🔍 Key Concepts

• Lower Explosive Limit (LEL) vs Upper Explosive Limit (UEL) and what they represent • How a combustible gas indicator scale is usually calibrated (often in % of LEL) • What happens to the meter reading when the gas concentration is too rich to burn (above UEL)

💭 Think About

• Think about what a combustible gas indicator is actually measuring: does it show accurate readings when the gas concentration is beyond its designed measuring range? • If the atmosphere is richer than the UEL, is it more similar (from the meter’s perspective) to a gas-free condition or to a maximum explosive condition? • Consider what the meter needle would do if the sensor element becomes saturated with too much fuel — will it peg high, drop low, or oscillate?

✅ Before You Answer

• Check how most meters are marked: usually in % of LEL, not % of UEL • Confirm what "too rich to explode" means in relation to the meter’s calibrated range • Verify which choice describes the needle behavior when the gas level is beyond the instrument’s measurable explosive range