Ignition of Mulch Beds Exposed to Continuous Wind-Driven Firebrand Showers

A series of experiments were conducted to examine ignition of mulch beds to continuous, wind-driven firebrand showers. Shredded hardwood mulch, fitted in beds 1.2 m by 1.2 m with a thickness of 51 mm, was attached to a non-combustible reentrant corner assembly. The mulch/reentrant corner assembly was then exposed to continuous, wind-driven firebrand bombardment generated by the NIST full-scale Continuous Feed Firebrand Generator installed in the Fire Research Wind Tunnel Facility at the Building Research Institute in Japan. These experiments have determined ignition behavior of mulch beds installed in realistic building configurations under wind-driven firebrand showers. Experiments were performed by varying the wind speed and moisture content (MC) of the mulch beds. It was observed that continuous application of small wind-driven firebrands, with sizes similar to those observed in actual wildland–urban interface fires in California and Texas, resulted in flaming ignition of mulch beds held at MC up to 83% under wind speeds of 8 m/s. The accumulation of firebrands was a key factor to produce ignition.