VTWarrenG
Guest
Tom,
An empty cylinder (i.e. inside pressure = ambient pressure) at 100 fsw will be 3 bar higher than ambient at the surface. Considering you'll breathe about 0.353 bar per breath at the surface (2265L / 4L tidal volume), that 44.1 psi will provide you with something like 8 lungfuls of air, at the surface. If you care, you can perform the integral and determine how many lungfuls you'll have with breaths at arbitrary depths. So, certainly, your scuba rig might give you some additional lungfuls as you ascend.
However, let us not forget that the reason a diver runs dry on the bottom is (hopefully) an equipment failure. The air remaining in the tank would not be usable, because it would escape through the same failure as the diver ascends.
jbd,
How could you have "excessive" positive buoyancy when your goal in life at the moment is to surface as quickly as possible? I assume you're speaking from the perspective that the chance of injury increases with increasing ascent rate. This is perhaps true, but only of marginal concern -- you can survive the bends, or even a minor lung overexpansion, but you cannot survive drowning. If you decide to make a buoyant ascent to the surface, make that decision once, and follow through with it. Forget about controlling your ascent rate, because you're way past that concern. Leave the air in the BC, and don't mess with it -- ascend as quickly as possible. The last thing you'd like to happen is to accidentally vent too much air and find yourself sinking. Don't forget to exhale.
Hawk,
SpareAirs are useless. Do the math. SpareAirs are designed to allow helicopter pilots to ascend from 20 fsw from a scuttled helicopter. They're useless beyond 20 fsw, and only serve to foster a false sense of security for mathematically-impaired divers.
- Warren
An empty cylinder (i.e. inside pressure = ambient pressure) at 100 fsw will be 3 bar higher than ambient at the surface. Considering you'll breathe about 0.353 bar per breath at the surface (2265L / 4L tidal volume), that 44.1 psi will provide you with something like 8 lungfuls of air, at the surface. If you care, you can perform the integral and determine how many lungfuls you'll have with breaths at arbitrary depths. So, certainly, your scuba rig might give you some additional lungfuls as you ascend.
However, let us not forget that the reason a diver runs dry on the bottom is (hopefully) an equipment failure. The air remaining in the tank would not be usable, because it would escape through the same failure as the diver ascends.
jbd,
How could you have "excessive" positive buoyancy when your goal in life at the moment is to surface as quickly as possible? I assume you're speaking from the perspective that the chance of injury increases with increasing ascent rate. This is perhaps true, but only of marginal concern -- you can survive the bends, or even a minor lung overexpansion, but you cannot survive drowning. If you decide to make a buoyant ascent to the surface, make that decision once, and follow through with it. Forget about controlling your ascent rate, because you're way past that concern. Leave the air in the BC, and don't mess with it -- ascend as quickly as possible. The last thing you'd like to happen is to accidentally vent too much air and find yourself sinking. Don't forget to exhale.
Hawk,
SpareAirs are useless. Do the math. SpareAirs are designed to allow helicopter pilots to ascend from 20 fsw from a scuttled helicopter. They're useless beyond 20 fsw, and only serve to foster a false sense of security for mathematically-impaired divers.
- Warren
