Testing of revised unlimited-duration upward excursions during helium-oxygen saturation dives

As originally published in 1978, the U.S. Navy Unlimited-Duration Saturation Excursion Limits were found to result in an occasional case of vestibular decompression sickness (DCS) after upward excursions from storage depths in the 800-1000 feet of seawater (fsw) range. A series of dives was undertaken to revise these limits. Fifty divers performed a total of 164 man-excursions during 9 saturation dives with maximum storage depths of 36 to 1100 fsw. All excursions tested were upward excursions taken after saturation at the initial storage depth. A total of 130 man-excursions were at or greater than the maximum limits, which were calculated according to the empirical relationship: UEXD = [(0.1574.D1 + 6.197)0.5 - 1]/(0.0787) where UEXD is the upward excursion distance and D1 is the pre-excursion storage depth in fsw. During testing, 9 cases of DCS occurred that were all type 1. All of these cases occurred 8 h or more into the saturation decompression, which was begun immediately after some of the upward excursions. None of these cases of DCS were ascribed to the excursion itself, but rather to a saturation decompression rate that was too fast. As a result of the described testing, excursions computed according to the above formula were accepted for operational use in 1987. The theoretical aspects of the excursion distance calculation are discussed, including the compatibility with some current decompression models.