After a fire has flashed over, it is considered fully developed (in a stage of full room involvement) in which the fire can be characterized as having a relatively steady HRR.
Full Room Involvement: The condition in a compartment fire in which the entire volume is involved in fire. |
Due to the increasing HRR prior to flashover, all involved fuels are at temperatures high enough to pyrolyze. Fuel vapour is produced from all of the fuels in the room. There is so much fuel vapour being formed and heat being released that combustion occurs wherever there is an appropriate mixture of oxygen and fuel. Since there is most often an excess of fuel vapour in the enclosure, the fire is ventilation-controlled and the HRR value in this steady-state condition is usually the maximum HRR for a given fire situation. The actual value will depend on the ventilation available to the fire. Therefore, the HRR (or size of fire) and overall enclosure temperature at this stage will depend on the size of the compartment, the size of any compartment openings and the amount of incoming air.
Figure 10: Fully developed fire in a residential structure
The overflow of hot gases and combustion products from one compartment to another during the fully developed stage may allow for ignition within other compartments and the fire may then spread from one compartment to the next. At this stage, hot smoke will definitely be flowing out of the enclosure and into any other accessible areas within the full structure.