Chapter 4 - Gases Under Pressure Flashcards
What is boyles law?
Volume is inversely proportional to pressure provided temperature remains constant.
Pressure increases - volume decreases
What is Henry’s law?
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
What is Dalton’s law?
That in a mixture of gases each gas has a partial pressure and the sum of these partial pressures is the absolute pressure
What is daltons triangle?
Pgas = Fgas x Pabs
Partial pressure of gas = fraction of the gas x absolute pressure
What are the depths and partial pressures of oxygen and nitrogen in air?
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
What is Charles Law?
A change in volume or pressure of a gas is directly related to the change in absolute temperature
What are the application of Charles law when diving?
Cylinders, inflatable boats and diving chambers
Why May divers experience gas narcosis?
When a diver breathes compressed air, the partial pressure of nitrogen is increased.
What does gas narcosis effect?
Higher brain functions such as... Judgement Reasoning Memory Concentration
What are the signs and symptoms of gas narcosis at depth?
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
What are the 2 forms of oxygen toxicity?
Central nervous system and pulmonary
What is central nervous system toxicity?
Short term
Caused by breathing oxygen at a raised partial pressure
Exercise or cold increases the risk
What is pulmonary toxicity?
Caused by breathing oxygen with a pressure of 0.6 bar or over
Measured in units of pulmonary toxicity dose
What is a UPTD?
1 unit = 1 minute of 100% O2 breathed at 1 bar
Units of pulmonary toxicity dose
What are the signs and symptoms of CNS toxicity?
Visual disturbance Ears Nausea and sickness Twitching of lips or face Irritability Dizziness
What is usually the first seen indication of CNS oxygen toxicity?
Convulsions similar to an epileptic fit
What are the stages of CNS toxicity convulsions?
TONIC - becomes rigid
CLONIC - convulsions
POST CONVULSIVE DEPRESSIVE PHASE - becomes relaxed / unconscious
What are the first aid steps to CNS toxicity?
Stop patient breathing hyperbaric oxygen
Monitor closely
Reassure
Injury assessment
What are the signs and symptoms of pulmonary toxicity?
Coughing
Soreness of the chest
A condition similar to pneumonia
What is the first aid of pulmonary toxicity?
Return the casualty to normobaric oxygen
What is carbon monoxide?
A colourless, tasteless, odourless and poisonous gas
How does carbon monoxide poisoning work?
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
What are the signs and symptoms of carbon monoxide poisoning if noticed?
Dizzy Headache Tired Staggering Mental confusions Slurred speech Nausea and vomiting Unconsciousness Cherry pink colour of the mucous membranes
What is the first aid for carbon monoxide?
Get clean air supply
Administer pure oxygen
Recompression chamber if serious case
What are the signs and symptoms of carbon dioxide poisoning?
Breathlessness Nausea Headache Dizzy Weak Inability to think clearly
What is the first aid?
Stop, breathe, think and if the situation can’t be controlled abort the dive
Administer oxygen
What is enriched air nitrox?
Nitrox 36 - 36% oxygen
Nitrox 32 - 32% oxygen
What are the advantages of nitrox?
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
What are the disadvantages of nitrox?
Specialist equipment required Greater care of the cylinder Could result in oxygen toxicity Can only be used for shallow diving Could lead to Hyperoxia
What calculations must you do for nitrox?
Partial pressure
Maximum operating depth (MOD)
Equivalent air depth (EAD)
What is the maximum operating depth?
The depth they can go to staying within the 1.4 partial pressure scuba limit
What are the MODs for nitrox 36 and nitrox 32?
29m
33m
How do you calculate EAD?
EAD = (N2 content of gas mix x depth ) / normal air n2 fraction - depth conversion
