What Does a "30% Contained" Fire Mean?

In this photo, a vehicle patrols a bull-
dozed swath of fireline for any
possible sparks crossing the clearing.

    CalFire and other fire-fighting organizations use the term "contained" when referring to the size of the fire. What does that mean exactly?

    "Containment" according to one fire personnel we spoke with, refers to the amount of the fire that has a line of firefighters or a wide bulldozed clearing around it.

    Just because a fire is 30% contained doesn't mean it can't still spread.