The standard hot wire combustible gas detector reads in what units?

• A. Percent LEL
• B. Parts per million (ppm)
• C. Percent by volume
• D. Pounds per square inch (psi)

Answer: (A)

When assessing flammable gas risk, readings are given as a percent of the Lower Explosive Limit (LEL). A standard hot-wire detector uses a catalytic bead sensor that responds to the oxidation of any combustible gas, and the electronics are calibrated to express the signal as %LEL. This provides a gas-independent way to gauge how close the ambient mixture is to the point where ignition could occur, so a given %LEL conveys the same relative risk whether the gas is methane, propane, or another hydrocarbon. Using ppm would require knowing exactly which gas is present and its specific concentration, while percent by volume and psi don’t directly reflect flammability risk in a cross-gas sense. Therefore, percent LEL is the appropriate and standard unit for this type of detector.