Exposure to reduced barometric pressure shortly after diving can increase a diver’s risk of decompression sickness (DCS). Before flying, a diver should remain at sea level long enough to allow elimination of excess inert gas, mainly nitrogen, from tissues. If a diver flies too soon, then the inert gas can come out of solution, form bubbles in tissues and result in decompression illness. Preflight surface intervals vary and depend on the type of diving done before the flight.
Flying after diving recommendations are designed to reduce the risk of developing decompression illness. Unfortunately, there is little consensus among experts and guidelines. The US Navy advises a 2-hour interval prior to flying, while the US Air Force and the Divers Alert Network both recommend 24 hours. Others recommend a 12-hour delay after a single dive and an 18-hour delay after multiple dives.
Strong evidence supporting minimum preflight surface intervals is lacking. Most studies have been performed in hyperbaric and hypobaric chambers, not in real diving and flying conditions. For recreational divers, the most widely used flying after diving guidelines are from a published consensus of attendees at the 2002 Flying After Diving Workshop held by Divers Alert Network (DAN) and Undersea and Hyperbaric Medical Society (UHMS). These recommendations do not apply to military, commercial, scientific, or public service diving, nor for recreational divers who dive with gas mixtures other than air, for example, those divers who use Nitrox or Trimix.
Compressed gas diving results in increased uptake of inert gas, mainly nitrogen, in tissue during descent. On ascent or decompression, the excess inert gas is eliminated from the tissues. Once at the surface, there is residual inert gas that continues to be released from the tissue. The amount of residual inert gas depends on the type of diving done. If a diver ascends to the surface too fast, the inert gas comes out of solution and forms bubbles in the tissues and the bloodstream causing decompression sickness. These bubbles can cause injury that ranges from mild joint pain and rash to severe neurological injury and death. Similarly, if a diver flies shortly after diving, the reduction in pressure can cause the residual inert gas to come out of solution and form bubbles. To reduce the risk of decompression sickness when flying after diving, a diver should remain at sea level long enough to allow elimination of excess inert gas from tissues. Preflight surface intervals vary and depend on the type of diving done before the flight.
Recommended preflight surface intervals for recreational divers:
These recommendations were the consensus of attendees at the 2002 Flying After Diving Workshop held by Divers Alert Network (DAN) and Undersea and Hyperbaric Medical Society (UHMS). They apply only to recreational divers doing air dives followed by flights at cabin altitudes of 610 to 2438 meters (2000 to 8000 feet) for divers who do not have symptoms of decompression sickness (DCS). The recommended preflight surface intervals do not guarantee avoidance of DCS. Longer surface intervals will reduce DCS risk further. At altitudes lower than 610 meters (2000 feet) the effect of a flight is considered mild enough not to warrant special consideration.
Non-divers can also develop decompression sickness (DCS) during exposures to altitude. Altitude decompression sickness has been observed during high-altitude balloon and unpressurized aircraft flights, extravehicular activity (EVA) from a spacecraft, and rapid depressurization of pressurized aircraft. Rapid exposures to altitudes between 18,000 feet and 25,000 feet have shown a low occurrence of altitude decompression sickness. However, at altitudes of 25,000 feet or higher, the risk of developing decompression sickness increases significantly. Additionally, repetitive exposures (within a few hours) and longer exposures to altitudes above 18,000 feet increase the risk of developing decompression sickness. Exercise at altitude has also been shown to increase the risk.
Other factors that can affect the decision of how long one should wait prior to flying include prior history of DCS, availability of a recompression chamber at the destination, and the depth and time of the recent dives. The use of enriched air nitrox can also ameliorate DCS risk. Avoiding deep diving and repetitive diving before a flight is recommended.
Studies are looking at healthy divers with echocardiography. There has been variability among divers as to their susceptibility to forming bubbles in the bloodstream. In one study, half the divers never formed detectable bubbles, but approximately a quarter of the divers always bubbled. After 24 hours, before flying, no diver had detectable bubbles; however, half of the frequent bubbling divers exhibited bubbles at altitude although they all resolved within 90 minutes. Of note, none of these divers had symptoms of DCS. However, it does seem to indicate that there are people at higher than usual risk for DCS after a dive, and these divers are at increased risk from flying after diving as well.
The situation of flying after having had DCS and being treated in a recompression chamber is special. This scenario carries a very high risk of DCS recurrence. One study noted that in divers with residual symptoms, that DCS recurrence occurred in over half of cases. Flying with symptoms is associated with an adverse outcome. Avoidance of flying or even exposure to an altitude such as driving over a mountain pass is recommended to be as long as possible with a week being considered very reasonable and some recommendations being much longer. Certainly, there is evidence that a 72-hour pre-flight interval would be an absolute minimum given a large number of patients having relapses of DCS symptoms. Diving in remote locations may necessitate flying earlier than would be medically recommended. Use of oxygen in such cases could be considered.