The first step in a fire investigation is the preliminary scene examination/size-up. For best results, a trained fire investigator should be notified about and respond to serious fires or possible arson fires immediately after fire apparatus is dispatched. The investigator should survey both the exterior and interior of the fire building. This permits investigators to secure obvious evidence, help to control fire overhaul procedures, protect potential evidence, and orient themselves to probable fire origins. The second general step consists of interviewing witnesses. The investigator should immediately attempt to locate occupants, passersby, or abutters of the fire building. In potential arson-for-profit or revenge fire cases, the investigator should first interview the person who stands to gain by the fire. The third step involves full-scene examination. A full fire scene examination generally consists of nine steps that focus on the observation and collection of evidence pertinent to the origin and cause of the fire. The fourth general step is the follow-up investigation. This involves following up leads that have been generated. The contents of a fire investigation file are also listed.