Which instrument detects concentrations of flammable or combustible gases and vapors in the air?

• A. Gas chromatograph
• B. Infrared camera
• C. PID
• D. Mass spectrometer

Answer: (C)

Detecting concentrations of flammable or combustible gases and vapors in air is best done with a photoionization detector. A PID works by exposing VOC molecules in the air to ultraviolet light, which ionizes many organic vapors. The resulting ions create an electrical current that is proportional to the vapor concentration, giving a fast, real-time reading in parts per million (ppm). This makes PIDs particularly well suited for quickly screening air for flammable vapors that are common in hazmat scenarios.

Gas chromatographs separate and identify individual compounds, but they require sampling and more time, and aren’t the quick-field screening tool you need for standing in a potentially hazardous environment. Infrared cameras can visualize gas plumes and leaks and help locate them, but they don’t provide a direct, reliable concentration reading for all vapors in air. Mass spectrometers identify and quantify compounds with high sensitivity, but they’re typically large, expensive, and not used for immediate ambient screening in the field.