

AP Photo/Guillermo Arias

We hear it all the time when talking wildfires. "The Sayre Fire is 64% contained," "the Tea Fire is 100% contained," etc. But what does that mean? How is it measured?

First, you have to understand fire control lines, which is "an inclusive term for all constructed or natural barriers and treated fire edges used to control a fire," according to the National Wildfire Coordinating Group's glossary of Wildland Fire Terminology that LA Fire Department spokesman Brian Humphrey said was a good source for such understanding.

As for what containment means, Humphrey explains: "In essence, anything less than a 'full' (aka 100%) fire control line surrounding a wildland blaze is estimated by the Incident Commander in a percentage, and that number is the containment factor."

As for the NWCG's glossary, it offers this definition for "contained" and "containment":

The status of a wildfire suppression action signifying that a control line has been completed around the fire, and any associated spot fires, which can reasonably be expected to stop the fire’s spread.

Humphrey warns that there is some "relative meaningfulness or meaninglessness," in the numbers. After all, a fire can easily go from 80% contained back to 25% if winds pick up and spread the fire beyond the control line.