100+ Free DMT Practice Questions

Explanation: Boyle's law states that, at constant temperature, the volume of a fixed mass of gas is inversely proportional to its absolute pressure (P1V1 = P2V2). This is the fundamental law explaining barotrauma in air-filled spaces such as the lungs, sinuses, and middle ear during descent and ascent.

Explanation: Every 33 feet (10 m) of seawater adds one atmosphere of pressure. At the surface a diver is at 1 ata; at 33 fsw the diver experiences 1 atmosphere of water plus 1 atmosphere of air above, giving 2 ata absolute pressure.

Explanation: By Boyle's law, P1V1 = P2V2. At 4 ata the pressure is four times surface pressure, so the volume is reduced to one quarter: 6 L / 4 = 1.5 L. This crushing of gas volume is why bubbles shrink during recompression.

Explanation: Dalton's law states that the total pressure exerted by a mixture of gases equals the sum of the partial pressures that each gas would exert alone. Each gas's partial pressure is proportional to its fractional concentration multiplied by the total pressure.

Explanation: By Dalton's law, PO2 = fraction of oxygen x total pressure = 0.21 x 4 ata = 0.84 ata. As depth increases, the partial pressure of each component gas rises proportionally even though the percentage composition stays the same.

Explanation: Henry's law states that the amount of a gas dissolving into a liquid is proportional to the partial pressure of that gas. At depth, the higher partial pressure of nitrogen drives it into solution in body tissues; on ascent, reduced pressure can cause it to come out of solution as bubbles, the basis of decompression sickness.

Explanation: Nitrogen narcosis results from the increasing partial pressure of nitrogen as a diver descends. At higher partial pressures nitrogen exerts an anesthetic-like effect on the central nervous system, impairing judgment and coordination, often noticeable beyond about 100 fsw on air.

Explanation: The risk of CNS oxygen toxicity increases above approximately 1.4 ata PO2 and rises sharply above 1.6 ata. For this reason 1.6 ata is widely used as a contingency maximum PO2 limit for working divers, with 1.4 ata commonly used as the planning limit.

Explanation: Each 33 fsw adds one atmosphere. 132 fsw divided by 33 equals 4 atmospheres of water, plus 1 atmosphere of surface air, giving 5 ata absolute pressure.

Explanation: As ambient pressure increases with depth, the breathing gas is compressed and its density rises. Denser gas increases airway resistance and the work of breathing, contributing to CO2 retention and fatigue, which is one reason helium (a lighter gas) is used at greater depths.