Whenever you work with power tools or on electrical circuits, there is a risk of electrical hazards, especially electrical shock. Anyone can be exposed to these hazards at home or at work. Workers are exposed to more hazards because job sites can be cluttered with tools and materials, fast-paced, and open to the weather. Risk is also higher at work because many jobs involve electric power tools.
Electrical workers must pay special attention to electrical hazards because they work on electrical circuits, and contact can cause electrical current to flow through the body, resulting in shock and burns. Serious injury or even death may occur.
As a source of energy, electricity is used without much thought about the hazards it can cause. Because electricity is a familiar part of our lives, it often is not treated with enough caution. As a result, an average of one worker is electrocuted on the job every day of every year!
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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. If the same tank was placed at ground level, your water pressure would not be as great. 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. Using our water analogy: 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".
What is a "series" circuit? The current in a series circuit takes only one path. For example, water from high in the mountains may flow down one stream (series) into a river that flows to the ocean.
What is a "parallel" circuit? The current in a parallel circuit takes many paths. For example, the water flowing from a water tank up on a hill will flow through many different water pipes (parallel) before it reaches the ocean.
The severity of injury from electrical shock depends on the amount of electrical amperage (current) and the length of time the current passes through the body. For example, 1/10 of an ampere (amp) of electricity going through the body for just 2 seconds is enough to cause death.
The amount of internal current a person can withstand and still be able to control the muscles of the arm and hand can be less than 10 milliamperes (milliamps or mA).
Currents above 10 mA can paralyze or "freeze" muscles. When this "freezing" happens, a person is no longer able to release a tool, wire, or other object. In fact, the electrified object may be held even more tightly, resulting in longer exposure to the shocking current. For this reason, hand-held tools that give a shock can be very dangerous.
If you can't let go of the tool, current continues through your body for a longer time, which can lead to respiratory paralysis (the muscles that control breathing cannot move) and you may stop breathing.
People have stopped breathing when shocked with currents from voltages as low as 49 volts. Usually, it takes about 30 mA of current to cause respiratory paralysis.
Currents greater than 75 mA may cause ventricular fibrillation (very rapid, ineffective heartbeat). This condition will cause death within a few minutes unless a special device called a defibrillator is used to save the victim. Heart paralysis occurs at 4 amps, which means the heart does not pump at all. Tissue is burned with currents greater than 5 amps.
The muscle structure of the person also makes a difference. People with less muscle tissue are typically affected at lower current levels. Even low voltages can be extremely dangerous because the degree of injury depends not only on the amount of current but also on the length of time the body is in contact with the circuit.
This table shows what usually happens for a range of currents (lasting one second) at typical household voltages. Longer exposure times increase the danger to the shock victim. For example, a current of 100 mA applied for 3 seconds is as dangerous as a current of 900 mA applied for a fraction of a second (0.03 seconds).
|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.|
|6-25 milliamps (women)
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.
The most common shock-related, nonfatal injury is a burn. Burns caused by electricity may be of three types:
Electrical burns can result when a person touches electrical wiring or equipment that is used or maintained improperly. Typically, such burns occur on the hands. Electrical burns are one of the most serious injuries you can receive. They need to be given immediate attention. Additionally, clothing may catch fire and a thermal burn may result from the heat of the fire.
Arc-blasts occur when powerful, high-amperage currents arc through the air. Arcing is the luminous electrical discharge that occurs when high voltage exists across a gap between conductors and current travels through the air. This situation is often caused by equipment failure due to abuse or fatigue. Temperatures as high as 35,000°F have been reached in arc-blasts.
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.
There are three primary hazards associated with an arc-blast.
To make sure all employees are safe before, during and after electrical work is performed, electrical workers should follow the three-step process of the Electrical Safety Model:
To be safe, you must think about your job and plan for hazards. To avoid injury or death, you must understand and recognize hazards. You need to evaluate the situation you are in and assess your risks. You need to control hazards by creating a safe work environment, by using safe work practices, and by reporting hazards to a supervisor or trainer.
If you do not recognize, evaluate, and control hazards, you may be injured or killed by the electricity itself, electrical fires, or falls. If you use the safety model to recognize, evaluate, and control hazards, you will be much safer at work.
Use the safety model to:
The first step of the Electrical Safety Model is recognizing the electrical hazards around you. Only then can you avoid or control the hazards. It is best to discuss and plan hazard recognition tasks with your co-workers.
The most frequent causes of electrical injury/death are:
Evaluation is a judgment call, and it's based on the perceived level of risk of injury. Risk is determined by analyzing the probability of an injury occurring and the severity of the injury if it occurs. The greater the probability and higher the severity, the greater the risk.
When evaluating risk, it is best to identify all possible hazards first, then evaluate the risk of injury from each hazard. Do not assume the risk is low until you evaluate the hazard. It is dangerous to overlook hazards.
Once electrical hazards have been recognized and evaluated, they must be controlled. You control electrical hazards in two main ways:
One way to implement this safety model is to conduct a job hazard analysis (JHA). Below is a simple JHA using three columns:
|Removing the cover||Electric shock from exposed live wires||De-energize by opening circuit breaker or removing fuse|
|Removing the GFCI||Possible other live wires in opening||Test wires with appropriate voltmeter to ensure all wires are de-energized|
|Installing the GFCI||Possible connecting wires incorrectly||Check wiring diagrams to ensure proper connections|
|Replace cover and re-energize||Possible defective GFCI||Test GFCI|
Once the JHA is completed, use it to train employees who are not familiar with the job, for retraining if employees demonstrate a lack of knowledge, skills, or ability (SKAs). Make sure the JHA is reviewed each time an employee must perform a hazardous procedure.
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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.