Complete first stage failure?

[copter53]

I was just looking up scuba gear on LP and I read a review where the guy mentioned having a "complete first stage failure" what does that mean exactly?

Will you suddenly have no air if that happens? How common is it?

 

[Mr Carcharodon]

Well that is of course your first stage failing to deliver any gas at all. I have only heard of a few cases of this happening, but like most things in scuba there is no centralized body that tracks this sort of thing so it is hard to know how common it is. DAN does collect statistics on causes of fatalities and equipment failure is a comparatively rare cause. Off the top of my head I can think of two types of first stage failure. The first involve debris from the tank clogging the first stage filter stopping the flow of gas. This can happen with both aluminum and steel tanks if a faulty compressor pumps moisture into the tank causing it to corrode. Of course the compressor operator should have a condenser and filter that prevents this but these are not always maintained as well as they should be. In my experience the compressors on boats are more suspect than land based compressors.

The other type of complete failure involved failure of the first stage swivel bolt. This is the bolt that connects the swivel to the middle part of the first stage. If it is overtorqued the neck of the bolt can be yielded which sets it up for subsequent failure. Of course if the bolt goes the swivel comes off and you have a spectacular free flow. The DIN and yoke bolts can also be overtorqued and crack the body of the first stage, although I have not heard of that leading to a complete failure of a first stage at least while diving.

Looking into the high pressure side of your regulator should give you an indication if there is a tank contamination concern. The second problem can be solved by torqueing the bolts to the prescribed values, which while that seems to be uncommon problems are also rather uncommon. Other problems like failed o-rings, hoses and cold water freeze ups leading to freeflow seem to be far more common by anecdote at least. But those are not complete failures.

 

[Dr Wu]

Will you suddenly have no air if that happens?

Probably.

But it depends on "the guys" definition of failure.

How common is it?

Depends on your definition of "common".

 

[SDAnderson]

If the main spring breaks the first stage will fail in the closed position, resulting in no air. Very rare but definitely not unknown.

 

[Rick Murchison]

If the main spring breaks the first stage will fail in the closed position, resulting in no air. Very rare but definitely not unknown.

Yeah, I think I heard of a fellow who knew a guy who had a cousin that had a friend who had a main spring break back in '56. But I've never been able to verify it. You?

Rick

 

[redacted]

Anything can fail. It is clearly possible for a 1st stage to suddenly or very quickly stop effectively delivering gas. All of the failure modes that would cause such a situation are rare but can happen. The key is your training and preparation for such an event. Plan on it happening, practice your response, and you should have no problem.

 

[Gilldiver]

The most common 1st stage failure is the lack of gas pressure upstream of it. I would imagine that for every 10,000 low gas events there might be one (1) 1st stage mechanical event.

The next failure is a cold water freeze causing a free flow. But freeze of the 1st stage is nowhere near as common as a freeze of a 2nd stage ; a differentiation that seems to escape just about all the “experts” on these boards.

 

[copter53]

Anything can fail. It is clearly possible for a 1st stage to suddenly or very quickly stop effectively delivering gas. All of the failure modes that would cause such a situation are rare but can happen. The key is your training and preparation for such an event. Plan on it happening, practice your response, and you should have no problem.

What kind of response is best for a complete first stage failure? What about if you have no buddy/are solo? What if you are solo and have no redundant air supply?

Would you quickly screw your 1st stage off the tank and breath from a direct tank free flow?

 

[sled600]

What kind of response is best for a complete first stage failure? What about if you have no buddy/are solo? What if you are solo and have no redundant air supply?

If you are solo.....you know the risk. If you are solo without a redudndant air suppy you know you should have paid attention to the risk....

 

[ReefHound]

What kind of response is best for a complete first stage failure? What about if you have no buddy/are solo? What if you are solo and have no redundant air supply?

Would you quickly screw your 1st stage off the tank and breath from a direct tank free flow?

Unacceptable. The solution is not to put yourself in that situation. If you dive solo you need to have redundancy.

But if somehow it happens and suddenly you have no air, it's time for a CESA. You don't have time to diagnose the problem. Removing the reg and breathing from the tank sounds cool but what if you can't remove the reg or you do but there's no air in the tank? Maybe you're failure wasn't a first stage failure but a SPG failure with the needle getting stuck at 1000 psi? Now you've wasted valuable seconds and you may be screwed.