OSHA standards focus on the design and use of electrical equipment and systems. The standards cover only the exposed or operating elements of an electrical installation such as lighting, equipment, motors, machines, appliances, switches, controls, and enclosures, requiring that they be constructed and installed to minimize workplace electrical dangers. Also, the standards require that certain approved testing organizations test and certify electrical equipment before use in the workplace to ensure it is safe.
Every good safety and health program provides measures to control electrical hazards. The measures suggested in this course should be helpful in getting a better understanding of Introduction to Electrical Safety practices and will introduce you to the electrical safety program. The responsibility for this electrical safety program should be delegated to someone with a complete knowledge of electricity, electrical work practices, and the appropriate OSHA standards for installation and performance.
Everyone has the right to work in a safe environment. Safety and health add value to your business and your workplace. Through cooperative efforts, employers and employees can learn to identify and eliminate or control electrical hazards.
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Electricity has long been recognized as a serious workplace hazard, exposing employees to electric shock, electrocution, burns, fires, and explosions. According to the Bureau of Labor Statistics, in 2016, 134 workers died from electrocutions, which represents a decrease from 174 in 2011. What makes these statistics tragic is that most of these fatalities could have been easily avoided.
The first step toward protecting yourself is recognizing the many hazards you face on the job. To do this, you must know which situations can place you in danger. Knowing where to look helps you to recognize hazards.
What is a "volt?" A Volt is a measure of the electrical force that seems to push the current along. Think of voltage as a lot of water stored in a high water tank. Because the water tank is high, the water will have more force behind it as it flows down the water pipe to your home. This is why they put water tanks up high! If the same tank was placed at ground level, your water pressure would not be as great. By the way, the symbols commonly used for voltage are "E" or "V".
What is an "ampere?" An ampere is the unit used to measure the amount of electrical current. Amperage is often referred to as "current" by electrical workers and engineers. Let's go back to our water tank. If the diameter of your pipe coming from the water tank is large, a lot of water (amperage) will flow through the pipe. If the pipe's diameter is small, a smaller amount of water will flow through the pipe. If you need a lot of current (many amps) to operate your equipment, you'll need large wires to run the current or they'll burn up! The symbol for amperage is "I".
What is an "ohm?" Think of an ohm as "resistance". An ohm is the unit used to measure the opposition (a.k.a. resistance) to the flow of electrical current. This is pretty easy to understand. A small water pipe is going to oppose a lot of water from flowing. Relatively little water will be able to flow through the pipe. So, the pipe offers a high resistance to the flow of water. You can see that a large pipe would offer little resistance to the flow of water. Big pipe: a lot of water! It's that simple. In an electrical circuit, components are usually sources of resistance. Any component that heats up due to electrical current is a source of resistance. The symbol for resistance is "R".
Electricity flows easier through some materials compared to others. Some substances such as metals generally offer very little resistance to the flow of electric current and are called "conductors." A common but perhaps overlooked conductor is the surface or subsurface of the earth. Glass, plastic, porcelain, clay, pottery, dry wood, and similar substances generally slow or stop the flow of electricity. They are called "insulators." Even air, normally an insulator, can become a conductor, as occurs during an arc or lightning stroke.
Pure water is a poor conductor. But small amounts of impurities in water like salt, acid, solvents, or other materials can turn water itself and substances that generally act as insulators into conductors or better conductors. Dry wood, for example, generally slows or stops the flow of electricity. But when saturated with water, wood turns into a conductor. The same is true of human skin. Dry skin has a fairly high resistance to electric current. But when skin is moist or wet, it acts as a conductor. This means that anyone working with electricity in a damp or wet environment needs to exercise extra caution to prevent electrical hazards.
Electricity travels in closed circuits, normally through a conductor. But sometimes a person's body — an efficient conductor of electricity — mistakenly becomes part of the electric circuit. This can cause an electrical shock. Shocks occur when a person's body completes the current path with:
An electric shock can result in anything from a slight tingling sensation to immediate cardiac arrest. The severity depends on the following:
A severe shock can cause considerably more damage than meets the eye. A victim may suffer internal hemorrhages and destruction of tissues, nerves, and muscles that aren't readily visible. Renal damage also can occur. If you or a coworker receives a shock, seek emergency medical help immediately.
This table shows the general relationship between the amount of current received and the reaction when current flows from the hand to the foot for just 1 second.
|1 milliamp||>Just a faint tingle.|
|5 milliamps||>Slight shock felt. Disturbing, but not painful. Most people can "let go." However, strong involuntary movements can cause injuries.|
9-30 milliamps (men)
|>Painful shock. Muscular control is lost. This is the range where "freezing currents" start. It may not be possible to "let go."|
|50-150 milliamps||>Extremely painful shock, respiratory arrest (breathing stops), severe muscle contractions. Flexor muscles may cause holding on; extensor muscles may cause intense pushing away. Heart fibrillation possible. Death is possible.|
|1,000-4,300 milliamps (1-4.3 amps)||>Rhythmic pumping action of the heart ceases. Muscular contraction and nerve damage occur; death likely.|
|10,000 milliamps (10 amps)||>Cardiac arrest and severe burns occur. Death is probable.|
|15,000 milliamps (15 amps)||>Lowest overcurrent at which a typical fuse or circuit breaker opens a circuit!|
*Effects are for voltages less than about 600 volts. Higher voltages also cause severe burns.
Differences in muscle and fat content affect the severity of shock.
Burns are the most common shock-related injury. An electrical accident can result in an electrical burn, arc burn, thermal contact burn, or a combination of burns.
Electrical burns are among the most serious burns and require immediate medical attention. They occur when electric current flows through tissues or bone, generating heat that causes tissue damage.
Arc or flash burns result from high temperatures caused by an electric arc or explosion near the body. These burns should be treated promptly.
Thermal contact burns are caused when the skin touches hot surfaces of overheated electric conductors, conduits, or other energized equipment. Thermal burns also can be caused when clothing catches on fire, as may occur when an electric arc is produced.
In addition to shock and burn hazards, electricity poses other dangers. For example, arcs that result from short circuits can cause injury or start a fire. Extremely high-energy arcs can damage equipment, causing fragmented metal to fly in all directions. Even low-energy arcs can cause violent explosions in atmospheres that contain flammable gases, vapors, or combustible dusts.
The U.S. Department of Energy (DOE) Electrical Safety Guidelines classify high voltage as over 600 volts. OSHA also classifies any use of electrical service over 600 volts as high voltage, and requires that permanent warning signs that read, "DANGER-HIGH VOLTAGE - KEEP OUT," be posted.
Sometimes high voltages lead to additional injuries. High voltages can cause violent muscular contractions. You may lose your balance and fall, which can cause injury or even death if you fall into machinery that can crush you. High voltages can also cause severe burns.
At 600 volts, the current through the body may be as great as 4 amps, causing damage to internal organs such as the heart. High voltages also produce burns. In addition, internal blood vessels may clot. Nerves in the area of the contact point may be damaged. Muscle contractions may cause bone fractures from either the contractions themselves or from falls.
When a person receives an electrical shock, sometimes the electrical stimulation causes the muscles to contract. This "freezing" effect makes the person unable to pull free of the circuit. It is extremely dangerous because it increases the length of exposure to electricity and because the current causes blisters, which reduce the body's resistance and increases the current.
The longer the exposure, the greater the risk of serious injury. Longer exposures at even relatively low voltages can be just as dangerous as short exposures at higher voltages. Low voltage does not imply low hazard.
In addition to muscle contractions that cause "freezing," electrical shocks also can cause involuntary muscle reactions. These reactions can result in a wide range of other injuries from collisions or falls, including bruises, bone fractures, and even death.
If a person is "frozen" to a live electrical contact, shut off the current immediately. If this is not possible, use boards, poles, or sticks made of wood or any other nonconducting materials and safely push or pull the person away from the contact. It's important to act quickly, but remember to protect yourself as well from electrocution or shock.
Static electricity also can cause a shock. However, static electricity causes a shock in a different way and is generally not as severe as the type of shock described earlier.
Static electricity can build up on the surface of an object and under the right conditions, can discharge to a person. This causes a shock. The most familiar example of this is when a person reaches for a door knob or other metal object on a cold, relatively dry day and receives a shock.
However, static electricity also can cause shocks or can just discharge to an object with much more serious consequences. For example, when friction causes a high level of static electricity to build up at a specific spot on an object, it can cause serious consequences. This can happen simply through handling plastic pipes and materials or during normal operation of rubberized drive or machine belts found in many worksites.
In these cases, for example, static electricity can potentially discharge when sufficient amounts of flammable or combustible substances are located nearby and cause an explosion. Grounding or other measures may be necessary to prevent this static electricity buildup and the results.
Overloads in an electrical system are hazardous because they can produce heat or arcing. Wires and other components in an electrical system or circuit have a maximum amount of current they can carry safely. If too many devices are plugged into a circuit, the electrical current will heat the wires to a very high temperature. If a tool uses too much current, the wires will heat up.
The temperature of the wires can be high enough to cause a fire. If their insulation melts, arcing may occur. Arcing can cause a fire in the area where the overload exists, even inside a wall.
To prevent too much current in a circuit, a circuit breaker or fuse is placed in the circuit. If there is too much current in the circuit, the breaker "trips" and opens like a switch. If an overloaded circuit is equipped with a fuse, an internal part of the fuse melts, opening the circuit. Both breakers and fuses do the same thing: open the circuit to shut off the electrical current.
If the breakers or fuses are too big for the wires they are supposed to protect, an overload in the circuit will not be detected and the current will not be shut off. Overloading leads to overheating of circuit components (including wires) and may cause a fire.
You must recognize that a circuit with improper overcurrent protection devices - or one with no overcurrent protection devices at all - is a hazard.
Now that we've looked at the basics of electricity and associated hazards, we'll discuss how to protect yourself against electrical hazards in Module 2.
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In this WorkSafeBC video, a house painter contacts a power line with a ladder. A work plan should always be created by a supervisor and communicated to all workers on site to reduce the risk of electrical contact.