Preparation for a fire scene investigation requires an unbiased attitude, authority for the investigation, proper equipment, knowledge and training, and information on the specific fire (when the fire started, who reported it, who was present, who responded to it, how long to control it, and who has been on the scene since the fire). When investigating the scene to determine the fire's origin, items that should be noted include safety hazards, utility networks, construction details, and items removed from the structure during overhaul. A walk-through of the interior should locate dangerous conditions and assess relative damage to various areas. This will include photographs. A dimensioned, labeled sketch of the overall structure should indicate door and window locations and whether they were open or closed when found. The condition of the fuse or circuit-breaker box should be noted along with any evidence of forced entry. A systematic examination of the structure should begin with the least damaged area and proceed to the most severely damaged area. When the point of origin has been located, the fire cause should then be determined. All possibilities of natural or accidental causes should be considered and eliminated before an incendiary cause can be substantiated. In concluding that a fire was arson, a report should explain how it was set and how the fire progressed. The explanation must be substantiated and documented. A fire scene examination checklist, 5 figures, and 9 suggested readings.