Physical Principles of Diving
The environment in which diving and caisson operations are conducted dictates specific physical laws. As depth increases, the pressure of the water column rises uniformly: every 10 meters of depth adds 1 atmosphere. For example, at a depth of 90 meters, the external environmental pressure on the human body reaches an impressive 10 atmospheres.
Under these conditions, a person cannot physically breathe air at normal atmospheric pressure. Air or another breathing gas mixture must be delivered at a pressure that strictly matches the diver's current depth.
Effect of Gases and the Problem of Solubility
Pressure changes directly affect how gases interact with body fluids. When descending to great depths (exceeding 100 meters, corresponding to a pressure of over 10 atmospheres), a serious physiological problem arises: the amount of gases dissolved in the blood increases sharply.
This primarily involves oxygen and nitrogen. Excessive dissolution of nitrogen in the blood leads to severe consequences—so-called nitrogen narcosis—rendering standard air unsuitable for deep-water operations.
Artificial Gas Mixtures
To avoid nitrogen narcosis and ensure adequate breathing at great depths, specialized helium-oxygen mixtures (heliox) are used in physiology and diving practice.
- Helium. This inert gas is chosen as the base because it practically does not dissolve in human blood even under high pressure. This property reliably prevents nitrogen narcosis.
- Oxygen. Its proportion in the mixture is variable. Oxygen is added in precisely the concentration required so that its partial pressure at the working depth exactly matches the partial pressure under normal surface conditions.
The use of pure oxygen for underwater breathing is strictly limited. This practice is possible exclusively at shallow depths—up to 20 meters. Descending deeper causes the pure gas to exhibit pronounced toxic effects, clinically manifesting as severe muscle convulsions.
Decompression Rules
The process of returning a diver to the surface requires no less attention than the descent itself. The body needs a specific, strictly calculated transition regimen from high pressure to normal atmospheric pressure—decompression.
This process takes significant time to allow dissolved gases to safely leave the body without forming bubbles. A telling example: if a specialist spends just 1 hour working at a depth of 160 meters, the return journey to the surface, including decompression in a specialized hyperbaric chamber, takes 3 days.