1. 1 of 20 Snorkel Diver

2. 2 of 20 Benefits of BSAC membership l The organisation l International recognition l Support materials l Snorkelling is fun

3. 3 of 20 Basic Equipment

4. 4 of 20 Basic Theory l Pressure l Breathing l Buoyancy l Buoyancy Aids

5. 5 of 20 THE EFFECTS OF PRESSURE Atmospheric Pressure Weight of air in a 1 cm = Weight of air in a 1 cm square column of the square column of the atmosphere atmosphere = 1kg / cm 2 = 1 bar

6. 6 of 20 THE EFFECTS OF PRESSURE Pressure of water = approx. 1 bar every 10 metres SEA LEVEL 1.0 bar 10m20m30m40m 2.0 bar 3.0 bar 4.0 bar 5.0 bar Water pressure

7. 7 of 20 GASES UNDER PRESSURE AIR Depth 0m 10m 30m 20m 2 bar 3 bar 4 bar 1/2 1/4 1/3 Volume Absolute Pressure 1 bar

8. 8 of 20 GASES UNDER PRESSURE Avoid pressure damage never hold breath during never hold breath during ascent ascent Breathe normally during Breathe normally during ascent ascent Air space compression on descent, expansion on ascent descent, expansion on ascent Equalisation of pressure in Equalisation of pressure in flexible body air spaces flexible body air spaces Volume

9. 9 of 20 BODY AIR SPACES Sinuses Middle ear Airways Lungs Gut

10. 10 of 20 EFFECTS OF COMPRESSION The Ear Outer ear Inner ear Middle ear Ear drum Eustachian tube

11. 11 of 20 EFFECTS OF COMPRESSION Pressure on the ear Normal External pressure Reversed ear Normal External pressure Reversed ear Prevent discomfort by ‘ear clearing’

12. 12 of 20 EFFECTS OF COMPRESSION Sinuses Air spaces Do not dive with a cold

13. 13 of 20 EFFECTS OF COMPRESSION Airways Lungs Mask squeeze Heart Lungs and Airways

14. 14 of 20 EFFECTS OF COMPRESSION Breath-holding diving 0m At 30m, lung volume is compressed to ¼ of normal volume

15. 15 of 20 BUOYANCY Full lungs Empty lungs Normal breathing Positive Negative Neutral

16. Actualimage SENSES UNDERWATER Water Air Apparentimage Focusing of the eye in air and underwater Refracted rays pass from water to air

17. Actualimage SENSES UNDERWATER Water Air Apparentimage Focusing of the eye in air and underwater Refracted rays pass from water to air

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

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

20. 20 of 20 Basic Theory l Pressure l Breathing l Buoyancy l Buoyancy Aids

21. 21 of 20 Safe Snorkelling l Choice of Site l Conditions l Buddy - Group l Dive Plan l Protective Clothing l Marine Life l Snorkelling is Fun