Wildland Firefighting Practice Exam

At what relative humidity percentage is air said to be overly dry, increasing wildland fire risk?

1. 40%

2. 30%

3. 20%

4. 10%

The correct answer is: 30%

The correct choice, which indicates that air is overly dry at a relative humidity of 30%, is significant because it highlights the critical threshold at which moisture in the air becomes insufficient to help suppress wildland fire activity. When relative humidity levels drop to around 30%, the air lacks enough moisture to effectively support vegetation, meaning that fuels such as grasses and shrubs can dry out more quickly. This dryer condition allows wildfires to ignite more easily and spread rapidly due to the increased flammability of these fuels. Understanding the role of relative humidity in fire behavior is vital for wildland firefighters and those managing forestry resources. At this level, the environment becomes increasingly conducive to fire development, prompting the need for heightened caution and readiness for firefighting measures. Higher humidity levels, such as 40%, tend to maintain some degree of moisture in the vegetation, which can help reduce fire risk. Meanwhile, relative humidity values lower than 30% pose even greater risks to fire ignition and progression, with values around 20% or 10% significantly elevating the danger. Thus, recognizing 30% as the threshold helps in operational decision-making and planning in wildland fire management.