Fl Keys accident reports

[PuyallupCoug]

The change in pressure is the same from 15ft to surface than from 45ft to 30ft and 90ft to 75ft. The pressure change with depth is always density * gravity accelaration * depth

rho * g * h

It is correct that the last 15ft are the most dangerous when it comes to lung expansion. According to whichever law it is (charles? Boyle? I always forget. I'm a scientist so I just know the ideal gas law, the other ones are just a subset):

P_low * V_low = P_up * V_up

where low refers to the conditions at the bottom and up refers to the condtions 15ft higher. The damage comes from volume expansion

V_up / V_low = P_low / P_up

P_low = P_up + r*g*h and hence

V_up / V_low = (P_up + r*g*h) / P_up = 1 + r*g*h / P_up

Long story short, for the same depth change, the greatest volume expansion occurs when the final (up) pressure is the lowest. This always occurs when you finish at the surface, so there's more volume expansion in going from 15ft to the surface than in going from 90ft to 75ft or 45ft to 30ft.

Sorry for the lecture, same conclusion, just the proper explanation. So yes, the last 15ft are more dangerous.

What (s)he said


Thanks for the detailed explanation though, it's nice to know someone else confirms my thought.

 

[netmage]

It is correct that the last 15ft are the most dangerous when it comes to lung expansion. According to whichever law it is (charles? Boyle? I always forget. I'm a scientist so I just know the ideal gas law, the other ones are just a subset):

Boyle....... Breathe Or Your Lungs Explode....

 

[DiveRich]

Well, you shouldn't run out of air...

But should you... you should go to your buddy...
But should they be absent/gone... you should do a cesa....

And if all of this happens, you should rethink your dive planning and buddy selection...

Of course, to all of this.

Yes.

Also, if you're thinking nice and clearly, just remember not to take in a huge last breath and that will further reduce your risk of lung expansion injury.

Dave C

I've only run out of air once - novice, strong current, and poor dive plan. I didn't get a chance to take a deep breath. Fortunately, it was a shallow dive off Alligator Reef, and I was only 10 feet from the surface when it happened.

That was 17 years ago, hasn't happened again.

Thanks guys.

 

[hgroberts]

Experienced free-diver reported missing. He was later found deceased on bottom (17') near his anchored jet ski. Speargun found attached to body by line entangled around wrist. Line led to deceased jewfish wedged in hole.

 

[=C=]

A suprising number of events stem from mistakenly breathing from a pony bottle.

I dive with the Zeagle bail-out bottle and have the reg marked... Seems common sense. Hose routing should also alert you to which airsource in-use and at the very least having the same tank pressure 5 minutes into the dive as at the start should be a sign.