🔍 Key Concepts

• Combustible gas indicators (CGIs) measure gas concentration as a percentage of the lower explosive limit (LEL) • CGIs have limits in low-oxygen (oxygen-deficient) atmospheres • Proper tank testing requires multiple samples at different levels and locations

💭 Think About

• Think about what a combustible gas indicator is actually designed to measure: is it explosion probability, gas concentration, or oxygen content? • Consider how the presence or absence of oxygen might affect an instrument that relies on burning (oxidation) a sample to get a reading. • When checking a tank for gas hazards, ask yourself whether one reading from one spot can safely represent the entire tank atmosphere.

✅ Before You Answer

• Verify how a CGI scale is usually labeled (look for % of LEL vs. probability of explosion). • Check whether a standard CGI can or cannot indicate oxygen deficiency on its own. • Recall safe tank-entry procedures and whether they call for single-point or multi-point atmosphere sampling.