Mr T's Wild Freedive

[IncreaseMyT]

It’s not the equivalent of dropping 6 pounds of weight at depth. It’s like being 4 pounds negative (you’re slowly dropping) then taking a full breath off your regulator, which makes you then 2 pounds positive. You’ll slowly stop dropping, then slowly start rising. Swimming against 2 lbs is easy; you already did it to get off the surface!

What?

 

[drk5036]

What?

How much buoyancy does one full breath of air contain?

 

[IncreaseMyT]

How much buoyancy does one full breath of air contain?

You're confused. At the surface we are estimating we are 2 lbs positive with a full breath. When you free dive as you go down your lungs compress and that is what makes you less buoyant, also other air spaces like the one in your mask contribute.

If you take a breath, you immediately go back to +2, just as if you were at the surface.

 

[drk5036]

You're confused. At the surface we are estimating we are 2 lbs positive with a full breath. When you free dive as you go down your lungs compress and that is what makes you less buoyant, also other air spaces like the one in your mask contribute.

If you take a breath, you immediately go back to +2, just as if you were at the surface.

Right. The different between lungs fully empty/collapsed is about 6 pounds of buoyancy. So completely empty you’re at -4 pounds and completely full at +2 pounds. I guess we are in agreement on this point.

But you won’t rocket to the surface by taking a breath. You’ll be at +2 pounds of buoyancy, which will make you ascent but slowly. By comparison, when scuba diving you make yourself close to neutral by using your BCD. If you’ve take a full breath you could be upwards of +6 pounds of buoyancy. But we can easily control our depth.

 

[IncreaseMyT]

Yea exactly what I said. Your free dive is over unless you grab on to something, or swim down. For someone not realizing this would happen it could be startling. Thats all I said.

You will cork if you drop weight at that point though, just like when you take a weight integrated BCD off at depth.

 

[drk5036]

Yea exactly what I said. Your free dive is over unless you grab on to something, or swim down.

Or you just let out 1/3 or the air and are now neutrally buoyant!

 

[IncreaseMyT]

Or you just let out 1/3 or the air and are now neutrally buoyant!

Ok so your 70 foot down and your gonna let 30% of the gas in your lungs out, which at that depth is all oxygen, and then go up?

Good luck to you sir.

 

[drk5036]

Ok so your 70 foot down and your gonna let 30% of the gas in your lungs out, which at that depth is all oxygen, and then go up?

Good luck to you sir.

Wait what? Why would it be all oxygen? That doesn’t make any sense?

And anyway you have a ton more molecules of air in your lungs at this point since you breathed compress gas. As you start to ascend you’ll quickly end up with a lung full of air, which you have to start expelling quickly or else you’re going to have a really bad day.

 

[IncreaseMyT]

You are confused again, when free diving the nitrogen compresses, and leaves the body with almost all oxygen. If you take a breath off a reg, when you exhale the nitrogen would compress and the oxygen would flow out, severely increasing your chance of blacking out when you hit 15 feet. Oh and remember you're going too fast and that also increases your chances, since we are 2 pounds positive when we shouldn't be.

Hopefully the diver you got the gas from was diving a high nitrox mix, don't forget to look horizontally and don't look up, cause you really increased your chances of passing out.

 

[The Chairman]

Many years ago, while teaching in Alexander Springs (a mere 20 ft), I had a free diver demand I give him some air. I waved him off and the next thing I know, he grabbed my regulator out of my mouth. I popped him in the chest, took my reg back and then took my students on a tour of the spring in the shallows.

As we are finally exiting the water, a Park Ranger approaches me and tells me that this guy is accusing me of assault. Realizing who it was, I told the officer all that happened, and that a free diver taking a breath at depth is putting themselves in danger of an embolism if they don't exhale enough on their ascent. My accuser was led away in cuffs. It was gratifying.

Never, ever give air to a free diver. You don't know what they understand or how well they understand it or if they even remember. The danger doesn't lie in becoming positively buoyant, but rather in not remembering to exhale on ascent and incurring a lung over-expansion injury. After all, the first rule of diving is "Don't stop breathing". BOYLES is really an acronym for "Breath Or Your Lungs'll Explode, Stupid. Thought you should know.