Fire Sources
Specifying the source of the fire is one of the prerequisites for performing fire simulation in Fenix+. The source of the fire in the program can be specified using the Fire source element placed in the scenario or through the “On fire” object property.
The source of the fire can be any object on the scene (a solid object, wall, floor landing) for which the Material property is defined. The exception is objects made of non-combustible materials (see the Material Editor for the exact reference).
“On Fire” Property
To specify the location of the fire source in one of the buildings within a Fire Protection Distances project, select the desired object on the scene using the Pointer tool 
and check the On Fire box in the object properties. As a result, the selected object will be set as the source of the fire for the current scenario.
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When the On Fire property is enabled, fire modeling for an object functions similarly as if a Fire Source is set on top of it. The differentiating quality of this property is that the entire surface of the object quickly reaches the maximum burning power specified for its material and stays this way. At the same time, the start of the process is artificially delayed for simulation stability. For a more detailed explanation, see Technical User Guide, Fire Source section.
Setting a fire source using the “On Fire” property can be used for cases in which it is not necessary to get the data on the transitional period of a fire gaining power before its maximum. This case is often observed when heat flux is measured between two separate buildings. In Fenix+, this property could be paired with the Master Plan view.