Scuba diving and flying are governed by the physics of pressure, and combining them without a proper break is strictly prohibited for diver safety. Flying immediately after diving is forbidden due to the serious physiological risks involved. A rapid ascent to altitude, even in a pressurized airplane cabin, mimics an uncontrolled, fast ascent from a deep dive. This rapid change in pressure is the core danger that can trigger a severe medical condition for a diver.
How Pressure Affects Nitrogen in the Body
The air divers breathe underwater is a mixture of gases, primarily nitrogen and oxygen, delivered at the high ambient pressure of the water column. According to Henry’s Law, the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas. As a diver descends and the surrounding pressure increases, the body’s tissues and blood absorb more nitrogen from the compressed breathing air.
The body metabolizes the oxygen, but nitrogen is an inert gas that accumulates in the tissues during a dive. This nitrogen remains dissolved until the pressure decreases. When a diver ascends slowly, the nitrogen is gradually released from the tissues back into the bloodstream and then exhaled through the lungs, a process called off-gassing.
A rapid decrease in external pressure, such as ascending too quickly or taking a flight, prevents this slow off-gassing process. Gas laws, specifically Boyle’s Law, dictate that as pressure decreases, the volume of a gas increases. The residual dissolved nitrogen gas expands rapidly inside the body’s tissues and blood. If the pressure drop is too fast, the nitrogen comes out of solution violently, forming bubbles, similar to opening a carbonated drink bottle.
The Danger: What Is Decompression Sickness
The dangerous outcome of this rapid gas expansion is Decompression Sickness (DCS), often referred to as “the bends.” DCS results from nitrogen bubbles forming within the body’s tissues, joints, and bloodstream. These bubbles can obstruct blood flow, damage tissue, and disrupt nerve function, causing a wide range of symptoms.
Mild symptoms of DCS include general fatigue, an itchy skin rash (cutis marmorata), or joint pain, especially in the elbows and shoulders. The name “the bends” originated because the intense joint pain often caused sufferers to bend over. These symptoms do not indicate a minor problem, as they can quickly progress to more severe issues.
The more serious forms of DCS involve the central nervous system and can be life-threatening. Symptoms may include muscle weakness, numbness, tingling, paralysis, or severe neurological impairment that mimics a stroke. Bubbles blocking the blood supply to the spinal cord are particularly damaging, and pulmonary DCS, while rare, can cause severe respiratory distress.
Any suspected case of DCS requires immediate medical attention. The standard treatment is recompression in a hyperbaric chamber, which involves placing the patient in a pressurized environment to breathe pure oxygen. The increased pressure reduces the size of the nitrogen bubbles, forcing the gas back into a dissolved state for safe elimination by the body.
Mandatory Waiting Times Before Flying
The potential for DCS is why diving organizations mandate specific surface intervals before a diver can board an aircraft. Commercial airliners maintain cabin pressure equivalent to an altitude between 6,000 and 8,000 feet above sea level. This pressure drop is significant enough to cause the residual nitrogen in a diver’s system to expand.
The Divers Alert Network (DAN) and the Professional Association of Diving Instructors (PADI) provide the widely accepted minimum safety intervals. For a single, no-decompression dive, the minimum recommended surface interval before flying is 12 hours. This period allows a significant portion of the excess nitrogen to off-gas safely at normal surface pressure.
If a diver has completed multiple dives over a day or several days, or if the dives were particularly deep, a longer wait is necessary. The minimum recommended surface interval for repetitive dives or multiple days of diving is 18 hours. Many experts suggest a more conservative 24-hour wait for added safety, as these guidelines are intended to reduce the risk of altitude-induced Decompression Sickness.