The 1987 arson data cover the ages of those arrested for arson, the number of structure fires, the number of vehicle fires, and the number of arson structure fires by community size. Types of arsonists are those who set fires for profit and revenge, emotionally disturbed juveniles, persons with a sick propensity for firesetting, terrorists, and criminals attempting to cover up a crime. The arson investigator attempts to answer the following questions: Who set the fire? How was the fire set? Why was the fire set? The arson investigator should inspect the fire scene before firefighters disrupt the fire scene to look for hidden fires. The investigator should begin by examining the structure's exterior, recording its structure, height, use, and possible occupancy. Containers, suspicious vehicles, burned clothing, and other evidence of arson may be found outside the building. The investigator's priority is to determine the cause and origin of the fire. In most cases, accidental fires will be traced to a relatively small point of origin. Arson fires, on the other hand, will have a fairly large, and often multiple, points of origin. The fire investigator should work backwards from the areas that have sustained the least amount of fire damage toward the areas with the most fire damage. A study of building blueprints is vital in assessing the reasons for a fire's ignition and spread. The investigator should look for ignition devices, trailers (materials to spread the fire), accelerants, and protected areas.