Outgassing in Scuba Diving

Outgassing, a critical concept in scuba diving, refers to the diffusion of gases, such as nitrogen, from bodily tissues into the blood and its further transportation to the lungs, where it diffuses into the lung gas and is eliminated by exhalation. This physiological process plays a vital role in preventing decompression sickness (DCS), a potentially life-threatening condition that can occur when a diver ascends too quickly from depth. This comprehensive entry will cover the science of outgassing, its significance in scuba diving, and the best practices to ensure diver safety.

The Science of Outgassing

When a diver descends and breathes pressurized air, inert gases like nitrogen dissolve into their tissues. The deeper the dive and the longer the duration, the more gas is absorbed. During ascent, the pressure decreases, and these dissolved gases start to come out of the tissues in a process called outgassing. If the ascent is too rapid, the dissolved gases can form bubbles in the body, leading to decompression sickness.

Decompression sickness (DCS) is a potentially serious condition that occurs when gas bubbles form in the body due to rapid changes in pressure. DCS can manifest in various forms, ranging from mild joint pain (colloquially known as “the bends”) to severe neurological complications, paralysis, or even death. Outgassing plays a crucial role in preventing DCS by allowing the body to gradually eliminate the dissolved gases during ascent.

Factors Affecting Outgassing

Several factors can influence the rate and efficiency of outgassing during a dive:

  1. Depth and duration: Deeper and longer dives result in a greater amount of dissolved gases in the tissues, requiring more time for outgassing.
  2. Breathing gas composition: The choice of breathing gas affects the rate of outgassing. For example, using a nitrox mix (a blend of nitrogen and oxygen) instead of compressed air can reduce the amount of nitrogen absorbed, leading to faster outgassing.
  3. Individual factors: Age, fitness, body composition, and hydration levels can all impact a diver’s ability to outgas efficiently.
  4. Dive profiles: Diving at a constant depth or performing multiple dives in a day can affect outgassing rates and decompression requirements.

Outgassing and Decompression Stops

To facilitate safe outgassing and reduce the risk of DCS, divers must follow proper decompression procedures during ascent. One such technique is the use of decompression stops or safety stops, which involve pausing at specific depths during ascent to allow the body to eliminate dissolved gases gradually.

Recreational divers typically perform a single safety stop at a depth of 15 feet (approximately 5 meters) for 3-5 minutes after dives deeper than 60 feet (18 meters) or when they have been diving close to their no-decompression limits. Technical divers, who often undertake deeper and longer dives, may require multiple decompression stops at various depths, as determined by dive planning software or decompression tables.

Best Practices for Safe Outgassing

To ensure safe and efficient outgassing, scuba divers should adhere to the following guidelines:

  1. Plan the dive and dive the plan: Proper planning, including dive profiles, gas management, and decompression stops, is crucial for safe outgassing. Divers should strictly adhere to their planned ascent rates and decompression stops.
  2. Use appropriate breathing gas: Divers may consider using nitrox or other gas mixes to reduce nitrogen absorption and improve outgassing rates.
  3. Maintain proper buoyancy control: Good buoyancy control allows divers to ascend at a steady, controlled rate and make necessary decompression stops without difficulty.
  4. Stay within no-decompression limits: Recreational divers should avoid diving beyond their no-decompression limits, as this increases the risk of DCS and the need for longer decompression stops.
  5. Be mindful of individual factors: Divers should be aware of their own physical condition, fitness, and health, and adjust their dive plans accordingly. Staying well-hydrated, avoiding alcohol, and maintaining overall health can improve outgassing efficiency.
  6. Follow a conservative ascent rate: A slower ascent rate allows for more gradual outgassing, reducing the risk of bubble formation. A general guideline is to ascend no faster than 30 feet (9 meters) per minute.
  7. Monitor dive computer or tables: Divers should use a dive computer or decompression tables to keep track of their decompression requirements and ensure they are following the appropriate ascent rates and stops.
  8. Account for multiple dives and repetitive dive profiles: When performing multiple dives in a day or over consecutive days, divers should consider residual nitrogen levels and adjust their dive plans and decompression requirements accordingly.
  9. Continuous education and training: Divers should stay up-to-date with the latest research, guidelines, and best practices for safe outgassing and decompression procedures. Participating in specialized courses or workshops can provide valuable insights and practical experience.


Outgassing is a fundamental physiological process that plays a vital role in ensuring diver safety. By understanding the science behind outgassing and adhering to best practices, divers can minimize the risk of decompression sickness and enjoy a safe, enjoyable underwater experience. As with all aspects of scuba diving, continuous education, training, and adherence to safety guidelines are essential for promoting responsible and sustainable diving practices.