🔍 Key Concepts

• Flammable range of a fuel/air mixture (lower explosive limit and upper explosive limit) • What happens when there is too much fuel vs. too much air in a mixture • Basic idea of combustion: correct fuel-to-oxygen ratio needed for burning

💭 Think About

• Consider what the term lower explosive limit suggests about the amount of fuel vapor present in the air. • Think about whether being below this lower limit means there is too much fuel or not enough fuel to sustain combustion. • Ask yourself: if a mixture won’t ignite because there isn’t enough fuel vapor present, how would you describe that mixture in everyday language?

✅ Before You Answer

• Verify that below the lower explosive limit (LEL) means the concentration of fuel vapor is less than the minimum needed for ignition. • Confirm that a mixture with excess fuel (not enough air) relates to the upper explosive limit (UEL) instead, not the lower one. • Make sure the adjective you choose matches a mixture with insufficient fuel vapor to support combustion.