BY DOUG LEIHBACHER
At 1423 hours, Yonkers, New York, fire dispatchers received a call from an off-duty police sergeant who reported that, while he was driving home, he observed a crew repairing a utility pole and noticed a flash of light and then smoke as he passed by. Shortly thereafter, several additional calls reporting rolling blackouts in the southeast section of the city were received.
An engine, a ladder, and a battalion chief were dispatched to the scene for a possible transformer fire. The engine was first to arrive. The officer, Captain Curtis Bracy, reported a snapped utility pole with primary and secondary wires down across the utility truck, which, along with a transformer, was on fire. The engine also reported that the wires were still “live” and arcing. When Battalion Chief Stan Nowak arrived, he scanned the scene and observed, in addition to the burning truck, smoke coming from the house across the street, which prompted him to request a full first-alarm assignment (three additional engines, another ladder, the rescue, and the safety battalion).
With two separate fires to deal with, the chief quickly sized up each. The first fire involved a large utility truck parked at the curb next to the severed utility pole. The pole had snapped in half approximately 20 feet above the ground and was lying across the cab of the truck. Wires were pulled down, crossed, and lying on the street. A transformer was on the ground next to the front tire on the driver’s side of the utility truck. It had ruptured, spreading on the street dielectric mineral oil, which fueled the fire and created a potential environmental hazard. The crossed wires were arcing periodically. Flames and black smoke were issuing from the transformer and the truck, and the weather coatings on several electrical cables were burning.
All members of the utility crew were standing nearby; no one was trapped in the vehicle. Members of the engine had stretched from a hydrant and were standing by with class B/C extinguishers at a safe distance from the wires. A size-up of the adjacent poles showed that they carried three-phase, 4-KV (kilovolt) high-tension wires as well as 110/220-volt secondary house lines and telephone and cable wires.
With the very real potential hazard of electrocution present and the absence of a life hazard in the burning truck, the chief ordered members to cordon off an area equivalent to a pole span in every direction and make no attempt to extinguish the fire in the truck until the power was cut. The safety chief was assigned to set up the safe zone and keep members a secure distance from the wires. With brown smoke showing from the 1 1/2-story house across the street, it became the higher priority. Crews were immediately redirected to operate in the house located approximately 30 feet to the east of the utility truck. Flames from the truck were not impinging on the house, but the crossed power lines had apparently caused the fire in the house.
While later-arriving companies checked surrounding homes for additional fire conditions, the earlier-arriving units went to work on the house fire. Two 1 3/4-inch lines were stretched, one into the basement through the back door and one through the front door into the first floor. An elderly resident was found in the house during a primary search and was assisted to safety. The fire originated in the southeast corner of the basement at the electric meter pan and service panel. Flames spread up the paneled wall, across the open wood-joist ceiling, and out the rear door as it was opened by crews. A hose team worked its way down the back stairs into the basement and brought the fire under control before it could extend to the first floor or attic. A later examination of the electric meter pan by fire investigators showed that the glass housing was forcibly blown to pieces and there was extreme heat damage to the interior components. Part of the copper contacts and the lower section of the meter base housing were melted and blown through.
CAUSE ANALYSIS
Utility company employees on the scene told fire investigators that they were there to replace a cracked and leaning utility pole that carried primary wires and a transformer. The crew had arrived in the morning, towing a replacement pole, and had parked the truck next to the pole. The truck was not running at the time of the incident. They were in the process of digging a new hole just to the south of the damaged pole when the damaged pole snapped and fell onto the utility truck. The transformer separated from the pole, hit the ground, and split open, expelling some 50 gallons of dielectric transformer oil. When the secondary lines crossed the primary lines, arcing ignited the oil and initiated the fire. Fortunately, no utility workers were in the utility truck when the pole fell, and none were injured.
Investigators labeled this fire accidental, the result of a voltage surge that traveled to the service panel and meter of the house, igniting surrounding structural framing in the basement. A cast-iron sewer line was next to the service panel and raceway, offering an attractive path to ground for the excess current. The utility pole failed just above the telephone lines, approximately 20 feet above the ground, and the top section fell across the parked utility truck. When it fell, the transformer hit the ground, ruptured, and spilled dielectric transformer oil on the street around the truck. Although dielectric oil has a high flashpoint (> 300°F) and an ignition temperature of more than 700°F, the heat of the arcing wires can reach temperatures of 7,000°F, which can easily ignite it. Whenever a transformer ruptures, a potential polychlorinated biphenyl (PCB) release is possible. Utility company representatives took samples of the unburned transformer oil. A laboratory analysis found PCB contamination to be within safe limits (< 50 ppm). As a precaution, the Water Department was notified in case any dielectric oil entered the sewers.
When the wires from surrounding poles were pulled down, they twisted, and a primary line came into contact with a secondary line. The resulting arc and voltage surge followed the neutral into the house and sparked the fire. At all incidents involving transformer fires, service panels in the surrounding properties should be checked. In this case, circuits were blown in five houses; fortunately, only one house sustained a fire.
DISCUSSION
Firefighters may not encounter an incident directly involving electrical utilities for long periods, but we must be mindful that electrical hazards are present at virtually all fire incidents and we should not take them for granted. The above incident was handled appropriately, with caution and common sense, and no one was injured. Since there was no life hazard associated with the utility truck, there was no reason to put firefighters where they might accidentally touch the arcing electrical wires. Moreover, using water may have spread PCBs into the sanitary sewer system. Although it was an expensive piece of equipment, extinguishment operations on the truck were wisely curtailed until the power was cut. Burning wires could have severed and whipped around. Members advancing hoselines could have stepped on hot wires or have been subjected to ground gradient current. When extinguishment of the truck was initiated, full protective clothing, including breathing apparatus, was required because of the potential presence of PCBs in the transformer oil. The house was a more strategic exposure. The life hazard there was unknown, and the value was greater. Although the truck was ultimately totaled, the house was saved with relatively minor damage. Approximately 300 customers lost power for several hours.
Although some firefighters may have a background as electricians, few are experts in electricity. Electrical hazards can occur anywhere along the vast electrical distribution grid, from high-voltage electrical substations to belowground electrical vaults to overhead wires. The dangers associated with electrical utilities have killed and injured firefighters, and electricity remains an ever present risk for firefighters. Care, attentiveness, and patience are essential when dealing with electricity because it can be precarious and unforgiving. As firefighters, we don’t have to be experts in electricity to be safe-as long as we remember that if you touch it, you get hurt.
In many cases, weather plays a role in causing the hazard, and the electrical systems we encounter are often compromised. High winds can damage house service drops, sever hot or neutral conductors, or send trees down onto primary lines. In these situations, electrical current can initiate a fire that poses the electrical hazard on arrival. In other cases, electrical hazards can occur as a result of a fire and become a safety hazard later in the incident.
ELECTRICAL HAZARDS ON THE FIREGROUND
When operating on the fireground, firefighters are generally at greater risk of electrocution when operating in proximity to outside electrical lines than when working inside the building. If a firefighter using a tool perforates an electrical cable that is part of a branch circuit while inside the structure, he may receive a shock but will in all likelihood be protected by a breaker, fuse, or ground fault circuit interrupter (GFCI). There are rarely such over-current devices to open a circuit on the outside of the building. For this reason, officers and firefighters operating on the exterior should take a moment to look up and keep an eye on all overhead wires in the vicinity of where they are working. Any downed wires should be cordoned off with yellow crime scene tape or barricades, or a member should be posted at the location to warn other firefighters.
Members should note where the house line meets the weather head and service raceway and enters the building. The line is usually found near the corners of the house. If the wire is subject to flame impingement or is otherwise compromised, it is not safe to work beneath it. Copper wires will melt at 1,981°F and can sever quickly and fall when in direct contact with flame. Many newer services are made of aluminum, which melts at only 1,218°F and will come down even more quickly. A fire captain from Santa Clara County, California, was killed by a fallen wire in 2005 while fighting an early morning structure fire. A high-voltage cable fell onto a tree and was dangling in the dark; tragically, Captain Mark McCormack came in contact with it and was electrocuted.
Members carrying metal tools, working exposure lines, raising aerials, or operating fire pumps should be aware of potential electrical hazards over their heads. The danger is that if contact is made, their bodies can create a path to ground through which the electrical current will readily flow. It is, therefore, important that the incident commander notify electric utilities early in the fire so they can cut the power at the scene before it becomes a hazard.
History has shown that firefighters moving metal ground ladders are at heightened risk of electrocution, especially in wet or icy conditions where members could lose their footing and fall. Metal ground ladders are constructed of high-tensile aluminum alloys that conduct electricity readily. When overhead wires are nearby, do not carry metal ground ladders in the vertical position unless absolutely necessary. Instead, carry them horizontally to the point of operation and then raise them. If a vertically carried ladder gets away, it can fall against electrical lines and create a path to ground. Whenever a ground ladder is to be raised, the officer in charge of the crew must ensure that there are enough firefighters to safely carry and raise the ladder under control. The officer must check for overhead wires or obstructions before the ladder is brought to a vertical position.
When placing the ladder against the building, make note of the siding. Although not a common occurrence, aluminum siding can become energized at structure fires, as can metal rain gutters (photo 4). An open neutral or wire in contact with the siding can energize it and send current down the ground ladder. Because of these hazards, many departments, particularly on the West Coast, continue the sensible tradition of using wooden ground ladders. For wooden or fiberglass ladders to maintain their electrical resistance, however, they must be kept clean and dry.
Operating from aerials or tower ladders can also present an electrical hazard. It is challenging to “stick” a building when faced with a maze of primary and secondary wires at various heights in front of the building. When victims are trapped and awaiting rescue, aerial ladder operators can feel compelled to take risks in positioning the aerial, resting it on secondary lines whose weatherproofing may be damaged or extending it through the gap between the secondary and primary wires. When this is done before the power is cut, it can create an undue risk to members operating on or around the aerial ladder. If the jacks are grounded by means of their contact with the street, the member working on the ladder can be at risk of completing the circuit to ground and thereby be electrocuted. On a well-grounded apparatus, any firefighter who makes contact with a wire while climbing the aerial is taking a gamble of being killed or critically injured. It is not feasible to determine how well-grounded an aerial ladder may be at a fire scene. The presence of water or rock salt on the street below the steel jack plates can increase the grounding effect.
If the apparatus is not well-grounded and is in contact with an overhead wire, individuals standing on the ground and touching the apparatus to get a tool could complete the circuit to ground and be electrocuted. This is one reason aerial ladder operators, unlike pump operators, stand up off the ground on a turntable. Members removing a tool or ladder from a truck in operation should look up and assess the position of the ladder aloft before touching the rig or opening a cabinet door. The best way to prevent an arc is to keep the boom or ladder 10 feet from overhead power lines. Remember that the presence of smoke and moisture can reduce the insulating effect of air between the power lines and the aerial, allowing arcs to jump. Do not lean tools against a ladder truck in operation; they can provide an alternate path to ground. If a wire should fall onto an apparatus, all members operating on the apparatus should jump clear of the rig so they are not in contact with any part of the apparatus when they touch the ground.
Fences may present an attractive place to rest an exposure line or lean a tool. Sometimes fences must be cut to gain access to the rear of a building. However, be careful when operating in proximity to metal fences. Falling electrical lines can energize a metal fence and conduct electricity throughout (photo 5). Before touching a metal fence, look to see that no wires are in contact with it along its full length. Similarly, if working inside, avoid touching BX cable, water pipes, gas pipes, or structural steel, which may be carrying neutral return current.
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CONTROLLING ELECTRICAL UTILITIES AT STRUCTURE FIRES
The incident commander should notify the electric power company to respond early in the fire. If electricity is the cause of the fire, the power should be cut directly. If electrical involvement is not the cause of the fire, the power can often be cut later in the incident if it evolves to the point where circuits are impinged on. Branch circuits are frequently damaged as fire moves through a structure. Circuits can be saturated with water or insulation may be burned off of Romex cables or extension cords, leading to arcing and short circuits that can potentially injure members. That’s the reason members feeling for hot sports are advised to use the back of their hands-if shocked, their fist will not clench a live wire.
Cutting the power early can eliminate these hazards. However, there can be tradeoffs to cutting off the power. Elevators, fire pumps, and ventilation exhaust systems may need to be kept operating until the fire is under control. As a rule, the power should be cut before extensive overhaul begins. When the power is cut, it should be isolated to the involved apartment or section of the building whenever possible.
Utility company employees should be used for this purpose. They are a great resource. They know their business and are there to make our job safer. In addition, their advice about potential hazards can be invaluable, and a representative should be stationed at the command post. When utility officials are not available, firefighters trained as electricians can provide expert advice to the incident commander.
Sometimes the utility company cannot send a lineman in a timely fashion, and it is necessary to use firefighters to shut off the power. In these instances, it is not a safe practice to have firefighters cut service drops or remove electric meter pans. They are not trained to do this. If they must be used to shut off the power to a building, they should shut off the power at the main service panel only. Only trained firefighters should be used for this job. The service panel, though usually safe under normal conditions, may be compromised under fire conditions, or an arc can be produced when the switch is thrown. Therefore members performing this operation should be equipped with full dry protective clothing including clean, dry gloves (rubber lineman’s gloves are best); a clean, dry, nonconducting instrument such as a wooden chock or dowel; a noncontact voltage detector; and a helmet with eye shields.
 (7) A noncontact voltage detector can be used to determine if an electrical component (service panel, fuse box, switch, or fixture) is charged with current or safe to touch. |
Electric service panels are usually found in the garage or basement. Members should not enter a basement or garage if the water level is high enough to be in contact with electric motors or receptacles. If in contact with the above, the water could be carrying an electrical charge. In such cases, the power should be cut only at the pole by a utility company lineman. By contrast, a small puddle on the floor, if not in contact with an energized wire, does not increase the electric hazard. Some firefighters feel that wearing rubber boots shields them from electrical injury. The rubber boots we wear will not necessarily protect you from stray current. They have steel shanks and toes, may have tiny holes or cuts, and are often contaminated with carbon particles that can track electrical current.
Fuse panels are usually disconnected by pulling the handle down on the side of the unit or removing the cartridge bank. Breaker panels are disengaged by opening the door and throwing the main breaker. The metal cabinet is usually grounded and will not convey electrical current, but there is no guarantee of this on the fireground. Before touching the panel, carefully inspect it. Is the panel grounded to the water pipe? Is the cover in place? Is it dry? If a service panel with a missing cover is encountered, if it is not properly grounded, if buzzing sounds or sparks are coming from it, or if water is dripping through the service panel, you risk serious injury if you touch it. Also, make sure no hanging wires are touching the panel.
If the panel is found to be in safe condition, the next step is to use a noncontact voltage detector to make sure the panel is not charged. These voltage detectors are inexpensive and are about the size of a magic marker, which makes them easy to carry in a turnout coat. Test the panel and main breaker with the voltage detector; if the detector registers no current, it is safe to throw the main breaker or handle. Stand to the side, use the wood dowel, and look away as you throw the breaker in case there is a carbon monoxide (CO) buildup behind the panel or there is an arc. CO buildup occurs most often in instances where a nearby manhole is burning, which will be discussed later.
Note that cutting the power at the pole or service panel is not an absolute guarantee that it is safe to work around electrical fixtures in the building. At some buildings, particularly commercial occupancies, emergency generators may kick on once the power is cut. Additionally, some homeowners may be illegally pirating electricity to adjoining properties with jumpers or extension cords. There are also cases where open neutrals continue to conduct current into metal pipes or wire lath even after the power is cut. (See “Electrical Hazards Warrant Firefighter Vigilance,” Bill Gustin, Fire Engineering, October 1999.)
ELECTRICAL HAZARDS AND WATER
Although distilled water is a nonconductor, the water we use does conduct electricity. However, it is not a good conductor as compared with metals. The amount of electricity water will conduct depends on several factors, including the dissolved mineral content in the water stream, the continuity of the hose stream pattern, and the distance between the energized source and the nozzle. Often, the water pumped through the nozzle from a hydrant has a high iron content, as evidenced by the rust color, particularly in the early stages of the stream’s application. A solid stream from a smooth bore nozzle would theoretically conduct electricity more readily than the stream from a fog nozzle because of the insulating quality of the air in between the water droplets of the latter. Nevertheless, examples of water streams conducting electric current back to the nozzle team at standard voltages are very rare, especially inside a building. The rapid movement of an advancing nozzle breaks up the stream continuity and makes the stream a poor conductor of electrical current. Sparks may fly, but current is seldom conducted back unless the nozzle team is extremely close to the electric source and the source is high voltage (> 600 volts). Water fog patterns (30°) are recommended as the safest application method, and the greater the distance from the energized source, the safer it is.
When water is applied to an energized source, the amount of voltage charge traveling back to the nozzle team through the hose stream may not be as great as it is in the water flowing on the ground. If a wire is down and arcing on the ground near where a hoseline is operating, current can flow along the ground back to the hose team through the puddling water. Firefighters have reported a tingling in their feet in such instances, as current seeking to complete the circuit flows along the ground toward them in the increasing moisture. Though their protective effect is minimized by steel toes, rubber boots can provide some measure of insulation from ground current, but they must be dry, free of carbon particles, and undamaged.
A distinction should be made between unintentionally applying water to energized low-voltage electrical equipment at a common structure fire and applying water to high-voltage electrical equipment at a switching station, transformer vault, or other utility company facility. At the latter, firefighting operations cannot begin until the power has been positively cut off. In fact, even entrance into such a facility should be curtailed until a utility company supervisor arrives and assures the chief that the power has been shut off and it is safe to enter the facility. This is standard practice when operating near high-voltage equipment.
DOWNED WIRES
Often electrical hazards or fires are the result of wind, rain, or ice storms. Fire departments are commonly the first to be called to “sit” on a downed wire. Frequently, these runs are of long duration when utility crews are overwhelmed by the volume of calls for assistance. It is important to bear in mind that our function at these incidents is not to move or secure wires. At these alarms, our primary function is to keep others from being injured until the utility company can respond, cut the power, and repair the wires. In carrying out this task, it is important to operate in a safe manner so that members are not injured. When approaching the location of a downed wire, proceed at a reduced rate of speed so that the apparatus can stop a safe distance from the site of the wire.
Utility poles are typically spaced 100 feet apart. Utility companies recommend that the apparatus be positioned at least one span (two poles) or 100 feet away from the downed wire. One reason for this is wire memory. After being manufactured, overhead cables are stored and installed from a spool. Because of this, an overhead line that is severed and falls can whip around in several directions as it recoils. This movement can continue for some time; firefighters must allow room for this phenomenon. Typically when breaks occur, two wires are down. Depending on where the break occurs, both ends may reach the ground, or one may be on the ground and the other dangling in the air. Identify both ends of the downed wire so that no one walks into one of the wires. One side may appear live, exhibiting movement or sparking, while the other side may appear quiet. However, both lines should be treated as live. Many overhead wires are fed from both directions.
Be particularly careful of wires lying across a road and in contact with painted pavement markings. The paint contains metallic particles to make it reflective, and it could conduct electricity. Avoid stepping on the double yellow line or other continuous painted pavement markings. Also, be equally as cautious with regard to guardrails that are in contact with a wire and with autos in contact with energized guardrails.
After a safe distance has been established, use the apparatus to block the street if necessary, and place caution tape across sidewalks and walkways to prevent pedestrians from wandering into harm’s way. Post members to direct pedestrians to safer areas. Check to see that the wires are not touching any metal fences. Transmit the pole number and address to the utility company. If conditions are unsafe and prevent you from approaching the pole to read the number, take the number off a nearby pole.
Sometimes downed wires start brush fires. When operating at brush fires sparked by a downed wire, do not work in proximity to the downed wire or touch any metal fences that may be in contact with the wire. In a charred area, a downed wire is well camouflaged and can easily be stepped on. When brush or railroad tie fires are sparked by a third rail along the tracks, refrain from using water, and remain a safe distance from the tracks until the trains are stopped and the power to the third rail is cut. Similarly, when trees are leaning on wires, curtail tree and branch removal until the power is off.
When downed wires are in contact with an automobile, the individuals inside the vehicle are generally considered to be safe from electrical danger as long as they stay in the vehicle. They in effect are part of the circuit, and, like a bird on a wire, are not in danger from electricity unless they create a path to ground. A member touching the car would create the path to ground through the member’s body. Members should reassure persons in the vehicle and advise them to remain in the vehicle until the power is cut. Unfortunately, wires frequently fall onto vehicles as a result of an accident, and the persons inside often need medical attention in a timely fashion. Nevertheless, when wires are involved, members should approach the vehicle cautiously, maintain a safe distance, and avoid touching the vehicle or wire. Some units are experimenting with the use of a tac stick as they approach utility emergencies. This handheld device measures unshielded AC current from a distance of up to 50 feet away and produces an audible/visual alarm to alert members of the presence of live wires.
Firefighters should not attempt to move the wire or touch the vehicle until the power is cut. Remember that a primary wire has enough power to cut through concrete or welded steel. It carries enough juice to charge all but first-rate linemen’s equipment. Trying to move a wire with firefighting equipment is foolhardy. Similarly, using a winch and cable to stabilize the vehicle when electric wires are touching it or are nearby is dangerous and should not be done. If a downed wire sparks a fire in the vehicle with people inside, instruct them to jump clear of the vehicle. If they cannot do so, firefighters may have to use a fog pattern or class “C” extinguisher to save lives. Refrain from touching the vehicle until you are sure the power is cut and the wire is not live.
GROUND GRADIENT
The term “ground” or “voltage gradient” refers to current that flows away in all directions from the point where a downed wire touches the ground. The highest voltage is on the ground closest to the point of contact, and it gradually dissipates in concentric rings as the distance away from the point increases. As the voltage emanates out from the energized source, it decreases from high voltage to low voltage. This is the reason you are safer the farther away you are from the wire. However, the voltage differential creates a danger sometimes referred to as “step potential.” As you walk toward or away from the point of contact, there is a difference of electrical potential from one foot to the other-i.e., one foot is touching one voltage while the other is stepping onto another voltage. The two voltages will try to equalize by flowing up one leg through your body and flowing out the other leg. If you begin to feel a tingling in your boots, stop immediately; reverse direction; and use a shuffling motion, hop on one foot, or hop with your feet together instead of taking large steps as you move away. A similar situation can occur when you stand in place holding a charged hoseline. A voltage differential can occur between where your feet are planted and the hose is contacting the ground. A ground gradient can occur regardless of whether the ground is wet or dry.
IDENTIFYING WIRES
Standard wooden utility poles reach 40 to 45 feet high and carry a variety of wires-some hazardous, some not. Identification of the damaged wire (phone, cable, or electrical) is necessary so that the proper agency can be notified (Figure 1). Electrical wires often give themselves away by the sparking and arcing; however, a wire that emits no sound or visible light can still be live. Therefore, keep in mind the axiom: Consider all wires to be live.
 Figure 1. Identification of Wires |
Primary lines carry 4 kilovolts (KV) or 13 KV up to 33 KV in urban residential neighborhoods. Although wood is considered a poor conductor of low-voltage electricity, high voltage can be another thing. That is the reason primary wires are linked to ceramic insulators instead of attached directly to the pole. Secondary lines (house lines) carry less than 600 volts, usually single-phase 110/220V (two 110-volt hot leads and a neutral). The position of the wire on the pole can indicate the type of wire and voltage carried (Figure 1). As a rule, the higher a wire is on a utility pole, the higher the voltage it carries. Therefore, primaries are found at the top of the pole in three phases spaced at least one foot apart. They are not insulated and may or may not be affixed to cross arms. Below these are the secondary wires spaced approximately four to eight inches apart. Below them are telephone and cable lines.
However, there is an important exception to the pole-height rule: Insulated high-tension aerial cables carrying as much as 33 KV, enclosed in a metal sheath and held by a messenger, are often mounted below the secondary wires on the pole. Either gray or black in color, they can be mistaken for telephone trunk lines, which are also mounted with a messenger just below them. When high-tension aerial cables come down, treat them as you would primaries.
 (9) Utility poles are labeled with the pole number and voltage of the cables they carry. Checking the pole label can assist in identifying the hazard. |
Cable and telephone wires are the most frequently encountered downed wires, especially if there has been no storm. Because they are mounted low on the pole, they often are dislodged when tall trucks drive down the street. Although they themselves do not carry sufficient current to injure a firefighter, there might be instances where they are carrying surplus electrical current from another source, such as a severed secondary line. Therefore, use caution when dealing with cable lines. If a pole is down, assume all lines are live.
When dealing with downed wires or fires in utility vaults or substations, patience is important. You must override your natural instincts and simply stand by. Do not use forcible entry metallic tools or raise ladders. Curtail all firefighting activities until a utility company supervisor arrives on the scene, cuts the power, and deems it safe to operate. There is no reason to risk firefighter lives to save equipment. Moreover, applying water to energized electrical equipment or transformers is ineffectual. The fire will continue to reignite until the power is cut.
POLE-MOUNTED TRANSFORMERS
Fires in overhead transformers can occur as a result of a voltage surge. Common transformers contain 50 to 75 gallons of dielectric mineral oil, though some can still contain PCBs that were used in the past to keep electrical equipment cool. Water and oil don’t mix; therefore, avoid using a hose stream to extinguish a transformer fire. It takes a very long time for flames to burn through a utility pole, so applying water to protect the pole is not usually necessary. Since flames impinging on primary wires above can cause them to fall, the best course of action is to create a safe zone of one span on either side of the transformer, keep onlookers back, and call the utility company. In the majority of cases, any firefighting activity will be curtailed until the power has been shut and confirmed to be off. Once the power has been cut, you can use dry chemical applied from an elevating platform to extinguish the burning oil, if necessary. If oil is pouring out, wear full personal protective equipment, dike nearby sewers, and notify a haz mat specialist so he can take samples. If at the request of a utility company supervisor water is used to protect exposed equipment or cool the cross arms before the power is off, apply it at a 30° fog pattern from a distance of at least 30 feet away. Apply the water from the flank at a safe distance so that if a wire fails, it will not fall on firefighters. The fire officer decides whether to use water after doing a risk/benefit analysis.
 (8) A pole-mounted transformer fire is both a class “B” and class “C” fire. Once power was cut, this fire was extinguished with a dry chemical extinguisher. (Photo by Jim Clark.) |
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MANHOLES
Manhole fires often occur in the winter when salt and snow runoff degrade the insulation on cables below the street. When the insulation degrades, the heat from the energized cables can cause them to smolder; the resultant built-up CO can cause manhole covers to blow. The CO can also back up into nearby basements and, with an explosive range of 12.5 percent to 74 percent, can cause secondary fires there. As with other utility equipment, do not apply water or foam until the power is cut by utility officials. Members should stay back a safe distance and avoid parking over or standing near manhole covers in the area. Once the power is cut, the burning insulation will usually self-extinguish. Consult with utility company officials before applying an extinguishing agent. Using water or foam to flood a vault below the street can displace CO and send it into adjacent vaults or basements. Manholes can contain high voltage and explosive gases. Do not enter manholes unless a life is at stake, and even then use extreme caution and enter under the guidance of a utility company supervisor after readings have been taken.
HIGH-VOLTAGE HYBRID VEHICLES
Hybrid vehicles are becoming more and more common in the United States. The Ford Escape, Lexus RX 400H, Toyota Prius, and Honda Insight are some of the hybrids already in production; others are to follow. Most of these companies have published emergency response guides that can be accessed on the Internet. You should become aware of the special hazards associated with these vehicles. In addition to an internal-combustion engine, hybrids contain specialized electrical systems that include +300 volt DC battery packs that supply 165 HP electric motors operating on 650 volts AC. These battery packs are usually located in the rear of the vehicle or under the back seat. Power is transmitted to the electrical engine under the hood through high-voltage cables situated under the floorboards. Do not cut, crush, or touch these cables during extrication or overhaul. At this time, there are no warnings advising against using water to extinguish fires in these vehicles. Nor is there any apparent danger of electric shock from touching the car body when it is partially or wholly submerged. Additional information is available at http://www.mufrti.org/download/hybridvehicles.zip/.
Electrocution on the fireground is an infrequent occurrence, partly because of caution, common sense, and a healthy dose of respect for the unpredictability of electrical current. Electrical wires are usually present on the fireground and at other emergency scenes. To operate safely, we must be aware of the hazards of electrical current and adjust operations accordingly.
Thanks to James Clark, Con Edison emergency operations supervisor; Lieutenants Matt Williams, Joe Forshaw, and Robert Rousseau of the Yonkers (NY) Fire Department; and James Pryor, electrical engineer, Cesco Inc., for their valuable assistance with this article.
DOUG LEIHBACHER is a 26-year veteran of the fire service and a battalion chief in the Yonkers (NY) Fire Department, currently assigned as chief of training. He has a bachelor’s degree in education and an associate’s degree in fire protection technology. He has served as a senior instructor at the Yonkers Fire Department Probationary Firefighter’s Training School and as an adjunct instructor at the Westchester County Training Center. He is a certified fire instructor, municipal training officer, fire investigator, and code enforcement officer. He has served as a classroom and hands-on instructor at FDIC and FDIC East and has been a contributing author to Fire Engineering since 1994. He has an associate’s degree in fire protection technology and a bachelor’s degree in education. He is a New York State-certified fire instructor and municipal training officer.
