Investigations of Fires of Electrical Origins. Factory Mutual System.

Abstract: This article provides guidelines and techniques for investigating electrical fires. The article is in outline form and starts with some basic electricity principles. The article then discusses possible electrical ignition sources and lists common indicators of each. An overheated wire is an example of a possible ignition source and can be identified by swelled insulation, internal charring, discolored conductors, and improper or defeated fuses. The other sources the article outlines are arcing, an overheated apparatus, and lightning.

The article lists important safety rules regarding electrical systems. The most important rule is to always assume that there is still power in the structure even if it has been turned off or the meter has been removed.

The next section of the article provides a list of questions to ask witnesses and people who occupied the building. Included are specific questions about the electrical systems of the structure. Witnesses should be asked about what they saw, heard, smelled, and about the weather. Questions about the fuses, circuit breakers, switches, wires, and appliances should be asked of the people who lived, worked, etc. in the building.

The last section discusses wiring, enclosed disconnecting switches, and relays. The article lists problems in these areas and offers solutions on how to fix them to prevent fires. For example, if a switch blade is burned or oxidized from overheating, the article suggests cleaning the blades and providing new contact clips if the tension is gone. There are also other suggestions on how to fix common problems in these areas.

For more information, contact:
Factory Mutual Research Corporation
1151 Boston-Providence Turnpike
Norwood, MA 02139
Phone: (781) 762-4300