 "How long can you stay down there?" ... "It
depends on how deep I am diving. The deeper I dive the less bottom time I have."
The deeper you dive,
the more air you consume in a given period of time.
Your scuba regulator is designed to adjust the pressure of the air supplied to
you, to match the pressure of the surrounding water.
As you dive deeper, the surrounding water pressure and the pressure of the
air supplied to you increases.
As the pressure of the air supplied to you increases, the density of this air also
increases.
Since you still breathe in the same lung full amounts of air, each lung full you breathe
has more molecules of air from the tank, and thus the tank does not last as long.
The table below, shows the depth, pressure, density, and time relationships for dives to
33', 66', and 99' assuming that a tank of air would last 120 minutes at the surface.
Depth - Pressure - Density - Time
Relationships |
Depth
Feet |
Pressure
Atmospheres
Absolute |
Density
Relative
to
Surface |
Time
Tank
Lasts
(Minutes) |
| 00 |
1x |
1x |
120 |
| 33 |
2x |
2x |
60 |
| 66 |
3x |
3x |
40 |
| 99 |
4x |
4x |
30 |
From the table above, you can see that the deeper you go, the less time you have to dive.
The amount of time you have at
depth is simply the amount of time you have at the surface, divided by the pressure in
Atmospheres Absolute at the depth you are diving.
For example; how long will a tank of air last at 172 FSW (6.21 AtA) if it would last 120
minutes at the surface?
The answer is 120 minutes divided by 6.21 AtA or 19.32
minutes. Then the tank will be EMPTY.
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