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Diving Theory BSAC > Adapting To The Underwater World > Flashcards

Adapting To The Underwater World Flashcards

1
Q

What type of gas is air?

A

Compressible has

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2
Q

How deep is the layer of air around the earth?

A

12-12km

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3
Q

What does the layer of gas around the earth do under the influence of gravity?

A

It exerts pressure

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4
Q

What is the weight of 1cm squared of air at sea level?

A

1kg

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5
Q

What happens to air as you get further away from the earth?

A

It gets thinner and weighs less

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6
Q

What does one atmosphere or one bar mean?

A

1kg per cm squared

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7
Q

How much downwards pressure does 1cm squared of water exert every 10m?

A

1 bar

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8
Q

How do you calculate absolute pressure?

A

Add how many bars of water you have (relating to the depth you are) with an extra bar or atmospheric pressure of the air around us also.

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9
Q

What happens to pressure and volume as depth increases?

A

The pressure will increase and thus volume will decrease.

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10
Q

How does the compression of air change for every 10m?

A

10m-2 bar pressure so air reduces to 1/2
20m-3 bar pressure so air reduces to 1/3
30m-4 bar pressure so air reduces to 1/4
Etc.

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11
Q

Why is a divers body mainly unaffected by pressure?

A

Because we are made from 70-85% water which is incompressible so it’s unaffected by pressure volume changes.

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12
Q

What happens to your lungs as you go to a higher pressure (deeper down)?

A

The air compresses and the lungs reduce in size.

We don’t feel this though, we come up for air as we feel we need to breathe not because of the pressure.

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13
Q

What is the purpose of a mask?

A

It allows clear vision underwater.

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14
Q

Key features of a mask. (5)

A 
Ridged frame 
Tempered glass (break into balls rather than shards)
flexible seal that moulds to face
 It’s enclose the nose
Adjustable strap
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15
Q

Why should the nose be enclosed in a mask?

A

You need to breathe into the mask to equalise the pressure or the mask will be very tight on your face.

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16
Q

Why do you have a seal on the mask?

A

If water enters the mask, breathing out through your nose will expel water.

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17
Q

How do you care for your mask?

A

Wash in fresh water and don’t dry in sun (affect flexibility of rubber and thus the fit of mask)

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18
Q

What’s the job of the fin?

A

It provides a larger s.a to propel the diver through the water more easily and with less effort.

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19
Q

Two types of fins?

A

Shoe fin -warm conditions with no extra foot protection

Strap fin - go overs boots and adjusts to hold fin in place

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20
Q

What happens if the fin is too big or small?

A

Cramps and discomfort

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21
Q

What should the design of a fin include? (3)

A

Stiffening ridges - maintain shape
graduating stiffness towards the tip
Slots or grooves or shapes blades (assist finning action)

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22
Q

Caring for fins

A

Fresh water and stand then up foot pocket end

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23
Q

Features of a snorkel (6)

A

Rigid or semi rigid open topped tube
Flexible corrugated section towards mouthpiece
40-45cm long
20mm diameter (anything more and would be hard to breathe)
Some have self drain valve at lowest point
Some have intake protection valves

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24
Q

Care for snorkels

A

Fresh water and dry thoroughly before storing

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25
Q

What pressure will of air does a snorkel diver breathe?

A

Atmospheric pressure

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26
Q

Why must scuba gear deliver air at a higher pressure?

A

To maintain the balance of air and outside pressure (because air pressure is increased and thus volume is reduced).

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27
Q

Other name for SCUBA?

A

Aqua lung

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28
Q

What does SCUBA mean?

A

Self contained underwater breathing apparatus

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29
Q

Components of scuba equipment? (3)

A

Cylinder
Buoyancy compensator
Regulator

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30
Q

How does a cylinder work?

A
  1. Cylinder pressurised from a compressor via the cross flow or pillar valve in the cylinder neck.
  2. Valve used for opening or closing the gas flow.
31
Q

What are the cylinder working pressures?

A

232-300bar

32
Q

What are cylinders made from?

A

Still or aluminium

33
Q

What is done to show that the cylinder is safe?

A

Manufacturing stamp is on the neck

34
Q

What is the job of a rubber foot on a cylinder?

A

It protects the cylinder base

35
Q

Why is it important that cylinders are safe?

A

They contain a lot of stored energy which can explode and cause damage.

36
Q

What does PED mean?

A

Pressure Equipment Directive

37
Q

A cylinder in the EU can’t be put on the market unless….?

A

It conforms with the PED (implemented into UK legislation by pressure equipment regulations 1999).

38
Q

What mark will PED cylinders have?

A

A CE mark

39
Q

What 2 tests must be carried out on cylinders and how often?

A

Hydrostatic test every 5 years

Visual inspection 4 years after hydrostatic test

40
Q

Care of cylinders (5)

A 
Fresh water
Boot cleaned periodically
Store dry
Don’t store completely empty
Store upright (makes sure it can’t fall over)
41
Q

What is a nitrox mix?

A

Gas that has extra oxygen rather than nitrogen

42
Q

Content of normal air?

A

21% O

79% N

43
Q

Content of nitrox 32 and 36?

A

32% O
68% N

Or

36% O
64% N

44
Q

What is capacity measured in?

A

Litres

45
Q

What does the mark WP on a cylinder mean and what does it indicate?

A

It means Working pressure and it indicates the operating pressure the cylinder has been designed to work at.

46
Q

What is the usual WP of a cylinder?

A

232-300bar

47
Q

What does CP mean? What is it the same as?

A

CP means Charging pressure and it is the same as WP or working pressure.

48
Q

What does TP mean on a cylinder Andy what is this used for?

A

This stands for Test Pressure and is used during the Hydraulic test.

49
Q

What does the phrase “nitrox tanks need to be in oxygen service” mean? why do we need to do this?

A

They need to have oxygen compatible parts in valves and need to be oxygen clean to ensure no hydrocarbons are present in them.

50
Q

When should you clean a nitrox tank?

A

Every 15 months.

51
Q

What is an A Clamp?

A

It has an O ring set into the valve outlet and the regulator clamps around it.

52
Q

What is another name for an A Clamp?

A

An international fitting cylinder valve

53
Q

What cylinders can an A Clamp valve be used on?

A

Cylinders with a working pressure up to 232 bar.

54
Q

What is a DIN cylinder valve?

A

It has no sealing O Ring as this is on the diving reg instead.

55
Q

What cylinders can DIN valves be fitted to?

A

Cylinders up to 300 bar.

56
Q

What’s the difference between a 232bar DIN valve and a 300bar DIN valve? what does this mean?

A

232-5 thread rotations
300-7 thread rotations

This means you can’t attach a 232 to a 300 but you can attach an A Clamp into some 232’s

57
Q

What is a BC?

A

Buoyancy compensator

58
Q

Features of a BC (4)

A

Gas bladder-filled via direct feed
Back up oral inflation
Over inflation pressure relief valve
Manual dump mechanism

59
Q

Why should you not breathe from the bladder of a BC via the oral inflation mouthpiece?

A

Risk of lung/chest infection due to the bladder building up bacteria inside.

60
Q

How should you care for a BC?

A

Should be washed inside and out with fresh water
Dry before storing
Store slightly inflated

61
Q

What is the job of the regulator?

A

It reduces the cylinders high pressure gas and delivers it to the diver at the surrounding ambient pressure.

62
Q

What is another name for the regulator?

A

Demand valve or DV.

63
Q

Where is air expelled when breathing out?

A

Through the exhaust valve

64
Q

Why do you use the purge button?

A

To get the water out of the second stage of the reg

65
Q

What is the additional second stage reg called?

A

Octopus

66
Q

What measures the gas?

A

Contents gauge

67
Q

What do weights help improve?

A

A divers trim

68
Q

What should a diver never do as they ascend? Why?

A

Hold their breath, because the breathing gas volume in the lungs will increase and cause serious lung damage

69
Q

Why do heavy boats float?

A

Because they have a large displacement and contain a large volume of air

70
Q

What would you need to do differently if you If you move from fresh water to salt water?

A

Add more weight

71
Q

How much faster is the rate of conduction in water than air?

A

25 times faster

72
Q

How much clothing do you need for each temp?

A

21 degrees-minimal insulation

10-20 degrees-wet or semi dry suit

Less than 10 degrees-drysuit

73
Q

Two types of dry suits

A

Neoprene and membrane

Diving Theory BSAC (3 decks)

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