NAUI Diving Physics & Physiology 3 — Questions and Answers
Question 1: What is the partial pressure of nitrogen in air (78% N2) at a depth of 99 feet (4 ATA)?
- 0.78 ATA
- 1.56 ATA
- 3.12 ATA (Correct answer)
- 4.00 ATA
Correct answer: 3.12 ATA
Dalton's Law: partial pressure = fraction × total pressure, so 0.78 × 4 ATA = 3.12 ATA of nitrogen.
Question 2: Decompression sickness (DCS) Type II involves which body systems, making it more serious than Type I?
- Skin and lymphatic system only
- Joints and muscles only
- Neurological and cardiopulmonary systems (Correct answer)
- Ears and sinuses only
Correct answer: Neurological and cardiopulmonary systems
Type II DCS affects the spinal cord, brain, and lungs (chokes), and is considered a medical emergency requiring immediate recompression.
Question 3: A diver ascends too quickly after a deep dive. Nitrogen bubbles form in the tissues. What physical law best describes why bubbles form during ascent?
- Gay-Lussac's Law — pressure and temperature relationship
- Henry's Law — gas dissolving from solution as pressure drops (Correct answer)
- Archimedes' Principle — buoyancy forces on the diver
- Dalton's Law — partial pressures of mixed gases
Correct answer: Henry's Law — gas dissolving from solution as pressure drops
Henry's Law states that gas dissolved in liquid will come out of solution when pressure decreases, which is why rapid ascent causes nitrogen bubble formation.
Question 4: Sound travels approximately how much faster in water than in air?
- About the same speed
- Approximately 2 times faster
- Approximately 4 times faster (Correct answer)
- About 10 times faster
Correct answer: Approximately 4 times faster
Sound travels at about 1,500 m/s in water versus approximately 340 m/s in air, making it roughly 4 times faster underwater.
Question 5: What physiological effect does cold water have on a diver's susceptibility to nitrogen narcosis?
- Cold water reduces narcosis effects
- Cold water increases narcosis susceptibility (Correct answer)
- Temperature has no effect on narcosis
- Cold water causes narcosis only above 40 feet
Correct answer: Cold water increases narcosis susceptibility
Cold water, along with anxiety and exertion, increases a diver's susceptibility to nitrogen narcosis, lowering the effective depth threshold.
Question 6: The 'afterdrop' phenomenon after a cold dive refers to what?
- Drop in tank pressure after surfacing
- Continued core temperature fall after exiting cold water (Correct answer)
- Sudden buoyancy loss at the surface
- Pressure drop in the ears after equalization
Correct answer: Continued core temperature fall after exiting cold water
Afterdrop occurs when cold blood from the extremities returns to the core after exiting the water, causing core temperature to continue falling even after warming begins.
Question 7: At what depth does the maximum recommended partial pressure of oxygen (1.4 ATA for working dives) occur when breathing normal air (21% O2)?
- Approximately 187 feet (57 m) (Correct answer)
- Approximately 218 feet (66 m)
- Approximately 130 feet (40 m)
- Approximately 100 feet (30 m)
Correct answer: Approximately 187 feet (57 m)
PO2 = 0.21 × total pressure; solving for 1.4 ATA: total pressure = 1.4/0.21 ≈ 6.67 ATA, which equals about 187 feet of seawater.
NAUI Diving Physics & Physiology 3
What is the partial pressure of nitrogen in air (78% N2) at a depth of 99 feet (4 ATA)?