What is a key concept behind using a baseline ROS in S-390?

• A. Baseline ROS is the maximum possible value.
• B. Baseline ROS provides a reference point adjusted by WAF and SF to reflect wind and slope.
• C. Baseline ROS is used only for training.
• D. Baseline ROS replaces all other inputs.

Answer: (B)

Baseline ROS acts as a reference rate of spread under standard conditions, serving as a neutral starting point for calculations. In S-390, you take this baseline and adjust it with wind and slope factors to reflect real-world conditions. The wind adjustment factor modifies the baseline based on wind speed and direction, while the slope factor accounts for how terrain steepness influences spread. This setup lets you compare scenarios on a common footing and then determine the actual spread by applying these environmental modifiers. It isn’t the maximum possible spread, it isn’t used only for training, and it doesn’t replace other inputs—it's the foundational reference that gets scaled to match the conditions.