Which of the precautions listed should be observed when taking on diesel fuel?

Correct Answer: Option D — Prohibit smoking in the area.

Prohibiting smoking during bunkering is a fundamental safety requirement under 33 CFR 156.120. Fueling operations involve the potential release of flammable vapors; eliminating all ignition sources, including smoking, matches, and lighters, is essential to prevent fire and explosion during the transfer of diesel or other fuel oils.