🔍 Key Concepts

• Combustible gas indicator (explosimeter) operation and purpose • Meaning of meter movement toward the explosive (LEL/UEL) range on the scale • Safe sampling practices when there may be liquid or vapors in a tank

💭 Think About

• Look at each labeled part in the illustration (catalytic bead filament, flash back arrestor screen, charcoal filter, aspirator bulb). How does gas actually move through and get measured? • Think about what a reading at the extreme right side of the scale would represent in terms of gas concentration near the lower explosive limit (LEL) — would that condition ever be called ‘safe’? • If you put the sampling tube directly into liquid, what would that do to the filters and sensors that are designed for vapor, not liquid?

✅ Before You Answer

• Verify which components in the diagram show burning/combustion contained at the sensor versus open burning in the case. • Verify on the scale whether ‘safe’ is associated with low readings, not pegged-high readings at the right edge. • Confirm that the instructions for this type of meter say to avoid drawing liquid into the sampling hose or sensor chamber.