What could have happened?

[idive2]

Having the buckle properly tightened is very important. Look at some divers
sometime before going in the water and you will see their tank strap kind of
sagging from the weight of their tank. Their tank strap or straps are to loose
and they will possibly lose their tank. You will get the feel for what is the right
amount of pressure that should be required when closing the tank strap buckle. If your
buckle closes with no resistence it is to loose. How tight varys from diver to diver, one
strap or two straps, things like that. All this being said after something like this happens
a quick inspection of the condition of the buckle would also be in order.

 

[Graeme Tolton]

With my jacket bcd that I use in warm water, if i don't wet the band a few minutes before putting the bcd on the tank, it will come loose. the nylon stretched a great deal when it gets wet. The velcro is convenient for keeping the strap looking clean and preventing it from snagging on something and potentially coming undone, but a lot of times, the velcro will wear out and divers will leave it hanging.

There is normally a safety strap at the top of the bcd that should go around the tank valve and be snugged up. This will prevent loss of the tank underwater and will let you get to the surface with the tank and not HAVE to deal with the problem at depth.

 

[tracydr]

I did see a tank come off completely one time. We were in Galapegos and the DMs had changed our tanks out, it was my husband's tank. He usually double, triple checks so don't know how he missed it. He removed his BC at the bottom and replaced the tank, which was pretty challenging given the conditions. Glad it was him and not me! He's an instructor so the remove and don gear was second nature for him.

 

[Jim Lapenta]

if you wet the strap as shown in ow class the tank will not come out.

 

[Graeme Tolton]

if you wet the strap as shown in ow class the tank will not come out.

As You should be shown in OW. Not always the case, unfortunately.

 

[Selchie in LB]

Wetting the strap was mentioned and suggested throughout my OW class. In real diving situations I rarely if ever see anyone wetting the strap. So, yes like a lemming I have been remiss in wetting my strap.

This brings to mind another post of the value of training people to don gear underwater that tracydr states above allowed her husband to doff re-strap the tank and don his gear without much thought.

 

[theduckguru]

if you wet the strap as shown in ow class the tank will not come out.

Unless you also have failed to properly rig the strap in the buckle.

 

[idive2]

A wet strap still has to be properly tightened. With a dry strap it is
very important that you feel a moderate resistance when closing
the buckle. You also need to feel resistance when closing the
buckle on a wet strap. I have not seen a lot of equipment problems
when diving but a tank that has come loose is probably the one I see
more often. Unfortunately if this happens at the absolute worst time
(murphys law) it will certainly take your attention away from other
important things that are going on at that time.

 

[Graeme Tolton]

Some straps will stretch more than others once wetted, I do believe. My single tank BCD, if I use a steel tank and do not wet the strap.... it's coming loose. No matter how tight I make it while dry, it will come loose. I made the mistake once and will never again.. That being said, I no longer dive this type of setup. I use either doubles or a double strap STA.

 

[MXGratefulDiver]

Therein lies the reason why I prefer diving rigs that have two straps ...

... Bob (Grateful Diver)