What size fuels make up the 1 hour timelag fuel category?

The correct size fuels that make up the 1-hour timelag fuel category are those that have a diameter of 0.0 to 1/4". This classification is based on the time it takes for these fuels to respond to changes in moisture content in the environment.

Fuels in the 1-hour timelag category are small enough that they can absorb or release moisture relatively quickly, typically within a period of about one hour. This rapid response to moisture changes allows for fluctuations in their combustibility and fire behavior. Smaller fuels like these can ignite quickly and contribute significantly to fire spread, especially in conditions of low moisture or high temperatures.

In contrast, larger fuels with diameters greater than 1/4" fall into different timelag categories (such as 10-hour, 100-hour, or 1,000-hour fuels) which will have slower responses to moisture and different behaviors in combustion and heat release.