|Class Ignition Potential||Interpretation|
|Low||Fires will be self-extinguishing.|
|Medium||Fire can be easily suppressed with hand tools.|
|High||Most fire can be successfully controlled using power pumps and hose.|
|Extreme||Some fires will be difficult to control.|
The ISI is a measure of the head fire indicator and rate of fire spread. The higher ISI index indicates higher difficulty of control in grassland. It is a combination of the effects of the wind speed and Fine Fuel Moisture Code.
Image courtesy of the Malaysian Meteorological Department.