Wildland Firefighting Practice Exam

What range of relative humidity is recommended for setting prescribed fire prescriptions?

1. 15 to 25%

2. 20 to 30%

3. 25 to 35%

4. 30 to 40%

The correct answer is: 25 to 35%

The recommended range of relative humidity for setting prescribed fire prescriptions is typically between 25 to 35%. This humidity range is crucial for several reasons. First, relative humidity significantly influences fire behavior and the effectiveness of the prescribed burn. At lower humidity levels, fine fuels, like grass and leaf litter, tend to burn more easily and intensely, which can lead to the fire spreading uncontrollably. Conversely, too high of humidity can result in inadequate burning, where fuels may not ignite properly, making it difficult to achieve the management objectives of the prescribed fire. Maintaining a relative humidity in the 25 to 35% range allows for a balance where there is enough moisture present in the air to help mitigate the risk of the fire escaping, while still being low enough to allow for efficient ignition and consumption of fuel. This range is supported by fire management practices and models that assess fire risk and behavior, ensuring that the burns can be safely executed and controlled. Considering other options: ranges outside of 25 to 35% typically either introduce too much risk for escape (as seen in lower humidity ranges) or create conditions non-conducive for burning (as candid in higher humidity).