To blow out all air out of your lungs is physically impossible. When you are blowing hard and feel you can blow out no more, your lungs will still contain between 15 % and 25 % of their original volume - this is known as Residual air. You can never get rid of this volume of residual air. The existence of residual air is very important in Buoyant-Ascent. The reason for this is that when you are ascending through the water, the surrounding water pressure will decrease allowing the residual air inside the lungs to expand. This residual air volume will give more air to blow out all the way to the surface. Owing to this you should,
-BUOYANT-EXHALING ASCENT ( from 30 ft. Depth )
This technique of ascending is used in the states as follows Water level inside the hood will rise to mouth level from a rupture due to a broken sliding fastener (zipper) or a collapsed ascent hood. If no time for closing ascent hood completely at the exit point during the rush escape. In such cases with breathing difficulty, without delay escaper must reach the surface using buoyant-exhaling ascent (to avoid gas embolism) Escaper
must BLOW OUT ALL THE WAY TO THE SURFACE
The training compartment is located at 30 ft. depth of the 60 ft. tank and it is basically a small compartment that can be flooded and pressurized. Of the two hatches one is opened into the tank and the other into the compartment.
TOWER ESCAPE ( from 60 ft. depth)
Normally, the free-breathing ascent technique is used during tower escapes. It does mean that escapers will breathe normally all the way to the surface. The pressure inside the ascent hood is always above the surrounding water pressure. While he is ascending through the water, the surrounding water pressure will decrease allowing the air inside the stole to expand out through the relief valves and into the hood area giving him a continuous supply of fresh clean air. So, he should be absolutely confident that during all phases of his ascent he will have a good supply of fresh, clean air to breathe and all he has to do throughout escape is 'BREATHE NORMALLY ALL THE WAY TO THE SURFACE. NEVER EVER AT ANY STAGE, HOLD HIS BREATH'