What is the maximum percent of oxygen, by volume, allowed to be maintained in the cargo tanks prior to the commencement of crude oil tank washing?

Correct Answer: Option D — 8%

33 CFR 157.160 mandates that the oxygen content in cargo tanks must not exceed 8% by volume before crude oil washing begins or at any time during the washing operation. Maintaining an inert atmosphere below this threshold ensures the tank atmosphere remains non-flammable, preventing ignition from static electricity generated by oil jets.