🔍 Key Concepts

• Combustible gas indicators (CGIs) measure flammability, not toxicity • Effect of oxygen-deficient atmospheres on gas detection instruments • Difference between what is measured right at the sampling point vs. the whole space

💭 Think About

• Ask yourself whether a combustible gas indicator tells you anything about how poisonous a vapor is, or only about how close it is to its lower explosive limit (LEL). • Consider how a combustible gas indicator actually draws in its sample: does it measure conditions everywhere in a tank/space, or only where the sample is pulled from? • Think about what most catalytic-bead type CGIs need in order to burn the sample gas on the sensor—what role does oxygen level play?

✅ Before You Answer

• Verify whether CGIs are designed to measure toxicity or flammability/LEL only. • Check if proper operation requires a normal oxygen concentration, and what happens if oxygen is too low. • Confirm that the reading represents conditions only where the air is sampled, not automatically the entire compartment.