Fires: Why the Cause May Not Be Electrical

Electrical appliances or wiring are often fire cause scapegoats, simply because they're there. It's unusual to find a burned structure without some electrical wire or device in or near the fire origin.

Ceiling fans, overhead light fixtures, and circuit wiring are common victims of misinterpretation, for a number of reasons:

1. Because fans and light fixtures are normally located near the ceiling, they can be exposed to more direct flames than other items in the room, so it's not uncommon to see them substantially burned by a fire. The more severe damage makes them prime suspects for many investigators.
2. Ceiling fans are usually installed through the protective layer of drywall which forms the ceiling. During installation, a hole is cut in the drywall, which compromises the ceiling's fire-barrier effectiveness.

If a fire occurs in the room below the fan, the flames and heat tend to "vent" through that opening in the drywall, and the fan, of course, becomes significantly burned as a result. A typical post-fire observation is a charred ceiling joist right where the ceiling fan (and the hole in the drywall) was, but to some that becomes evidence that the ceiling fan had "overheated".

3. Electrical wiring is commonly found melted in moderate to severe fire scenes. The melting can occur for several reasons - a] extreme temperature, b] electrical arcing, and c] alloying.

Melted copper wiring due to extreme temperature is potentially a red flag, especially in fires of minor to moderate overall damages. Fire temperatures in most fires are rarely sustained high enough to melt copper wiring. Melted wiring due to arcing does not necessarily mean that the cause was electrical, since arcing can result from the fire. And breakers will often trip due to fire exposure even though no evidence of arcing is readily apparent in the circuits. Alloying is by far the most encountered condition, probably the most misunderstood by fire investigators, and is often confused with melting due to extreme temperature and elecrical arcing.

It's important to be able to distinguish which of these conditions has caused the melting, and why that condition existed at the fire scene.

The Overload Myth

One of the least understood electrical failures by the general public, and far too many fire investigators, is the "overload".

An "overload" occurs when a conductor has to carry much more current than it was designed for; it may get so hot that it will burn or melt off its protective insulation and cause a fire by igniting nearby combustibles. An overload of this severity is quite uncommon, though - especially in home wiring.

An image which may spring to many people's minds is the overburdened electrical outlet covered with multi-adapters and half a dozen appliances plugged in to them.

The outlet and the house wiring, under most normal household situations, are usually quite capable of handling the extra current required by the devices plugged in, and the circuit breaker provides added protection. A fire is far more apt to begin here because of mechanical damage (abuse) or a poor connection (which can produce abnormal heating) than an overload of current.

Extension cords, often accused as overload culprits, can carry at least twice their rated current amounts without getting warm to the touch, and are difficult to overload in the average house. Common failings of these cords include poor connections or arcing or "short circuits" caused by damage to the cord's insulation. Extension cords are frequently abused and used incorrectly, and do cause fires as a result. In addition, the construction quality of some imported extension cords can be questionable.

Arson by Electric

Occasionally an arsonist will set a fire with the idea of simulating an electrical malfunction. If done correctly, at least here in Florida, the arsonist has a good chance at avoiding detection. In some areas of our state, electrical fires supposedly cause more overall damages than arson, a statistic which stretches credibility since structural arson fires, by their nature, are typically more severe fires.