Regulator shutdown at depth

[mafi]

Hi,

As a fresh AOWD, I was browsing through the TDI Extended Range and Trimix book lying on the table in LDS. In there, I've found this paragraph:

Oh, and if you are diving with someone and the signal you to shut down your regulator at 55 msw, give them "pack sand" signal back... and get a new dive buddy!​

Honestly, I cannot see the reasoning behind this. What is inherently risky on shutting down a regulator at depth, in comparison to shallow water? The only thing that comes to my mind is that it can somehow get stuck in the closed position, losing you all the gas in the cylinder.

Is that it or am I missing something important?

 

[AJ]

At 55 msw you don't mess around Every problem regarding to gas supply at that depth is serious enough to be potentially deadly. If you want to practice do it at 10 msw.

 

[RainPilot]

What AJ said, but here's a little more background...

Training in Threat and Error Management is very tricky, especially when you cannot safely simulate the "danger".
So, we put safeguards in place to prevent over eager instructors or students turning a "drill" into an emergency.

RAID stipulates NO actual regulator shutdowns deeper than 30m unless it is a REAL emergency. We always plan to have contingency for one or two actual failures. There is no reason these could not happen on a training dive.

So, imagine I tell a student at 40m that they have a "free flowing reg" scenario. While they are dealing with this, I have a manifold rupture, losing all my backgas. I go to them to get gas, but they have shut down one reg and are breathing off the other. I have the rest of my life to buddy breathe (off a bungeed secondary?) and get their gas on so i can use their long hose.

I am putting that student at a great deal of risk for very little return. If they, instead of shutting down, do a "touch drill" and show the sequence they would use, without turning anything off, that is enough to demonstrate ability to think through a scenario without adding risk.

The competence to do the actual live drill would be demonstrated in confined water and shallower dives for a loooong time before then.

Its the same reason we don't do actual shut downs of aircraft engines for training, if the second one goes then starting that "failed" one up may be longer than you have, and not likely to go smoothly with adrenaline etc.

As far as the mechanics of it go, with an increase in depth, there is a higher load on the regulators and a slightly higher chance of things going wrong if you start doing weird stuff.

If it ain't broke, don't mess with it, especially if you are deeper than a CESA depth.

 

[CuzzA]

That paragraph doesn't read as if it's a training situation. It reads as if TDI is training students to not shut down a reg failure.