Simulation of flame spread over discrete fire load

Introduction. Fires at high-rack storages with a discrete fire load develop dramatically fast, while fire detection and suppression systems might activate too late, which leads to significant property damage. The objective of this work is to demonstrate applicability of the thermal pyrolysis model in predictions of fire development in high-rack storage facilities.
Methods. The simulations are performed using FDS 6.6. In the thermal pyrolysis model, the solid material is ex­posed to inert heating until its surface temperature reaches the ignition temperature; combustible material then ignites and burns at a prescribed burning rate. The advantage of this approach is its simplicity and a limited number of input parameters, which include ignition temperature, mass loss rate per unit area, burn-out time and heat of gasification. The model parameters selection procedure is based on literature and experimental data. In this work, FDS simulations are performed for 3- and 5-tier high racks with 2 rows of cardboard boxes (243 = 24 and 245 = 40 boxes in total). Fire suppression systems are not activated.
Results and discussions. Simulations results show that high-rack storage fire dynamics can be replicated using thermal pyrolysis model provided that model parameters are properly selected. Fire growth mechanisms include upward and horizontal flame spread over the combustible surfaces. Net heat flux and surface temperature distributions, in-rack gas velocity and temperature are also reported. When number of tiers is increased to 5 the heat ­release rate grows faster compared to the 3-tier case.
Conclusions. Thermal pyrolysis model enables reasonable replication of high-rack storage fire dynamics, which is proven by comparison with the full-scale experimental data. The model could be used to simulate fire dynamics in rack storages of different configurations at different ceiling heights, with the purpose of predicting fire detection and the performance of fire suppression systems.

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