Crossbar and isolator valve: do they help?

[AJ]

Of course everybody can say "I'm careful, it can't happen to me", but truth is that human error by distraction has happened to the best divers too, and it's wise to make one's gear more foolproof not only for beginners but for everybody if you use it often.

True, but beginners normally don't do doubles, at least that's what I presume. They better learn to dive properly first before they do dives where doubles are needed. The people who need doubles should know how to handle them with correct procedures. I use GUE EDGE for example. Other agencies have their own version I guess. No reason not to check the manifold (and other valves) pre dive and while diving.

Hence on average over the complete population of divers, if a training agency would recommend the non-isolation manifold instead of the isolation manifold, their students' safety record after class should improve. I think the problem here is it's hard to convince people that taking away an option (not being able anymore to shut off the manifold) improves their safety. People tend to underestimate their personal risk of human error and overestimate risk of gear failure.

Manifolds are important for deep (tech) dives. In these depths (with deco obligation) you don't want to loose more gas than necessary in case of trouble. So a manifold is an important piece of kit for these dives. When doing these dives you should be well aware of opened valves and check them regularly during your dive. I was trained to check valves while kitting up together with light check, gear check and everything. Then the GUE EDGE while in the water combined with buddy bubble check. While diving I do a flow check and gas check every 5 to 10 minutes.

So, I don't see why a manifold should not be recommended. Imo, learn to dive properly in stead of looking for solutions for a problem that does not exist.

 

[leadduck]

So, I don't see why a manifold should not be recommended.

Once again, I didn't say they should not recommend a manifold. The question is: why is the isolating valve inside the manifold still required if its safety track record is so bad?

See this picture:
File:Scuba Manifolds Schematic.png - Wikipedia

The upper right one is the "non-isolation manifold" as used by Bill Hogarth Main, or in Jeff Bozanic's blog. It gives you access to the complete remaining gas after turning off one 1st stage regulator, just like the "isolation manifold" in the upper left. But it doesn't come with the hazard of accidentally closing the isolation valve.

Imo, learn to dive properly in stead of looking for solutions for a problem that does not exist.

Agree. In that argumentation one could say the isolation *valve* (not the manifold!) is a solution to a problem that does not exist, but introduces a safety hazard that exists very much and has caused fatalities and numerous near misses.

 

[AJ]

Agree. In that argumentation one could say the isolation *valve* (not the manifold!) is a solution to a problem that does not exist, but introduces a safety hazard that exists very much and has caused fatalities and numerous near misses.

Is it the existence of the isolation valve or lack of training and complacency by the diver that caused the problem? I would not dive without isolation valve or manifold with my D12. Way to risky in my opinion. In that case I rather diving a single tank, less effort more fun.

To me it feels you're blaming the tool in stead of the fool. But that's just my opinion

 

[leadduck]

Is it the existence of the isolation valve or lack of training and complacency by the diver that caused the problem?

It's neither complacency nor lack of training, but human error. The one near-miss I witnessed was a GUE trained diver with GUE trained buddies. They certainly knew how the valve works and had done V drills before. Nobody could explain why it was closed during the dive, other than that he may have been distracted by something else (had another unrelated gear issue before the dive) and made a mistake.

Human error is not your fault. Once you focus on one task or thought, your brain filters a lot of other stimulus from your attention that's not related to it, and you're prone to making mistakes that you can't explain to yourself afterwards. This is a biological function that you can hardly get around. E.g, you missed the highway exit although the street signs were in plain sight right in front of you, but you were distracted by a phone conversation.
The invisible gorilla The Invisible Gorilla: And Other Ways Our Intuitions Deceive Us is a famous experiment. Even the best diver is not immune to this, it's natural.

People often say "don't use gear solutions for training issues". Sure, training can fix a lot of incompetence, or increase risk-awareness, or help make better decisions. But training alone cannot eliminate fatal human error; error-tolerant design is as important.

 

[AJ]

People often say "don't use gear solutions for training issues". Sure, training can fix a lot of incompetence, or increase risk-awareness, or help make better decisions. But training alone cannot eliminate fatal human error; error-tolerant design is as important.

Can't disagree on that. However should cars be limited to 10 Mph/Km because someone could crash? Should we stop flying because a plane can fall out of the sky because of pilot error? Every endeavour we undertake has its own risks and rewards. It's up to you to how many risk you're willing to take in regard to the reward. Foolproof does not exist, not by design as long as humans are involved. If you don't want to take the risk, that's fine. Find an other solution that mitigates the risk, but don't force others to use the same solution and even enhance risk for them. That's all I'am saying.

In other words: for me, I would rather take the risk of having a isolation valve closed unexpectedly (really small problem, I will normally detect within 5 minutes doing gas and flow check) than losing all my gas due to a leak while being down at 50 metres (really big problem). Not having an isolation valve would in this case mean more risk, than having a closed valve.

P.s. GUE divers are just ordinary divers. They also make mistakes although some of them might think otherwise. The team should have noticed this before descending, but sometimes we miss important signs. Happened to me also, that's a learning curve we all go through.

 

[stuartv]

Human error is not your fault. Once you focus on one task or thought, your brain filters a lot of other stimulus from your attention that's not related to it, and you're prone to making mistakes that you can't explain to yourself afterwards. This is a biological function that you can hardly get around. E.g, you missed the highway exit although the street signs were in plain sight right in front of you, but you were distracted by a phone conversation.

I agree with you.

It seems to me that what you are proposing is to eliminate one single potential source of problems that could arise as a result of human error. And, in exchange for that, you are giving up the ability to mitigate a whole other class of problems that could arise whether you have the isolation valve or not.

Is that a fair assessment?

The whole class of problems that could arise is "problems that result in gas loss, that cannot be stopped by closing the cylinder valve." E.g. tank valve O-ring blowout, burst disk failure, etc..

That question that you have raised is, is that class of problems "real" or is it only theoretical? I.e. Do problems in that class actually happen in the real world, or only on paper or only at the fill station?

An example was given earlier of some divers who had burst disk failures in the water. But, the example was dismissed because in both cases the failures happened at relatively the start of the dive, so the divers were able to simply abort the dive and surface. I don't think that is an acceptable reason to dismiss these examples. The examples demonstrate that burst disk failures CAN happen in the water. The divers were lucky (in my opinion) that the failures happened early. Nothing that was related about those incidents gave me any indication that the failures could ONLY happen at the beginning. They were just lucky. The same failures could have happened just as they turned the dives, from their maximum points of penetration.

So, unless you or someone else can make a better case that that particular whole class of problems is not "real", I think I would not be willing to accept the tradeoff I described above. I would rather depend on myself and my training to not make a mistake than to rely on something that I really cannot predict or control to not happen.

 

[cerich]

Reality is just that.

The reality is that the very low statistical chance of a burst disc or tank neck o ring failure lead to the isolation manifold as the solution for a very low statistical risk and introduced more potential failure points mechanically and also a much higher statistical risk of human failure and we have seen more death, injury and near calls with isolation manifolds than with non isolation manifolds.

It has been a fantastic sales pitch that the entire industry (including me) bought into but reality has proven otherwise.

However, people are people and most that firmly believe in something are loathe to change for fear of admission they made a bad decision when they bought into and will defend the decision.

 

[helodriver87]

We're talking about it like it's this big cosmic thing. It's a valve. When you put on your tanks, check it like you do the other two. If it was closed, don't dive until you have a chance to verify that it's safe. That's it. That's the only mitigation necessary. People roll in with their O2 turned off on CCR, but I don't hear calls to remove O2 bottles because it's simpler to just dive SCR. A straight bar manifold removes actual redundancy from doubles. It creates a class of unsolvable problems. Removing the isolation valve because people don't do proper valve checks is the definition of a gear solution to a training problem.

 

[stuartv]

We're talking about it like it's this big cosmic thing. It's a valve. When you put on your tanks, check it like you do the other two. If it was closed, don't dive until you have a chance to verify that it's safe. That's it. That's the only mitigation necessary. People roll in with their O2 turned off on CCR, but I don't hear calls to remove O2 bottles because it's simpler to just dive SCR. A straight bar manifold removes actual redundancy from doubles. It creates a class of unsolvable problems. Removing the isolation valve because people don't do proper valve checks is the definition of a gear solution to a training problem.

There is at least one near-miss that was described in an earlier post in this thread that would not have been mitigated by what you just posted.

 

[stuartv]

I'm glad for this conversation. I'm not too proud to share my own shortcomings.

I was teaching an Intro to Tech student this past weekend and we were going over failure scenarios. He asked me if it would not be just as good or better, when he hears bubbles, to turn off the isolator first, instead of turning off the actual post where he believes the bubbles are coming from.

At the time, I did not have a good answer for why tuning off the post first is the way it is taught. I admitted that and told him that, since I didn't have a solid reason why the post first is better, I would have to fall back to, "because I don't have a solid answer and either way seems equally valid on paper, we're going to stick with doing it the way I was trained and the way I'm teaching you." I.e. turn off the post first.

This discussion has now given me what I feel like is a solid answer for why we turn the post off first. The vast majority (maybe even all) of the times you have a failure to deal with, it's going to be something that is mitigated by turning off the post. If you turn off the isolator first, you still are going to have to turn off the post. Thus, by turning off the isolator first, all you've done is waste time and the gas you lost during that time. Basically, you will lose more gas by turning off the isolator first, rather than turning off the post first.

The only time that would not be true is if you have a tank valve O-ring or burst disk blowout. And, those are so rare in comparison to other possible failures, that when we hear bubbles we start with the presumption that it will be addressed by turning off the post - because that is what the statistics tell us makes sense.