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Physics of Nitrox
Depth and Pressure
In this module we will explore the relationship between depth and pressure. This understanding is needed as a tool in subsequent modules.
As divers we are interested in depth, here measured in feet of sea water (FSW).
But our bodies, from a physiological standpoint, react to pressure, here measured as atmospheres absolute (AtA).
Using these terms, we see in Table 4 that, at the surface, the pressure on our bodies is one atmosphere. This is the pressure that results from the weight of the air in space pressing down on us. As we descend in the water, this pressure increases e.g. at 33 FSW the pressure is 2 AtA, etc. |
Table 4
Depth and Pressure |
| Depth |
Pressure |
Feet
of
Sea Water
(FSW) |
Atmospheres
Absolute
(AtA) |
| 00 |
1 |
| 33 |
2 |
| 66 |
3 |
| 99 |
4 |
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In the modules that follow it will be necessary to convert FSW to AtA and visa versa. The formulas below will be used for that purpose.
Given FSW find AtA: (FSW/33) + 1 = AtA
Example: Given a dive to 130 feet of sea water (FSW), find the pressure in atmospheres absolute (AtA).
Answer: (130/33) + 1 = 4.94 AtA
Or, for Dummies ...
Note: To use the calculator, enter your data for Line A. Then click the Calc Button to calculate the additional lines.
Given AtA find FSW: (AtA-1) X 33 = FSW
Example: Given a pressure of 7 atmospheres absolute (AtA), find the depth in feet of seawater (FSW).
Answer: (7 - 1) X 33 = 198 FSW
Or, for Dummies ...
Note: To use the calculator, enter your data for Line A. Then click the Calc Button to calculate the additional lines.
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