Which calibration gas is specified for EFRS air monitoring equipment?

• A. O2 19.5-23%
• B. CO 25PPM, 50PPM
• C. MX4
• D. H2S 10PPM, 15PPM

Answer: (C)

Calibrating air monitoring equipment requires a gas mix that matches all the sensors inside the detector. These devices typically have four sensors: oxygen, carbon monoxide, hydrogen sulfide, and the hydrocarbon-based LEL sensor. A four-gas calibration gas like MX4 provides known concentrations for each component, so you can calibrate all four sensors in one step and verify that the readings are accurate across the board. That’s why MX4 is the specified gas for EFRS equipment. Using single-gas mixes (oxygen only, CO only, or H2S only) wouldn’t calibrate the other sensors or the LEL sensor, so they wouldn’t ensure proper overall detector performance.