Regulator bungie for recreational diver

[SangP]

If you guys really believe the manufactured reliability is as poor as these failure rates that are being argued about, maybe it is time to become freedivers instead

Lol it's for illustrations purposes, if regs had a 1% failure rate I'll stop diving already.

 

[avengerki]

But... it does increase the chance of failure... Because now you've got two things that can break/leak/come apart, etc. We went over this a few pages back with the coin flipping analogy. The trick is that the benefit is far outweighed by the disadvantages.

Your coin flip analogy does not work for me, yes those are the possible outcomes but take a coin and flip it 100 times and you will not get 50/50. When flipping a coin there are a lot more variables to it over the fact that it has two sides.

 

[TSandM]

You guys are doing the math wrong.

If you have two things with a 10% chance of failure, the chance of both of them failing at the same time (assuming they are completely independent) is 1%. But the chance of one or the other of them failing is ADDITIVE, because they are totally independent. (See Addition Rules for Probability) In perfect math, the chance of one of the connections failing is actually slightly smaller, because you have to subtract the probability of BOTH of them failing (unless you include that as a subset of one connection failing). But it's additive, not mutiplied, and the more possible failure points you put into a system, the greater the chance that some one of them will fail.

However, in recreational diving, where the surface is always an option, a leak from a right angle adapter is unlikely to be disastrous. AJ and I inhabit a diving world where even small failures can be of tremendous impact -- a big leak from a connector can be a major problem, if you have a couple of hours yet to swim in order to end your dive. To cope with that, we use a system which has MANY more failure points than a single tank setup, and which requires the diver to learn a whole set of behaviors to cope with those failures. We put up with that because what we get in return is redundancy, so that in the case of the vast majority of common failures, we cannot be left without a gas supply.

Any decision one makes about gear has to consider the benefit that a change offers, and the potential downsides of that change. Adding another static o-ring connection is a pretty low risk change.

 

[PfcAJ]

Sigh.

First, lets get it out in the open that I do NOT think that a regulator has a 50% chance of failure, that's baloney. In reality, its very very low, sub 1%. However, 50% is a nice number and easy for people to understand and talk about since everyone has coins and it's a familiar scale. Also, coin flipping is pretty darn close to 50% if the sample size is large enough (100 is not a very large sample, btw), all variables included. Close enough for discussion's sake. That said...

Two DOES increase the chance of failure. 1/2x1/2=.25, this is correct. What's the balance of that equation? (Hint: It's .75)

Falling back on the toss of the coin model from earlier in this very thread, there are 4 possible outcomes from tossing two coins. HH, HT, TH, TT. If 'H' represents failure, 3/4 (.75, or 75%) of them include a failure (H). 25% do not include a failure (TT). 25% is less than 50%, 75% is more than 50%. Adding a second coin increases your chances of a coin landing on heads, in this case, by 25% (from 50% up to 75%).

You're simply not paying attention to the variables, just the numbers. Gotta watch both. Adding more gear increases your chances of something breaking/failing. I've done more than a handful of dives where there were about 30 (thirty) regulators within the team, not counting the setup guys. 30. You're nuts if you think that having thirty regs decreases the chances of ONE of them failing.

And I think something has been lost in translation over the interwebs regarding the swivels. You mentioned something regarding confusing redundancy with failure points. I am not at all confused on the two. Redundancy gives you options when something fails at the expense of added chance of someTHING failing. I can get down with that. Swivels don't add much to most people's diving kit, yet increase orings and moving parts. I don't get down with that.

 

[rx7diver]

You guys are doing the math wrong.

If you have two things with a 10% chance of failure, the chance of both of them failing at the same time (assuming they are completely independent) is 1%. But the chance of one or the other of them failing is ADDITIVE, because they are totally independent. (See Addition Rules for Probability) In perfect math, the chance of one of the connections failing is actually slightly smaller, because you have to subtract the probability of BOTH of them failing (unless you include that as a subset of one connection failing). But it's additive, not mutiplied, and the more possible failure points you put into a system, the greater the chance that some one of them will fail.

Not completely correct.

Here's a simplified example to illustrate (some of) the basic rules of elementary probability:

S'pose 'A' = a certain random event, and 'B' = a certain other random event. Then

1. Pr(A) denotes the probability that event A "happens" or "occurs".
2. Pr(B) denotes ... .
3. Pr(A or B) denotes the probability that either event A happens or event B happens or events A and B both happen.
4. Pr(A and B) denotes the probability that both events A and B happen.

Then

5. Pr(A) + Pr(B) = Pr(A or B) + Pr(A and B)
5a. ... which can be rewritten: Pr(A or B) = Pr(A) + Pr(B) - Pr(A and B)
5b. ... or rewritten: Pr(A and B) = Pr(A) + Pr(B) - Pr(A or B)
5c. ... etc.
5d. ... etc.

What's important here is that statements 5, 5a, 5b, 5c, and 5d are always true regardless of statistical independence.

6. Now, if events A and B are statistically independent, then Pr (A and B) = Pr(A) x Pr(B) ...
7. ... which means Pr(A or B) = Pr(A) + Pr(B) - [Pr(A) x Pr(B)], etc.

Safe Diving,

rxdiver

 

[JamesK]

You people argue about some really silly crap. Lol.

 

[divad]

I'm getting veritgo.

 

[fnfalman]

If you guys really believe the manufactured reliability is as poor as these failure rates that are being argued about, maybe it is time to become freedivers instead

Then there would be nearly zero failure points!!!

 

[TSandM]

In perfect math, the chance of one of the connections failing is actually slightly smaller, because you have to subtract the probability of BOTH of them failing (unless you include that as a subset of one connection failing)

rx7diver, I believe that the sentence I quote above says in words what you wrote in equations. We are not arguing with one another. The bottom line is that when you have two events, the probability of BOTH of them occurring (assuming they are independent) is the product of their individual probabilities, but the problem of ONE of them occurring is the sum of the probabilities, adjusted slightly to remove the lower likelihood of both of them occurring at once. This means that, the more failure points you have on a piece of equipment (or as AJ points out, on a team) the higher the likelihood that something is going to give you trouble. Keep stuff simple, wherever you can, if you want the fewest problems.

 

[rx7diver]

rx7diver, I believe that the sentence I quote above says in words what you wrote in equations. We are not arguing with one another. The bottom line is that when you have two events, the probability of BOTH of them occurring (assuming they are independent) is the product of their individual probabilities, but the problem of ONE of them occurring is the sum of the probabilities, adjusted slightly to remove the lower likelihood of both of them occurring at once.

TSandM,

Consider these three examples:

a. Pr(Both) = Pr(A and B), = Pr(A) x Pr(B) = 0.1 x 0.1 = 0.01 if events A and B are statistically independent.

b. Pr(One) = Pr(Exactly one) = Pr(A and B) + Pr(A and B), = Pr(A) x Pr(B) + Pr(A) x Pr(B) if independent
= Pr(A) x [1 - Pr(B)] + [1 - Pr(A)] x Pr(B) = 0.1 x (1 - 0.1) + (1 - 0.1) x 0.1 = 0.18

c. Pr(At least one) = Pr(One, or the other, or both) = Pr(A or B)
= Pr(A) + Pr(B) - Pr(A and B), = Pr(A) + Pr(B) - Pr(A) x Pr(B) if independent
= 0.1 + 0.1 - 0.1 x 0.1 = 0.19

The equations, though a bit tedious, capture the nuance. Different probabilities can be switched in above so that one can really appreciate these relationships, if desired.

This means that, the more failure points you have on a piece of equipment (or as AJ points out, on a team) the higher the likelihood that something is going to give you trouble. Keep stuff simple, wherever you can, if you want the fewest problems.

This really depends on how the system incorporates those additional failure points. System failure should be the focus. For example, independent doubles introduces twice (say) as many failure points as single-cylinder scuba. But independent doubles yields greater system reliability (i.e., the system is less likely to fail, is more likely to provide a diver with breathing gas) than single-cylinder scuba, all other things being equal.

Safe Diving,

rx7diver