SCUBA : Effects of Dissolved Gases

Pascal’s Principle Pressure applied to fluids is equally transmitted in all directions, to all parts of the fluid and to all parts of a container. Think toothpaste…

Pascal’s principle = a fluid distributes the force in all directions equally

Hydraulic(fluid) brakes

Consider: Hold your hand out straight… you have more air on top of your hand than under it… do you feel a difference? If you go to the bottom of the pool,… do you feel the weight pushing straight down? You dive down 900ft (300m) into the ocean… what does it feel like?

Summary – Pascal’s principle Pressure in water (any fluid) is distributed equally. So if you are deep in water… you are squeezed from all sides, not just from the top!

Effects of pressure on lungs – Free diving At the surface 1atm & 6 liters 10m down (33ft) 2atm & lungs ½ the size now, 3 liters 30m down (99ft) 4atms & lungs squeezed to ¼ … 1.5 liters

How deep has a human dived on one breath of air? 214 meters / 702 feet. Total time was 5 minutes. Record swimming under water is 8 min 30 seconds, but that was “constant depth”

Most divers use SCUBA S – Self C – Contained U – Underwater B – Breathing A – Apparatus AKA – breaking air from a compressed air tank.

Why the pressurized air is important? More air in a small pack… can use it for a while The pressure of the air can hold back the water’s pressure so you don’t get crushed … up to a point (only to about 140ft safely)

Can the pressurized air be dangerous also? Now, when you are down deep technology has put a lot air particles in your lungs. What will happen to that air as you rise up and the pressure is less? You won’t like how it feels to have your lungs blown up this big!!

1st danger of SCUBA Rupturing your lungs as you come up!!! If a diver ascends too quickly, they will rip a hole in their lungs!

1st danger of SCUBA How do you avoid this? You ascend slowly, breathing out the whole way (or at least as much as possible) so you have the normal amount of air in your lung at the surface Release gas slowly

The problem of breathing compressed air #2 Higher pressure of gas in your lungs means your blood dissolves more gas! How do they get the CO2 in your water to make cokes? CO2 pressure pump

The problem of breathing compressed air #2 The carbonation in your soda is put there and held there by lots of “pressure”.. And what happens if you release that pressure? (open the can?)

The problem of breathing compressed air #3 Both oxygen and nitrogen are toxic if you breathe them under pressure!!!! Nitrogen gas: - Starts at 30m (90ft) - Feels like intoxication - Causes death most commonly because of bad choices. Oxygen gas: - Much more serious starts at deeper levels Most common with mixed gases with high levels of oxygen Effects are not as reversible Brain damage, blindness, convulsions…

Mixed gases Normal air is what most SCUBA uses, but to go deeper you must mess with the mix of air you breathe down there Air up here is 21% oxygen 78% nitrogen .99 % various other gases Diving deep often requires mixes other than these %’s

But the view is amazing

BCD – Buoyancy Control Device The BCD takes on some of the work so your lungs don’t do all the work. The work of the BCD is to compliment your lungs so the diver is “neutrally” buoyant

Maintaining “neutral” buoyancy is tricky Positive buoyancy = floating Negative buoyancy = sinking Neutral buoyancy = suspended … not going up or down