ELECTRICAL HAZARDS WARRANT FIREFIGHTER VIGILANCE
Electrical hazards are abundant in a firefighter`s line of work. Experienced firefighters, therefore, develop a healthy respect for, or even fear of, electricity. Most of us have our own personal “horror story” about coming within inches of electrical current that could have killed us or at least put an end to our careers.
Electricity, like many of the hazards threatening firefighters, is most dangerous when its danger is not readily apparent. Arcing and sparking wires in a sense are a blessing because they present a clear warning of danger. It`s the electrical hazards we don`t see, those hidden within walls or energizing metallic objects, that can place unsuspecting firefighters at greatest risk.
SOME BASIC PRINCIPLES
I don`t pretend to be an electrician. I am, however, very fortunate to have worked with firefighters who are electricians, and I realize what a tremendous asset they can be to a fire company. All firefighters should, however, possess a basic working knowledge of the fundamental principles of electricity. One of the most important facts is that for electrical current to complete its circuit, it must reach ground.
Electric power to most one- and two-family dwellings is supplied by a nearby transformer through two 110-volt wires. These two “hot” wires are insulated and wrapped around a noninsulated “neutral” cable, which completes the circuit by returning current from the house back to the transformer and, ultimately, to ground. Additionally, wiring in buildings is connected to ground through water pipes or rods driven into the soil.
Grounding is a safety requirement of electrical codes. Its purpose is to provide a lower resistance path to ground for dangerous current resulting from damaged wiring or faulty equipment, reducing the chances of a person`s getting into that path and becoming part of the circuit. A continuous path to ground also facilitates the operation of over-current safety devices, blowing fuses, or tripping circuit breakers. But there are no guarantees that grounding will function as it was intended because the grounding system has nothing to do with how efficiently electrical equipment operates. The washing machine will still wash, the stove will cook, and the lights will illuminate–even if the equipment is not properly grounded. Consequently, a fire or electrocution may be the first indication of an improper ground.
What makes electricity especially dangerous for firefighters is that it is not too particular about how it reaches ground; rather, it takes the path of least resistance. Interrupt or interfere in any way with electricity`s normal path to ground, and current can take a deadly detour–right through your body.
THE “UNEXPECTED” ASPECT OF CURRENT
When I was a young firefighter, I was assigned to an engine company that responded to a call for an odor of smoke in an old commercial building. The smell of burning wood was faint but unmistakable. Something had to be smoldering in a concealed space–perhaps inside a wall, under the floor, or above two ceilings in the cockloft. After a lengthy and tedious search, we found an exterior stucco-on-wood-frame wall that was hot to the touch. Confident that we had a fire inside the wall caused by faulty wiring, we shut off power at the main electrical panel and requested the utility company to respond. We then stretched a hoseline and meticulously opened the wall. Behind thick, heavy plaster and wire-mesh lath we found, as expected, a smoldering fire. Heavy char on a 2 2 4 stud indicated that it had been burning for a long time. What we didn`t expect was that there was no electrical wiring anywhere in the fire area! To our dismay, we found no wires or, for that matter, any gas lines, water pipes, or ventilation ductwork anywhere near the fire`s point of origin. We were baffled: How did this fire start in a closed void with no obvious source of heat or ignition?
Because we could not determine the cause of the fire, the lieutenant requested a fire investigator. Shortly thereafter, the power company arrived on the scene. Since we found no indication of electrical wiring involved, we told the troubleshooter that the power company was not needed and apologized for not canceling him sooner.
Fortunately, the troubleshooter did not immediately leave and, after observing the burnt portion of the wall, began to question the building`s occupant: “Have you experienced anything unusual with your electricity lately?” “Anything,” the troubleshooter emphasized, “such as lights flickering or dimming, or do you ever feel a shock when you touch an electrical appliance or a water pipe?”
“Yes,” replied the occupant. He went on to say that his lights occasionally dimmed and once he did feel a tingling sensation when he touched the sink while he was wearing wet shoes. The troubleshooter persisted: “Have you recently had any remodeling, electrical, or plumbing work done?”
“Not really,” replied the occupant. He added that his brother-in-law replaced the hot water heater. “But that couldn`t have anything to do with an electrical problem,” he added, “because it is a gas hot water heater.” The troubleshooter countered that it could have a lot to do with an electrical problem and went on to explain that the wiring in this old building was probably grounded through the water pipes.
When he examined the water service, the troubleshooter found that when the new hot water heater was installed, a section of galvanized steel pipe from the water meter was replaced with PVC plastic. This change would definitely interrupt the building`s continuity to ground. As a result, current “searching” for another way to reach ground may have found that the metal lath inside the walls was the path of least resistance.
“But how did electricity get into the lath?” we asked. “There are no wires or water pipes anywhere near the point of origin.” The troubleshooter explained that, in his experience, the fire was probably a result of a combination of problems with the building`s electrical wiring. First, he had to rule out that the power company`s neutral leg of the electric service wasn`t “open” (inadequate or had no capacity to conduct electricity). If his company`s neutral was open, current could not return normally to the transformer and would tend to “search” for another path to reach ground. Also, this old building still had most of its original wiring, consisting mainly of metal-clad BX cable. Like metal conduit, BX achieves its path to ground through its metal covering. A loose connection or a separation anywhere along the spiral metal sheath can break the continuity. If the BX happened to be in contact with anything metallic–say the plumbing or metal lath–either could become the new path to ground.
Another factor was the age of the building. The years can take a toll on wiring, giving it plenty of opportunity to “leak” electricity–insufficient current to trip a circuit breaker but enough to cause shocks and, over time, fires. Wiring can develop worn spots in its insulation, particularly where it is crammed into tight spaces, is jammed around sharp corners, and penetrates floors. A nail or screw that inadvertently penetrates wiring inside of a wall can energize any metallic object it touches.
The troubleshooter further explained that all piping systems, ventilation ductwork, metal structural members, and even aluminum siding can become energized. He told of a situation in which a restaurant`s gas piping became energized. The pipe was not connected to any electrical appliances and was not bonded to the electrical system. Evidently, a rat chewed through the insulation of a nonmetallic sheath cable, exposing the wires, which energized the gas piping. The tendency of current to use metallic objects to reach ground is increased significantly if the normal path to ground is interrupted by a section of plastic pipe, which cannot conduct electricity.
A voltmeter confirmed the power company troubleshooter`s suspicion: When the power was restored, wire lath nailed to the burnt stud was energized with 10 volts. The current flowing through the lath was sufficient to cause the lath to act like a heating element. The result was a slow, gradual process of heating the wood. It could have taken months or even years for this low-grade heat source to decompose the cellulose in the wood to a point that it would undergo the phenomenon of pyrophoric carbonization, which would gradually lower the ignition temperature of the wood and eventually ignite the stud.
Where the current was entering the metal lath was anyone`s guess, but it was clear that substituting PVC for steel water pipe had interrupted the building`s normal path to ground and the current followed the lath to complete its circuit.
Since that fire early in my career, I have responded to several fires in concealed spaces caused by open neutrals and faulty grounds. Electricians and linemen tell me that my company`s first-due district, replete with old buildings, is prime territory for electrical problems and fires because many of the structures have old, worn, and damaged wiring. Also, the power company`s electric service occasionally develops an open neutral, usually the result of a defective cable connection where the electric service neutral enters the weatherhead (the connection where the power company`s service wires enter a building).
ELECTRICAL HAZARDS IN NEW CONSTRUCTION
But electrical fires don`t occur only in old buildings. In many parts of the country, new homes are wired with a plastic-clad cable that has no metal covering. Unlike metal conduit and BX, this cable has a third wire (in addition to the hot and neutral wires) that is specifically for grounding. Its plastic sheath of insulation is vulnerable to penetration by a screw or nail driven into the wall. As a result, the nail or screw can become energized and arc, or the ground wire can be severed and lose continuity. Resistance caused by a loose connection can start a vicious cycle of heating-expansion-cooling-contraction that can eventually start an electrical fire.
MOBILE AND PREFABRICATED STRUCTURES
Mobile homes and prefabricated structures are also good candidates for faulty neutrals and grounding disruptions. A fire in a double-wide office trailer inside a warehouse at the Port of Miami was attributed to a combination of an open neutral and improper grounding. Firefighters opened the gable end of the attic and found arcing between metal wind bracing and an air conditioner. Open neutrals to old mobile homes usually force current to seek out the steel wind straps and follow them to where they are anchored in the ground. Arcing between the wind straps and steel chassis usually starts a smoldering fire in the old trailer`s particleboard floor.
In researching this article, I found that the most valuable documentation on open neutral electrical hazards was written by Lieutenant Larry Weintraub, fire/arson investigator with the City of Miami (FL) Fire Department and Luis Jimenez, chief electrical inspector for the City of Miami. In more than 25 years of investigating, Weintraub had seen hundreds of fires in concealed spaces that involved smoldering and heavy charring around nails, metal lath, water pipes, and other metal objects coming in contact with wood structural members. He suspected that many of these fires were electrical, but no wiring was found near the point of origin. Also, identifying a source of electrical power was difficult because, in most cases, the power had been cut at the electric service or the electric meter had been pulled before the fire investigator`s arrival.
Then in 1993, Weintraub and Jimenez investigated a fire in a wall that had been extinguished by fire companies approximately 24 hours earlier. When the investigator reached under a 2 2 4 stud to determine the depth of char, he was burned by extremely hot metal lath. The electrical inspector took voltmeter readings between nails in the wire lath and an old wall furnace and noted readings from 2 to 70 volts A/C. This seemed impossible because the electric meter had been pulled by the power company 24 hours earlier and had not been replaced. There should have been no electricity to the building!
The electrical inspector had the power company cut the neutral cable at the weatherhead of the electrical service. Once the neutral cable had been cut and separated, arcing was still visible on the lath inside the wall–with no electrical wires connected to the building. The inspector then took readings of the neutral cable connection at the weatherhead and found it to have approximately 115,000 OHMs of resistance where there should have been zero resistance. This is a classic example of an open neutral. With that much resistance, current could not flow normally back to the transformer. But that still didn`t completely explain how power was entering the building with all the electric service disconnected. Another fire in July 1993 would give Weintraub and Jimenez the answer they were seeking.
A fire in a wall was caused by arcing between a metal conduit and an outlet box. When investigators arrived the next morning, arcing could still be observed–more than six hours after the power had been disconnected. A voltage sensor indicated that not only was the conduit energized, but the refrigerator and kitchen sink registered significant readings as well. The power company confirmed that it did, indeed, have an open neutral in its system, but it was the water company that gave them the most startling news.
After removing the water meter, arcing was plainly visible when water company workers connected a jumper cable across the gap in the pipes where the water meter had been. This was the source of electricity that eluded Weintraub and the inspector for so long: An open neutral somewhere in the power company`s system prevented current from one or more buildings in the area from returning normally to the transformer. Instead, it followed metal water pipes to ground, energized the water main, and “back fed” current through the fire building`s water service. This incident also sheds some light on the reason water company meter readers sometimes wear rubber gloves to avoid being shocked. It also helps to explain why cable company installers and gas company employees have been shocked by electricity back feeding through their lines.
Since the 1993 fire, Weintraub and Jimenez have documented several other fires in which an open neutral has energized water and gas pipes. They produced an instructional video on open neutral electrical hazards for the City of Miami Fire Department. As a result of their research, firefighters should never again feel completely comfortable that the power to a building has been disconnected just because the electric meter was pulled or the service wires were cut: They could think that they have extinguished a fire and eliminated the source of ignition by disconnecting the power, only to have to return to extinguish a rekindled fire several hours later.
THE CURRENT CAN KILL
Open neutrals and faulty grounds cannot only fool you–they can kill you. A fire that began inside a wall between a bathroom and a living room quickly spread to the attic. During overhaul, the wall was opened, and heavy charring was observed on the studs next to the water pipes to the shower. Voltmeter readings by the power company indicated that the water pipes were energized to more than 100 volts–more than enough to electrocute a firefighter inadvertently bridged across the pipes with a steel tool. What makes this fire more frightening is that firefighters pulled the main fuses before they opened the wall!
LESSONS LEARNED AND RECOMMENDATIONS
Any fire in a concealed area such as a floor, a wall, a ceiling, an attic, a roof, or a soffit should be considered electrical until proven otherwise.
If electricity is suspected, do not touch any water or gas pipes, metal lath, conduits, BX, or other metal structural elements. Additionally, consider the risk of placing aluminum ladders against energized rain gutters or aluminum siding.
When an open neutral is suspected, open walls and ceilings cautiously and conservatively until the power company has confirmed that there is no power in the building.
Remember, shutting off mains, tripping breakers, pulling fuses, pulling meters, and even cutting electrical service wires to a building do not guarantee that the building is safe from electrical power.
Lights that flicker and dim and appliances and plumbing that give shocks are good indications of an open neutral or faulty ground. But it is important to remember that these conditions can also exist without any indication of a problem.
Faulty grounds and open neutrals can and have ignited more than one fire in a building. Be sure to check all concealed spaces, especially attics, before a fire is declared under control.
Before electrical power is confirmed to be disconnected, firefighters should go through areas of poor visibility and touch metallic objects with the back of their hands, palm turned toward the face. This way, if contact is made with a wire or energized object, the muscles will tend to involuntarily contract inward and pull the hand away from the current.
All fire companies should be equipped with voltage detectors. It is critical, however, that firefighters are trained to use them properly, fully understand their limitations, and realize that they are not 100 percent foolproof.
At a recent conference, I heard an administrator of a large fire department say that firefighting will become just a minor part of the future firefighter`s job. He based his predictions on statistics, which reflect a nationwide decrease in the number of fires and the skyrocketing increase of nonfire-related calls such as for emergency (usually nonemergency) medical service. I believe that his view of the future, one held by many in the fire service, is flawed. Further, it reflects a dangerously complacent attitude about the service that is most likely to get us killed–firefighting.
Perhaps this nationally recognized authority did not consider two realities concerning fires and firefighting: First, there will always be fires and a need for an adequate number of trained and properly equipped firefighters. You can`t prevent, sprinkler, or educate fires into extinction.
Second, the majority of fire departments in this country are largely suburban and haven`t yet realized their full potential for fires because most of the structures in their communities are relatively new. Give them another 10 years for problems like open neutrals and faulty grounds to rear their ugly heads. Electrical hazards are like ticking time bombs inside walls, under floors, and up in attics. It is just a matter of time before they start fires that will severely challenge the firefighters of the future.
Fire in a wall between the kitchen and the bathroom arcing between a 220-volt outlet for an electric stove and the water pipes started this fire.
The fire spread up the wall and melted the pipe connection directly above the top plate. The fire was extinguished by a leaking pipe, which acted as a “sprinkler.” The fire was attributed to an “open” neutral. Subsequent voltmeter readings indicated that water pipes were still energized after main circuit breakers had been opened.
The combination of open neutral and improper grounding evidently caused current to use metal lath inside the wall as an alternate path to ground. The metal lath acted as a heating element, causing pyrophoric carbonization and ignition of surrounding wood. This photo illustrates the importance of thoroughly opening around window frames to look for hidden fire. Here, the fire spread into the cavity for sash weight even though the old double-hung window had been replaced by an aluminum-frame awning window when the house was remodeled. Treat all electrical equipment and plumbing and metal structural elements as if they were energized until they are deemed safe by the power company. (Photos by Bill Gustin, Jr.)
A typical three-wire residential electric service consisting of two insulated 110-volt wires wrapped around noninsulated neutral cable. The neutral cable-splice connection has a tendency to build resistance over time, resulting in an “open” neutral. (Photo by author.)
Electric meter pedestal serving four mobile homes. The ground wire is no longer connected to the grounding rod.
The ground wire to this private residence is no longer connected to the grounding rod. It is quite common for weed trimmers to cut through ground wires lying in the grass. (Photos by author.)
Open neutrals to old mobile homes usually force current to seek steel wind straps and follow them to where they are anchored in the ground.
Arcing between the wind strap and steel chassis started a fire under the floorboard of this old trailer. (Photos by Bill Gustin, Jr.)
A fire in the wall between the bathroom and the living room. Arcing between the energized shower pipe and wire lath ignited a fire that rapidly spread to the attic. The pipe was energized with more than 100 volts of current after main circuit breakers had been opened.
Arcing between the cast iron plumbing stack (extreme left) and nails to the roof-soffit fascia started a small fire in the attic. Occupants of the old house complained that they had received minor shocks when they touched the soapdish while taking a shower.
A firefighter uses a voltage detector to check for dangerous current on the switch box. Such devices are reliable and easy to use, but firefighters must understand their limitations.
When going through areas of limited visibility, firefighters should touch metallic objects with the back of their hand. Current will involuntarily contract muscles and pull the hand away from an energized object. (Photos by author.)
The author gratefully acknowledges the technical assistance provided by Lieutenant/Investigator Larry Weintraub, CFI; Lieutenant/Electrician Tim Gibbons; Luis Jimenez; and Arthur L. Jackson, chief fire investigator, Peter Vallas Associates, Inc., in the preparation of this article.
BILL GUSTIN is a captain with Miami-Dade (FL) Fire Rescue (formerly Metro-Dade) and lead instructor in his department`s officer training program. He began his 26-year fire service career in the Chicago area and teaches fire training programs in Florida and other states. He is a marine firefighting instructor and has taught fire tactics to ship crews and firefighters in the Caribbean countries. He also teaches forcible entry tactics to fire departments and SWAT teams of local and federal law enforcement agencies. He is an editorial advisory board member of Fire Engineering.