On the use of sprays to intercept airborne embers during wildfires

Abstract

This technical note outlines an initial assessment of the feasibility of using water sprays to intercept and extinguish airborne embers, as a means to protect buildings during wildfires. An analytical model was developed to calculate the probability of inter-particle collisions within two intersecting streams of particles, and was then applied to a range of test cases involving embers and water droplets. Results from this simplified analysis indicated that water sprays could effectively protect buildings from ‘ember attack’ in this manner, but only when either: i) large water flow rates were used (in the order of 1 L s−1 per metre of building perimeter to be protected), or ii) the sprays were comprised of very small (~0.1 mm) droplets at moderate water flow rates (~0.1 L s−1 m−1). It is likely that the quantity of water required to satisfy (i) would not be available in many circumstances, and further investigation is required to determine whether sprays of ~0.1 mm droplets could operate effectively in the conditions of a wildfire. The analysis presented herein would be a suitable basis for further investigation into these spray systems, and for quantitative comparison with other types of wildfire sprinkler systems.