There are many areas where the fire investigator should institute the strongest safety precautions. The investigator should know of existing faults prior to entering a structure. On entering the basement, it is important to check the stairway, which may be damaged. Conditions may not be visible in the reduced light of most basements. Knowledge critical to personnel safety comes from a study of the construction of a building. The type of material used for flooring should also be of concern. Arson investigators also face a frequent lack of proper safety equipment in the form of breathing apparatus. The importance of a breathing apparatus that is compatible with the full range of duties of the fire investigator is to allow him to get into the fire scene sooner and to stay longer without compromising his health. One of the most dangerous conditions faced by the investigator is exposure to smoke and toxic gases while conducting the investigation of the fire scene. Caution is important also in the examination and collection of samples for evidence. The best precaution against injury while collecting evidence is in wearing protective clothes and gloves. A list of toxic byproducts of common combustibles is provided. An outline of points to be reviewed before an investigation is included. Seven footnotes are also included.