The product of the available heat of combustion per unit of ground and the rate of spread of the fire, interpreted as the heat released per unit of time for each unit length of fire edge. The primary unit is Btu per second per foot (Btu/sec/ft) of fire front.
Fireline intensity may also be defined as the rate of heat release per unit time per unit length of fire front. Numerically, it is the product of the heat yield, the quantity of fuel consumed in the fire front, and the rate of spread.
Source: National Wildfire Coordinating Group. 2012. Glossary of Wildland Fire Terminology. PMS 205. Accessed on 9 September 2013. Available at http://www.nwcg.gov