Depressurization in military aircraft: rates, rapidity, and health effects for 1055 incidents.

Introduction: Aircraft cabin depressurization is a rare event but one which demands attention because of the grave potential for aircrew incapacity in flight. The purpose of the current study was to determine rates of depressurization incidents for U.S. military aircraft, to examine their causes, and to evaluate the medical importance of these incidents.

Methods: The U.S. Navy and U.S. Air Force safety center databases were searched for decompression incidents during FY1981-FY2003. A total of 1055 incidents were analyzed as to the cause, speed of onset, and adverse health effects (hypoxia, barotrauma, DCS, or any combination of these). The causes of each incident were identified and classified by aircraft type.

Results: The number of incidents per airframe varied from 1 (in many airframes) to 276 in the T-38. The number of total hours flown ranged from 16,332 in the T-6 to 8,101,607 in the C-130. The number of sorties flown ranged from 8800 in the B-2 to 3,543,061 in the C-130. Of 35 common airframes, 30 showed rates between 0 and 20 incidents per million flying hours. Depressurization was "slow" in 83% of incidents. Of the 1055 incidents, only 350 (33.2%) involved adverse health effects. Hypoxia occurred in 221 incidents, DCS in 83, and barotrauma in 71. Only 4 (0.4%) resulted in a fatality. Of the 199 incidents involving hypoxia, 12 (6%) occurred below 4267 m (14,000 ft).

Conclusion: Most reported military aircraft depressurization incidents are slow and do not affect aircrew health. Rates have decreased dramatically since the 1980s. Still, this study lends support to continuing hypobaric chamber training for military pilots.