PADI Diving Theory & Safety 3 — Questions and Answers
Question 1: Henry's Law is most relevant to diving because it explains:
- How gas volume changes with depth
- How gas pressure changes with temperature
- How gases dissolve into liquids under pressure (Correct answer)
- How light refracts underwater
Correct answer: How gases dissolve into liquids under pressure
Henry's Law states that the amount of gas dissolved in a liquid is proportional to the partial pressure of that gas, explaining nitrogen absorption during diving.
Question 2: Dalton's Law of Partial Pressures states that the total pressure of a gas mixture equals:
- The pressure of the most abundant gas
- The average pressure of all component gases
- The sum of the partial pressures of each individual gas (Correct answer)
- The product of all component gas pressures
Correct answer: The sum of the partial pressures of each individual gas
Dalton's Law states total gas pressure equals the sum of each individual gas's partial pressure in the mixture.
Question 3: A diver experiences vision disturbances and convulsions underwater. This is most likely caused by:
- Nitrogen narcosis
- Carbon monoxide poisoning
- Oxygen toxicity (CNS toxicity) (Correct answer)
- Hypercapnia
Correct answer: Oxygen toxicity (CNS toxicity)
CNS oxygen toxicity causes visual disturbances, twitching, and convulsions when the partial pressure of oxygen exceeds safe limits.
Question 4: What is the maximum operating depth (MOD) for EAN32 (Nitrox with 32% oxygen) based on a ppO₂ limit of 1.4 ATA?
- 33.75 meters (Correct answer)
- 30 meters
- 40 meters
- 28.4 meters
Correct answer: 33.75 meters
MOD = [(ppO₂ limit / FO₂) - 1] × 10m = [(1.4/0.32) - 1] × 10 = 33.75 meters.
Question 5: Which condition describes the 'rapture of the deep' experienced by divers breathing compressed air at depth?
- Oxygen toxicity
- Nitrogen narcosis (Correct answer)
- Hypercapnia
- Decompression sickness
Correct answer: Nitrogen narcosis
Nitrogen narcosis ('rapture of the deep') causes impaired judgment and euphoria similar to alcohol intoxication, typically below 30 meters on air.
Question 6: What fraction of the water surface is illuminated by light absorbed at approximately 10 meters depth?
- Red wavelengths are completely absorbed (Correct answer)
- Blue wavelengths are completely absorbed
- All colors are equally absorbed
- Green wavelengths are the first to disappear
Correct answer: Red wavelengths are completely absorbed
Red wavelengths are absorbed first and are almost completely gone by 5-10 meters, which is why blood appears green underwater.
Question 7: During a dive, a buddy notices the diver's SPG reads 50 bar. According to the rule of thirds, what action should be taken?
- Continue diving normally since air remains
- Begin ascending immediately as this is the reserve
- Signal to the buddy and begin a normal ascent (Correct answer)
- Switch to the alternate air source
Correct answer: Signal to the buddy and begin a normal ascent
50 bar is typically the reserve level (rule of thirds: 1/3 in, 1/3 out, 1/3 emergency reserve); signal buddy and ascend.
PADI Diving Theory & Safety 3
Henry's Law is most relevant to diving because it explains: