A Study of Wildland Fire Direction Indicator Reliability Following Two Experimental Fires

August 26, 2016

Dr. Zachary Owens, Dr. Erik Christiansen, Dr. Abid Kemal, and co-author recently completed their paper, "A Study of Wildland Fire Direction Indicator Reliability Following Two Experimental Fires." Exponent collaborated with the U.S. Forest Service and the University of Edinburgh to complete the experiments.

Two experimental fires, with contrasting intensities, were conducted in March 2016, in the Pinelands National Reserve (PNR) of New Jersey, United States, in order to provide a preliminary assessment of the reliability of the fire direction indicators used in wildland fire investigation. The experiments were part of a larger project intended to measure firebrand production in a forested ecosystem. As part of this project, fire behavior, as well as the environmental and fuel conditions were also measured.

Two burn parcels, covering an area of approximately 30 hectares each, were ignited from unimproved forest roads, which delimited them. The forest canopy was comprised primarily of pitch pine with intermittent oaks. The understory contained a mixed shrub layer of huckleberry, blueberry, and scrub oaks. In order to explore a wide range of indicators, objects such as bottles, cans, and small fence elements were planted in the burn area and photographed before and after the fire. To obtain an accurate measure of pre- and post-fire fuel properties, fuel load, fuel bulk density, and fuel moisture content were also measured. In addition, environmental data (wind velocity and direction, air temperature and humidity) were recorded. 

The fire behavior can be reconstructed using measurements of fire rate of spread, fire front temperatures, fire front geometry, and heat fluxes. Video and infrared cameras were used to document the general fire behavior in selected locations.

This paper represents the first step in the analysis of the fire indicators and focuses on the more intense of the two burns and on the appearance of the macro- and microscale fire pattern indicators. A majority of the indicators were assessed, although the configuration of the burn parcels, the ignition technique, and precipitation immediately following the fires limited a full study.

The results show that some fire direction indicators are highly dependent on local fire conditions and fire behavior and may be in contradiction with the general spread of the fire. Overall, this study demonstrates that fire pattern indicators are a useful tool but must be interpreted in the frame of a general analysis of the fire, combined with a good understanding of fire behavior and fire dynamics.

The paper will be presented at the International Symposium on Fire Investigation (ISFI) Science & Technology and is also available through the California Conference of Arson Investigators.

A copy of the paper is also available here.