Do you really have to exhale while ascending?

[Sharky1948]

And could you carry some in your BC pocket to blow up in case your BC had a hole? No, no, forget about it! What was I thinking?

It's not as bad an idea as you think! An SMB with a dump valve can serve as an emergency buoyancy control device. The original buoyancy control devices (devised in the Florida caves) were inverted plastic milk jugs filled with air. That spawned the necessity for more than one LP port on the first stage. And, the story goes on. (Including the Apex "you've got a problem" indicator on the first stage, but don't get me going! :shakehead)

 

[Quarrior]

Very cool ideas. Is it difficult to blow the balloon up underwater?

Let's see, inhale off reg, remove reg, exhale into balloon. Repeat as needed. hmmm, could be tough.

 

[Gene_Hobbs]

The effects of a raised intrapulmonary pressure on the lungs of fresh unchilled cadavers.
Malhotra and Wright, 1961
Royal Naval Physiological Laboritory, Alverstoke, Hants
The Journal of pathology and bacteriology
PubMed ID: 13765778

Following a series of 'burst lung' cases following Submarine escape drills, the RN decided to look at information on pressures in the lung. Given that this can not be done on live subjects, five fresh, unchilled cadavers were used. They repeated observations made by Polak and Adams (1932) that dogs with bound chests and abdomens could tolerate high intrathacheal pressures.

The cadavers used were from persons aged from 27 to 64 years. One was unbound, one had abdominal binding and the other three had both abdominal and thoracic binding. It was found that the lungs on the unbound and abdominal only bound cadavers ruptured at approximately the same time. Appox. 80 mm Hg. (keep in mind this is fresh cadavers and that any lung pathology will also make a difference)

As for this pressure change over the water column, it seems to be well represented in this thread already.

 

[devilfish]

Six feet of pressure change is the same at any depth. On a full lung, I mean full lung if it takes 6ft ascent to cause a lung to rupture, it does not matter at what depth. From 6ft to the surface the change in pressure is 2.67psi, from 96ft to 90ft it's still 2.67psi. If that's what it takes to cause injury, it will happen at any depth.

 

[MXGratefulDiver]

Six feet of pressure change is the same at any depth. On a full lung, I mean full lung if it takes 6ft ascent to cause a lung to rupture, it does not matter at what depth. From 6ft to the surface the change in pressure is 2.67psi, from 96ft to 90ft it's still 2.67psi. If that's what it takes to cause injury, it will happen at any depth.

I think you should review Boyle's Law ...

... Bob (Grateful Diver)

 

[Quarrior]

Six feet of pressure change is the same at any depth. On a full lung, I mean full lung if it takes 6ft ascent to cause a lung to rupture, it does not matter at what depth. From 6ft to the surface the change in pressure is 2.67psi, from 96ft to 90ft it's still 2.67psi. If that's what it takes to cause injury, it will happen at any depth.

In a word, WRONG!!!!!!!!!!!!!!!!!!!!!!!

 

[devilfish]

I think you should review Boyle's Law ...

... Bob (Grateful Diver)

Sounds like you might believe that a 12in diameter baloon will compress to be 6in diameter at 2ATA. In actuality it would take 8 ATA to do that. Right?

 

[NJMike]

I don't know what to believe. I'm trying to work it out on paper...

 

[NJMike]

What I THOUGHT was....say you have an 80 cu. ft. tank on the surface. At 33' you would have half of that, since the pressure doubled...so you'd have 40 cu. ft. of air.

At 66' you'd have 1/3, or approx. 26 cu. ft. of air. At 99', 1/4 or 20 cu. ft.

So from 99' to 66', a change of 33', the volume of air would change by only 6 cu. ft.

The same change, from 33' to 0', would change by 40 cu. ft., meaning that the volume of air expands much more nearer the surface.

Am I wrong?

 

[Cacia]

pressure, but not volume?

It's the increasing volume that causes barotrauma, no?

maybe the change is constant.

Six feet of pressure change is the same at any depth.

pressure is a constant, no?