Diving Physics & Physiology Flashcards

A diver descends from the surface to 66 feet (20 m). What is the absolute pressure at that depth in ATA?

Answer: 3 ATA

66 feet of seawater equals 2 atmospheres of water pressure plus 1 ATA at the surface, totaling 3 ATA.

Which physiological condition results from breathing high partial pressures of oxygen at depth?

Answer: Oxygen toxicity

Breathing oxygen at partial pressures above 1.6 ATA can cause central nervous system (CNS) oxygen toxicity, leading to convulsions.

What happens to the volume of a flexible air pocket in a diver's body (like a sinus) during ascent if it cannot equalize?

Answer: It expands, potentially causing barotrauma

During ascent, decreasing pressure causes trapped gas to expand according to Boyle's Law, which can rupture surrounding tissue if it cannot vent.

A scuba tank filled to 3000 psi at 70°F is left in a hot car where temperature rises to 140°F. What happens to the tank pressure?

Answer: Pressure increases due to Gay-Lussac's Law

Gay-Lussac's Law states that at constant volume, pressure increases proportionally with absolute temperature, so the tank pressure will rise.

What is the primary cause of nitrogen narcosis during scuba diving?

Answer: Narcotic effect of nitrogen at high partial pressures

Nitrogen at high partial pressures (typically below 100 feet) exerts an anesthetic effect on the nervous system similar to alcohol intoxication.

Light refraction through a flat dive mask causes underwater objects to appear how?

Answer: Larger and closer than actual

The air-water interface in a flat mask refracts light, making objects appear about 25% larger and 33% closer than they actually are.

Which law explains why a diver must breathe more air per breath at 99 feet (30 m) than at the surface?

Answer: Boyle's Law

Boyle's Law explains that at 4 ATA (99 feet), gas is compressed to one-quarter its surface volume, so four times as many molecules are needed to fill the lungs.

What is the partial pressure of nitrogen in air (78% N2) at a depth of 99 feet (4 ATA)?

Answer: 3.12 ATA

Dalton's Law: partial pressure = fraction × total pressure, so 0.78 × 4 ATA = 3.12 ATA of nitrogen.

Decompression sickness (DCS) Type II involves which body systems, making it more serious than Type I?

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.

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?

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.

Sound travels approximately how much faster in water than in air?

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.

What physiological effect does cold water have on a diver's susceptibility to nitrogen narcosis?

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.

The 'afterdrop' phenomenon after a cold dive refers to what?

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.

At what depth does the maximum recommended partial pressure of oxygen (1.4 ATA for working dives) occur when breathing normal air (21% O2)?

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.

A diver experiences pain in the ear during descent that stops only when they ascend slightly. What is the most likely cause?

Answer: Middle ear barotrauma due to failed equalization

Failure to equalize the middle ear during descent causes increasing pressure differential across the eardrum, resulting in pain and potential rupture.

Which of the following best describes the term 'residual nitrogen' in dive planning?

Answer: Excess nitrogen dissolved in tissues from a previous dive

Residual nitrogen is the excess dissolved nitrogen that remains in body tissues after a dive that has not yet been eliminated through normal breathing.

Hyperventilation before a breath-hold dive is dangerous because it does what?

Answer: Removes CO2, delaying the urge to breathe until hypoxia causes blackout

Hyperventilation lowers CO2 levels, which suppresses the breathing reflex, allowing a breath-hold diver to become hypoxic and lose consciousness before feeling the urge to breathe.

When using the NAUI dive tables, what does 'surface interval time' (SIT) determine for a repetitive dive?

Answer: How much residual nitrogen has been eliminated before the next dive

The surface interval allows residual nitrogen to off-gas; the longer the SIT, the lower the repetitive group letter and the more bottom time available on the next dive.

What is the effect of increased water density on a diver's buoyancy compared to fresh water?

Answer: Saltwater makes divers more buoyant because denser water exerts greater upward force

Saltwater (density ~1.025 g/cm³) exerts more upward buoyant force than fresh water (1.0 g/cm³), so divers typically need extra weight when diving in saltwater.

Which condition describes a diver who ascends rapidly from a deep dive and develops chest pain, coughing, and shortness of breath?

Answer: Pulmonary over-inflation syndrome (air embolism)

Rapid ascent with breath-holding or airway obstruction can cause lung over-expansion, leading to arterial gas embolism (AGE) with the symptoms described.