Influence of bottom time on preflight surface intervals before flying after diving

Previous trials of flying at 8,000 ft after a single 60 fsw, 55 min no-stop air dive found low decompression sickness (DCS) risk for a 11:00 preflight surface interval (PFSI). Repetitive 60 fsw no-stop dives with 75 and 95 min total bottom times found 16:00. Trials reported here investigated PFSIs for a 60 fsw, 40 min no-stop dive and a 60 fsw, 120 min decompression dive. The 40 min trials began with a 12:05 PFSI (USN guideline) which was incrementally reduced to 0:05 (three DCS incidents in 281 trials). The 120 min trials began with a 22:46 PFSI (USN guideline) which was reduced to 2:00 (nine incidents in 281 trials); 2:00 was rejected with six incidents. Low-risk PFSIs for the 40 min dive were nearly 12 hours shorter than for the 55 min dive, and low-risk PFSIs for the single 120 min decompression dive were 12 hours shorter than for the 75-95 min repetitive dives. With the dry, resting conditions of these dives, low-risk PFSIs appeared to be sensitive to dive profile characteristics such as bottom time, repetitive diving, and decompression stops. Whether this is so for wet, working dives is unknown.