Water has a high heat capacity. Molecules are closer together (denser), therefore water dissipates heat faster than air. We lose heat 20 times faster in water than in air.

Factors of heat transmission in order of effect on a diver:

• conduction (direct contact)
• convection (via fluids and movement)
• radiation (electromagnetic waves)

HEAT LOSS = Mainly due to conduction

The speed of light depends on the density of the medium (denser = slower)

REFRACTION = as light waves enter water (a denser medium), they bend. This causes objects to appear 33% larger and 25% closer. 33 is “LARGER” than 25.

VISUAL REVERSAL = turbidity (suspended particles in water) may cause objects to appear farther away.

REFRACTION = 33% larger; 25 % closer
VISUAL REVERSAL = far away (turbidity)

Sound (pressure waves) travel faster in a denser, more elastic medium. In water, sound travels four times faster than in air. SOUND and FOUR both contain the vowel combo of ‘ou’

Our brain determines sound direction by delay between sound waves reaching the ears. This makes determining the direction of sound difficult, it is usually perceived as being overhead.

SOUND = travel 4 times faster
SOUND comes OVERHEAD

“An object wholly or partially immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object”

These constants are provided on every exam:
1 liter fresh water (lfw) = 1kg
1 liter salt water (lsw) = 1.03kg

You must know:

O ↓ (weight of object)
W (weight of water = constant)
D ↑ (displaced fluid)

If one is missing “the answer can’t be determined“. The depth is irrelevant.

Pressure = a force or weight acting on some unit of area (kg/cm2)

ATMOSPHERIC PRESSURE= the air pressure at sea level = 1 atm /bar (14.7 psi)
GAUGE PRESSURE = measured pressure minus atmospheric pressure (atm gauge)
ABSOLUTE PRESSURE = total pressure exerted, gauge + atmospheric (ata)
AMBIENT PRESSURE = surrounding pressure, same as absolute pressure.

Constants
Sea Water = 1 atm every 10 m = 0.100 atm per meter (1msw = 0.1atm/bar)
Fresh Water = 1 atm every 10.3 m = 0.97 atm per meter (1mfw = 0.097atm/bar)

Example: What are the gauge and absolute pressures in fresh water at a depth of 22.5 metres? (2.18atm gauge ; 3.18ata)
Example: The pressure at 18 metres in sea water equals the same pressure as which depth in fresh water? (18.5m)

“Gas volume is inversely proportional to pressure. If the pressure increases, the volume must decrease proportionately. If the pressure decreases, the volume must increase proportionately”

PV = K
P = absolute pressure (ata / bar)
V = volume
K = constant

For example:
V1 x P1 = V2 x P2
V2 = P1 / (P2 x V1)

Example: If you take a gas volume of 27l from 32m to 17m in fresh water, what will the new volume be? (41.8)

Example: A diver’s air consumption rate is 2 bar/minute at the surface. What is the diver’s air consumption rate likely to be at 30 m? (8)

Example: if a diver air consumption rate is 8 bar/minute at the 10 m. What is it likely to be at 40m? (20)

Heat is the energy of molecular motion.

If you heat gases in a inflexible container and the volume remains unchanged (such as in a scuba tank), the molecules move more rapidly, increasing the pressure.

Describes the influence of temperature on gas behavior.

“If the pressure remains constant, the volume increases as the temperature increases. If you keep the volume constant, the pressure increases as the temperature increases”

Example: If you put a tank and a balloon in a freezer, what will happen? The balloon’s volume will change as it is a flexible container. Tank volume will remain (non-flexible container) therefore its pressure will change.

In a scuba cylinder, pressure will change 0.6 bar for every change in temperature of 1°C

Ideal General Gas Law combines Boyle’s and Charles’ Laws: pressure, volume and temperature.

P x V = K x T
P = absolute pressure (ata)
V = volume (liters)
K = constant
T = absolute Temperature

How to convert Celsius to Kelvin (K = °C + 273)

Example: A 12 liter cylinder reaches 52°C while being filled to 200 bar. Later, will be use in 7°C water. What will the pressure be when the tank enters in the water? (173bar)

PARTIAL PRESSURE = in a gas mixture, each gas exerts it individual pressure, independent of other gases in the mixture

Total pressure of air (100%) = Partial pressure of oxygen (21%) + partial pressure of nitrogen (79%)

The body responds to a gas based on its partial pressure – the higher the partial pressure, the greater the potential physiological effect.

“The total pressure exerted by a mixture of gases is equal to the sum of the pressures of each of the different gases making up the mixture -each gas acting as if it alone were present and occupied the total volume”

Ptotal = P1 + P2 + P3 ….

Where Ptotal is the total absolute pressure
and P1 (etc) is the partial pressure of each component gas

P1 = Ptotal x % volume gas1

Example: What is the PO2 of air at 40 meters? (1.05 ata)

Example: what is the PO2 when breathing 100% at the surface? (1 ata)

Example: An air mixture has 0.5% Carbon Monoxide. Breathing this air at 40m would be the equivalent of breathing what percent at the surface? (2.5%)

“The amount of gas that dissolves into a liquid at a given temperature is directly proportional to the partial pressure of that gas”

SATURATION = when the gas pressure within a liquid is the same as the pressure of the gas in contact with the liquid.

What happens when you raise the pressure of gas in contact with a liquid? More gas dissolves into the liquid until eventually reaches equilibrium or saturation.

SUPERSATURATION = when the gas pressure within a liquid is greater than the pressure of the gas in contact with the liquid

What happens when you quickly reduce the pressure on a liquid that is saturated? The gas within the liquid cannot remain in solution and bubbles form.