Failure points vs redundancy

[datho87]

Interested to hear thoughts around failure points versus redundancy.

When is it better to pursue redundancy, and when is it better to reduce failure points? While both pursuits make sense in isolation, they’re clearly mutually exclusive in some cases. An example that comes to mind is running a backup spg to a transmitter. On one hand it provides redundancy, but on the other hand it increases failure points. Perhaps it’s a case by case basis, in terms of risk management…?

 

[Cthippo]

I think a lot of it comes down to perception of risk, or, to put it another way, what scares us more.

A lot of people are more concerned with equipment failure and consider the liklihood of themselves making an error to be very low. On the other hand, actual equipment failures are exceedingly rare.

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. It's more likely that I will have a brainfart and forget something important than it is that A piece of my gear will fail underwater. Fortunatly, a lot of the same solutions can mitigate both problems.

For example, a pony bottle can mitigate against both an OOA emergency from not checking gauges and a regulator or hose failure.

 

[tursiops]

Need also to consider the impact of a failure, which depends on the kind of diving.

 

[inquis]

Basically, the answer to your question is "whichever has lower risk". However, it's important to understand that "risk" is the combination of two aspects: likelihood of failure AND severity of consequence.

I don't use an SPG & transmitter because of the increased probability of failure, while the severity of consequence of the failure is minimal either way. ETA: it's also a personal assessment of these aspects, especially the severity of consequence.

OTOH in a deco situation, redundant gas is worth the increased probability of failure because that results in a negligible severity of consequence. Without redundancy, the consequence could be quite severe and therefore an overall higher risk.

 

[MB NZ]

It's a good question. Along the same lines, where do you cross a line where you're carrying so much gear that it becomes a hazard in itself, the Christmas tree diver. There was a good discussion on the Solo Diving forum about whether an octopus is a help or hindrance where a side slung redundant cylinder is also carried.

 

[Kendall Raine]

I think a lot of it comes down to perception of risk, or, to put it another way, what scares us more.

A lot of people are more concerned with equipment failure and consider the liklihood of themselves making an error to be very low. On the other hand, actual equipment failures are exceedingly rare.

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. It's more likely that I will have a brainfart and forget something important than it is that A piece of my gear will fail underwater. Fortunatly, a lot of the same solutions can mitigate both problems.

For example, a pony bottle can mitigate against both an OOA emergency from not checking gauges and a regulator or hose failure.

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.

 

[Cthippo]

Just because I like to ...

This comes up with backmount doubles versus sidemount or a pony. All three are redundant against equipment failure, but only the latter two are redundant against user error. With backmount doubles you can use all your air without having to do anything. With a pony or SM you have to take intentional action by switching regs to use all your gas. Hence why I think that BM doubles give more gas but less redundancy than SM or a pony.

 

[inquis]

With backmount doubles you can use all your air without having to do anything

I would need to grossly deviate from my dive plan.

 

[Kendall Raine]

With backmount doubles you can use all your air without having to do anything. With a pony or SM you have to take intentional action by switching regs to use all your gas. Hence why I think that BM doubles give more gas but less redundancy than SM or a pony

If one needs to change the equipment configuration to compensate for bad gas management skills maybe the problem isn't in the equipment configuration. Besides, in cave you don't need to use all your gas to die. You just need to use more than you need to get out. After that it's just waiting...

 

[rx7diver]

System failure versus component failure. Build your system and protocols in such a way that a component failure is survivable.

Yes, there might be more things that can fail. However, if built "correctly" the system is more survivable.

rx7diver