Snorkel Diver Benefits of BSAC membership l l

Snorkel Diver

Benefits of BSAC membership l l The organisation International recognition Support materials Snorkelling is fun

Basic Equipment

Basic Theory l l Pressure Breathing Buoyancy Aids

THE EFFECTS OF PRESSURE Atmospheric Pressure = Weight of air in a 1 cm square column of the atmosphere = 1 kg / cm 2 = 1 bar

THE EFFECTS OF PRESSURE Water pressure SEA LEVEL Pressure of water = approx. 1 bar every 10 metres 1. 0 bar 10 m 2. 0 bar 20 m 3. 0 bar 30 m 4. 0 bar 40 m 5. 0 bar

GASES UNDER PRESSURE Volume Depth 0 m AIR 10 m Absolute Pressure 1 bar 2 bar 1/2 20 m 3 bar 1/3 30 m 4 bar 1/4

GASES UNDER PRESSURE Volume • Air space compression on descent, expansion on ascent • Equalisation of pressure in flexible body air spaces • Avoid pressure damage never hold breath during ascent • Breathe normally during ascent

BODY AIR SPACES Middle ear Sinuses Airways Lungs Gut

EFFECTS OF COMPRESSION The Ear Outer ear Inner ear Ear drum Middle ear Eustachian tube

EFFECTS OF COMPRESSION Pressure on the ear Normal External pressure Reversed ear • Prevent discomfort by ‘ear clearing’

EFFECTS OF COMPRESSION Sinuses Air spaces • Do not dive with a cold

EFFECTS OF COMPRESSION Lungs and Airways Mask squeeze Lungs Airways Heart

EFFECTS OF COMPRESSION Breath-holding diving 0 m At 30 m, lung volume is compressed to ¼ of normal volume

BUOYANCY Full lungs Empty lungs Normal breathing Positive Negative Neutral

SENSES UNDERWATER Focusing of the eye in air and underwater Water Actual image Refracted rays pass from water to air Apparent image Air

SENSES UNDERWATER Focusing of the eye in air and underwater Water Actual image Refracted rays pass from water to air Apparent image Air

SENSES UNDERWATER 5 m 10 m 15 m 20 m 25 m 30 m GREY BLUE GREEN YELLOW ORANGE RED Absorption of colour underwater

SENSES UNDERWATER Sound • Sound passes through water four times faster than through air • Difficult to judge direction of sound underwater

Basic Theory l l Pressure Breathing Buoyancy Aids

Safe Snorkelling l l l l Choice of Site Conditions Buddy - Group Dive Plan Protective Clothing Marine Life Snorkelling is Fun