Which statement describes the relationship between rate of spread (ROS) and heat release I when H is constant?

• A. I increases linearly with ROS
• B. I decreases as ROS increases
• C. I is independent of ROS
• D. I increases exponentially with ROS

Answer: (A)

With a fixed fuel depth, the amount of energy available per unit area doesn’t change. What changes the heat release rate is how much ground gets heated each second, which is determined by how fast the fire front advances. If the rate of spread increases, more area is burned per unit time, so more fuel is consumed and more heat is released each second. Because the fuel depth is constant, this relationship is proportional: doubling the spread rate roughly doubles the heat released per unit time. That’s why the heat release rate increases linearly with the rate of spread.

The idea that it would be independent doesn’t fit, since more area burning per second means more energy release. It wouldn’t naturally be exponential in this simple setup, unless there were other nonlinear feedbacks or changing fuel, which aren’t present when H is constant.