BCD Failure

[BRT]

I dont know if this is the proper subforum but here's the story. Was doing a dive last week with an experienced dive buddy. Surface chop was a bit rough. The boat did not use a tag line for divers waiting their turn in the water. My buddy and I both ascended and I proceeded to board the boat. After sitting down, I looked and saw a different diver boarding. I figured the guy just skipped ahead of my buddy (as happened to my on a previous dive). I didnt see my buddy but figured it was the choppy water and my angle of vision obscuring him. He did board a minute or two later and turns out the rear shoulder dump on his Mares BCD came completely unscrewed allowing the air out and water to fill his BCD. He didn't realize what had happened and kept sinking despite repeatedly inflating his BCD and finning. After dropping 30ft, he dropped his weights and surfaced. Once on the boat, the failure became apparent. The BCD is only a few years old and had been serviced about a year ago. How often does this occur and how does one prevent it from happening?

They disassembled it when they serviced it.

 

[Couv]

See this video to get an idea of the hardware involved holding the dump valve or elbow assembly on the bladder:

If your buddy has a pull dump assembly on the elbow, then there are a few more components that need to be checked periodically.

 

[Eric Sedletzky]

In my opinion the BCD is the most abused piece of gear in modern diving.
There was a time when there were no BCD’s and divers knew what proper weighting was just by default. It would have been virtually impossible to dive the way many divers weight themselves in this day and age. The BC covers for the overweighting problem very well, until it doesn’t.
I have maintained that proper weighting would not allow a diver to sink like that especially at the end of the dive when the tank is spent. I can only imagine how grossly overweighted the diver must have been at the beginning of the dive. Good thing the connection didn’t come loose early in the dive when the diver was at the deep part.
I believe in the 15’ rule. If the diver was neutral at 15’ at the end of the dive with no air in the BC and controlling their stop with breathing alone then they would have most likely been a little light on the surface and would have had to actually work to get down. I’m just glad they had ditchable weight and didn’t subscribe to the non ditchable weight fad that seems to be so in-fashion now.

 

[jejton]

Thanks for all the input. To answer some questions that have been brought up:

- This involved a REAR shoulder dump, not a front, airhose connected dump
- It seems that it really did unscrew, as nothing is obviously broken and it was able to be screwed back on. He is an engineer by profession so I imagine he would be able to tell if the threads were broken, but I'll ask him again
- This occurred at the end of the last dive of a week of diving
- As the airhog in the team, I was down to 750PSI but he still had about 1500PSI in his Al80
- It was serviced about a year ago, and was not used between then and this trip
- He has many years worth of diving experience over me, though doesn't claim to be an expert diver, but I didn't notice him having any trouble with his bouancy at any point during our diving, nor did he report any.
- This incident occured at the surface, after inflating the BCD, while awaiting his turn to board the boat. He dropped his weights after failing to reinflate his BCD and having trouble maintaining surface position, with 5ft chop and not knowing what the cause of the problem was. I don't know, in my inexperienced opinion, whether he really should be faulted for dropping his weight as opposed to attempting any other maneuver. In those conditions, I imagine that was the quickest, and therefore safest, method of reestablishing surface buoyancy and getting onboard the boat. After all, his buddy and the DM, were already on board and neither noticed immediately what had happened either.

 

[Scraps]

So how much weight was he carrying? How big is he? What was he wearing (besides khakis)?

My daughter had a BCD fail in the same spot--broke, not just unscrewed. We believe hers happened at depth. Neither of us noticed when it happened. I saw it when she signaled she was down to 1000 PSI.

We had performed a weight check at the beginning of the dive. She was just right at 8 pounds with a 5 mm wetsuit.

She was able to ascend by changing her aspect in the water and slowly finning. She had no trouble maintaining proper depth at our safety stop, and it required only gentle kicking to stay afloat once we surfaced.

I don't have any problem with his response--using the SMB while sinking would have been difficult. However, my general sense is that if dumping weight is the right answer to an emergency, the diver is almost certainly overweighted.

 

[Centrals]

I don't have any problem with his response--using the SMB while sinking would have been difficult. However, my general sense is that if dumping weight is the right answer to an emergency, the diver is almost certainly overweighted.

Overweight/underweight is the in-topic recently.
Don't jump to the conclusion too quickly.
Have you ever tried to float with half a full tank and the bc taking in water?
Dumping weight in that situation was the ONLY way.

 

[Scraps]

Overweight/underweight is the in-topic recently.
Don't jump to the conclusion too quickly.
Have you ever tried to float with half a full tank and the bc taking in water?
Dumping weight in that situation was the ONLY way.

You do understand that water in a bcd is neutral, right?

If water fills the bcd, the buoyant force supporting you in the water is increased by an amount equal to the weight of the water in the bcd because the volume of water you displace is increased by same amount as the volume of the water you take in.

You’ll feel that weight when you climb the ladder, but not when you’re in the water.

That’s why we use lead instead of water balloons for weights.

 

[Edward3c]

Thanks for all the input. To answer some questions that have been brought up:

- This involved a REAR shoulder dump, not a front, airhose connected dump
- It seems that it really did unscrew, as nothing is obviously broken and it was able to be screwed back on. He is an engineer by profession so I imagine he would be able to tell if the threads were broken, but I'll ask him again
- This occurred at the end of the last dive of a week of diving
- As the airhog in the team, I was down to 750PSI but he still had about 1500PSI in his Al80
- It was serviced about a year ago, and was not used between then and this trip
- He has many years worth of diving experience over me, though doesn't claim to be an expert diver, but I didn't notice him having any trouble with his bouancy at any point during our diving, nor did he report any.
- This incident occured at the surface, after inflating the BCD, while awaiting his turn to board the boat. He dropped his weights after failing to reinflate his BCD and having trouble maintaining surface position, with 5ft chop and not knowing what the cause of the problem was. I don't know, in my inexperienced opinion, whether he really should be faulted for dropping his weight as opposed to attempting any other maneuver. In those conditions, I imagine that was the quickest, and therefore safest, method of reestablishing surface buoyancy and getting onboard the boat. After all, his buddy and the DM, were already on board and neither noticed immediately what had happened either.

If you buddy had 1,500 left when they surfaced, they made the right choice by dumping their weights. Some have been advocating being neutrally buoyant at 15ft (5m) [I don’t agree with the depth, it is better at 1 or 2m]. However, your buddy would have still been negatively buoyant because of the gas they still had.

 

[Centrals]

You do understand that water in a bcd is neutral, right?

If water fills the bcd, the buoyant force supporting you in the water is increased by an amount equal to the weight of the water in the bcd because the volume of water you displace is increased by same amount as the volume of the water you take in.

You’ll feel that weight when you climb the ladder, but not when you’re in the water.

That’s why we use lead instead of water balloons for weights.

I knew that part.
Would you float with no air in your bc and half a full tank? That is most important!
You were NOT prepared to offer benefit of the doubt instead of saying " most certainly over-weighted"

 

[Scraps]

You need to create some doubt to get the benefit of it.

An 80AL cylinder goes from a bit negative to a bit positive as its contents are consumed. At 1500 PSI, it’s about neutral.

We’ve already agreed that water in a BCD doesn’t make one negative.

Given that the buddy was sinking, what factor besides being overweighted might have caused it?