Wildland Firefighting Practice Exam

How might grass behave if humidity levels change and rise above 40%?

1. It will burn instantly

2. It may burn even more easily

3. It may take longer to catch fire

4. The grass will not burn

The correct answer is: It may take longer to catch fire

When humidity levels rise above 40%, grass typically experiences changes that affect its flammability. Increased humidity often leads to higher moisture content in the grass itself. This additional moisture acts as a barrier to ignition, making it less likely for the grass to catch fire quickly. The presence of water in the plant material requires more heat to evaporate this moisture before combustion can occur. As a result, it may take longer for the grass to ignite or sustain a fire under these conditions. Understanding the impact of humidity on fire behavior is crucial for wildland firefighters. It allows them to assess fire risk based on environmental conditions. In dry climates, lower humidity levels can lead to rapid fire spread and easier ignition, while higher humidity can slow down that process. Therefore, the option indicating that grass may take longer to catch fire when humidity rises is aligned with fire behavior principles.