WildfiresEmberometer Gauges Threat of Wildfire-Spreading Embers

Published 20 August 2021

Wildfire fronts spread not only on the ground, but also from above, as the fire launching volleys of glowing embers, also known as firebrands, into the air. These specks of burning debris can glide for up to about 24 miles before landing. They cause up to 90 percent of home and business fires during wildfires.

As wildfire fronts advance through landscapes or communities on the ground, they also attack from above, launching volleys of glowing embers into the air. Also known as firebrands, these specks of burning debris can glide for up to 40 kilometers (approximately 24 miles) before landing and can cause up to 90 percentof home and business fires during wildfires.

Guidance on fending off ember attacks is sparse, largely because so little is known about embers’ behavior. But a new instrument, dubbed an emberometer, could offer a glimpse at their true nature. In a paper published in Experiments in Fluids, researchers at the National Institute of Standards and Technology(NIST) showcase the tool’s ability to characterize the size and trajectory of embers, which may provide insights into their level of threat. With NIST’s new tool, fire engineers may be better equipped to protect buildings from embers and could produce data to support cost-effective guidance in building codes.

The dangerous conditions in which embers arise and their seemingly random nature have made measuring them an uphill battle. One go-to approach has been to collect embers from water-filled pans, which allows researchers to count and size up embers after a fire has gone out, but it paints far from a complete picture of what happens during ember exposures, where structures are swarmed by flaming debris.

Because embers act so erratically, measuring how their behavior changes from one second to the next while they are still airborne is crucial. NIST combustion specialist Nicolas Bouvet and his colleagues built the new instrument to do just that.

The emberometer is composed of a metal stand, shaped like a capital H on its side, with point-and-shoot digital cameras attached to the end of each of its four arms. The researchers designed it to be operated from more than a kilometer away and embedded its electronic components in fireproof materials to make the system deployable in fiery conditions.

Through a method known as particle tracking velocimetry, the emberometer uses data from its four perspectives to trace the path of brightly lit objects (such as embers) as they pass through a 2-cubic-meter (more than 70-cubic-foot) box-shaped space in front of the device. The system also captures the silhouettes of each ember from four different angles and merges the perspectives to digitally reconstruct their 3D shapes.