Prescribed Burn Planning

The Slope factor in this model grows with the SQUARE of the slope's tangent, not linearly, so its effect accelerates as terrain gets steeper — a real feature of how fire preheats fuel uphill of the flame front. At 10% slope the multiplier is only about 1.05, but by 50% slope it has grown past 2x, meaning the same fuel and wind conditions can push an otherwise moderate fire into a much faster-spreading one purely from terrain.

Yes, across the full 1-40% declared range — higher Fine Fuel Moisture lowers the moisture-damping factor that multiplies Rate of Spread, so Rate of Spread, Flame Length, and both heat-release outputs never increase as moisture rises. Past roughly 12% moisture in this model the damping factor hits its floor and further moisture stops changing the result further, which mirrors how very wet fuel simply stops carrying fire rather than burning progressively slower without limit.

Heat Release Intensity is the heat released per square foot of burned area — the figure that matters for fireline behavior and firefighter safety at any one point on the fire. Total Heat Release is that same intensity multiplied out over a full acre (43,560 square feet), which is more useful for thinking about the overall energy released by the burn unit as a whole rather than conditions at the flame front.

No — treat it only as a rough sanity check against the qualitative ranges commonly used in prescribed-fire planning (moderate wind, moisture roughly in the 8-20% band, and a controllable flame length). An actual go/no-go decision requires your unit's approved burn plan, a real-time on-site weather and fuel-moisture check, and sign-off from a qualified burn boss — this calculator has no visibility into any of that.

Richard C. Rothermel published the underlying fire-spread model in 1972 as USDA Forest Service Research Paper INT-115, "A Mathematical Model for Predicting Fire Spread in Wildland Fuels." It calculates spread rate from an energy balance between the heat a fire generates and the heat needed to ignite fuel ahead of it, and — along with Byram's 1959 flame-length-from-intensity relationship, which this calculator's flame-length formula is styled after — it remains the mathematical foundation of the fire behavior prediction systems US wildland fire agencies use today. This calculator is a simplified educational approximation of that model, not the full multi-variable Rothermel calculation.