean that a convulsion could still occur even after a diver stopped breathing a high PO2, basically because the epileptogenic stimulus had reached a point where it was going to happen no matter what the diver did. Baz is effectively saying the same thing.

In answer to this:

"Any stats on how many people have survived an Ox TOx, verus fatalities?"

Not for the general diving population. However, there were some stunning data published by the French Navy in the journal "Military Medicine" in 2011. They reported a series of ~50 loss of consciousness events during diving by French Navy divers, and only two of these resulted in fatalities (IIRC). To those of us accustomed to hearing of such events and learning their outcomes this seemed like a very low rate of fatalities. There may be a number of contributing factors, but one of them (almost certainly) is that all the divers were wearing mouthpiece retaining straps. This is the best data of relevance to this issue we are ever likely to have, and I think it makes a powerful argument for using of these straps.

Simon M
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Simon do you not think that the rate of rescue was high due to the tethering and the oc equipped instructor as well? a lot of rebreather accidents are "diver missing" or solo divers, what would the rescue results have been if they didnt have a gag strap but were tethered to their buddy?
Gag straps seem like a good idea but the diver still has to be found and rescued, if hes not wont he just suffocate instead of drowning?
 
Dave,

I think the point that Paul was making at RF3.0 and OZTek 15 was that if the diver isn't wearing a mouthpiece retaining strap and is lost he is dead, if he is found, he will still likely be dead. However, if he is wearing a mouthpiece and found, then there is a better chance of recovery than if he wasn't wearing one. Dead is dead, irrespective of how they died :(

I am sure that tethering will have certainly helped identify the LOC in a much shorter timeline, but what about if you have good active and passive communications, you are likely to notice that your team mate is missing. Solo diving is another matter...

Therefore, IMHO, a mouthpiece retaining strap is only part of a much wider jigsaw puzzle which includes good team skills, communication and (situational) awareness. Each one of the pieces won't solve the puzzle, but adding them together will certainly make things better.

Regards
 
Agreed Gareth,
I know Paul has been campaigning for the gag strap for a while and in isolation I absolutely agree with him. In fact I fitted one and tried to drown myself and the gag strap makes it very much harder but still not impossible to ingest water. I have been on the rescue end of a toxing diver and one thing I noticed is after the initial tox they open their mouths very wide (at least my subject did) and this makes for very hard work for the gag strap so im not 100% convinced they will always work. but I do agree its better than nothing as long as you use a dreager one.

I also agree its a chain of events we need to address not just a gag strap in isolation
 
Hello again,

I completely agree that strict buddy systems / tethering etc played a part in the result reported in the French paper. But even allowing for that, a tiny number of deaths in a large number of LOC events is a surprising result. I would be certain that the prevention of water aspiration while a buddy effected a rescue would have played a large part.

Simon M
 
Simon Mitchell said:
Hello again,

I completely agree that strict buddy systems / tethering etc played a part in the result reported in the French paper. But even allowing for that, a tiny number of deaths in a large number of LOC events is a surprising result. I would be certain that the prevention of water aspiration while a buddy effected a rescue would have played a large part.

Simon M
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I was most surprised by the number of LOC whether they lived or not. Seems awfully high to me. Glad the straps and FFM minimize the fatality rate but hopefully they are also working to not have so many LOCs to begin with.


Sent from my iPhone using Tapatalk
 
Michael Thornton said:
I was most surprised by the number of LOC whether they lived or not. Seems awfully high to me. Glad the straps and FFM minimize the fatality rate but hopefully they are also working to not have so many LOCs to begin with.
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Appears that high workload (elevated CO2?) and high pO2 were predominate causes for the high OxTox numbers.

A great majority of these biochemical troubles were encoun-tered by student divers in whom the intensity of physical exer-tion (sustained finning), difficulty to adapt breathing to thedevice at the start of the course, and the long duration of trainingdives led to an imbalance between CO2 production and elimina-tion with subsequent arterial CO2 build-up. Additionally, exces-sive work of breathing and exercising for any length of timeare prone to make a diver less tolerant to high oxygen levels,5and consequently, acute hyperoxia was also predominant in CSstudent during the initial part of their course. The associationbetween hypercapnia and susceptibility to CNS-O2 toxicity wasascribed mainly to the vasodilatory effect of CO2 antagonizingthe protective O2-induced cerebral vasoconstriction,6,7 therebyincreasing delivery of O2 to neural tissue, resulting in increasedproduction of deleterious reactive oxygen species.
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In training I would think it would be difficult to understand your own physiological changes due to the pressures of completing the training task and in operations, there might not be an option not to swim hard as the target isn't normally compliant ;) They might not be able to totally control the risk, but they have certainly tried to mitigate the impact once it materialises.

Regards
 
Simon Mitchell said:
Hello again,

I completely agree that strict buddy systems / tethering etc played a part in the result reported in the French paper. But even allowing for that, a tiny number of deaths in a large number of LOC events is a surprising result. I would be certain that the prevention of water aspiration while a buddy effected a rescue would have played a large part.

Simon M
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Simon, I was hoping you would weigh in on this one. Could you possibly address the original question? Quoted below. No buddy, no tether, but with gag/ffm. Tox happens, you just keep toxing? or? is there a point where the tox itself kills you?

"But the question has come to mind, if you tox or go hypercapnic, whilst on either ffm or gag strap, what happens? You ob dont spit a reg/dsv out and drown. No one bails you out, so what happens? Has anyone experienced this?
I'm assuming youll loose buoyancy and sink, or rise, and continue to tox/go uncon unless some intervention is given. IE ffm/gag strap might save you from drowning, but you'll just keep on with the original disabling influence. "
 
One doesn't tox indefinitely.

In my case I was out of it (on the deck of the boat, fortunately) for around 20 minutes, although it was many hours before I regained what little lucidity I normally get-by on.
 
The big thing with a full O2 seizure is your not breathing and exchanging gas. That's why during a tox you DO NOT change depth as barotrauma is very likely.

I feel that the gag strap or ffm would be of use to prevent water ingestion but if you don't have a buddy to rescue you during the event, your quite possibly done.

Cam
 
Cameron said:
The big thing with a full O2 seizure is your not breathing and exchanging gas. That's why during a tox you DO NOT change depth as barotrauma is very likely.
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This does not appear to be the case. There are pig data and I think a human trial that illustrated that during a seizure your airway is patent (open). Which makes sense because seizing people are still breathing not breathholding. I wouldn't want to find out either way, but I am a lot less worried about barotrauma than I am about drowning.
 
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