NAUI Diving Physics & Physiology 5 — Questions and Answers
Question 1: What is the recommended maximum ascent rate according to NAUI standards?
- 60 feet (18 m) per minute
- 30 feet (9 m) per minute (Correct answer)
- 100 feet (30 m) per minute
- 10 feet (3 m) per minute
Correct answer: 30 feet (9 m) per minute
NAUI recommends ascending no faster than 30 feet (9 meters) per minute to allow adequate off-gassing and reduce the risk of decompression sickness.
Question 2: A diver notices that colors disappear at depth, with red being the first to vanish. What physical principle explains this?
- Pressure compresses light waves, shortening their wavelength
- Water selectively absorbs longer wavelengths (red) before shorter ones (blue) (Correct answer)
- Turbidity increases with depth, blocking all wavelengths equally
- The human eye adapts to darkness by losing color sensitivity first
Correct answer: Water selectively absorbs longer wavelengths (red) before shorter ones (blue)
Water absorbs red wavelengths within the first few meters, followed by orange and yellow, leaving predominantly blue-green light at depth.
Question 3: What is the physiological basis for the 'bends' (decompression sickness) occurring primarily in joints and fatty tissues?
- These tissues have the highest blood flow and absorb nitrogen fastest
- Nitrogen is more soluble in lipid-rich and poorly perfused tissues, which absorb and release it slowly (Correct answer)
- Joints and fat contain water pockets where bubbles form preferentially
- Nitrogen bonds chemically with collagen in joints during diving
Correct answer: Nitrogen is more soluble in lipid-rich and poorly perfused tissues, which absorb and release it slowly
Nitrogen is approximately five times more soluble in lipids than in water, causing fatty tissues and slow-perfusion sites to accumulate nitrogen and off-gas slowly, making them bubble-prone.
Question 4: A diver experiences vertigo underwater with nausea. One possible cause is caloric stimulation. What triggers this?
- Nitrogen narcosis stimulating the vestibular nerve
- Unequal cooling of the inner ear canals by water entry (Correct answer)
- Rapid depth changes affecting semicircular canal fluid pressure
- High CO2 levels stimulating the labyrinth
Correct answer: Unequal cooling of the inner ear canals by water entry
If cold water enters one ear (from a hood leak or perforated eardrum) and not the other, unequal temperature stimulation of the inner ear canals creates a false sensation of rotation.
Question 5: What distinguishes a 'no-decompression limit' (NDL) dive from one requiring decompression stops?
- NDL dives occur shallower than 60 feet, decompression dives deeper
- NDL dives allow direct ascent to the surface; decompression dives require mandatory stops to off-gas safely (Correct answer)
- NDL dives use enriched air; decompression dives use regular air
- NDL dives last less than 30 minutes at any depth
Correct answer: NDL dives allow direct ascent to the surface; decompression dives require mandatory stops to off-gas safely
Within the NDL, tissue nitrogen saturation remains low enough that a direct, controlled ascent to the surface can be made safely without mandatory decompression stops.
Question 6: Carbon monoxide (CO) in a scuba tank is particularly dangerous because it does what in the body?
- Displaces nitrogen, increasing narcosis risk
- Binds to hemoglobin with 200× greater affinity than oxygen, preventing O2 transport (Correct answer)
- Increases CO2 levels, causing hyperventilation
- Reacts with nitrogen at depth to form toxic compounds
Correct answer: Binds to hemoglobin with 200× greater affinity than oxygen, preventing O2 transport
CO binds hemoglobin to form carboxyhemoglobin, which cannot carry oxygen, leading to tissue hypoxia even when the diver appears to breathe normally.
Question 7: When a diver's wetsuit is compressed at depth, what happens to their buoyancy?
- Buoyancy increases because the suit becomes more rigid
- Buoyancy is unaffected since the suit's mass stays constant
- Buoyancy decreases because the suit's volume (and displaced water) is reduced (Correct answer)
- Buoyancy increases because compressed neoprene is denser than water
Correct answer: Buoyancy decreases because the suit's volume (and displaced water) is reduced
Neoprene wetsuit bubbles compress at depth, reducing suit volume and therefore displaced water volume, which decreases buoyant force and makes the diver negatively buoyant.
NAUI Diving Physics & Physiology 5
What is the recommended maximum ascent rate according to NAUI standards?