Wildland Firefighting Practice Exam

When does the situation become favorable for wildfires regarding relative humidity?

1. Below 20 percent

2. Below 25 percent

3. Below 30 percent

4. Below 35 percent

The correct answer is: Below 30 percent

The situation becomes favorable for wildfires when relative humidity drops below 30 percent because at this level, the atmospheric moisture is low enough to allow for increased evaporation of moisture from vegetation and fuel sources. When relative humidity is below this threshold, organic materials such as leaves, grass, and timber lose moisture more rapidly, making them more susceptible to ignition and combustion. As relative humidity decreases, the fire behavior also becomes more intense; fires can spread more quickly and be more difficult to control. Additionally, a relative humidity below 30 percent indicates drier conditions that can lead to fire starts more easily from common ignition sources like lightning strikes or human activities. In contrast, higher relative humidity levels contribute to moister conditions that can help suppress fire activity, making it less favorable for wildfires. Thus, fires are more likely to ignite and spread when relative humidity is below that crucial level of 30 percent.