Flammable gas is defined as any fuel with a flash point less than 37.8 °C (100.0 °F). Fuels with a flash point above that temperature are called combustible. A substance with a high vapor pressure at normal temperatures is often referred to as volatile.
If you need to measure hydrogen, the MPS Flammable Gas Sensor provides real-time 0-100% LEL measurement of 14 different combustible gases - including hydrogen.
Need to measure propane for safety or alarms? The CU-SBH-2 NDIR Propane Gas Sensor detects 0-2% levels of C3H8 propane gas in ambient environments.