(A component of the NFDRS-National Fire Danger Rating System) The Ignition Component is a number which relates the probability that a fire will result if a firebrand is introduced into a fine fuel complex. The ignition component can range from 0 when conditions are cool and damp, to 100 on days when the weather is dry and windy. Theoretically, on a day when the ignition component registers a 60 approximately 60% of all fire brands that come into contact with wildland fuels will require suppression action. Ignition normally takes place in the dead component of the fine fuels. Three distinct steps must be considered in this ignition process.
- A firebrand must come into contact with the dead fuel.
- The fuel particle must be dry.
- The temperature of the fuel particle must be raised to the kindling point which is about 380 degrees Celsius.
Living material in the fine fuel complex reduces the efficiency of ignition. Therefore, an adjustment to the ignition component is made based on the percentage of live fuel (herbaceous vegetation) in the fine fuel complex.
The moisture content of the dead component of the fine fuel (1-hr. timelag fuel moisture) is determined by the state of the weather (sunny or cloudy), air temperature, and relative humidity at the time of the 2 p.m. fire weather observation.
The condition of the herbaceous (live) vegetation and the 1-hr. timelag fuel moisture are then integrated in the calculation the fine fuel moisture (FFM) which expresses the effective moisture content of the fine fuels.
The closer the initial temperature of the fuel is to the ignition temperature, the more likely a fire will result when a firebrand in introduced into the fine fuel complex, since not a much energy is required to raise the fuel particle to its ignition temperature.