Which statement describes the relationship between H and R in fireline intensity calculation?

• A. I = H × R, with H in Btu/ft^2 and R in ft/s (R must be converted from ft/min by dividing by 60)
• B. I = H + R
• C. I = H × R^2
• D. I = H × R, with H in Btu/ft and R in m/s

Answer: (A)

Fireline intensity comes from how much heat is released per unit area of fuel and how fast that fire line moves. That means the intensity is determined by multiplying the heat release per area (H) by the rate of spread (R). So the correct relationship is I = H × R. For consistent units, H should be in Btu/ft^2 and R in ft/s. If R is given in ft/min, convert it to ft/s by dividing by 60 before multiplying. This keeps the physical meaning intact: more heat per area and a faster moving line both drive a higher intensity.

Why the other forms don’t fit: adding H and R mixes quantities that don’t share the same dimensional meaning, so they can’t represent a heat-per-length quantity. using H × R^2 would distort the units and the physical interpretation by squaring the rate of spread. using H with units of Btu/ft and R in m/s mixes an incorrect heat-unit (per length instead of per area) and a different length unit, which breaks dimensional consistency. The stated convention (H in Btu/ft^2 and R in ft/s, with the conversion from ft/min to ft/s) aligns with the standard fireline intensity calculation.