Fl Keys accident reports

[DeltaWardog]

Perhaps he ran out of air doing the 3 minute safety stop? To many people are rigid, and don't realize it is more important to have reserve in the tank than to complete the "optional" safety stop. I know my nephew did that, as a beginner, you don't comprehend the safety aspect of having reserve air for the surface.

Sounds likely. Safety stop almost over, "oh no I'm out of air", holds breath on the way up.... but that's just speculation of course.

Never thought about whether a safety stop or a couple hundred PSI is more important, lesson noted.

 

[netmage]

Sounds likely. Safety stop almost over, "oh no I'm out of air", holds breath on the way up.... but that's just speculation of course.

Never thought about whether a safety stop or a couple hundred PSI is more important, lesson noted.

It still boggles that people think it's 'ok' to run out of air...

An ounce of prevention = a pound of obscure.... [ORQ]

 

[DeltaWardog]

I meant more along the lines of 500 to 300, not 200 to 0 at 15 feet.

 

[netmage]

I meant more along the lines of 500 to 300, not 200 to 0 at 15 feet.

Saying it's ok to 'break glass' in case of emergency lulls you into a false sense of security... Especally when arbitrary numbers like 500psi are thrown about.

Keep in mind, you are an air breathing mammal... Going into a foreign environment where you can not survive, and the notion or mindset, while I agree in practice, really dosn't solve the overall problem. complacency, lack of attention, and maturity to manage and acknowledge the situation people are putting themselves in...

There is no replacement for proper dive planning... take a look at the concept of 'rock bottom'....

 

[PuyallupCoug]

Well I have seen some reports that suggest that those last 15 feet can be the most dangerous.

I was under the impression that the last 15ft were the most dangerous as far as change in pressure is concerned. The pressure change from 15ft-surface is greater than say from 45ft-30ft which is greater still than say 90ft-75ft.

 

[DeltaWardog]

Sorry, I am not getting my meaning across I think. I will move on.

 

[cold_water]

I was under the impression that the last 15ft were the most dangerous as far as change in pressure is concerned. The pressure change from 15ft-surface is greater than say from 45ft-30ft which is greater still than say 90ft-75ft.

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.

 

[DiveRich]

So, if you run out of air during the safety stop, you should exhale going up the last 15 feet to relieve the overexpansion?

 

[netmage]

So, if you run out of air during the safety stop, you should exhale going up the last 15 feet to relieve the overexpansion?

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...

 

[dave4868]

So, if you run out of air during the safety stop, you should exhale going up the last 15 feet to relieve the overexpansion?

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