Flying immediately after scuba diving creates a dangerous situation due to the extreme pressure changes that affect the human body. The conflict between diving and flying is rooted in the physics of how gases interact with tissues under pressure. A diver’s body absorbs a significant amount of inert gas during a dive. The rapid reduction in atmospheric pressure experienced during flight can trigger a serious medical condition. Following established waiting periods, known as no-fly intervals, is a safety measure to allow the body to return to a stable, pre-dive state before ascending to altitude.
How Pressure Affects Nitrogen Absorption
The physical principle governing gas absorption during a dive is Henry’s Law, which states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. When a diver descends, the ambient pressure increases considerably. The compressed air breathed contains a high partial pressure of nitrogen, an inert gas. This increased pressure forces the nitrogen from the lungs into the bloodstream and eventually into the body’s various tissues. The longer a diver remains submerged, the more time the tissues have to absorb this nitrogen. Tissues with a high blood flow, such as the brain and major organs, absorb the gas quickly, while others, like fat and cartilage, absorb it more slowly. This process, known as nitrogen loading, continues throughout the dive, leaving the diver with an elevated level of dissolved nitrogen.
The Risk of Bubble Formation
The danger arises when the external pressure is reduced too quickly, which happens during a rapid ascent or when flying. When the pressure drops, the nitrogen dissolved in the tissues and blood begins to come out of solution. If this pressure drop is too fast, the gas cannot be eliminated safely through the lungs and instead forms physical bubbles inside the body, defining Decompression Sickness (DCS).
A commercial airplane cabin is pressurized, but typically only to an equivalent altitude of 6,000 to 8,000 feet above sea level. This pressure reduction acts as a secondary, uncontrolled decompression event for a recent diver. Even if a diver surfaces without symptoms, the additional pressure drop in the airplane cabin can cause existing, microscopic nitrogen bubbles to expand or precipitate the formation of new ones. These gas bubbles can lodge in small capillaries, blocking blood flow, or compress nerves and tissues.
The symptoms of DCS, often called “the bends,” can manifest in various ways depending on where the bubbles form. Common signs include deep, aching pain in the joints and muscles. More severe, neurological symptoms can occur if bubbles affect the spinal cord or brain, leading to numbness, paralysis, or even death. Flying exacerbates this bubble formation and expansion, representing a direct and significant risk for a recently-dived individual.
Establishing Safe No-Fly Intervals
To mitigate the risk of DCS, divers must observe a mandatory surface interval before flying, allowing the excess nitrogen to off-gas safely through normal respiration. Diving organizations like the Divers Alert Network (DAN) and the Professional Association of Diving Instructors (PADI) have established specific consensus guidelines based on extensive research and trials. These guidelines distinguish between different dive profiles to determine the necessary waiting time.
For a single no-decompression dive, which is the most common type of recreational dive, a minimum surface interval of 12 hours is suggested before flying. For repetitive dives, multiple-day diving, or any dive that pushes close to the no-decompression limits, a more conservative minimum of 18 hours is recommended. Dives that require mandatory decompression stops necessitate an even longer surface interval, often exceeding 18 hours, due to the higher gas levels absorbed.
These intervals are based on the time required for the majority of excess nitrogen to be eliminated from the body’s tissues at sea-level pressure. Following these timeframes significantly reduces the risk of in-flight DCS. Divers should treat these guidelines as the minimum waiting time.