Which of the following would be the most dangerous for cleaning engine parts because of its flammability?

• A. Gasoline
• B. Water
• C. Alcohol
• D. Diesel

Answer: (A)

The key idea is how easily a liquid can form ignitable vapors. Gasoline has a very low flash point and high volatility, so it can release enough vapors to ignite at room temperature and near-ambient ignition sources. Those vapors can also travel and pool in low spots, creating a widespread fire hazard. Diesel has a higher flash point, so it’s less prone to ignition under typical shop conditions, and alcohol, while flammable, generally doesn’t ignite as readily as gasoline in the same environment. Water doesn’t burn at all. So gasoline poses the greatest fire risk when used to clean engine parts.