IFSAC Wildland Pro Board Practice Exam

Logs or down trees are classified as 100-hour fuels based on the time lag classification system. This classification system categorizes fuels into different groups according to how quickly they can absorb or lose moisture, which is directly related to their size.

The rationale is that larger diameter fuels, such as logs and downed trees, take significantly longer to respond to changes in environmental moisture conditions compared to smaller fuels. The 100-hour time lag refers to fuels that take roughly 100 hours to gain or lose 63% of their moisture content in relation to changes in relative humidity. Typically, these larger fuels are more stable and do not dry out or saturate as quickly as smaller fuels, which is indicative of their prolonged moisture-holding capacity.

Other classifications include 1-hour fuels (small twigs and fine grasses), 10-hour fuels (small branches), and 1000-hour fuels (very large logs and large chunks of wood). Each of these categories helps firefighters and land managers assess fire behavior and formulate effective fire control strategies based on the type of fuel present.