Failure points vs redundancy

[Lorenzoid]

My own belief is that diver error, and yes I mean me, is far more likely than equipment failure and so design my rig around mitigating the conseqiences of an error rather than focusing on redundant systems.

I agree that diver error is more likely than equipment failure, but I believe the best way to mitigate the consequence of diver error is team diving--a redundant brain. Redundant gear and failure point considerations are all secondary to having someone there to double-check me.

 

[inquis]

Redundant gear and failure point considerations are all secondary to having someone there to double-check me.

I would expand that to redundant self-processes as well. For example, test the reg functionality during setup, before standing up, and again before splashing. It's conceivable I could be distracted and miss one, but the likelihood of missing all three is significantly lower.

Additionally, I have configured my tank height such that if the holes aligned in the cheese and I did somehow splash without my air on, I can easily turn the valve myself. Also importantly, I do not let this obviate the need for the earlier checks.

 

[datho87]

Well put. The biggest failure point is the diver. If redundancy adds to task loading, does that add to the potential for diver error thereby negating the benefit of redundancy? Even if not, does the increase in failure points from added equipment justify increased surviability from having redundancy?

Redundancy is no substitute for diver competency (including maintenance). For example, do pony bottles add a false sense of security (plus more failure points) when the real point is proper gas planning? If so, how is the redundancy/failure point balance established? Is it better to use a crossover manifold or independent back mount doubles? Is side mount better still? A manifold is a failure point. Independent doubles eliminate the manifold but add task loading/the need for another SPG (failure point), alternating seconds/gas balancing plus the inability to use one reg on both tanks. Side mount has the same task loading/failure points as back mount independents but offers the ability to swap firsts/hand off a bottle, if necessary. These debates have raged for decades with no end in sight. As has been pointed out, risk is the product of odds of equipment failure times the odds of serious injury times the reduction in diver performance from task loading.

Can a competent team mate constitute redundancy without adding failure points? Does team diving (not the same as diving in the same ocean buddy diving) reduce both the potential for diver failure and consequences of equipment failure, thereby lowering the need for redundancy, plus adding another brain for problem solving and reducing task loading? I think it does if done right.

Bottom line for me is: 1) dive within a competent team-including the boat crew/support divers, 2) be anal about equipment maintenance, 3) streamline and simplify the gear package observing the less is more principle, 4) recognize the team is as strong as its weakest member and the fact that adding equipment doesn't make up for poor skills, weak team mates or stupidity.

You’ve all provided great perspectives.

Kendall’s contribution about a ‘false sense of security’ adds an interesting layer. There is quite convincing research around “risk homeostasis”. Essentially the idea that we all have a set level of comfortable risk, and adding safety measures leads to us taking more risk, such that it all nets out in the end.

 

[Dark Wolf]

The great majority of my dives are solo, so I like redundancy.

DW

 

[boulderjohn]

The problem with the term "failure point" is that for too many people, it becomes a substitute for thinking. They just throw the term at some suggested item as if that issue itself was enough to exclude it. The truth is that everything we use in scuba is a potential failure point. We just have to think things through.

How likely is the failure? The harness strap on your backplate, for example, is highly unlikely to fail.

How serious is a failure? Losing a dive light in a cave is pretty darn serious, so we take several lights for multiple redundancy.

What benefit does it provide? The wing of a backplate and wing system does have a reasonable chance of failing, and it is often essential, so we are going to be looking for something we can use in case that happens.

Do they add other detrimental problems? It could be entanglement hazards, etc.

So what about adding an SPG to a system with air integration?

• SPGs rarely fail.
• They can fail, but in this case, failure would only bring you to where you would be without it.
• They provide the benefit of allowing you to continue the dive.
• They create a very minor and unlikely entanglement possibility.

 

[Whitrzac]

The problem with the term "failure point" is that for too many people, it becomes a substitute for thinking. They just throw the term at some suggested item as if that issue itself was enough to exclude it. The truth is that everything we use in scuba is a potential failure point. We just have to think things through.

How likely is the failure? The harness strap on your backplate, for example, is highly unlikely to fail.

How serious is a failure? Losing a dive light in a cave is pretty darn serious, so we take several lights for multiple redundancy.

What benefit does it provide? The wing of a backplate and wing system does have a reasonable chance of failing, and it is often essential, so we are going to be looking for something we can use in case that happens.

Do they add other detrimental problems? It could be entanglement hazards, etc.

So what about adding an SPG to a system with air integration?

• SPGs rarely fail.
• They can fail, but in this case, failure would only bring you to where you would be without it.
• They provide the benefit of allowing you to continue the dive.
• They create a very minor and unlikely entanglement possibility.

Except SPGs fail quite often and you dont know they failed until you drain the reg/tank and find it sticking at 1300psi.

 

[Whitrzac]

One thing people fail to consider is that in an emergency your brain turns to an anxiety filled bowl of mush. Whatever redundancy you have needs to be simple enough for you're 3 remaining brain cells to do quickly and effectively.


I think everyone has gone through a phase of RB diving where they added useless complexity in the name of redundancy to their setup.

 

[datho87]

The problem with the term "failure point" is that for too many people, it becomes a substitute for thinking. They just throw the term at some suggested item as if that issue itself was enough to exclude it. The truth is that everything we use in scuba is a potential failure point. We just have to think things through.

How likely is the failure? The harness strap on your backplate, for example, is highly unlikely to fail.

How serious is a failure? Losing a dive light in a cave is pretty darn serious, so we take several lights for multiple redundancy.

What benefit does it provide? The wing of a backplate and wing system does have a reasonable chance of failing, and it is often essential, so we are going to be looking for something we can use in case that happens.

Do they add other detrimental problems? It could be entanglement hazards, etc.

So what about adding an SPG to a system with air integration?

• SPGs rarely fail.
• They can fail, but in this case, failure would only bring you to where you would be without it.
• They provide the benefit of allowing you to continue the dive.
• They create a very minor and unlikely entanglement possibility. in a rig with both AI and an spg, an spg failure wouldn’t “only bring you to where you would be without it”. It would lead to thumbing the dive. Without it in the first place, one wouldn’t be thumbing the dive right?

The problem with the term "failure point" is that for too many people, it becomes a substitute for thinking. They just throw the term at some suggested item as if that issue itself was enough to exclude it. The truth is that everything we use in scuba is a potential failure point. We just have to think things through.

How likely is the failure? The harness strap on your backplate, for example, is highly unlikely to fail.

How serious is a failure? Losing a dive light in a cave is pretty darn serious, so we take several lights for multiple redundancy.

What benefit does it provide? The wing of a backplate and wing system does have a reasonable chance of failing, and it is often essential, so we are going to be looking for something we can use in case that happens.

Do they add other detrimental problems? It could be entanglement hazards, etc.

So what about adding an SPG to a system with air integration?

• SPGs rarely fail.
• They can fail, but in this case, failure would only bring you to where you would be without it.
• They provide the benefit of allowing you to continue the dive.
• They create a very minor and unlikely entanglement possibility.

Great points John. However, on a rig with AI and SPG backup, a failed SPG wouldn’t “only bring you to where you would be without it”. You would thumb the dive. With AI only, you wouldn’t be thumbing the dive.

 

[boulderjohn]

Except SPGs fail quite often and you dont know they failed until you drain the reg/tank and find it sticking at 1300psi.

OK, try reading my post again.

Yes, SPGs can fail, but if you are using one as a redundancy for your air integration, then in that case you are left with the same situation you would be in if you didn't take one with you because of your fear of a failure point.

 

[boulderjohn]

Great points John. However, on a rig with AI and SPG backup, a failed SPG wouldn’t “only bring you to where you would be without it”. You would thumb the dive. With AI only, you wouldn’t be thumbing the dive.

Why would you thumb the dive?