It is important for divers to understand gas laws in order to dive safely. Knowing how and why gases behave while we dive helps divers avoid things like decompression sickness and barotraumas (pressure injuries). Knowing how gases behave also helps a diver fine tune their buoyancy while diving.
The first gas law divers learn about is Boyle’s Law. In the late 1600s, Sir Robert Boyle wanted to fine out how a given gas will behave under pressure. He discovered that if the temperature remains constant, the volume of gas is inversely proportional to the absolute pressure, or; when the pressure is increased on a certain amount of gas, the volume will decrease.
Divers apply Boyle’s Law when they equalize their ears while descending, adjusting their buoyancy while diving and by remembering to never hold their breath when breathing compressed air while diving.
Charles’ Law went a step further and took into consideration temperature. Charles found out if a gas is compressed, its volume will decrease and it will get hotter. When a compressed gas is heated, and it cannot expand, the pressure rises.
Divers apply Charles’ Law when they do not leave full scuba tanks in direct sunlight, especially in the trunk of a car.
Dalton’s Law states that within a mixture of gases such as air (21 percent oxygen and 79 percent nitrogen) the partial pressures of the individual gases within the mixture are equal to the total pressure of the mixture. This helps us understand the toxic effect of different gases at depth.
Henry’s Law demonstrates that a gas can be contained within a liquid and remain there until certain conditions (like pressure) change. A good example of this is when a can or bottle of carbonated soda is shaken and then opened quickly. The fizzy spray is the carbonated gas forming bubbles when the pressure changes quickly.
In diving, this law concerns how a diver’s body absorbs and releases nitrogen. Predicting how inert gases enter and leave the body is complex, but divers need guidelines to help prevent nitrogen narcosis and decompression sickness. The Dive Tables and Dive Computers used by divers to keep track of their nitrogen level are constructed with decompression models built using Henry’s Law.