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Snorkel Diver Benefits of BSAC membership The organisation International recognition Support materials Snorkelling is fun Basic Equipment Basic Theory Pressure Breathing Buoyancy Buoyancy Aids THE EFFECTS OF PRESSURE Atmospheric Pressure = Weight of air in a 1 cm

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Presentation Transcript
benefits of bsac membership
Benefits of BSAC membership
  • The organisation
  • International recognition
  • Support materials
  • Snorkelling is fun
basic theory
Basic Theory
  • Pressure
  • Breathing
  • Buoyancy
  • Buoyancy Aids
the effects of pressure
THE EFFECTS OF PRESSURE

Atmospheric Pressure

= Weight of air in a 1 cm

square column of the

atmosphere

= 1kg / cm2

= 1 bar

the effects of pressure6
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

gases under pressure
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

gases under pressure8
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
BODY AIR SPACES

Sinuses

Middle ear

Airways

Lungs

Gut

effects of compression
EFFECTS OF COMPRESSION

The Ear

Outer ear

Inner ear

Ear drum

Middle ear

Eustachian tube

effects of compression11
EFFECTS OF COMPRESSION

Pressure on the ear

Normal External pressure Reversed ear

  • Prevent discomfort by ‘ear clearing’
effects of compression12
EFFECTS OF COMPRESSION

Sinuses

Air spaces

  • Do not dive with a cold
effects of compression13
EFFECTS OF COMPRESSION

Lungs and Airways

Mask squeeze

Airways

Heart

Lungs

effects of compression14
EFFECTS OF COMPRESSION

Breath-holding diving

0m

At 30m, lung volume is compressed

to ¼ of normal volume

buoyancy
BUOYANCY

Empty lungs

Full lungs

Normal breathing

Positive

Neutral

Negative

senses underwater
SENSES UNDERWATER

Focusing of the eye in air and underwater

Water

Air

Actual

image

Apparent

image

Refracted rays pass from

water to air

senses underwater17
SENSES UNDERWATER

Focusing of the eye in air and underwater

Water

Air

Actual

image

Apparent

image

Refracted rays pass from

water to air

senses underwater18
SENSES UNDERWATER

Absorption of colour underwater

RED

BLUE

GREY

GREEN

YELLOW

ORANGE

5m

10m

15m

20m

25m

30m

senses underwater19
SENSES UNDERWATER

Sound

  • Sound passes through
  • water four times faster
  • than through air
  • Difficult to judge direction
  • of sound underwater
basic theory20
Basic Theory
  • Pressure
  • Breathing
  • Buoyancy
  • Buoyancy Aids
safe snorkelling
Safe Snorkelling
  • Choice of Site
  • Conditions
  • Buddy - Group
  • Dive Plan
  • Protective Clothing
  • Marine Life
  • Snorkelling is Fun