On the Effect of Fuel Moisture Content on the Smoldering Ignition of a Natural Fuel by Firebrands

摘要

Firebrand/ember spotting is an important mechanism by which wildland fires can rapidly spread. This process occurs when embers from a fire upwind land on a fuel downwind. These embers may initiate a fire directly or a smolder, which later may transition to a flame in the fuel. The Fuel Moisture Content (FMC) plays an important role in determining whether a firebrand will ignite the fuel. In this work, the effect of FMC on the smoldering ignition of coastal redwood sawdust by a firebrand is studied experimentally, flaming ignition was not studied or observed. The firebrands were made from wooden cylinders of various sizes from 1.6 to 11 mm in diameter and length. The wooden cylinders were brought to glowing combustion with a flame and dropped onto the sawdust below. From these experiments, we were able to determine an ignition boundary based on FMC and ember diameter. As expected, the results show that larger firebrands are capable of igniting sawdust with a higher FMC. We then found that, for the conditions tested, 3.17mm was the smallest ember size which would ignite have a 50% chance to ignite the fuel with a FMC <1%.