🔍 Key Concepts

• Vapor density compared to air for common marine fuels • Difference between flash point and auto-ignition temperature • Basic fire triangle: fuel, oxygen, ignition source (spark/heat)

💭 Think About

• Look at which choices make absolute claims like 'can not' or 'nontoxic in all concentrations' and think about whether that sounds realistic for any flammable fuel vapor. • Consider where fuel vapors tend to collect on a vessel (bilges, low areas, overhead) and what that tells you about whether they are heavier or lighter than air. • Think about whether a spark can ignite a flammable vapor below its auto-ignition temperature, as long as the vapor-air mixture is within the flammable range.

✅ Before You Answer

• Eliminate any option that says fuel vapors are never toxic or can not be ignited under common conditions. • Recall that many hydrocarbon vapors (including diesel and gasoline) have a specific gravity of vapor relative to air that determines whether they sink or rise. • Verify in your study materials whether diesel vapor tends to settle in low spaces or rise toward the overhead.