When checking the oxygen content of the cargo tanks prior to loading cargoes requiring vapor recovery, the atmosphere must be sampled __________.

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

Title 46 CFR 39.2009 requires sampling the cargo tank atmosphere at one-half the ullage of the tank and one meter below the tank top. This ensures a representative measurement of oxygen levels throughout the vapor space before initiating vapor recovery operations, preventing explosive mixtures.