Flying After Diving: Remember the Rules

Ed.'s note: Answers to questions are offered as information only and not as medical diagnosis or advice and should always be used in conjunction with advice from your personal diving physician.

A few years ago, I took a dive trip to South Bimini. We dived on Friday, Saturday and Sunday morning (70-foot dive, then a 40-foot dive each day). Sunday afternoon, about three to four hours after we surfaced from the last dive, we took a charter flight back to Fort Lauderdale. The pilot asked us if we had dived that day and then wanted to know our profile. He said that he would "keep the ceiling below 1,200." When I mentioned this to a friend recently, she wondered why we didn't get bent. At the time of the flight, I assumed that we were safe. The plane was a small twin-engine Cessna, holding about 12 passengers. Were we in danger of getting bent?
via e-mail

Your pilot was probably correct in that your diving pattern had been relatively safe from the point of view of onloading nitrogen before the flight. We get bubbles when we:

1. Ascend to the surface after a dive.
   
   
2. Ascend to altitude after a dive (a continuance of the dive while flying).
   
   
3. Ascend to a high altitude from the surface without pressurization.
   

Therefore, we need to allow a longer time to offgas nitrogen after diving (the same reason we spend a designated time on the surface between dives).

To answer your friend's question, you didn't get bent because you didn't have very much nitrogen in your system and you didn't fly high enough for what you did have to come out of solution as bubbles.

In two of his books on diving, Bruce Wienke says that we "should not worry too much about ascending to altitudes below 3,000 feet as far as sea level diving is concerned—corrections to ordinary protocols are minimal."

The most recent guidelines concerning flying after diving are:

• A minimum surface interval of 12 hours is required before ascent in a commercial aircraft.
  
  
• Wait an extended surface interval beyond 12 hours after daily, multiple dives for several days or dives that require decompression stops.
  
  
• The deeper or longer the diving, the longer the duration recommended before flying.
  

These guidelines are for recreational diving and should not apply to commercial diving or nitrox diving. Because of the complex nature of decompression illness and because decompression schedules are based on unverifiable assumptions, there can never be a fixed flying-after-diving rule that can guarantee prevention of bends completely.

DAN is in the midst of a study concerning flying after diving. All reported cases of DCS after a single no-decompression dive have occurred when the pre-flight surface interval was 12 hours or less. After a repetitive dive, DCS occurred even at pre-flight surface intervals as long as 17 hours. The data so far suggest that the original recommendation of waiting 12 hours or more after making single no-decompression dives is reasonable. In addition, current research suggests that it may be wise to wait 17 hours or more after making repetitive dives. However, the research is as yet incomplete and further work is continuing.