Snorkel Diver

1
Snorkel Diver
2
Benefits of BSAC membership

• The organisation
• International recognition
• Support materials
• Snorkelling is fun

3
Basic Equipment
4
Basic Theory

• Pressure
• Breathing
• Buoyancy
• Buoyancy Aids

5
THE EFFECTS OF PRESSURE
Atmospheric Pressure
Weight of air in a 1 cm square column of
the atmosphere 1kg / cm2 1 bar
6
THE EFFECTS OF PRESSURE
Water pressure
SEA LEVEL 1.0 bar
2.0 bar 3.0 bar 4.0 bar 5.0 bar
10m 20m 30m 40m
Pressure of water approx. 1 bar every 10 metres
7
GASES UNDER PRESSURE
Volume
Absolute Pressure 1 bar
AIR
Depth 0m
10m
2 bar
1/2
20m
3 bar
1/3
30m
4 bar
1/4
8
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

9
BODY AIR SPACES
Sinuses
Middle ear
Airways
Lungs
Gut
10
EFFECTS OF COMPRESSION
The Ear
Outer ear
Inner ear
Ear drum
Middle ear
Eustachian tube
11
EFFECTS OF COMPRESSION
Pressure on the ear
Normal External pressure
Reversed ear

• Prevent discomfort by ear clearing

12
EFFECTS OF COMPRESSION
Sinuses
Air spaces

• Do not dive with a cold

13
EFFECTS OF COMPRESSION
Lungs and Airways
Mask squeeze
Airways
Heart
Lungs
14
EFFECTS OF COMPRESSION
Breath-holding diving
0m
At 30m, lung volume is compressed to ¼ of normal
volume
15
BUOYANCY
Empty lungs
Full lungs
Normal breathing
Positive
Neutral
Negative
16
SENSES UNDERWATER
Focusing of the eye in air and underwater
Water
Air
Actual image
Apparent image
Refracted rays pass from water to air
17
SENSES UNDERWATER
Focusing of the eye in air and underwater
Water
Air
Actual image
Apparent image
Refracted rays pass from water to air
18
SENSES UNDERWATER
Absorption of colour underwater
RED
BLUE
GREY
GREEN
YELLOW
ORANGE
5m
10m
15m
20m
25m
30m
19
SENSES UNDERWATER
Sound

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

20
Basic Theory

• Pressure
• Breathing
• Buoyancy
• Buoyancy Aids

21
Safe Snorkelling

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