When flying after diving, the ascent to altitude increases the risk of decompression sickness (DCS) because of the additional reduction in atmospheric pressure. The higher the altitude, the greater the risk.
Cruising cabin pressure in commercial aircraft is usually maintained at a constant value regardless of the actual altitude of the flight. The equivalent effective cabin altitude generally ranges from 6,000 to 8,000 feet, though it varies somewhat with aircraft type. The maximum value is 8,000 feet, which equates to about 0.75 atmospheres absolute (ATA).
DAN-Funded Research at Duke University Medical Center
Because there was little human experimental data that was relevant to commercial flying after recreational diving, DAN funded a series of trials at the Duke University Center for Hyperbaric Medicine and Environmental Physiology. From 1992 to 1999, dry, resting volunteers tested nine single and repetitive dive profiles that were near the recreational diving no-decompression limits. The divers then had 4-hour simulated flights at 8,000 feet (2,438 meters).
In 802 trials, there were 40 DCS incidents during or after flight. For single no-stop dives to 60 fsw (18 msw) or deeper, there were no cases of DCS with surface intervals of 11 hours or longer. For repetitive, no-stop dives, DCS occurred with surface intervals shorter than 17 hours.
The 2002 DAN Flying After Recreational Diving Workshop
In 2002, DAN hosted a one-day workshop to review what was known about flying after diving and discuss the need for new flying-after-diving (FAD) guidelines in recreational diving. Representatives from the recreational diving industry and experts from other diving communities had two goals:
- To review the guidelines and experimental data developed since the first flying-after-diving workshop in 1989
- To achieve a consensus for new flying-after-recreational-diving guidelines
The previous consensus was to wait 12 hours after a single no-stop dive, 24 hours after multiday repetitive dives and 48 hours after dives that required decompression stops. In response to some participants viewing this consensus as too conservative, DAN proposed a simpler 24-hour wait after all recreational diving. Objections to DAN’s proposal were that DCS risks of FAD were too low to warrant such a long delay.
The Consensus Process
The workshop participants endeavored to reach consensus concerning:
- Whether flying-after-diving guidelines were necessary for recreational diving
- Whether the current guidelines were adequate
- What the longest-duration guideline might be
- If shorter guidelines were appropriate for short dives
The participants determined that guidelines were needed, and the available evidence demonstrated that existing guidelines were inadequate. After some debate, the participants agreed that unless they could rely on dive computers, written guidelines for recreational diving should be simple and unambiguous, without the need for reference to tables as the U.S. Navy procedures required. They considered three groups of divers:
- Uncertified people who took part in an introductory scuba experience
- Certified divers who made an unlimited number of no-decompression air or nitrox dives over multiple days
- Technical divers who made decompression dives or used helium breathing mixes
Provisional Flying-After-Diving Guidelines
The following recommendations for recreational divers represent the consensus reached by attendees at the 2002 Flying After Recreational Diving Workshop. The attendees created the recommendations based on earlier published work and experimental trials. They apply to air dives followed by flights at cabin altitudes of 2,000 to 8,000 feet (610 to 2,438 meters) for divers who do not have symptoms of DCS.
The recommendations should reduce the DCS risk associated with flying after diving but do not guarantee avoidance of DCS. Preflight surface intervals longer than the recommendations will further reduce DCS risk.
Dives Within No-Decompression Limits
- For a single no-decompression dive, the recommendation is a minimum preflight surface interval of 12 hours.
- For multiple dives per day or multiple days of diving, the recommendation is a minimum preflight surface interval of 18 hours.
Dives Requiring Decompression Stops
There is little experimental or published evidence on which to base a recommendation for decompression dives. A preflight surface interval substantially longer than 18 hours appears prudent.
Flying with DCS Symptoms
The workshop attendees reviewed recent FAD trials and available field data regarding flying after diving and flying with DCS symptoms and identified potentially important differences between field and chamber studies. Diving in the field involved immersion, exercise and multiple days of diving, while the chamber trials occurred on a single day with dry, resting divers. The chamber trials may not have adequately simulated flying after diving.
It is more common for divers to fly with DCS symptoms than to develop symptoms during or after a flight. Flying with symptoms may be a greater health problem than symptoms that arise during or after a flight. Divers should seek medical advice and avoid flying if they note signs or symptoms that may indicate DCS.
The workshop proceedings stressed that because the experimental trials described in the workshop used a dry hyperbaric chamber with resting volunteers, the guidelines might need to be longer for divers who were immersed and exercising.
The participants determined that the effects of exercise and immersion on preflight surface intervals would need an experimental study. Additional studies have occurred and results are awaiting publication.
Download the complete Flying After Recreational Diving Workshop proceedings in our Publication Library.