The vapors given off by heated fuel oil are flammable, explosive, and __________.

Correct Answer: Option B — heavier than air

Fuel oil vapors are significantly denser than air. When released, they do not dissipate upward but instead collect in bilges, double bottoms, and other low-lying areas. This characteristic increases the risk of fire and explosion in confined spaces, necessitating robust ventilation and gas detection systems in machinery spaces.