Experimental Study of Firebrand Transport

Abstract

The NIST Firebrand Generator (NIST Dragon) has been used to quantify the vulnerability of structures to ignition by firebrand attack. The Firebrand Generator is a useful device to study firebrand transport, and has been used to validate transport models of firebrand showers. During this series of experiments, the Firebrand Generator was fed with wood cubes of uniform size. The glowing firebrands generated were collected in an array of water-filled pans that were arranged to collect the bulk of the lofted firebrands. The pan arrangement was determined from repeated preliminary studies. These experiments were performed over a range of wind speeds (up to 9 m/s) to determine the lofting distance. The major change in these experiments from prior work was that, for a given wind speed, the firebrand size and mass was determined at each pan location. In the past, it was only possible to determine the number distribution; specifically the number of firebrands at each spatial location was counted (not resolved at every pan but only across a given row of pans). Statistical analysis indicated that a normal distribution was able to capture the number/mass percentage versus horizontal distance. This study provides even greater fidelity measurements to validate transport models of firebrand showers, and further insights into firebrand generation.