Ingassing, a critical concept in scuba diving, refers to the uptake of inert gases in the body tissues of a diver during a dive. Inert gases are those that do not participate in metabolic processes within the body. The two primary inert gases relevant to scuba diving are nitrogen and helium, which comprise the majority of the breathing gas mixtures used by divers. Understanding ingassing and its implications is essential for managing decompression and ensuring diver safety.

I. Process of Ingassing

  1. Breathing gas mixtures: Scuba divers typically use a breathing gas mixture, which contains oxygen and one or more inert gases. The most common mixture is air, consisting of approximately 21% oxygen and 79% nitrogen. Technical divers may use different mixtures, such as Nitrox (enriched air), Trimix (a combination of oxygen, nitrogen, and helium), or Heliox (a mixture of helium and oxygen).
  2. Partial pressure: The partial pressure of a gas is the pressure that the gas would exert if it were the only gas present in a given volume. In a breathing gas mixture, each gas component contributes to the total pressure proportionally to its concentration. As a diver descends, the ambient pressure increases, raising the partial pressure of the inert gases in the breathing mixture.
  3. Gas solubility: Gases dissolve in liquids according to Henry’s Law, which states that the amount of gas that dissolves in a liquid is proportional to its partial pressure. As the partial pressure of inert gases increases with depth, more of these gases dissolve into the diver’s bloodstream and body tissues.
  4. Saturation: The process of ingassing continues until the diver’s tissues reach saturation, at which point the amount of dissolved gas in the tissues is in equilibrium with the partial pressure of the gas in the breathing mixture. The time it takes to reach saturation varies among tissues, depending on their blood supply and metabolic rates.

II. Factors Affecting Ingassing

  1. Depth and time: The deeper and longer a diver stays underwater, the more inert gas dissolves into their tissues. This is due to the increased partial pressure and the longer exposure time.
  2. Breathing gas mixture: The concentration of inert gases in the breathing mixture affects the amount of gas that dissolves into the tissues. For example, Nitrox has a higher oxygen content and lower nitrogen content than air, leading to less nitrogen ingassing.
  3. Individual factors: Personal factors, such as body composition, fitness level, and age, can influence the rate of ingassing. For instance, adipose tissue (body fat) is less perfused with blood, resulting in slower gas exchange and longer saturation times.

III. Ingassing and Decompression

  1. Decompression sickness (DCS): When a diver ascends too quickly or omits necessary decompression stops, the dissolved inert gases in their tissues may come out of solution and form bubbles. These bubbles can cause various symptoms, ranging from mild joint pain to severe neurological issues, collectively known as decompression sickness (DCS).
  2. Decompression tables and algorithms: To minimize the risk of DCS, divers follow decompression tables or use dive computers, which employ algorithms to calculate the required decompression stops based on the dive profile, depth, and breathing gas mixture. These tools take into account the ingassing and outgassing rates of different body tissues.
  3. Gradient factors: Technical divers often use gradient factors, which are ratios that modify decompression schedules to account for individual preferences and risk factors. By adjusting gradient factors, divers can increase or decrease the conservatism of their decompression plan, balancing the risk of DCS against the time spent decompressing.

IV. Mitigating Ingassing Risks

  1. Proper training: Ensuring that divers receive adequate training in decompression theory and techniques is crucial for mitigating the risks associated with ingassing. Divers should be familiar with using decompression tables or dive computers and adhere to the prescribed ascent rates and decompression stops.
  2. Dive planning: Meticulous dive planning helps divers minimize ingassing by limiting their depth and bottom time. Furthermore, divers can select appropriate breathing gas mixtures, such as Nitrox, which reduces nitrogen ingassing compared to air.
  3. Safety stops: Although not mandatory, many divers perform a safety stop at a depth of 15-20 feet (5-6 meters) for 3-5 minutes during their ascent. This practice provides an additional margin of safety by allowing more time for outgassing and reducing the risk of DCS.
  4. Hydration: Staying well-hydrated before and during a dive can improve gas exchange in body tissues and reduce the risk of bubble formation. Dehydration can slow down the outgassing process and increase the likelihood of DCS.
  5. Fitness and health: Maintaining good physical fitness and overall health can positively impact a diver’s ability to manage ingassing. Divers should avoid diving if they are sick, fatigued, or have a pre-existing medical condition that could affect their ability to off-gas efficiently.
  6. Sequential dives: If multiple dives are planned in a day or over a short period, divers should be aware of the residual inert gas in their tissues from previous dives. Adequate surface intervals should be allowed between dives to facilitate outgassing and reduce the risk of DCS.

In conclusion, ingassing is a fundamental aspect of scuba diving that divers must understand and manage to minimize the risk of decompression sickness. By following proper training, adhering to dive plans, using appropriate breathing gas mixtures, and considering individual factors, divers can safely enjoy the underwater world while minimizing the hazards associated with ingassing.