As a gas turbine controls engineer, part of my job involves working with ancillary systems such as the fire and gas system. In gas turbine packages, fire and gas systems are used detect fires and flameable gases which are hazards to the operating environment.
If you are curious to know how an IR flame detector detects a fire caused by hydrocarbons, the answer is by monitoring the IR released from CO 2 and H 2 O in their excited states.
2 C 6 H 14 + 19 O 2 + Energy → 12 CO 2 * + 14 H 2 O *
CO 2 * → CO 2 + hv (2.8 µm – 4.3 µm)
H 2 O* → H 2 O + hv (2.9 µm)