Buoyant ascent rate profiles for the MK10 and MK11 submarine escape and immersion equipment

Introduction: Since the U.S. Navy transitioned from the MK10 to the MK11 submarine escape and immersion equipment (SEIE) there has been an increase in the incident rate of pulmonary barotrauma during submarine escape training. This study compares ascent rate profiles of the MK10 and MK11 SEIE to determine if ascent rate differences between the escape suits are associated with an increase in pulmonary barotraumas. Methods: Buoyant ascent rates of the MK10 and MK11 SEIE were compared using weighted manikins equivalent to the 1st, 50th, and 99th percentile body weight of a submariner. Human ascents using the MK11 (n=126) were compared to human ascents in the same trainer wearing the MK10 (n=124). Results: Manikin mean ascent times were faster for the MK10 compared to the MK11 (5.19 seconds vs 5.28 seconds, p < 0.05). Terminal velocity (Vt) was affected by manikin weight (p < 0.001). Human trials confirmed the manikin results. The average mean ascent velocity for the MK10 group was 0.155 meters/second faster than the MK11 group mean ascent velocity (p < 0.001). Mean ascent velocity was inversely correlated with all anthropometrics for the MK10 group (p < 0.01). Neither height nor body mass index showed a significant association with mean ascent velocity for the MK11 group. Conclusions: The Vt of buoyant ascents are significantly affected by body weight. As the mean ascent rate of the MK11 is slower than that of the MK10, ascent rate profile differences between the suits do not appear to explain the recent increase in pulmonary barotrauma incident rates during escape training.