Dead fuel moisture responds solely to ambient environmental conditions and is critical in determining fire potential. Dead fuel moistures are classed by timelag. A fuel’s timelag is proportional to its diameter and is loosely defined as the time it takes a fuel particle to reach 2/3’s of its way to equilibrium with its local environment. Dead fuels in NFDRS have four timelag classes: 1-hr: Fine flashy fuels, less than 1/4″ (< 0.63 cm) diameter. Responds quickly to weather changes. Computed from observation time temperature, humidity and cloudiness. 10-hr: 1/4 to 1″ (0.63 to 2.54 cm) diameters. Computed from observation time temperature, humidty, and cloudiness, or may be a standard set of “10-Hr Fuel Sticks” that are weighed as part of the fire weather observation. 100-hr: 1 to 3″ (2.54 to 7.62 cm) diameter. Computed from 24 hour average boundary condition composed of day length, hours of rain, and daily temperature/humidity ranges. 1000-hr: 3 to 6″ (7.62 to 15.24 cm) diameter. Computed from a 7-day average boundary condition composed of day length, hours of rain, and daily temperature/humidity ranges.