Which two sensors are commonly found?

• A. Oxygen (O2) and LEL
• B. pH and Conductivity
• C. Oxygen (O2) and CO2
• D. Temperature and Humidity

Answer: (A)

Monitoring atmospheric safety often centers on two critical hazards: not enough breathable oxygen and the presence of flammable gases. An oxygen sensor checks how much O2 is in the air, warning if the level is too low or if there’s a risky enrichment. An LEL sensor measures the concentration of combustible gases and signals when you’re approaching the lower explosive limit. Together, these two sensors cover the main air-borne risks in many industrial and confined-space environments, which is why they’re commonly found together.

Choices involving pH and Conductivity sit in liquids, not air safety. Temperature and Humidity track environmental conditions rather than gas hazards, and while CO2 sensors are important in some contexts, they aren’t as universally paired with O2 as LEL is in standard gas detectors.