Instructor Manual
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Ocean Diver
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Adapting to the underwater world
Copyright © BSAC 2017
10
Breathing underwater
Snorkelling equipment
• Diver breathes gas at atmospheric pressure
Using basic equipment, the diver breathes gas at
atmospheric pressure on the surface and then breath
holds during a surface dive.
• Lungs are compressed on descent
The lungs react as a sealed balloon does; the air volume compresses but we do
not feel this. The reason for returning to the surface is the urge to breathe.
Scuba equipment
To spend more time underwater, divers take their breathing supply with them.
• Diver breathes gas at surrounding pressure
If the lungs are compressed the action of breathing becomes difficult. Divers
need a gas supply that will maintain, as near as possible, their normal lung
volume. Scuba equipment does this by delivering breathing gas at the same
pressure as the surrounding water. A higher pressure of gas is needed
the deeper a diver goes and this is incorporated into the design of scuba
equipment.
• Lungs are not compressed on descent
When diving with scuba equipment the lungs are not compressed on descent.
Scuba equipment
Scuba
Scuba gear is also known as the aqualung.
• Self
• Contained
• Underwater
• Breathing
• Apparatus
