Why is unit consistency crucial in S-390 calculations?

• A. Unit consistency helps simplify calculations and speed up work.
• B. To ensure correct results; mismatched units lead to erroneous ROS and I values.
• C. Units improve the accuracy of weather forecasts.
• D. Standardized units reduce the need for fuel models.

Answer: (B)

Unit consistency ensures calculations stay dimensionally valid, which is essential for S-390 calculations. In fire behavior modeling, rate of spread and fire intensity come from inputs that rely on specific distance and time units. Mixing feet with meters or minutes with seconds scrambles the relationships in the equations, producing values that don’t reflect real behavior. The result is erroneous ROS and I values, which leads to unreliable predictions of how fast a fire will spread and how energetically it will burn. Keeping all inputs in uniform units preserves the correctness of the results. While standardized units can reduce confusion and streamline work, the main reason to maintain consistency is to prevent incorrect ROS and I values. Weather forecasts or fuel models aren’t directly improved by unit consistency alone; they depend on accurate inputs and models, with consistent units ensuring those inputs are interpreted correctly.