What is fire intensity and how is it different from rate of spread?

• A. Fire intensity is energy release per unit length of fire front; rate of spread is speed of fire front
• B. Fire intensity is wind speed; rate of spread is humidity
• C. Fire intensity is airflow; rate of spread is flame height
• D. Fire intensity is fuel moisture; rate of spread is fire color

Answer: (A)

Fire intensity is the amount of energy released along a given length of the fire front, often expressed as energy per unit length (heat output per meter of fire line). Rate of spread is how fast the fire front advances, i.e., the speed of the leading edge through the landscape. These are different ways of describing fire behavior: intensity tells you how hot the flames along the line can heat fuels ahead, while rate of spread tells you how quickly that line is moving forward. The other options mix up concepts that aren’t definitions of these terms—wind speed and humidity affect spread but aren’t energy release per unit length; airflow or flame height relate to flame characteristics but aren’t the standard definitions; fuel moisture or color aren’t the measurements used for these two factors.