The Blue Bell Fire began as a very hazardous fire. The flame lengths were observed to be 'very high' and caused a number of spot fires. The spot fires were as much as a 1/2 mile in front of the head of the fire. Spot fires are very dangerous because they can cause responders and residents to be trapped between the initial fire and the new spot fires. Additional observed fire behavior included numerous torching. Torching is when a tree preheats and then ignites completely into flames. This behavior is an extreme sign of severe fire behavior. The original evacuation notices were based on these observations.
You can view some photos and videos from the fire here: