or below the maximum external design pressure differential; and (iii) Admits inert gas, cargo vapor from a source other than a cargo vapor header, or air except as prohibited under ??154.1710. (b) A vacuum protection system does not have to be installed if the cargo tank is designed to withstand:(1) A maximum external pressure differential exceeding 24.5 kPa gauge (3.55 psig); and (2) The maximum