A cargo tank is designed for vacuum loading and has a full-opening rear head. Per 49 CFR 180.407, what periodic pressure retest interval applies to this tank?

49 CFR 180.407(c)

Vacuum-loaded tankers undergo different structural stresses during loading than gravity-loaded tanks, which is why DOT shortens their retest cycle. A driver who knows this exception can correctly read the tank's test-date marking instead of assuming the standard 5-year cycle applies.