Electricity has become essential to modern life. Perhaps because it is such a familiar part of our surroundings, it often is not treated with the respect it deserves. Safety and health programs must address electrical incidents and the variety of ways electricity becomes a hazard. In general, OSHA requires that employees not work near any part of an electrical power circuit unless protected. The following hazards are the most frequent cause of electrical injuries [29 CFR 1926.416(a)(1)]:
Am I In Danger?
Overhead and buried power lines at your site are especially hazardous because they carry extremely high voltage. Fatal electrocution is the main risk, but burns and falls from elevations are also hazards. Using tools and equipment that can contact power lines increases the risk.
Examples of Equipment That Can Contact Power Lines
How Do I Avoid Hazards?
Scaffold Too Close To Power Line:
Seven employees of a masonry company were erecting a brick wall from a tubular, welded-frame scaffold approximately 24 feet high. The scaffold had been constructed only 21 horizontal inches across from a 7,620-volt power line. A laborer carried a piece of wire reinforcement (10 feet long by 8 inches wide) along the top section of the scaffold and contacted the power line with it. The laborer, who was wearing leather gloves, received an electric shock and dropped the wire reinforcement, which fell across the power line and simultaneously contacted the metal rail of the scaffold, energizing the entire scaffold. A 20-year-old bricklayer standing on the work platform in contact with the main scaffold was electrocuted.
Crane Boom Too Close To Power Line:
A 56-year-old construction laborer was removing forms from a concrete wall poured several days earlier. As he removed the forms, he wrapped them with a length of cable called a choker, which was to be attached to a crane. The victim signaled the operator of the crane to extend the boom and lower the hoist cable. Both the operator and the victim failed to notice that the boom had contacted a 2,400-volt overhead power line. When the victim reached down to connect the choker to the hoist cable, he suddenly collapsed. Co-workers provided CPR, but were unable to revive the victim. Only after a rescue squad arrived about 4 minutes later did anyone realize that the crane was in contact with a power line -- all those present had assumed that the victim had suffered a heart attack.
Crane Boom Swung Into Power Line:
A 29-year-old worker was electrocuted when he pushed a crane cable into a 7,200-volt power line. The victim was part of a crew that was constructing a concrete wall. Before work began, the company safety director made sure that insulated line hoses were placed over sections of the the power line near the jobsite and that a safety clearance zone was marked off for arriving cement trucks. After the wall was poured, one driver cleaned the loading chute of his cement truck with a water hose mounted on the truck. As he began to pull away, the crew supervisor yelled to him, asking if the crew could use his water hose to wash out their cement bucket suspended from the crane. The driver stopped the truck under the power line, and the victim, not realizing that the truck had moved, swung the boom to position the bucket behind the truck. When he grasped the handle of the bucket to pull it down, the crane cable came into contact with the overhead line. The victim provided a path to ground and was electrocuted.
Am I In Danger?
Due to the dynamic, rugged nature of construction work, normal use of electrical equipment at your site causes wear and tear that results in insulation breaks, short-circuits, and exposed wires. [Flexible Cords and Power Tools] If there is no ground-fault protection, these can cause a ground-fault that sends current through the worker's body, resulting in electrical burns, explosions, fire, or death.
How Do I Avoid Hazards?
No Ground-Fault Circuit Interrupters (GFCIs):
A journeyman HVAC worker was installing metal duct work using a double-insulated drill connected to a drop light cord. Power was supplied through two extension cords from a nearby residence. The individual's perspiration-soaked clothing/body contacted bare exposed conductors on one of the cords, causing an electrocution. No GFCI's were used. Additionally, the ground prongs were missing from the two cords.
Am I In Danger?
If the power supply to the electrical equipment at your site is not grounded or the path has been broken, fault current may travel through a worker's body, causing electrical burns or death. [Flexible Cords and Power Tools]. Even when the power system is properly grounded, electrical equipment can instantly change from safe to hazardous because of extreme conditions and rough treatment.
How Do I Avoid Hazards?
Ground Wire Not Attached:
A fan connected to a 120-volt electrical system via an extension cord provided ventilation for a worker performing a chipping operation from an aluminum stepladder. The insulation on the extension cord was cut through and exposed bare, energized conductors which made contact with the ladder. The ground wire was not attached on the male end of the cord's plug. When the energized conductor made contact with the ladder, the path to ground included the worker's body, resulting in death.
Adapter For 3-Prong Cord Not Grounded To Outlet:
On May 27, 1986, two workers were using a 110-volt auger to install tie-down rods for a manufactured home. The auger has a one-quarter horsepower motor encased in a metal housing with two handles. One handle has a deadman's switch. Electricity to the auger was supplied by a series of 50-foot extension cords running to an adjacent property. Since the outlet at the adjacent property had no socket for a ground prong, the extension cords were plugged into the outlet using an adapter, but the ground wire of the adapter was not grounded. Two of the extension cords had no ground prongs, and some of them were repaired with electrical tape. The workers had removed their shirts and were sweating. One worker, holding the deadman's switch, received a shock from a ground fault in the auger and was knocked back from the machine. The auger then fell across the other worker, the 24-year-old victim. The first worker knocked the auger off the victim, but saw that the electric cord was wrapped around the victim's thigh. He yelled for his co-workers to disconnect the power, which they did. The workers administered CPR to the victim, but to no avail.
Short In Power Saw/Ungrounded Temporary Power Supply:
On July 10, 1986, a 22-year-old carpenter was working at the construction site of large apartment complex, using a portable electric saw to construct the wooden framework of a laundry building. Electricity to operate portable power tools was supplied by a temporary service pole 50 feet away. The pole had not been inspected by the city and was not in compliance with code requirements (it was not grounded). The victim used two extension cords to supply power: a home-made cord plugged into an ungrounded receptacle on the pole, and a UL-approved cord extending from the homemade cord to the saw. The accident site was wet; also, humidity was high and the victim was sweating. Reportedly, he was shocked throughout the morning, and he had replaced one of the extension cords in an effort to eliminate the shocks. The source of the shocks -- the saw -- was not replaced. As the victim climbed down a makeshift ladder, he shifted the saw from his right hand to his left, and was shocked. This caused him to fall from the ladder and land in a puddle of water, still holding the saw. Apparently, his hand contracted and he was "locked" to the saw. A co-worker disconnected the power cord to the saw, too late to save the victim.
Am I In Danger?
If electrical equipment is used in ways for which it is not designed, you can no longer depend on safety features built in by the manufacturer. This may damage your equipment and cause employee injuries. [Power Tools]
Common Examples of Misused Equipment
How Do I Avoid Hazards?
Damaged Extension Cord Leaves Arc Welder Ungrounded:
A 29-year-old welder attempted to connect a portable arc welder to an electrical outlet using an extension cord. The power switch on the welder was already in the "on" position, and the female end of the extension cord, which was spring loaded, had apparently been dropped and broken. As a result, the ground prong of the welder plug did not insert into the ground terminal of the cord, so that as soon as a connection was made, the outside metal case of the welder became energized, electrocuting the victim. An examination revealed that the spring, cover plate, and part of the melamine casing were missing from the face of the female connector (the spring and some melamine fragments were found at the accident site). The victim was totally deaf in one ear and suffered diminished hearing in the other. He may have dropped the extension cord at the site and not heard the connector break.
Handling Damaged Extension Cord When Energized:
A 19-year-old construction laborer was working with his foreman and another laborer to construct a waterfront bulkhead for a lakeside residence. Electricity for power tools was supplied from an exterior 120-volt, grounded AC receptacle located at the back of the residence. On the day of the incident, the victim plugged in a damaged extension cord and laid it out towards the bulkhead. There were no eyewitnesses to the accident, but evidence suggests that while the victim was handling the damaged and energized extension cord, he provided a "path to ground" and was electrocuted. The victim collapsed into the lake and sank 4-1/2 feet to the bottom.
Electrical Equipment In Poor Condition:
An 18-year-old worker at a construction site was electrocuted when he touched a light fixture while descending from a scaffold for his afternoon break. The source of the electricity was apparently a short in a receptacle, but examination revealed that the electrical equipment used by the contractor was in such poor condition that it was impossible to make a certain determination of the source of the short. Extension cords had poor splices, no grounds, and reversed polarity. One hand drill was not grounded, and the other had no safety plate. Out of several possible scenarios, the most likely was contact between the exposed wires of an extension cord and a screw that protruded from the receptacle, which had its face plate removed. The light fixture, which served as a ground, was known to be faulty for at least 5 months before the incident.
Improper Modification of Plugs:
An employee was texturing a wall using an air compressor. The plug of the compressor and an extension cord had been modified to fit a wall outlet for a common household clothes dryer (220 V). While attempting to unplug the compressor from the extension cord, the employee was fatally shocked. The modification of the plug was not an intended use or prescribed by the manufacturer.
Am I In Danger?
The normal wear and tear on extension and flexible cords at your site can loosen or expose wires, creating hazardous conditions. [Flexible Cords] Cords that are not 3-wire type, not designed for hard-usage, or that have been modified, increase your risk of contacting electrical current.
How Do I Avoid Hazards?
Flexible Cord Not 3-Wire, Hard Service Variety:
A worker received a fatal shock when he was cutting drywall with a metal casing router. The router's 3-wire power cord was spliced to a 2-wire cord and plug set which was not rated for hard service. A fault occurred, and with no grounding and no GFCI protection, the worker was electrocuted.
No Strain Relief:
A worker was operating a ¾" electric chisel when an electrical fault occurred in the casing of the tool, causing him to be fatally electrocuted. An OSHA inspection revealed that the tool's original power cord had been replaced with a flat cord, which was not designated for hard service, and that strain relief was not provided at the point where the cord entered the tool. Additionally, the ground prong was missing and there was no GFCI protection.
Operating an electrical switch is like turning on a water faucet. Behind the faucet (or switch) there is a source of water (or electricity), a way to transport it, and pressure to make it flow. The faucet's water source is a reservoir or pumping station. A pump provides enough pressure for the water to travel through the pipes. The switch's electrical source is a power generating station. A generator provides the pressure for the electrical current to travel through electrical conductors, or wires.
Three factors determine the resistance of a substance to the flow of electricity.
Substances with very little resistance to the flow of electricity are called conductors. Examples are metals. Substances with a high resistance to the flow of electricity are called insulators. Examples are glass, porcelain, plastic, and dry wood.
Pure water is a poor conductor of electricity, but small amounts of impurities, such as salt and acid, make it a ready conductor. Perspiration contains both water, salts, and impurities. When the skin is dry, it is a poor conductor of electrical current. When it is moist, it readily conducts electricity. Use extreme caution when working with electricity where there is water in the environment or on the skin. This concept applies to other items such as wood. When wood is dry it is a poor conductor, when wet wood conducts electricity more readily.
Electricity travels in closed circuits, normally through a conductor. Shock results when the body becomes part of the electrical circuit; current enters the body at one point and leaves at another. Typically, shock occurs when a person contacts:
Metallic parts of electric tools and machines can become energized if there is a break in the insulation of their wiring. A low-resistance wire between the metallic case of the tool/machine and the ground - an equipment grounding conductor - provides a path for the unwanted current to pass directly to the ground. This greatly reduces the amount of current passing through the body of the person in contact with the tool or machine. Properly installed, the grounding conductor provides protection from electric shock.
Three primary factors affect the severity of the shock a person receives when he or she is a part of an electrical circuit:
Other factors that may affect the severity of the shock are:
Effects can range from a barely perceptible tingle to severe burns and immediate cardiac arrest. Although it is not known the exact injuries that result from any given amperage, the following table demonstrates this general relationship for a 60-cycle, hand-to-foot shock of one second's duration:
Probable Effect on Human Body
|Perception level. Slight tingling sensation. Still dangerous under certain conditions.|
|Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary reactions to shocks in this range may lead to injuries.|
6mA - 16mA
|Painful shock, begin to lose muscular control. Commonly referred to as the freezing current or "let-go" range.|
17mA - 99mA
|Extreme pain, respiratory arrest, severe muscular contractions. Individual cannot let go. Death is possible.|
100mA - 2000mA
|Ventricular fibrillation (uneven, uncoordinated pumping of the heart.) Muscular contraction and nerve damage begins to occur. Death is likely.|
|Cardiac arrest, internal organ damage, and severe burns. Death is probable.|
Wet conditions are common during low-voltage electrocutions. Under dry conditions, human skin is very resistant. Wet skin dramatically drops the body's resistance.
Dry Conditions: Current = Volts/Ohms = 120/100,000 = 1mA a barely perceptible level of current
Wet conditions: Current = Volts/Ohms = 120/1,000 = 120mA sufficient current to cause ventricular fibrillation
If the extensor muscles are excited by the shock, the person may be thrown away from the circuit. Often, this can result in a fall from elevation that kills a victim even when electrocution does not.
When muscular contraction caused by stimulation does not allow the victim to free himself from the circuit, even relatively low voltages can be extremely dangerous, because the degree of injury increases with the length of time the body is in the circuit. LOW VOLTAGE DOES NOT IMPLY LOW HAZARD!
100mA for 3 seconds = 900mA for .03 seconds in causing fibrillation
Note that a difference of less than 100 milliamperes exists between a current that is barely perceptible and one that can kill.
High voltage electrical energy greatly reduces the body's resistance by quickly breaking down human skin. Once the skin is punctured, the lowered resistance results in massive current flow.
Ohm's law is used to demonstrate the action. At 1,000 volts, Current = Volts/Ohms = 1,000/500 = 2 Amps which can cause cardiac arrest and serious damage to internal organs.
Please be advised these images are of a graphic nature.
Shock-related injuries include burns, internal injuries, and injuries due to involuntary muscle contractions.
The most common shock-related injury is a burn. Burns suffered in electrical incidents may be one or more of the following three types:
Electrical burns cause tissue damage, and are the result of heat generated by the flow of electric current through the body. Electrical burns are one of the most serious injuries you can receive and should be given immediate attention.
High temperatures near the body produced by an electric arc or explosion cause arc or flash burns. They should also be attended to promptly.
Thermal contact burns occur when skin comes in contact with overheated electric equipment, or when clothing is ignited in an electrical incident.
Excessive electricity flowing through the human body can cause serious damage to internal organs. Resulting medical problems include hemorrhage (or internal bleeding), tissue destruction, and nerve or muscle damage. These internal injuries may not be immediately apparent to the victim or observers; however, left untreated, they can result in death.
Normal muscle contraction is caused by very small amounts of electricity that are created within our bodies. Muscles violently contract when stimulated by excessive amounts of electricity. These involuntary contractions can damage muscles, tendons, and ligaments, and may even cause broken bones. If the victim is holding an electrocuting object, hand muscles may contract, making it impossible to drop the object and prolonging contact with the current. Also, injury or death may result when violent muscle contractions cause workers to fall from ladders and scaffolds or inadvertently strike other objects.
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