Can you sink by blowing up your BC below 40m?

[richmonddiver]

Sure they do! It's the instant variety just heat it up and your ready to serve!

You have to use an AC battery to make it.

 

[joe10540]

As the great Haldane once said "Hey whatever floats your goats"

 

[guruboy]

Don't forget to flip you wing if you go south of the equator.

 

[CuzzA]

The only possible logic I can apply to what the guy was saying is that the deeper you go the more gas you will need to generate lift.

Where this could be deadly is in an uncontrolled descent, overweight, inexperienced, going down too fast, narcosis hits you, panic, hypercapnia, death.

This happened to a couple guys who thought they could do what a team of tech divers did a few days earlier. I'll link the article when I find it.

 

[MichaelMc]

As you go deeper the air you breath and inflate your BC with gets denser and does not flow through hoses as easily. If your BC hose or inflator were very restricted, your ability to put enough 'bubbles' in your BC to keep up with a decreasing depth, might get limited by that increased friction due to air density. I'm not sure how many regs and BC inflators fall in this category though. That might be what they meant. Maybe.

Edit: What CuzzA said. Part of the idea is that you are negative, loosing depth, and loosing BC volume faster than your reg and inflator can replace it and gain volume to cancel the negative buoyancy. Of course at depth, each foot of drop makes a smaller and smaller change to the volume of your BC. Maybe you just do not recover before you are even more narced and decide to not worry anymore.

 

[Steve_C]

Interesting theoretical question. Its a LOT more than 40 meters, and may not exist in the ocean, but I expect that there is a theoretical depth at which to generate enough pressure the air would have to be condensed so much that it would weigh more than an equal amount of water. The air might have to be some sort of compressed molecular (atomic ?) fluid. Maybe if you were deep diving on air on Saturn or Jupiter? Of course no equipment we know could deliver that type of pressure but just as a physics question it is amusing.

 

[dmaziuk]

Nice. When you're down there, grab me about 100 feet of water line and a bucket of steam, would ya?

Steam, huh. In car shops it's compression they keep in the storeroom.

 

[CuzzA]

Too Fast To Live, Too Young To Die

 

[BoltSnap]

You aren't going "down" but actually going up to the other side of earth and will end up on the surface in North Korea!!

 

[Kevrumbo]

Today I heard an interesting thing from a very experienced diver:

When you put air into your BC and you are at 40m you start to sink because of negative bubbles. If you are a lot below 40m, adding air in your BC does nothing, hence there is no fast ascend like that from beyond 40m.

Is this the case? wth are "negative bubbles"?

I think this is a misunderstanding of the loss of buoyancy at depth due to wetsuit compression (the "bubbles" or positive air spaces in the neoprene, especially in a thick wetsuit, are essentially squeezed out by ambient pressure at depth). If you are overweighted at deep depth, full BCD inflation may not compensate for the resultant negative buoyancy, or worst case with a BCD failure -->You might not be able to swim/kick back to the surface without ditching your weightbelt of lead, resulting in an uncontrolled ascent.
It's all covered and explained fairly well in this video: