This effort combines expertise from multiple USGS partners that could reduce the harmful effects of smoke impacts from use of prescribed burns. Lessening the risk to property and lives during wildfires is a primary purpose of prescribed burns.

“We aim to use drones to better understand the relationship between fire intensity and what type of particulates are released from fires of greater or lesser intensity,” said USGS lead scientist Todd Hoefen. “This can tell us what a fire leaves behind and how that could affect people and the environment.”

Role of Prescribed Fires

Fire plays an important role in the ecological landscape of the southeastern United States, where prescribed, or planned, burning is used to manage more than 8 million acres of land every year. However, much remains to be learned about the physics of fire behavior and how fire dynamics relate to emission levels. Continued growth of residences and public buildings into forested areas has increased the wildland-urban interface and the consequent risks for property and health from uncontrolled wildfires.

The use of prescribed burning offsets this risk by periodically reducing the woody fuel source to limit the spread and intensity of wildfires. Past research has examined how to conduct prescribed burns efficiently, depending on knowledge of meteorological and biomass characteristics. Scientists expect these same characteristics to affect the nature of a fire’s emissions but have not yet been examined them in a manner that enables fire managers to reduce the potential health impact of the smoke and particulates.

This cutting-edge collaboration, funded by the USGS Innovation Center and the USGS Environmental Health and Ecosystems Mission Areas, includes the U.S. Environmental Protection Agency, Canadian Forest Service and the University of Dayton Research Institute with support from the University of Florida Unmanned Aircraft Systems Research Program.

The overall goal is to use UAS to combine and analyze data about fire dynamics with information about fire emissions to better understand how prescribed burns can be conducted with minimal safety and public health risks.

Working Together: The Prescribed Fire Science Consortium

A series of burn events at the Prescribed Fire Science Consortium at Tall Timbers Research Station occurred between April 17 and 23, 2017. The goal was to coordinate as much complementary research as possible around three objectives: testing new sensors on UAS, documenting variability in the rate of radiant heat output from fire and connecting this data to fine-scale fire effects. The week-long event burned four small paired units at Pebble Hill Plantation and two operational units on Tall Timbers.

As part of the consortium, the USGS Innovation Fund project, Determination of Forest Fire Intensity Effects on Emissions and Particulate Matter Characteristics Using an Unmanned Multicopter, successfully flew a first-of-its-kind DJI S1000 UAS combined with a “Kolibri” sensor system. The Kolibri system is a lightweight sensor/sampling system developed by the EPA’s Office of Research and Development. It includes measurements of air pollutants (carbon monoxide, carbon dioxide, particulate matter, black carbon, brown carbon) and thermal infrared imagery.

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After the Fire: What’s in that Smoky Air?

USGS scientists have been studying ash composition from wildfires, like those that scorched Southern California in 2007, for a number of years, but had never sampled the smaller particulate matter or the gases in smoke. Smoke is likely to contain high levels of potentially toxic gases such as carbon monoxide, soot, and organic compounds such as formaldehyde and furans. It may also contain ash with caustic alkali salts and various heavy metals, or even minerals from the soil, such as asbestos fibers.

Post-burn sampling of ash has shown that ash type can be linked to burn severity. For example, residual white ash is usually produced from smoldering fires, the result of the complete combustion of organic material. Black ash, though, is the result of incomplete smoldering combustion of vegetation resulting in charred ash particles with remnant plant structure.

Water leach and simulated lung fluid tests with white ash (mixing white ash with water and simulated lung fluid) produces leachate with high pH and caustic alkalinity. The whiter the ash the more alkaline the test result. This suggests that exposures to high concentrations of respirable, caustic alkali particles of white ash in the smoke could pose an increased risk to human health. 

Fire Science Game-Changers? The Images from UAS

UAS can systematically be deployed over a study area to examine how fire intensity and rate of spread respond to different fuel types and different levels of fuel accumulation as well as how those variables dictate the type and amount of emissions. These measurements will also help scientists and managers understand what sorts of elemental and mineral toxics might be present in wildfire emissions, and how their abundance is influenced by combustion temperature and efficiency.

“The use of a small UAS platform remains novel and promises to significantly and effectively supplant ground- and airplane-based measurements while simultaneously reducing costs and risk to people,” said Hoefen.

Flaming combustion produces smoke that can contain a wide variety of ash particles depending on fire conditions and intensity. Thermal imagers, which are carried by the UAS, allow scientists to view valuable photographs of temperature; each pixel provides essentially the same data as an instrument placed inside or near the fire. In addition, this imagery can be geo-located to allow researchers to determine how fast flames spread through the landscape.

Putting It All Together – Taking Fire Science to New Heights

The UAS flown at Tall Timbers had an atmospheric particulate matter sampling device that collected samples of the smoke and airborne ash particles; at the same time the thermal camera was detecting the temperature of emission of the fire below. This will help scientists understand the types of particles that are produced from burning vegetation at different temperatures. The USGS will use a scanning electronic microscope to image and characterize smoke, ash and particulates with a resolution of 10 nanometers (the diameter of a human hair is about 100 microns). 

This combination of new thermal sensors, miniaturized pollutant sensors and samplers, and UAS technology may well offer a game-changing capability to extensively characterize fire dynamics and associated emissions. In turn, these tools, data and research can help fire and natural resource managers plan and manage both prescribed burns or wildfires.

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Smoke as Cues

The Canadian Forestry Service will analyze data provided by the IR sensor to produce rate of flame spread and fire intensity while the USGS, along with the EPA, will process the emissions data. Since health and climate implications of atmospheric particulate matter and aerosols released by wildfires and prescribed burns are not fully understood, additional research is necessary.

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For more information on the project, visit the USGS web page at:

https://geography.wr.usgs.gov/InnovationCenter/projects.html#!