What is the slope effect in fire spread?

What is the slope effect in fire spread?

• A. Fire moves faster downhill.
• B. Slope has no effect on fire spread.
• C. Slope affects only smoke production.
• D. Fire moves faster uphill because heat preheats fuels, increasing spread with steeper slopes.

Answer: (D)

The slope effect is that fire spreads faster uphill because heat preheats fuels upslope, and the steeper the slope, the more preheating occurs, boosting the rate of spread. When the ground rises, hot gases and flame contact better reach the fuels ahead of the fire front. The flame column tilts toward the slope, radiating and convecting heat upward to unburned fuels, so they ignite sooner. As slope increases, this preheating becomes more effective, making ignition quicker and the fire advance faster. Downhill, heat is less effective at preheating fuels below the fire, so the spread tends to be slower.

The slope effect is that fire spreads faster uphill because heat preheats fuels upslope, and the steeper the slope, the more preheating occurs, boosting the rate of spread. When the ground rises, hot gases and flame contact better reach the fuels ahead of the fire front. The flame column tilts toward the slope, radiating and convecting heat upward to unburned fuels, so they ignite sooner. As slope increases, this preheating becomes more effective, making ignition quicker and the fire advance faster. Downhill, heat is less effective at preheating fuels below the fire, so the spread tends to be slower.