1-hour fuels are fine dead fuels with diameters less than 0.25 inches (~0.64 cm), such as grasses. The moisture content of 1-hour fuels responds rapidly, changing within minutes to an hour based on weather conditions. 1-hour fuel moisture is expressed as a percentage, where lower values indicate drier conditions.
In Canada, the closest equivalent is the Hourly Fine Fuel Moisture Code (HFFMC).