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A List of Useful Wildfire Terms

If you're following coverage of wildfires, or trying to stay safe, here are some helpful definitions to know.
A burned classic car is seen in Little Tujunga Canyon during the Creek Fire on December 6th, 2017, near Sylmar, California.

 A burned classic car is seen in Little Tujunga Canyon during the Creek Fire on December 6th, 2017, near Sylmar, California.

Wildfires continue to burn across Southern California, threatening homes and buildings throughout the region. When reading or listening to coverage of these disasters, you may encounter a number of terms that you're not familiar with—terms such as firebrands, spot fires, or containment.

Below is a glossary of some of the most commonly used words in the coverage of the Thomas, Creek, and other wildfires. Definitions are largely derived from the National Wildfire Coordinating Group and the National Oceanic and Atmospheric Administration.


Air Quality

Refers to the amount of pollution in the composition of the air. Used most frequently in relation to the air standards as determined by any given region–for example, air standards in China are different from those in Canada or the United States–regarding the maximum acceptable pollutant concentrations.

Air Pollution Alert

Warns populations of a high measured concentration of pollutants. If circumstances worsen, an alert can be raised to a "warning" and then, potentially, to an "emergency." In California, once a pollution episode reaches the emergency level, physical exertion in public spaces and all local driving–except in the case of an emergency–are prohibited.

Burning Index

A report that quantifies fire danger by assigning it a number, with zero being the lowest (best) number; there is no limit on how high the number can go. According to the Los Angeles Fire Department, B.I. is determined by three factors: moisture readings in dead vegetation, a "fire weather forecast," and historical data. The fire department then puts these measurement into an algorithm that produces a number to reflect the risk. One hundred sixty-five is considered an extremely high risk; on Thursday night, in the area around the Thomas Fire, the number was at a record high of 296.


The material that results from an incomplete burn of organic material, most commonly wood.


Rapid oxidation of fuel that normally results in heat and flames. Combustion happens in four phases: preignition, flaming, smoldering, and glowing.


A strategy employed in response to a fire where the perimeter of the blaze is managed by a combination of direct and indirect actions, as well as by the use of landscape features, fuel, and wind.


Signifies that a control line has been completed around a fire and any associated spot fires. When a fire is fully "contained," it means that the fire has been suppressed and will not continue to spread.

Fuel Bed

Used to describe the composition of materials that could feed a wildfire.


Any source of heat capable of igniting wildland fuels, such as brush or trees. Firebrands can be transported by wind, convection currents, or gravity into previously unburned fuels, thus spreading the fire.


A fireline starves a wildfire of its fuel, and is made by cutting, scraping, or digging out the organic material would that feed the flames. In extreme cases, such as the Thomas Fire, these lines are dug using heavy machinery such as bulldozers.

Red Flag Warning

How weather forecasters alert populations to an ongoing or imminent weather pattern that may cause critical fires.

Santa Ana Winds

A weather condition in Southern California that brings strong, hot, dust-bearing winds to the coast from inland desert regions. Caused by a difference in high pressure in the West's Great Basin and lower pressure on the coasts, which drives intense winds toward the sea. These intense winds are part of what's causing the fires to spread so rapidly and uncontrollably.

Spot Fire

A fire ignited outside the perimeter of the main fire by a firebrand. Firefighters work to prevent these spot fires, which indicate the spread of the fire beyond a contained or confined area. Firefighters also refer to these small fires as "cat eyes" because of the way their light jumps out in small spots from hillsides at night.