Numerical prediction of the incoming heat fluxes on firefighter protective clothing
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Improving the performances of a firefighter protective clothing requires a better understanding of the conjugated thermal exchanges in the ambient-garment-body assembly [1]. As the protective clothing is believed to ensure, as long as possible, a skin temperature below the injury threshold, it is mandatory to quantify accurately the instantaneous thermal loadings provided by the fire source. Indeed, protective garments are commonly designed for incoming heat flux values that are recorded during isolated tests, under quasi-steady fire conditions [2]. Moreover, the scarce unsteady investigations devoted to heat flux predictions are based on presumed temporal laws for fire heat release and do not account for natural or mechanical ventilation effects on fire development.
The present study is a numerical attempt for the prediction of the incoming thermal flux on a firefighter protective clothing. The study focuses on ventilation conditions impact on the incident fluxes reaching the external garment’s face. A radiative and convective transfer modelling is considered for a 3D geometry compartment, equipped with a door, a window and subject to a localized fire, with stationary heat release rate (HRR) during a prescribed exposure time. An additive constraint on oxygen mass fraction threshold is considered to account for flame extinction. The outer layer of the protective garment is modeled as a solid medium, featuring both front (chest F) and rear (back R) sensors. The baseline case corresponds to a situation where the external temperature of the protective clothing and that of the fresh air adjacent to the firefighter's body are maintained at 25 °C. Despite the importance of mechanical ventilation devices in smoke clearance and temperature attenuation, critical values for ventilation flow rates may lead to tremendous heat fluxes revealing the apparition of backdraft situations
