The objective of the research we are conducting is to theoretically predict and experimentally verify the conditions that can lead to a fire initiation after the firebrands or heated metallic particles land. At the present time several studies have been published regarding firebrand/heated particle trajectories and physical characteristics at landing, but only a few of them have examined the conditions that may lead to a firebrand causing a spot fire when it lands. Furthermore, no rigorous theoretical models have been developed to analyze this problem.

Southern California Fire, October 2007
Photograph by Damian Dovarganes/AP for nationalgeographic.com

Enhanced theoretical models would improve the predictive capabilities of physics-based models of fire spread at the landscape scale, such as WUI Fire Dynamics Simulator (WFDS) developed by the National Institute of Standards and Technology (NIST). Land managers, city planners, and the fire service could greatly benefit from the application of improved landscape-scale fire modeling tools that can reliably predict fire development by simulating fire spread under fire weather conditions conducive to spotting.

To support and validate the theoretical models, small-scale laboratory experiments are being conducted in a bench-scale, horizontally placed combustion tunnel (Spotting Ignition Test, SIT). A sample fuel bed of different materials is placed in the tunnel simulating a layer of vegetation (mulch, grass, leaves, twigs, etc.) or a solid surface (shingle/shake, siding, wooden lumber). Different size smoldering or flaming firebrands of characterized materials are ignited and dropped on the fuel bed sample in order to observe their ignition behavior: whether embers do not ignite the fuel bed, cause smoldering only, cause smoldering and transition to flaming, or cause flaming with subsequent flame spread.

The ultimate aim of this project is to improve the capability of fire-prediction tools. This project is currently not funded and we are trying to find a sponsor to support this research.

Simplified schematic and photograph of prototype Spotting Ignition Test (SIT) apparatus.

Ignition and flame spread across powdered cellulose in prototype SIT apparatus. Airflow velocity is 0.25 m/s.

IR Camera Image - Smoldering brand (1.2cm diameter), Sawdust Fuel Bed and 2.5 m/s air flow (click on the image to download the video).

Preliminary simulations of ignition by firebrand in powdered cellulose. (a) Calculated temperature contours at 300 s; (b) Calculated pyrolysis rate at 300 s.