PADI PADI Physics & Physiology of Diving 2 — Questions and Answers
Question 1: What is 'oxygen toxicity' and under what conditions does it become a concern for recreational divers?
- A dangerous reaction to high partial pressures of oxygen, primarily a risk with nitrox at depth (Correct answer)
- Oxygen depletion at depths below 130 feet
- A mild headache caused by shallow breathing
- Increased nitrogen absorption when using oxygen-enriched air
Correct answer: A dangerous reaction to high partial pressures of oxygen, primarily a risk with nitrox at depth
Oxygen toxicity occurs when the partial pressure of oxygen exceeds safe limits (1.4 ATA working limit), causing convulsions — mainly a risk with nitrox at deeper depths.
Question 2: What physiological process does Henry's Law describe in the context of diving?
- The amount of gas dissolved in a liquid is proportional to the partial pressure of that gas above the liquid (Correct answer)
- Gas volume decreases as pressure increases
- Temperature changes affect gas pressure in a closed container
- The total pressure of a mixture equals the sum of partial pressures
Correct answer: The amount of gas dissolved in a liquid is proportional to the partial pressure of that gas above the liquid
Henry's Law explains why more nitrogen dissolves into a diver's blood and tissues at greater depths — as partial pressure increases, more gas goes into solution.
Question 3: What is 'barotrauma' as it relates to scuba diving?
- Tissue damage caused by unequal pressure between an air space and surrounding water pressure (Correct answer)
- A nitrogen bubble in the joint
- Oxygen toxicity symptoms
- Cold water causing hypothermia
Correct answer: Tissue damage caused by unequal pressure between an air space and surrounding water pressure
Barotrauma is injury to body tissues (ears, sinuses, lungs) caused by failure to equalize the pressure difference between an enclosed air space and the surrounding water.
Question 4: Which technique does PADI recommend for equalizing ear pressure during descent?
- Valsalva maneuver (pinch nose and gently blow) (Correct answer)
- Swallowing only
- Yawning repeatedly
- Descending as fast as possible to equalize quickly
Correct answer: Valsalva maneuver (pinch nose and gently blow)
The Valsalva maneuver — pinching the nose and gently blowing — opens the Eustachian tubes to equalize pressure on the eardrums during descent.
Question 5: What is hypercapnia and what typically causes it in scuba divers?
- A buildup of carbon dioxide in the blood, often caused by skip breathing or overexertion (Correct answer)
- Excess oxygen in the bloodstream
- Nitrogen narcosis combined with oxygen toxicity
- Low blood pressure caused by cold water
Correct answer: A buildup of carbon dioxide in the blood, often caused by skip breathing or overexertion
Hypercapnia is CO2 buildup resulting from inadequate ventilation, often triggered by skip breathing (holding breath between inhales) or heavy exertion underwater.
Question 6: What is the 'squeeze' that affects a diver's mask during descent, and how is it corrected?
- The mask presses against the face as external pressure increases; corrected by exhaling air into the mask through the nose (Correct answer)
- The mask strap tightening due to cold water
- Air escaping from the mask seal
- The lens cracking under pressure
Correct answer: The mask presses against the face as external pressure increases; corrected by exhaling air into the mask through the nose
Mask squeeze occurs because the airspace inside the mask becomes a low-pressure zone relative to surrounding water as depth increases; exhaling through the nose equalizes the pressure.
PADI PADI Physics & Physiology of Diving 2
What is 'oxygen toxicity' and under what conditions does it become a concern for recreational divers?