# A Review of Modelling and Simulation Methods for Flashover Prediction in Confined Space Fires
## 1 Introduction
If there is sufficient oxygen to consume the fuel pyrolysis gases released, this is known as an FC scenario. Conversely, if there is lack of oxygen to continue the reaction, this is a VC situation. Taking into account both enclosure situations (ventilated and under-ventilated), once the ignition in a material has occurred, there a several ways in which the situation may evolve. In a ventilated enclosure, if the fire dies after ignition, this can be because the energy released is not sufficient to further pyrolysis in the same material or in nearby materials. For that reason it is not possible for the fire to spread (FC). Alternatively, if the enclosure is under-ventilated, the lack of oxygen in early stages can result in a non-adequate mix with the fuel gases impeding the combustion process (VC). Another possibility is when the heat released from the flames is enough to generate new pyrolysis gases from new unburned material and sufficient oxygen is present to maintain the combustion process. Subsequently, fire reaches the growing stage, where fire can spread over the same surface as flames spread or reach other surface materials by radiation. In a ventilated confined space, all fuel can be burned and fire dies or a transition from FC to VC can take place causing the fire to die out due to lack of oxygen. In some cases, the fire can grow to become a fully developed fire after a transition stage known as flashover. Flashover phenomenon, or also called generalised sudden combustion, can be defined as a transition phase from growth to fully developed stage (see Figure 2a). As a consequence, all combustible surfaces inside the enclosure, that were not involve in the fire, begin to burn. It occurs due to the radiation received from the smoke layer which can be up to 170 kW/m\({}^{2}\)[4]. Once all fuels are involved in the fire the fully developed stage is reached. As a result, firefighters can't stay inside the enclosure under flashover conditions, 80 kW/m\({}^{2}\) is the maximum supported radiation by their clothes according to NFPA 1971, Standard on Protective Ensemble for Structural Fire Fighting. In the Table 3 different radiation values are shown, and they can be compared to the maximum heat flux for a post-flashover case in order to get an idea of this phenomenon's power. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Property Use** & **Fires** & **Civilian** & **Civilian** & **Direct Property** \\  & & **Deaths** & **Injuries** & **Damage (in Millions)** \\ \hline One- or two-family homes, including manufactured home 1 & 250,500 (70\%) & 2100 (84\%) & 8440 (66\%) & \$5,438 (81\%) \\ Other multi-family housing 2 & 107,800 (30\%) & 410 (16\%) & 4280 (34\%) & \$1271 (19\%) \\ Total & 358,300 (100\%) & 2520 (100\%) & 12,720 (100\%) & \$6710 (100\%) \\ \hline \hline \end{tabular}  
* One or more bedrooms are considered; 2 dwellings, duplexes, manufactured homes (also called mobile homes), apartments, terraced-houses and townhouses. Other residential properties, such as hotels and motels, dormitories, barracks, rooming and boarding homes and the like are not included. One or more bedrooms are considered.  
\end{table} 
Table 2: Reported home structure fires by property use (NFPA [3]), 2010–2014 annual averages. The NFPA [4] also defines flashover as the transient phase in the development of an indoor fire in which surfaces exposed to thermal radiation reach their ignition temperature almost simultaneously and the fire spreads rapidly throughout the space available within the enclosure. Flashover can occurs in two different scenarios related to the enclosure configuration and it depends on the fire is located inside a structure with constant air supply or not. The first one known as a fuel-limited fire is shown in the Figure 2a. In the growth stage there is enough oxygen to maintain the combustion process. If amount of fuel involved is sufficient therefore the energy level necessary for the occurrence of flashover can be reached followed by the full developed phase.