Low Temperature Limit Evaluation of Mk 21 Mod 1 UBA Using Reduced Overbottom(O/B) Pressure and Extended Gas Umbilical Length

摘要

This report addressed three issues regarding the performance of the MK 21 MOD 1UBA during unmanned testing. First, the influence of oral-nasal (OIN) mask seal integrity on work of breathing (WOB) levels was characterized. WOB Levels were measured with the O/N mask in three configurations: (1) cemented directly to a test mannequin; (2) fitted to, but not cemented on the mannequin; and (3) removed from the UBA. Second, the low temperature operating Limit, defined by the absence of ice formation in the UBA when operated to 60.65 msw (198 fsw), was established. Third, the performance of M 21 MOD 1 UBAs, modified by Navy Experimental Diving Unit and Diving Systems International to reduce the likelihood of free-flow, was compared using 621 and 931 kPa (90 and 135 psi) overbottom (0/B) pressure air delivered through 91.44 m (300 ft) 9.5 mm (.375 in) ID umbilicals.