Burning Index (BI) is a number used by the National Oceanic and Atmospheric Administration (NOAA) to describe the potential amount of effort needed to contain a single fire in a particular fuel type within a rating area. The National Fire Danger Rating System (NFDRS) uses a modified version of Bryam's equation for flame length – based on the Spread Component (SC) and the available energy (ERC) – to calculate flame length from which the Burning Index is computed.^[1]

The equation for flame length is listed below:^[1]

${\displaystyle F_{L}=j\left[\left({\frac {SC}{60))\right)(25(ERC))\right]^{0.46))$

where:

j is a scaling factor,

SC is the spread component,

and ERC is the Energy Release Component.

Consequently, the equation for the Burning Index is:^[1]

${\displaystyle BI=j_{1}\ F_{L))$

where ${\displaystyle j_{1))$ is the Burning Index scaling factor of (10/ft). Therefore, dividing the Burning Index by 10 produces a reasonable estimate of the flame length at the head of a fire. A unique Burning Index (BI) table is required for each fuel model.^[1]