Which of the following best describes a fire where flames run up a single tree or group of trees, making the tree look like a torch?

• A. Active crown fire
• B. Ground fire
• C. Passive crown fire
• D. Surface fire

Answer: (C)

When a fire climbs up the trunk of one or a few trees and makes them look like torches, the canopy is ignited from heat coming up from the surface rather than the canopy reacting and spreading on its own. This is known as a passive crown fire: the crown ignition is caused by a nearby surface fire, and the flames run up individual trees rather than sweeping rapidly through the whole canopy. In contrast, an active crown fire would involve the flames moving through and between crowns with high intensity and rapid, canopy-wide spread. Ground and surface fires stay on the substrate or burn surface fuels, not the crowns. So torching trees from below fits the idea of a passive crown fire.