It was prepared in the belief that an early recognition of incendiarism can increase the chances that investigators and local arson task forces will be able to identify and prosecute offenders. The text explains the information which should be recorded in the firefighter's report. En route to the fire, investigators are encouraged to note aspects of weather conditions, natural hazards, wind characteristics, and manmade barriers that may be related to the development or human origins of the fire. Conditions to observe upon arrival at the scene are reviewed, and tables present information on the color of smoke produced by various combustibles and on the temperatures related to various flame colors. Among the observations listed which should be made while the fire is being fought are the reaction of the fire to water, obstacles that hinder firefighting, and certain characteristics of burning. Another table relates unusual odors to possible fire sources. Observations to be made after the fire has been extinguished are also identified, and the text gives special attention to determining the origin of a fire. The direction of heat flow, heat colors, fire patterns, alligatoring and spalling, and spontaneous combustion are among the topics considered. Suggestions for the handling of evidence round off these discussions. Appendixes contain tables with data on the ignition temperatures of gases, woods, and liquids and on temperatures of incandescent lamps and saturated steam pipes. An arson investigation flow chart is also included.