The intensity of a fire and its difficulty of control is also affected by the quantity of grass in the pasture. Heavy pastures burn faster and with a greater intensity than light pastures. In addition the finer the grass the faster a fire will travel.
The rates of spread are average values for fires in annual and perennial pastures carrying a continuous body of fuel and occurring on level to undulating ground. Spread rates will be less than indicated in sparse, discontinuous pastures and will also vary according to topography.
|FIRE DANGER INDEX||
RATE OF SPREAD
|DIFFICULTY OF SUPPRESSION||
MAXIMUM AREA AT VARIOUS TIMES FROM START
AVERAGE FINAL SIZE OF FIRE
|½ hr||1 hr||2hr||4hr||Sparse Pasture||Average Pasture||Heavy Pasture|
Headfire stopped by road and tracks
Head attack easy with water.
Head attack generally successful with water
Head attack will generally succeed at this Index
Head attack may fail except in favourable circumstances and close back burning to the head may be necessary
Direct attack will generally fail. Backburn from a secure good line with adequate manpower and equipment. Flanks must be held at all costs.
|**Note: This assumes that the head fire burns unchecked. suppression action which is only partially successful wil reduce these areas.|
When the wind is gusty, fire behaviour will be erratic, particularly in fine fuels which respond rapidly to 'changes in wind speed.