Fire only burns if there’s available fuel. This means knowing the amount and condition of fuel is critical to predicting wildland fire behavior, the amount of smoke, and the impact of smoke on air quality. Wildland fuels take many forms, from dry needles and leaves, to medium-sized fallen branches, to large logs and duff that can smolder for days or even weeks. Fuel size, placement, and moisture content all influence fuel consumption and are part of the recipe for determining the fire behavior and emissions generated. Currently fuel biomass estimates represent the largest error in smoke modeling. To remedy this, scientists at the USDA Forest Service's Pacific Northwest Research Station developed protocols for collecting field data to characterize wildland fuels. The published field guide outlines how users of the Fuel Characteristics Classification System (FCCS) can then use their own data on local wildland fuel to project potential fire hazard and surface fire behavior. Inputs from FCCS also can be used to run fuel consumption and emission production models, such as Consume and BlueSky. The station’s fuels, fire, and smoke scientists also led the development of the North American Wildland Fuel Database, a compilation of measured biomass of wildland fuels throughout the United States and Canada. This work was funded by the Joint Fire Science Program to reduce uncertainty in wildland fuel mapping products and emissions modeling.