Please help me understand something about BCD's

[Bent Benny]

I started watching a documentary several weeks ago about the Blue Hole in Egypt. I didn't get very far into it, but I did get to a story about a diver who lost his life there. He was unqualified and under-equipped for the dive he was attempting. The narrator or host of the documentary was explaining the story of what happened to the diver and he made a statement that confuses me a little. It was something like "As the diver plummeted deeper into the depths, he had no hope as his recreational BCD was useless at these depths"

Why would his BCD be useless at a few hundred feet? Is it because the intermediate pressure is less than the ATA so the BCD won't inflate, or are there other reasons why a recreational BCD wouldn't work at depths beyond rec limits?

 

[DanielRJones]

Depending on the thickness of his wetsuit it coukd have been compressed to a level where his bcd could not provide enough lift to become positivle buoyant.

Without a wetsuit I am -3lb at a start of a dive with my 7mm semidry i need 22lb of lead to get me down and if my wetsuit lost all buoyancy i would be 23lb negative which woukd mean a 20lb lift bcd would be pointless

 

[northernone]

There's nothing I can think of about a common bcd design that works at 132ft that won't work at 300 ft.

 

[DanielRJones]

My rec rig is 30lb lift wing in warm weather in a 3mm shorty i would be at most -12lb so is fine

In the uk i would be wearing a drysuit and 22lb of lead. With a full catastrophic flood at the start of a dive i could be up to 26lb negative which woukd leave me at the max of what i could overcome with my bcd so i would rely on having assisted lift from my dsmb or a buddy.

When diving double cylynders i change to a 40lb wing and at the start i coukd be up to 30lb negative if i had a catastrophic failure of my drysuit

 

[DanielRJones]

There's nothing I can think of about a common bcd design that works at 132ft that won't work at 300 ft.

True it works the same at any depth the onky issue with common bcd is how much lift they provide

 

[Scared Silly]

The narrator like the diver was narked. What was useless were their brains.

FWIW modern regulators compensate for depth, that means the regulator will deliver gas at the intermediate pressure (<150 psi) regardless of the ambient water pressure until the pressure in the cylinder equals the absolute pressure. Which for the blue hole is 100m or 10ATM or simplicity ~150 psi. So gas will be delivered to the BCD until the cylinder is down to ~300 psi. At which point one is screwed. Actually one would be screwed well before that at that depth.

 

[Bent Benny]

Ok thanks for the replies. I thought it might have just been the host being dramatic, which he was.

 

[MargaritaMike]

I saw the same video. Good catch.

Cheers -

 

[diversteve]

don't believe everything you hear on TV...

 

[ScubaJCBS]

Lift capacity and depth? was a earlier thread I just can't get it to post it has some good information