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Re: Question
Charlie, I would highly recommend a scuba class. They cover Boyles, law,
Charle's law, and Dlaton's law. Fresh water density is 62.3164 lb/ft2 at 20
degrees C. Saltwater is ~64lb/ft2. Divide by 144 (12inches x 12 inches), and
you get 0.43 psi/ft for fresh water and 0.44 psi/ft for salt water. Rule of
thumb that keeps you safe is: half the depth to give you psi. Example: in
100 ft of H2O, you have 50 psig of pressure, even though it's actually 43 to
44 psig. The "g" in psig is gauge pressure. That means if the pressure gauge
on the surface measures 0 psi, then it would read 50 psi at 100 ft of water.
Psia is absolute pressure. We currently have 1 atmosphere, or 14.696 psi of
pressure from the air over our heads. Hope this helps,
Paul
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