High-intensity burning may develop on slopes, or in concentrations of fine fuel. Fire may become serious and their control difficult, unless they are hit hard and fast while small. Very High Fires start easily from all causes, and immediately after ignition, spread rapidly and increase quickly in intensity. Spot fires are a constant danger. Direct attack at the head of such fires is rarely possible after they have been burning more than a few minutes.
All fires are potentially serious.
Development into high-intensity burning will usually be faster and occur from smaller fires than in the very high danger class. Direct attack is rarely possible, and may be dangerous, except immediately after ignition. Fires that develop headway in heavy slash or in conifer stands may be unmanageable while the extreme burning condition lasts. Under these conditions, the only effective and safe control action is on the flanks until the weather changes or the fuel supply lessens.