Where do you check when measuring the oxygen content of the cargo tanks prior to loading cargoes requiring vapor recovery?

Correct Answer: Option D — one half the ullage of the tank and one meter below the tank top

Under 46 CFR 39.2009(a)(1), prior to loading cargo using a vapor recovery system, oxygen content must be sampled at two specific locations: at one-half the ullage of the tank and at one meter below the tank top. This sampling pattern ensures accurate representation of the atmospheric strata throughout the vapor space.