While reading a recent thread, I came across a claim that cascading failures, while often stressed in training are, in fact, extremely uncommon, and actively trying to avoid them can be counterproductive. I guess this would be true if major failures were uncorrelated. I wonder to what extent that's true. Has anyone experienced two or more major failures on the same dive? Did that appear to be a pure coincidence, or might the occurrence of those failures have been influenced by a common factor?
Are major failures uncorrelated?
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1500 dives over ten years, with a variety of buddies. I've had one dive with a major failure, and that was a freeflow. It did cascade a little, in that it resulted in a poorly controlled ascent because I couldn't see or hear and I was pretty anxious. I had been diving about six months when it happened. Other than that, no major failures for me or any of my buddies, in any kind of dive in any environment.
It's because we try to avoid them that they are so uncommon.
Major failures, in my mind, come in two main types as well. (1) failure of reg or BCD and (2) failure of the buddy system that can put a diver in severe danger as well. In my experience (1) is uncommon but (2) is not.
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Major failures, in my mind, come in two main types as well. (1) failure of reg or BCD and (2) failure of the buddy system that can put a diver in severe danger as well. In my experience (1) is uncommon but (2) is not.
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You have to look at what "correlation" is...
If we take the statistic wording for it, there is simply no way that your bcd going BANG! is correlated to spg going BANG as well.
But if it's due to poor maintenance of gear, you can expect someone to give roughly the same maintenance to all its gear. So if such a person's mouthpiece goes on the main reg, there is a chance that it happens on the backup as well, which you could assume is "higher" than normal, because since it has had the same treatment as the other, and the other went, with them having the same story, the likelyhood of it breaking increases.
Another example where issue 1 increases the likelihood of issue 2:
- your reg freeflows real bad, that's issue n°1
- you kind of suck at fixing it, you're now out of air, issue n°2.
Issue n°2 is obviously dependant on n°1, as it would have been unlikely to happen without it. But n°2 doesn't increase n°1 probability, so it's not exactly correlation, but it goes in the "cascading effect" you mention.
So imo, no such thing as "we had one issue, so there comes the other". My reg breaking won't cause yours to break. (but don't forget Murphy)
But, I'll end this with:
- I hate statistics, you'll have to get RJP over here, he'll even go and make a survey, you'll see!
- I'm far from being an expert in diving (or anything else)
If we take the statistic wording for it, there is simply no way that your bcd going BANG! is correlated to spg going BANG as well.
But if it's due to poor maintenance of gear, you can expect someone to give roughly the same maintenance to all its gear. So if such a person's mouthpiece goes on the main reg, there is a chance that it happens on the backup as well, which you could assume is "higher" than normal, because since it has had the same treatment as the other, and the other went, with them having the same story, the likelyhood of it breaking increases.
Another example where issue 1 increases the likelihood of issue 2:
- your reg freeflows real bad, that's issue n°1
- you kind of suck at fixing it, you're now out of air, issue n°2.
Issue n°2 is obviously dependant on n°1, as it would have been unlikely to happen without it. But n°2 doesn't increase n°1 probability, so it's not exactly correlation, but it goes in the "cascading effect" you mention.
So imo, no such thing as "we had one issue, so there comes the other". My reg breaking won't cause yours to break. (but don't forget Murphy)
But, I'll end this with:
- I hate statistics, you'll have to get RJP over here, he'll even go and make a survey, you'll see!
- I'm far from being an expert in diving (or anything else)
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For me, the thought of cascading failures is nice for avoiding the incident pit. It's a bit like gun safety: You want several layers of safety to avoid fatal accidents. To take the gun safety allegory: You don't point your gun at your buddy just because you "know" it's unloaded. You don't skimp on safe handling practice just because you "know" the safety is on. You don't leave a gun around the house just because you "know" that the ammo is locked up, or that your kids have been told to stay away. If the consequences of a fcuk-up are potentially fatal, you want to have a safety margin and at minimum one, preferably several layers of safety.
The incident pit is a well-known phenomenon. You have one malfunction, you are (usually) less well equipped for another. As sonn as the first malfunction has happened, the risk of a second one is equal to the risk of the first. You don't run a lower risk of another one just because you've had one (believing that is a very common fallacy, "I've thrown two sixes already, there's no way I'm going to throw a third six, because the chance of three sixes in a row is really low").
That's why if something goes tits-up, I'm getting out of the water until everything's fine again. Not because I believe in cascading failures, but because the first failure makes me less able to handle a second one. And the second one is just as probable as the first one, if hte first one has already happened. And training for multiple failures would then be a good thing if you are in a cave or have a deco obligation and can't get out of the water pronto, because you're further down in the incident pit and it's going to be difficult to fix multiple failures.
The incident pit is a well-known phenomenon. You have one malfunction, you are (usually) less well equipped for another. As sonn as the first malfunction has happened, the risk of a second one is equal to the risk of the first. You don't run a lower risk of another one just because you've had one (believing that is a very common fallacy, "I've thrown two sixes already, there's no way I'm going to throw a third six, because the chance of three sixes in a row is really low").
That's why if something goes tits-up, I'm getting out of the water until everything's fine again. Not because I believe in cascading failures, but because the first failure makes me less able to handle a second one. And the second one is just as probable as the first one, if hte first one has already happened. And training for multiple failures would then be a good thing if you are in a cave or have a deco obligation and can't get out of the water pronto, because you're further down in the incident pit and it's going to be difficult to fix multiple failures.
The cascade effect is not about multiple major failures in cascade.
It's about a series of small, seemingly-insignificant or non-critical problems that then cascade into a major failure when the problems are ignored.
The take-home message is that you should not ignore minor problems when they arise, but correct them promptly.
I was in the aviation business for many years, and the cascade effect is well known as the primary cause in most crashes (and gets lumped together in the news as "pilot error"). Case analysis formed the basis of a significant amount of our pilot training.
It's things like a little leak in your BC or a power inflator that doesn't work that can cascade with other problems into a catastrophic failure if you decide to jump in the water without first correcting those problems.
It's about a series of small, seemingly-insignificant or non-critical problems that then cascade into a major failure when the problems are ignored.
The take-home message is that you should not ignore minor problems when they arise, but correct them promptly.
I was in the aviation business for many years, and the cascade effect is well known as the primary cause in most crashes (and gets lumped together in the news as "pilot error"). Case analysis formed the basis of a significant amount of our pilot training.
It's things like a little leak in your BC or a power inflator that doesn't work that can cascade with other problems into a catastrophic failure if you decide to jump in the water without first correcting those problems.
Kharon
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I would add or you panic to ignored.
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I will give you an example.
During my trimix class I was at 260 feet on a reef in Cozumel. My instructor (diving Apeks regs) blew a diaphragm. He reached up and shut off his whatever post, no muss, no fuss. Except that, by the time he got the post shut off, he was at 120 feet, entrained in his bubbles.
I count 2 major failures, one brought on by the other. A failed regulator caused a complete loss of buoyancy control. Now, because he was a very experienced diver neither failure resulted in a big deal. He came down to 200, motioned us to come up, and we all ascended normally to a deco stop and finished out the dive. Had he been someone else, perhaps the reaction would have been different. We all practice S-drills, and he performed it as practiced, but who of us understand that a total regulator failure may result in us being pinned to the roof of the cave or worse, blowing through the first deco stop on an elevator to the surface (this was back when deep stops were in vogue).
During my trimix class I was at 260 feet on a reef in Cozumel. My instructor (diving Apeks regs) blew a diaphragm. He reached up and shut off his whatever post, no muss, no fuss. Except that, by the time he got the post shut off, he was at 120 feet, entrained in his bubbles.
I count 2 major failures, one brought on by the other. A failed regulator caused a complete loss of buoyancy control. Now, because he was a very experienced diver neither failure resulted in a big deal. He came down to 200, motioned us to come up, and we all ascended normally to a deco stop and finished out the dive. Had he been someone else, perhaps the reaction would have been different. We all practice S-drills, and he performed it as practiced, but who of us understand that a total regulator failure may result in us being pinned to the roof of the cave or worse, blowing through the first deco stop on an elevator to the surface (this was back when deep stops were in vogue).
halocline
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What's the light like at 260 ft in Cozumel?
I think of cascading failures as things like: Reg freeflows, diver reaches back to turn off post, loses buoyancy control and gets his fins in the silt and now converts situation to zero viz, and he's not close enough to the line to feel it, so he's now off the line and has lost his team.
This is why we drill and drill and drill single failures, so that we can be sure that a freeflowing reg WON'T result in a 100 foot ascent, or a siltout. In almost all cases, the cascade can be stopped by an effective response to the first problem.
This is why we drill and drill and drill single failures, so that we can be sure that a freeflowing reg WON'T result in a 100 foot ascent, or a siltout. In almost all cases, the cascade can be stopped by an effective response to the first problem.
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