All bodies produce infra-red radiation. The frequency and level of these emissions is dependant on the temperature and physical nature of the material and the event.

Selectively sampling the spectrum and degree of infra-red emissions permits defined analysis of the monitored condition. Fires, and even more importantly potential fire conditions, can be detected when other forms of fire or heat sensor would be ineffective due to the rigors of particular application parameters and environments.

A variety of infrared detector types target the different forms of fire hazard monitoring. These including spark monitors, flame sensors & black-body heat detectors.
 

Patol Limited's Series 5000 Sensors are black body IR heat emissions detectors. The systems are "tuned" to indicate temperature anomolies in solid objects. Coal is an almost perfect "black-body", but is far from the only application.

The 5000 infrared sensors detect ignited material in a full flaming fire condition, but they also respond to material at abnormal but much lower pre-ignition temperatures.
This latter ability is not matched by "Spark or Flame Detectors" that also monitor infra-red. These types are tuned to the different characteristics exhibited by those hazards.