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HSE Scuba > Chapter 4 - Gases Under Pressure > Flashcards

Chapter 4 - Gases Under Pressure Flashcards

1
Q

What is boyles law?

A

Volume is inversely proportional to pressure provided temperature remains constant.

Pressure increases - volume decreases

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2
Q

What is Henry’s law?

A

The idea that when a gas and a liquid are in contact, gas will dissolve into the liquid. As pressure increases more gas will dissolve.

Increased pressure dissolves more oxygen and nitrogen in the blood

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3
Q

What is Dalton’s law?

A

That in a mixture of gases each gas has a partial pressure and the sum of these partial pressures is the absolute pressure

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4
Q

What is daltons triangle?

A

Pgas = Fgas x Pabs

Partial pressure of gas = fraction of the gas x absolute pressure

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5
Q

What are the depths and partial pressures of oxygen and nitrogen in air?

A 
Depth  pressure  pO2   pN2
0m         1 bar.      0.2    0.8
10m       2 bar       0.4   1.6
20m      3 bar       0.6   2.4
30m      4 bar       0.8   3.2
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6
Q

What is Charles Law?

A

A change in volume or pressure of a gas is directly related to the change in absolute temperature

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7
Q

What are the application of Charles law when diving?

A

Cylinders, inflatable boats and diving chambers

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8
Q

Why May divers experience gas narcosis?

A

When a diver breathes compressed air, the partial pressure of nitrogen is increased.

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9
Q

What does gas narcosis effect?

A 
Higher brain functions such as...
Judgement
Reasoning
Memory
Concentration
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10
Q

What are the signs and symptoms of gas narcosis at depth?

A

30-45 m - lips tingle, loss of decision making, a feeling of well being
45-60 m - greater carelessness, dizzy
60-80 m - partial loss of co ordination and concentration, maybe hysteria
80+m - total loss of coordination, approaching unconsciousness

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11
Q

What are the 2 forms of oxygen toxicity?

A

Central nervous system and pulmonary

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12
Q

What is central nervous system toxicity?

A

Short term
Caused by breathing oxygen at a raised partial pressure
Exercise or cold increases the risk

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13
Q

What is pulmonary toxicity?

A

Caused by breathing oxygen with a pressure of 0.6 bar or over
Measured in units of pulmonary toxicity dose

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14
Q

What is a UPTD?

A

1 unit = 1 minute of 100% O2 breathed at 1 bar

Units of pulmonary toxicity dose

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15
Q

What are the signs and symptoms of CNS toxicity?

A 
Visual disturbance
Ears
Nausea and sickness
Twitching of lips or face
Irritability 
Dizziness
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16
Q

What is usually the first seen indication of CNS oxygen toxicity?

A

Convulsions similar to an epileptic fit

17
Q

What are the stages of CNS toxicity convulsions?

A

TONIC - becomes rigid
CLONIC - convulsions
POST CONVULSIVE DEPRESSIVE PHASE - becomes relaxed / unconscious

18
Q

What are the first aid steps to CNS toxicity?

A

Stop patient breathing hyperbaric oxygen
Monitor closely
Reassure
Injury assessment

19
Q

What are the signs and symptoms of pulmonary toxicity?

A

Coughing
Soreness of the chest
A condition similar to pneumonia

20
Q

What is the first aid of pulmonary toxicity?

A

Return the casualty to normobaric oxygen

21
Q

What is carbon monoxide?

A

A colourless, tasteless, odourless and poisonous gas

22
Q

How does carbon monoxide poisoning work?

A

It enters the blood stream and bonds with haemoglobin known as carboxyhaemoglobin. This decreases the oxygen carrying capacity of the blood and results in hypoxia (low level of O2 in tissue) and then anoxia (no O2 in tissue) then death

23
Q

What are the signs and symptoms of carbon monoxide poisoning if noticed?

A 
Dizzy 
Headache
Tired
Staggering
Mental confusions 
Slurred speech
Nausea and vomiting 
Unconsciousness
Cherry pink colour of the mucous membranes
24
Q

What is the first aid for carbon monoxide?

A

Get clean air supply
Administer pure oxygen
Recompression chamber if serious case

25
Q

What are the signs and symptoms of carbon dioxide poisoning?

A 
Breathlessness
Nausea
Headache
Dizzy
Weak
Inability to think clearly
26
Q

What is the first aid?

A

Stop, breathe, think and if the situation can’t be controlled abort the dive
Administer oxygen

27
Q

What is enriched air nitrox?

A

Nitrox 36 - 36% oxygen

Nitrox 32 - 32% oxygen

28
Q

What are the advantages of nitrox?

A

Air computers and dive tables assume 79% nitrogen so when this is reduced there is a greater margin of safety.
Reduced probability of DCI
Increased bottom time if using a nitrox specific dive table

29
Q

What are the disadvantages of nitrox?

A 
Specialist equipment required
Greater care of the cylinder
Could result in oxygen toxicity
Can only be used for shallow diving
Could lead to Hyperoxia
30
Q

What calculations must you do for nitrox?

A

Partial pressure
Maximum operating depth (MOD)
Equivalent air depth (EAD)

31
Q

What is the maximum operating depth?

A

The depth they can go to staying within the 1.4 partial pressure scuba limit

32
Q

What are the MODs for nitrox 36 and nitrox 32?

A

29m

33m

33
Q

How do you calculate EAD?

A

EAD = (N2 content of gas mix x depth ) / normal air n2 fraction - depth conversion

HSE Scuba (13 decks)

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