NAUI Diving Physics & Physiology 5

Question 1

What is the recommended maximum ascent rate according to NAUI standards?

Accepted Answer

30 feet (9 m) per minute

Answer

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?

Accepted Answer

Water selectively absorbs longer wavelengths (red) before shorter ones (blue)

Answer

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?

Accepted Answer

Nitrogen is more soluble in lipid-rich and poorly perfused tissues, which absorb and release it slowly

Answer

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?

Accepted Answer

Unequal cooling of the inner ear canals by water entry

Answer

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?

Accepted Answer

NDL dives allow direct ascent to the surface; decompression dives require mandatory stops to off-gas safely

Answer

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.

(NAUI) National Association of Underwater Instructors Certification Practice Test

(NAUI) National Association of Underwater Instructors Certification Practice Test

NAUI Diving Physics & Physiology 5