There are three states of Matter. Gases, Liquids and Solids.
psi - Lbs/in^2 - Pounds per Square inch.
ATM - Atmosphere, 1 Atm = 14.7psi. 14.7 psi is the pressure
of the air at sea level.
Atmospheric Pressure - Pressure at the water surface, usually
meaning at sea level where the pressure is 14.7psi or 1ATM
Ambient Pressure - Pressure applied by the weight of the
water. This is the pressure normally displayed by your depth guage.
Absolute Pressure - Combined pressure of the water and
the atmosphere. Adding an A to the unit means absolute. (12psiA)
Guage Pressure - Reads 0 at surface. Shows depth based
on water pressure only.
Safety reserve - 300psi of air in the tank remaining at
the end of the dive.
Density - Weight/Unit of Volume
1 cubic foot of Sea Water = 64lbs.
1 cubic foot of Fresh Water = 62.4lbs.
Pounds of pressure per square inch(PSI) caused by water:
12 cubic inches of Sea Water = 0.445lbs/ft
12 cubic inches of Fresh Water = 0.432lbs/ft
Positive Buoyancy - If a submursed body weighs less than
the volume it displaces, it will rise and float(with part of it's
volume above the surface.
Neutral Buoyancy - If a submirsed body remains in equilibrium,
neither rising or sinking if the volume it displaces is equal
to its own weight.
Negative Buoyancy - A submirsed body sinks if the weight
of the fluid it displaces is less than the weight of the body.
The Earth's atmosphere is made up of various gasses.
78% Nitrogen
21% Oxygen
1% Other Gasses. (Argon, Neon, Radon, Carbon Dioxide, Helium)
Nitrogen - N2 - (78% of the atmosphere) - Inert, Does not
support life. Odorless, Colorless, Tasteless, Selectively Soluble.
Fat absorbs five times more Nitrogen than water. Under increased
pressure N2 acts as an intoxicant and an anesthetic.
Oxygen - 02 - (21% of the atmosphere) - Odorless, Colorless,
only gas capable of supporting life. Under increased pressure
becomes toxic.
Carbon Dioxide - C02 - Waste product from the oxidation
of foods. Normally Colorless, Oderless, Tasteless. Slightly acidic
in high concentrations.
Helium - He - As Depth Increases, He, because of its non-toxic
effect does not cause Nitrogen Narcosis. Much less soluble in
fat as compared to Nitrogen. Rapidly conducts heat away from the
body.
Laws and Formulas
If the pressure is constant, the volume of a gas will vary
directly with the absolute temperature.
P1*V1=P2*V2 if temperature is constant.
P1 = Pressure 1
P2 = Pressure 2
V1 = Volume 1
V1 = Volume 2
Boyle's Law states "For Any gas at a constant temperature, the volume varies inversely with the absolute pressure while the density varies directly with the absolute pressure."
Written Mathematically it is expressed as P1V1 = P2V2
Example: An Aluminum 80 tank holds 80 cubic feet of air when the tank is at a pressure of 3000psi. How much space does the air take at 3000psi?
80cubic feet * 14.7psi = 3000psi * x
x = 80*14.7/3000 =.392 cubic feet.
Solubility of gas varies with pressure, and as pressure increases, solubility increases.
This is important to the sport diver with respect to the solubility of nitrogen in the human body as pressure increases.
In a mixture of gasses, each gas exerts a pressure proportional to the percentage of the total gas it represents.
A body wholly or partially immersed in liquid is bouyed upward by a force equal to the volume of the liquid displaced.