Electrical Safety, Arc-Flash Hazard, Switching Practices,and Precautions:Electrical Fire Emergencies

Electrical Fire Emergencies

This section is written as a guide for fire fighting personnel for handing electrical fire emergencies. Electrical personnel are not usually fire fighting experts but, because of their knowledge of electricity, they can provide vital and helpful information to others who are involved in fighting fires. Therefore, a cooperative effort is needed among the various groups when dealing with electrical emergencies. The various safety considerations dealing with such emergencies are discussed next.

Never Make Direct Contact with Any Energized Object

Electricity, whether from a power line or from a thundercloud, is always trying to get to the earth, which is at ground voltage—also called zero voltage. Voltage is a measure of the pressure that pushes electric charge through a conductor. An object with any voltage above zero is called energized. Any energized object will produce a flow of electric charge through a conductor placed between it and the earth or any other object at ground voltage, such as a grounded wire. Since nearly all common materials—including the human body—are conductors to some extent, the only way to keep the electricity where it belongs is to place some sort of insulator (nonconductor) between the energized object and the earth.

One can get just as shocked from l20 V house current as one can from a 500,000 V power line! In fact, a HV shock, because of the clamping action it has on the heart (cardiac arrest), may prevent the deadly irregular beating of the heart (fibrillation) often associated with lower-voltage shocks. Cardiac-arrest victims often respond readily to artificial respiration and external heart massage, whereas a fibrillation victim may only respond to an electrical defibrillator device. Also with the lower-voltage shock, instead of enough current to knock you out, you may get just enough to set your muscles so you cannot let go.

Stay Clear of Vicinity of Any Faulty Energized Object

One can be injured without touching an energized object. When an energized object is sparking, it emits excessive heat and ultraviolet rays. Such sparking occurs while trying to interrupt the flow of electric charge, such as when an energized wire is cut or when a fallen energized wire is lifted away from the earth. The electric charge tries to maintain its flow through the air—this results in a flash, an electric arc. The excessive heat from such a flash can bum human flesh several feet away.

The heat of an electric arc has been known to fuse contact lenses to the cornea of a human’s eyes. Ultraviolet rays emitted from an electric flash may also damage unprotected eyes. Eye injuries may not be immediately apparent there may be no noticeable eye irritation for several hours after exposure. If your eyes are exposed to an electric arc, consult a doctor for proper treatment without delay. Electrical employees should wear specially treated goggles to prevent ultraviolet ray damage whenever an electric arc may occur.

Be Alert in Vicinity of Any Energized Object

We have already emphasized the danger from contacting an energized object, or even getting in the vicinity of a faulty energized object, such as a fallen wire. It is just as important to be cautious in the vicinity of energized facilities that are operating properly. Most electrical emergency work is performed without de-energizing all electric facilities in the vicinity. In many cases, it is even advantageous to leave power on as long as possi- ble. However, all personnel must continuously be alert. Do not let the quiet, harmless appearance lull you into a false sense of security.

Beware of Covered Wires

Many overhead wires are covered. But, that covering is often designed to protect the wire from the weather or tree contact, not to protect you from the wire. Never consider a covered wire any safer than a bare wire. And remember, most wires on utility poles are bare, even though they may appear to be covered when viewed from the ground.

Beware of Telephone Cables

Telephone cables are rarely dangerous when accidentally contacted. But, are you so sure you can tell the difference between telephone cable and electric power cable, that you do stake your life on it—and the lives of others? Although higher voltage facilities are generally installed higher up on utility poles, this is not true always—electric power cables operating at 34,000 V may be attached below telephone cables on the same pole. And a fallen telephone cable may be contacting a power line!

• Never rest ladders on wires or on any other electric equipment

• Never drag hose over wires

• Never even come too close to wires—brushing against one can be fatal

You may have had some experience where you were able to contact energized facilities without incident. But, just because you “got away with it” before does not guarantee you will get away with it again. And remember, higher-voltage facilities have much greater pressure behind the electricity— something you “got away with” on 120 V facilities can bring disaster if attempted on 34,000 V facilities. And since normal water is a conductor of electricity, even slightly damp objects become much more hazardous.

Assume Every Fallen Wire Is Energized and Dangerous

Wire on Ground

Some fallen wires snap and twist-bursting warning sparks. Others lie quietly —no sparks, no warning rattles like a snake. Both types are equally deadly.

It is impossible to determine from the appearance of a wire whether or not it is energized. Also, automatic switching equipment may reenergize fallen wires. Always stay clear and keep everyone else clear until an electric company employee arrives and clears the wire or de-energizes it.

Wire on Object

If a wire is in contact with any object—fence, tree, car, or person—that object in turn may be energized and deadly. Keep yourself and others away from metal highway dividers and metal fences that may be in contact with fallen wires. A fallen wire draped over such dividers and fences can energize them for their entire length.

Wire on Vehicle

If anyone is in a vehicle which is in contact with a wire, the safest thing he or she can do is stay inside. If possible, he or she should drive the vehicle away from the contact. If the vehicle is on fire, tell him or her to jump free with both hands and feet clear of the vehicle when hitting the ground. At no time can the person simultaneously touch both the vehicle and the ground or any other object that is touching the ground, such as yourself. If he or she does, he or she will become a path for the electricity to flow to ground. Never board a vehicle that may be energized. A spray or fog nozzle should be used to direct water onto a burning vehicle—even then, stay back as far as practicable (at least 6 ft) whenever the wire on a vehicle may be energized.

Never Cut Wires Except to Protect Life

And even then, only thoroughly trained persons, such as electric company employees, using approved procedures and equipment can cut wires. Otherwise cutting wires can create more hazards than leaving them alone. When taut wires are cut, the change in tension may cause utility poles to fall or wires to slack off and sag to the ground some distance from where the wires are cut. Wire which retains some of its original “reel-curl” may coil up when cut and get out of control with resultant hazards.

Take Care after Cutting

Cutting a wire at one place does not necessarily ensure that the wire on either side of the cut is de-energized because

• Wires are frequently energized from both directions.

• Wires may be in accidental contact with other energized wires.

• Wires may be energized from a privately owned generator within a building.

Cutting Service Wires

When protection of life requires de-energizing a building, cutting service wires should be considered only when it is not practicable to remove fuses, open-circuit breakers, open the main switch, or wait for an electric company representative. Specialized equipment must be used to cut each wire individually and then bend each one back, to prevent short-circuiting the wires together.

All wires must be cut. Never assume that one wire is a ground wire and is therefore safe. Even a ground wire may be contacting an energized wire at some unseen location. If the service wires can be cut on the supply side of where they connect to the building’s wires, it will be possible to restore the service more quickly when required. However, far more important, service wires should always be cut on the building side of where they are first attached to the building—this avoids having wires fall on the ground.

Use Approved Procedures and Equipment If You Must Work Near Energized Facilities This rule certainly applies whether or not there is any victim to be rescued. However, the presence of a victim requires you to be even more conscientious. Follow recommendations given in safety standards, such as ANSI C2, OSHA regulations, NFPA 70E, and your company’s safety guide.

Notify the electric company: If you see no safe way of separating a victim from an energized object, request the electric company’s assistance. Your first consideration must be your own protection—you cannot help by becoming a victim yourself.

Moving the victim: Electric company employees have specialized equip- ment that they can use to drag a victim clear of electric equipment. They can use other specialized equipment to keep the wire in contact with the ground while the victim is being dragged clear—this reduces the amount of electric- ity flowing through the victim and minimizes further injury from additional burns.

Moving the wire: Electric company employees have specialized equipment that they can use to remove a wire from a victim. They can control the wire to prevent it from recontacting the victim. Electric company employees will put the wire toward themselves while walking away—rather than pushing and walking toward it—to reduce the danger to themselves in case the wire gets out of control. And, again, they can use other specialized equipment to keep the wire in contact with the ground while moving it—this reduces the amount of electricity flowing through the victim and minimizes further injury from additional bums.

Cutting the wire: If a victim is entangled with an electric wire, the wire on both sides of the victim must be cut to be certain that no source of electricity remains. Wires should only be cut by an individual who is thoroughly trained to cut wires safely and who uses specialized equipment.

First aid: A victim who has been separated from energized electric facilities does not retain an electric charge—so there is no danger in handling the victim, administering first aid, or applying artificial respiration. Electric bums, even if insignificant on the surface, may involve serious destruction of tissues and must receive expert medical treatment as soon as possible.

Avoid Using Hose Streams on Energized Facilities

The application of water on electric facilities by handheld hoses may carry the electricity back to the nozzle. This electricity might be sufficient to cause serious injury. Tabularized safe distances can be misleading, since water conductivity and nozzle design vary widely. The National Board of Fire Underwriters’ Special Interest Bulletin No. 91 advises that for 120 V facilities there is no danger unless the nozzle is brought within a few inches. However, fire fighters should consider all electric facilities to be HV, because even low-voltage wires may inadvertently be crossed with HV wires.

Spray or fog preferred: For maximum safety to the fire fighter, when either intentional or unintentional application of water on energized facilities may occur, a spray or fog nozzle should be used.

Beware of run-off water: A dangerously energized puddle of water may be formed by water running off energized electric facilities.

Beware of adjacent equipment: Take care not to damage uninvolved electric facilities nearby. A porcelain insulator supporting energized facilities may flashover (arc), and even explode, if hit by a straight stream (even spray or fog) directed onto it. Wires may swing together, short-circuit, and bum down if hit by the force of a straight stream.

Other extinguishing agents: Dry chemical and carbon dioxide are non- conductive and may be used around energized facilities. These may be used to extinguish a surface-type utility pole fire. Foam, soda acid, and the loaded-stream type are conductive and should not be used on fires around energized facilities.

Be Equally Alert Indoors and Outdoors

Medium-voltage installations: Medium-voltage services do exist in many larger buildings—commercial, institutional, and industrial facilities. Do not enter any transformer room or open any electric switch without the advice of an authorized individual. Besides the obvious electric hazard, privately owned transformers may be filled with flammable oil or with nonflammable liquids. Such equipment is not required to be isolated outdoors or in a fire resistant room and therefore may be located anywhere on the premises. The non-flammable liquid, while safe from a fire standpoint, may be caustic and may generate poisonous fumes. Call the plant electrician to identify specific hazards and to de-energize facilities as needed.

Low-voltage installations: Low-voltage services exist in practically every building and can be as dangerous as medium-voltage facilities.

Leave power on as long as possible: The power may be needed to operate pumps or other equipment which, if stopped, would cause additional damage to the building or to any materials being produced in it.

Remove fuses or open-circuit breakers: To shut off an affected section, remove fuses or open-circuit breakers.

Open main switch: Open the main switch to shut off entire building when electric service is no longer useful. If you must stand in water or if the switch is wet, do not grasp the switch handle in the palm of your hand. Use dry equipment such as a piece of rope, pike pole, or handle of fire axe to open the switch. Then attach a warning tag indicating that the power has been inten- tionally shut off.

Cut wires only to protect life: Cut wires only when life would be endangered by leaving a building energized, or when a victim must be rescued. However, cutting electric wires should only be considered when it is not practicable to remove fuses, open-circuit breakers, open the main switch, or wait for an electric company representative.

Pull electric meter: Pull the electric meter only to protect life when no other method is practicable. Wear gloves and face shield or goggles to protect against electric arcing. Meters at most large buildings, as well as many house meters, can produce extensive arcing when removed—especially if the inte- rior wiring is faulty. In addition, removing some meters does not interrupt the power. Such meters should be identified by a small label reading “CAUTION: Apply Jumpers Before Removing Meter.” If a meter is removed, cover panel to protect the public, and notify the electric company.

Flammable fumes: Whenever flammable fumes may be present, avoid operating any electric switch within the area—even a simple light switch— because even a small spark can cause an explosion.

Palms inward: When walking through a building or any enclosure where visibility is poor, proceed with arms outstretched and the palms of the hands turned toward the face. In this way, if contact is made with an energized object the tendency of the muscles to contract may assist in getting free from the contact.

Protect People and Property in Surrounding Area and Do Not Fight Fires on Electric Equipment Until an Electric Company Representative Arrives Where electric power equipment is involved, wait for the electric company representative and coordinate the fire fighting operation with him or her to ensure maximum effectiveness and safety. Cooperate with his or her requests because he or she knows what is necessary to fight fires on his or her equipment.

Danger from switches: Never operate electric company switches that are mounted on utility poles or located in manholes or within substation proper- ties. Many of these switches are not intended to open and drop the electric load, and attempting such an operation could damage the switch and even cause it to explode.

Danger from oil: Oil may be present in any pole—mounted, underground, or surface equipment, such as transformers. This oil will bum. Under the intense heat of a fire, the equipment may even rupture and spray its burning oil. This may be followed by subsequent explosions caused by ignition of the mixture of air with hot oil vapor or with burning insulation vapor.

Danger from water: Water greatly increases the danger of electrocution from energized facilities. Until it is confirmed that electric facilities are de- energized, use only dry chemicals, carbon dioxide, water sprays, or fog—and even then, take extreme care to avoid physical contact with energized facili- ties. Also, take care not to direct a straight stream onto uninvolved electric facilities nearby.

Contain liquids leaked from equipment: Any liquid leaked from electri- cal equipment may be flammable oil or a nonflammable liquid. Avoid contact with these liquids—they may be caustic and fumes may be irritating. Both types of liquids must be thoroughly cleaned up by appropriate personnel to prevent environmental damage. After extinguishing any fire, try to contain any leaked liquid—use absorbent granules, dry sand, ashes, or sawdust. Do not wash it away with a hose system.

Hose Streams May Be More Hazardous than Helpful Until Any Underground Fault Is De-Energized Electric wires are installed underground in industrial plants, many urban areas, and new residential developments. Switching equipment and trans- formers are installed in manholes or in metal cabinets on the surface, and they supply electricity through an interconnected network of electrical cables. Both high- and low-voltage cables may be directly buried beneath only 2 or 3 ft of earth—or they may be installed in ducts. The two major causes of fires are:

• Cable faults that ignite the cable insulation, or the fiber duct, or both

• Oil-filled manhole equipment which overheats and spills oil that ignites

Notify electric company: Specify location of all manholes involved. A cable fault usually clears itself, or it can be cleared manually by opening appropriate switches. Until the fault which caused the fire is de-energized, no attempt should be made to extinguish the fire. An electric arc cannot be extinguished by fire fighting techniques, and the arc is sustaining the fire.

Clear the area: Under normal conditions, the insulation and jacketing of underground cables provide adequate protection. However, an explosion or fire can remove these protective coverings and expose the energized conductors. Such a condition is a major hazard, and fire fighting personnel are cautioned to stay clear.

Beware of toxic or explosive gases: Flammable vapors, which are not always detectable by sense of smell, may be coming from (1) nearby sewers, (2) gas mains, or (3) buried gasoline or oil storage tanks, as well as from (4) smoldering insulation and fiber duct. Inside a duct, the vapor–air mixture may be too rich to ignite. Upon reaching a source of fresh air, such as a manhole, the vapor–air mixture may fall within the explosive limits. The resulting explosions may be intermittent, with their frequency depending on how fast the vapors are coming out and mixing with the air. They may vary in intensity from a slight puff to an explosion of sufficient violence to blow a manhole cover high in the air. If the mixture becomes too rich to ignite within the confined space of a manhole, an explosion may occur when the manhole cover is removed.

Prepare to assist electric company employees: The electric company may discharge water into a duct line to cool it after the circuit has been de-energized. If a hose line is supplied by the local fire company, let the electric company employees handle the nozzle, using their approved rubber gloves for protection.

Leave manhole covers as found: Only electric company employees should remove manhole covers using hooks or long-handled tools and standing safely to one side. And everyone must be kept at a reasonable distance back to avoid injury. Removing manhole covers may help to ventilate the conduit system and pin down the location of the fault. However, removing a manhole cover may reignite flammable vapors—or even cause low-order explosions, if the atmosphere was too rich to bum before removing it.

Never direct water into a manhole: Until requested by the electric company representative, never direct water into a manhole. The source of the fire and any other facilities that might be damaged must be de-energized before water can be used safely and effectively.

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