ELECTRICAL ASPECTS OF FIRE INVESTIGATION

ELECTRICAL ASPECTS OF FIRE INVESTIGATION

BY ARTHUR L. JACKSON

Electricity is involved in just about every fire you investigate. It either has to be ruled out as or determined to be the cause of the fire. As the use of electrical appliances in the home and workplace increases, so does the potential for fires caused by electricity. Be careful, however. Many times electricity is determined to be the cause of the fire when in fact it is a consequence. When a fire is set as the result of spite or rage, an accelerant such as gasoline, kerosene, or the like usually is the ignition choice. When the motive is fraud, the firesetters are extremely adept at covering their tracks.

About two years ago, I was assigned to investigate a fire in a multifamily structure in a large northern city. During the investigation, the room of fire origin was determined to be the living room. Further investigation determined the area of fire origin was at the end of a couch. In that area was an end table with a lamp on it. The lamp was plugged into a duplex electrical outlet. A clear V-pattern was observed from the floor directly below the electrical outlet.

Closer inspection of the lamp`s power cord revealed signs of arcing and beading near the back of the plug. It seemed at the time that the cause of the fire was pretty easy to figure out: An electrical failure occurred at the back of the lamp plug (a stress point) and the copper heads were expelled, igniting the rug below. Well, not so fast.

The only real hard facts I had at that time were that the power cord was energized when the short circuit occurred and that the short circuit was in the area of fire origin. Taking a few steps back, I thought about my investigation so far. I was not comfortable with the copper beads` igniting the carpet. Also, I observed that much of the burnt material did not come from the table or couch. Sifting the burnt and charred material revealed the remains of crumpled newspaper. The fire resulted from someone`s placing crumpled newspaper under the table by the electrical outlet and then lighting it with a match or lighter.

SOME COMMON ELECTRICAL FAILURES

Following are some situations involving electrical failures I have encountered during my investigations for the public and private sectors.

Electrical duplex outlets can be found when examining almost any fire scene. Carefully examine all outlets in the fire`s area of origin. First, ensure that the electrical power to the building is shut off. Some of you may not believe this is necessary, but twice in my career I was surprised by handling live electrical equipment.

Once, when digging out a grocery store fire in New York City, the electrical wire that started the fire arced again and rekindled the fire. After ensuring that the electrical power to the dwelling is off, take a photograph before beginning an invasive examination. Duplex outlets are connected to the building wiring in two basic ways–connecting the wire to the screw terminals on either side of the outlet or pushing the wire ends into holes in back of the outlet. A loose connection in either case could cause enough electrical power in the form of heat to ignite surrounding combustible material.

Sometimes, the wire on the screw terminals is not tightened properly when installed. When the outlet is pushed into the wall box, tension on the wire provides a fairly good connection. Over time, however, this tension in the wire relaxes, and contact at the screw terminal becomes poor. This can be easily observed by the eroding of the copper wire on the screw terminal. The high heat developed by the arcing destroys the area around the screw terminal as well. This condition can and will continue as long as the amperage rating of the circuit protection is not exceeded.

This same condition can develop with outlets connected through push connections. Damage to the wire ends or outlet-holding prongs during installation can result in a poor electrical connection.

Another area to look at is the outlet`s holding strap. You will encounter two general designs–the wire will bend and go around the outside of the outlet or it will go through the outlet just below the outlet`s face. The latter allows the holding strap, which is grounded, to pass very close to the hot and neutral receptors inside the outlet. With this type of outlet, if the small strip of insulation should be damaged by a plug or in some other way, the hot receptor could contact this strap and create a short circuit.

Lighting Fixtures

Examine the lighting fixture to make sure that the wiring connections are secure and appropriate. Also, check the bulb wattage to ensure that it does not exceed the wat-tage for which the fixture was rated. On fluorescent fixtures, failure of the ballast has the greatest potential for causing a fire. Fire departments receive many calls for a “burning odor”; the source of this odor often can be traced to an overheated ballast. Today, most ballasts are thermally protected. In the past, the older unprotected ballasts overheated and, if attached to wooden ceiling supports, caused fires. Nevertheless, even if the ballast is thermally protected, examine it closely. Internal components can fail and cause a fire. When examining a fluorescent light fixture, remove the ballast and look for any sign of arcing or blow-through. Look also at the area under the ballast where it rested against the fixture. It should still show traces of factory paint (usually white) because the ballast protected it from extreme heat. If this area has been severely affected by the heat, it could be a sign that the ballast has overheated. If your investigation of the fire patterns leads you to the ballast as the point of fire origin, you have found the cause.

Other common causes of electrical fires are building-fixed wiring and extension and poser cords. A good point to remember, however, is that an electrical failure means only that the wiring of a fixture was energized at the time of the failure and that it could be the cause or a consequence of the fire.

All fire investigations should include a complete examination of the electrical system. Begin with the incoming electrical service and proceed to the electrical distribution panel. Try to identify the circuit breakers that serviced the area of fire origin. Note the circuit breakers that are on, off, and tripped. If there is a fuse panel, remove the fuses and examine the sockets. If, during your fire scene examination, you find multiple blowouts in the same BXTM (metal jacket) wiring or multiple short circuits in a RomexTM wire, you may want to remove the circuit breaker and have it tested in a lab. An internal failure in the circuit breaker would prevent it from tripping out on an overload from a short circuit.

MULTIPLUG POWER STRIPS

Multiplug power strips are quite common and often are used with computers and fish tanks. They come in various styles and are constructed of metal and plastic. Some have their own built-in overload circuit breakers. A problem associated with these strips is poor construction. Internal connections are stamped instead of soldered. The stamped connections can become loose and cause overheating from the poor electrical contact. If undetected, the heat generated can ignite the plastic housing or nearby combustibles. The Consumer Product Safety Commission (CPSC) has been involved in the recall of some of the poorly constructed power strips.

Another potential problem posed by these power strips is that they usually are located under the computer desk on the floor. The plugs connected to the power strip extend up and expose the wire from the back of the plug to physical damage from kicking. This area of the plug wire is also an area of high stress because it makes a sharp bend to return to the floor. Also, books and papers stored in this area can accidentally damage the back of the power cord and cause a short circuit.

I have encountered a few fish tank fires recently. Some of them resulted from multiplug power failures caused by water contamination. Because the power strips face up from the floor or shelf under the tank, they get wet. Further aggravating the problem is that the water travels along the wire from the tank light, heater, and air pump directly into the power strip outlets. Eventually, corrosion occurs, and poor electrical connections develop. Over time, the heat from these poor electrical connections can cause a fire. My experience has been that saltwater fish tanks have a higher potential for fire because saltwater promotes a higher degree of corrosivity and electrical conductivity.

KEY POINTS

Following are some key points to remember:

As already noted, an electrical failure found at a fire scene signifies only that the item was energized at the time the failure occurred. It could be the cause or a consequence of the fire, depending on the outcome of the complete investigation.

Your investigation should include an examination of the fire scene, reconstruction of the fire scene, interviews with witnesses, and follow-up consultations with any experts in specialized areas you feel are necessary.

Never rush to a determination of the cause of a fire if you are not comfortable with it. If after your total investigation you are not sure of the cause of the fire, label the cause “undetermined.” It is always better to change a fire cause from undetermined to a specific cause as more information becomes available than to name the fire cause without having empirical data to support your choice. n


Bead at the end of stranded copper wire. Note the sharp ball formation indicative of electrical failure and heat from fire exposure. (Photos by author.)






(Top left) Close-up view of outlet. Note damage to area around the screw. (Top right) Front view of a duplex outlet that caused a fire. (Middle) Internal view of duplex outlet with mounting strap through center. (Bottom left) Insulation between outlet receptor and grounded mounting strap. Note arrow. (Bottom right) Internal failure caused blow-through on the back of this outlet.



(Top) Internal failure resulted in blow-through on the back of this ballast. (Bottom) A thermally protected ballast.


Failed BXTM wire can be a cause or a consequence of fire.

ARTHUR L. JACKSON is chief fire investigator for Peter Vallas Associates, Inc., a Hackensack, New Jersey-based company that provides fire and explosion analyses, investigation, and engineering services. He also is a fire official and a 25-year veteran of the Hasbrouck Heights (NJ) Fire Department.

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