🔍 Key Concepts

• Behavior of petroleum vapors in air (heavier vs lighter than air) • Where vapors can accumulate on a vessel during fueling • Basic fire and explosion triangle (fuel, oxygen, ignition source)

💭 Think About

• Think about what happens to fuel vapors in low, enclosed spaces like bilges, lockers, and lazarettes. • Consider whether vapors from gasoline or diesel will rise and disappear or sink and spread along the deck. • Ask yourself: during fuel spills, where does the greatest explosion risk usually occur—up high in the air or down low in enclosed spaces?

✅ Before You Answer

• Verify whether petroleum vapors are heavier or lighter than air. • Consider where you are trained to ventilate and test for vapors before starting engines (high spaces vs low spaces). • Check which option best explains why we avoid sparks, switches, and starting engines until we’ve checked for vapors in the bilge and enclosed low areas.