Variations in fire behaviour induced by slope. Slope can both support and hinder fire spread and development and the angle of the slope will have an important influence on the degree of effect. The following descriptions explain the general slope effect that would be expected from a fire spreading upslope and a fire spreading down slope: (1) Fires spreading upslope The flames of a fire spreading upslope will be angled towards the unburned fuel above it which will pre-heat the fuel in front of the advancing fire. This pre-heating increases combustibility and rate of spread for fires travelling upslope. (2) Fires spreading down slope - The flames of fires burning down slope will be angled away from the fuel and will, therefore, lead to less preheating of the fuel in front of the fire. Consequently, the effect of slope on a fire burning down slope is a reduction in combustibility and rate of spread