Impact of Wildfires on Asphalt

Understanding the behavior of asphalt under wildfire is necessary to ensure its durability and safety in wildfire-prone areas.

• High melting point: Bitumen is the main ingredient of asphalt and it melts at a fairly high temperature (generally between 150°C – 200°C(300°F – 400°F). Wildfires can burn up to 1,000°F (538°C) or hotter, but the asphalt itself is not easily set ablaze because the flashpoint (the temperature at which it ignites) is many times higher than the fiery temperatures present in a wildfire.

• Non-combustible components: Asphalt is made up of aggregates including gravel, sand, and crushed stone. These aggregates are resistant to fire. As discussed, the main component, bitumen, can soften or melt during a wildfire, but they do not catch fire.

• Surface effects: The surface of the asphalt can soften or distort during wildfires. Asphalt is a material, which can become flexible when exposed to high temperatures. Therefore, the surface won’t ignite during wildfires.

• Lack of Oxygen and Fuel: For the fire to burn, it needs heat, fuel, and oxygen (the fire triangle). Asphalt does not offer a serious fuel source (the sort of dry vegetation or wood) for a wildfire. The surface is in fact a barrier for the fire, preventing it from advancing in its path.

• Deformation: Asphalt can still be damaged at extreme heat, even if it does not catch on fire. Intense flames can melt, crack, or distort asphalt, but it won’t burn. Asphalt surfaces are more likely to be damaged than to catch fire.

• Wildfire Behavior: Typical wildfires consume plants, trees, and structures, which offer far more readily consumable fuel. Asphalt has a higher density and is less porous, thus not offering the same fuel for a wildfire to consume it, that’s why it generally is not harmed as much, even if nearby areas are burning.  The deformities in asphalt roadways can be further worsened by untreated oil leakages and fallen trees. 

Thus, even if wildfires soften, melt, or deform asphalt (since wildfires can burn in excess of 900 degrees Fahrenheit), asphalt surfaces themselves do not burn.