Quantifying production of hot firebrands using a fire-resistant fabric

Abstract

Identifying the number of firebrands generated during wildfires is an important aspect of understanding their propagation. A key challenge in quantifying the number of firebrands released is to distinguish those that are ‘hot’ and could lead to further fire spread from the total number released. Recently, a fire-resistant fabric was used to quantify the number of ‘hot’ firebrands released from different species of trees (based on char marks). However, information regarding the temperatures of the firebrands leaving the char marks was not reported. In this paper, we demonstrate a methodology for characterising the charring behaviour of fire-resistant fabrics and illustrate how the fabric can be used for firebrand generation studies. The results established a minimum temperature (300°C) for char mark formation. The sensitivities of charring to temperature and time of contact between the fabric and heater are reported. A first-order analysis estimated the char mark area to be an exponential function of the temperature, power input and time of exposure. Illustrating the usefulness of the approach, the fire-resistant fabric was deployed to study hot firebrand production rates for trees treated with and without a fire retardant. The number of hot firebrands produced was lower for trees coated with fire retardant.