🔍 Key Concepts

• Backfire flame arrestor purpose – what it protects against in an internal combustion engine • Fuel/air mixture in the intake – which fuels are mixed with air in a way that can ignite and send flame back through the carburetor or intake • USCG small passenger vessel requirements for gasoline vs. diesel propulsion systems

💭 Think About

• Which of these engine types uses an air–fuel mixture in the intake system (carburetor or throttle body) where a backfire could send flame back toward the atmosphere? • Which of these fuels/engines normally require special protection in enclosed spaces on small passenger vessels because of vapor explosion or fire risk? • For each option, ask: does this engine type normally have a carburetor or similar intake where a backfire flame arrestor would be installed?

✅ Before You Answer

• Identify which engines commonly have a carburetor or similar fuel–air mixing device in the intake • Consider which fuel produces heavier-than-air vapors that can accumulate in bilges and need ignition protection • Confirm in your study materials which propulsion systems on small passenger vessels are specifically required to have backfire flame arrestors under USCG regulations