Safety and Health                  Lawrence University Web Page

Mark D. Musser     LU- Safety Coordinator        mark.musser@lawrence.edu

Safety Coordinator's office located at
 the Physical Plant, 235 E. Water Street
(2nd Floor)     Phone    920.832.6575
                        Fax       920.832.7485                                      

Environmental, Health & Safety

Basic Electrical Safety

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This document provides an overview of basic electrical safety on the job.

Electricity is essential to modern life, both at home and on the job. Some employees — engineers, electricians, electronic technicians, and power line workers, among them — work with electricity directly.

Others, such as office workers and sales people, work with it indirectly. Perhaps because it has become such a familiar part of our daily life, many of us don’t give much thought to how much our work depends on a reliable source of electricity. More importantly, we sometimes overlook the hazards electricity poses and fail to treat it with the respect it deserves.

Everyone has the right to work in a safe environment. Safety and health add value to your workplace. Through cooperative efforts, employers and employees can learn to identify and eliminate or control electrical hazards.

Electricity has long been recognized as a serious workplace hazard, exposing employees to electric shock, electrocution, burns, fires, and explosions. In 1999, for example, 278 workers died from electrocutions at work, accounting for almost 5 percent of all on-the-job fatalities that year, according to the Bureau of Labor Statistics.

What makes these statistics more tragic is that most of these fatalities could have been easily avoided.

Most electrical accidents result from one of the following three factors:

Some ways to prevent these accidents are through the use of insulation, guarding, grounding, electrical protective devices, and safe work practices. NIOSH Preventing worker deaths

How do OSHA’s standards minimize electrical hazards?

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.

What training is required to protect employees from electrical hazards?

All employees should be trained to be thoroughly familiar with the safety procedures for their particular jobs. Electrical accidents are largely preventable through safe work practices.  The Control of Hazardous Energy program contains the methods and work practices used to prevent electrical accidents. When working on electrical equipment, for example, some basic procedures to follow are to:

Electrical safety-related work practice requirements for general industry are detailed in Subpart S of 29 CFR Part 1910

Basic Electrical Safety Index

The flow of electricity

Electricity flows more easily through some materials than 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.

How does water affect the flow of electricity?

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.

What protection does insulation provide?

Insulators such as glass, mica, rubber, or plastic used to coat metals and other conductors help stop or reduce the flow of electrical current. This helps prevent shock, fires, and short circuits. To be effective, the insulation must be suitable for the voltage used and conditions such as temperature and other environmental factors like moisture, oil, gasoline, corrosive fumes, or other substances that could cause the insulator to fail.

Identifying different types of insulation

Insulation on conductors is often color coded. Insulated equipment grounding conductors usually are either solid green or green with yellow stripes. Insulation covering grounded conductors is generally white or gray. Ungrounded conductors, or “hot wires,” often are black or red, although they may be any color other than green, white, or gray.

Before connecting electrical equipment to a power source, it’s a good idea to check the insulation for any exposed wires for possible defects. Insulation covering flexible cords such as extension cords is particularly vulnerable to damage.

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What role do tools play?

Appropriate and properly maintained tools help protect workers against electric hazards. It’s important to maintain tools regularly because it prevents them from deteriorating and becoming dangerous. Check each tool before using it. If you find a defect, immediately remove it from service and tag it so no one will use it until it has been repaired or replaced.

When using a tool to handle energized conductors, check to make sure it is designed and constructed to withstand the voltages and stresses to which it has been exposed.

Grounding offers protection

“Grounding” a tool or electrical system means intentionally creating a low-resistance path that connects to the earth. This prevents the buildup of voltages that could cause an electrical accident.

Grounding is normally a secondary protective measure to protect against electric shock. It does not guarantee that you won’t get a shock or be injured or killed by an electrical current. It will, however, substantially reduce the risk, especially when used in combination with other safety measures discussed in this document.

An equipment ground helps protect the equipment operator. It furnishes a second path for the current to pass through from the tool or machine to the ground.

This additional ground safeguards the operator if a malfunction causes the tool’s metal frame to become energized. The resulting flow of current may activate the circuit protection devices.

What are circuit protection devices and how do they work?

Circuit protection devices limit or stop the flow of current automatically in the event of a ground fault, overload, or short circuit in the wiring system. Well-known examples of these devices are fuses, circuit breakers, ground-fault circuit interrupters, and arc-fault circuit interrupters.

Fuses and circuit breakers open or break the circuit automatically when too much current flows through them.

When that happens, fuses melt and circuit breakers trip the circuit open. Fuses and circuit breakers are designed to protect conductors and equipment. They prevent wires and other components from overheating and open the circuit when there is a risk of a ground fault.

Ground-fault circuit interrupters, or GFCIs, are used in wet locations, construction sites, and other high-risk areas. These devices interrupt the flow of electricity within as little as 1/40 of a second to prevent electrocution. GFCIs compare the amount of current going into electric equipment with the amount of current returning from it along the circuit conductors. If the difference exceeds 5 milliamperes, the device automatically shuts off the electric power.

Arc-fault devices provide protection from the effects of arc-faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc-fault is detected.

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How can you protect yourself against metal parts that become energized?

A break in an electric tool’s or machine’s insulation can cause its metal parts to become “hot” or energized, meaning that they conduct electricity. Touching these energized parts can result in an electrical shock, burn, or electrocution.

The best way to protect yourself when using electrical tools or machines is to establish a low-resistance path from the device’s metallic case to the ground. This requires an equipment grounding conductor, a low-resistance wire that directs unwanted current directly to the ground.

A properly installed grounding conductor has a low resistance to ground and greatly reduces the amount of current that passes through your body. Cord and plug equipment with a three-prong plug is a common example of equipment incorporating this ground conductor.

Another form of protection is to use listed or labeled portable tools and appliances protected by an approved system of double insulation or its equivalent. Where such a system is employed, it must be marked distinctively to indicate that the tool or appliance uses an approved double insulation system.

Personal protective equipment

Employees who work directly with electricity must use the personal protective equipment required for the jobs they perform. This equipment may include rubber insulating gloves, hoods, sleeves, matting, blankets, line hose, and industrial protective helmets designed to reduce electric shock hazard. All help reduce the risk of electrical accidents.

What is guarding and what protection does it offer?

Guarding involves locating or enclosing electric equipment to make sure people don’t accidentally come into contact with its live parts. Effective guarding requires equipment with exposed parts operating at 50 volts or more to be placed where it is accessible only to authorized people qualified to work with it.

Recommended locations are a room, vault, or similar enclosure; a balcony, gallery, or elevated platform; or a site elevated 8 feet (2.44 meters) or more above the floor. Sturdy, permanent screens also can serve as effective guards.

Conspicuous signs must be posted at the entrances to electrical rooms and similarly guarded locations to alert people to the electrical hazard and to forbid entry to unauthorized people. Signs may contain the word “Danger,” “Warning,” or “Caution,” and beneath that, appropriate concise wording that alerts people to the hazard or gives an instruction, such as “Danger/High Voltage/Keep Out.”

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How can you prevent an accidental or unexpected equipment startup?

Proper lockout/tagout procedures protect you from the dangers of the accidental or unexpected startup of electrical equipment and are required for general industry by OSHA.

These procedures ensure that electrical equipment is de-energized before it is repaired or inspected and protects you against electrocution or shock.

Only qualified electricians who have been trained in safe lockout procedures should maintain electrical equipment.

Overhead power lines

Before working under or near overhead power lines, ensure that you maintain a safe distance to the lines and, for very high-voltage lines, ground any equipment such as cranes that can become energized. If working on power lines, ensure that the lines have been de-energized and grounded by the owner or operator of the lines.

Other protective measures like guarding or insulating the lines help prevent accidental contact.

Employees unqualified to work with electricity, as well as mechanical equipment, should remain at least 10 feet (3.05 meters) away from overhead power lines. If the voltage is more than 50,000 volts, the clearance increases by 4 inches (10 centimeters) for each additional 10,000 volts.

When mechanical equipment is operated near overhead lines, employees standing on the ground should avoid contact with the equipment unless it is located outside the danger zone. When factoring the safe standoff distance, be sure to consider the equipment’s maximum reach.

What causes shocks, and what effect do shocks have on the body?

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:

When a person receives a shock, electricity flows between parts of the body or through the body to a ground or the earth.

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What is the danger of static electricity?

Static electricity also can cause a shock, though in a different way and generally not as potentially severe as the type of shock described previously. Static electricity can build up on the surface of an object and, under the right conditions, can discharge to a person, causing 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, as when friction causes a high level of static electricity to build up at a specific spot on an object. 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.

How can you tell if a shock is serious?

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.

Effects of shocks on the body

An electric shock can result in anything from a slight tingling sensation to immediate cardiac arrest. The severity depends on the following:

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.

Effects of Electric Current in the Human Body

Current

Reaction

Below 1 milliampere

Generally not perceptible

1 milliampere

Faint tingle

5 milliamperes 

Slight shock felt; not painful but disturbing. Average individual can let go. Strong involuntary reactions can lead to other injuries.

6–25 milliamperes (women)

Painful shock, loss of muscular control* 

9–30 milliamperes (men)

The freezing current or “let-go” range.* Individual cannot let go, but can be thrown away from the circuit if extensor muscles are stimulated.

 

50–150 milliamperes

Extreme pain, respiratory arrest, severe muscular contractions. Death is possible.

1,000–4,300 milliamperes

Rhythmic pumping action of the heart ceases. Muscular contraction and nerve damage occur; death likely.

10,000 milliamperes

Cardiac arrest, severe burns; death probable

* If the extensor muscles are excited by the shock, the person may be thrown away from the power source.

Source: W.B. Kouwenhoven, “Human Safety and Electric Shock,” Electrical Safety Practices, Monograph, 112, Instrument Society of America, p. 93. November 1968.

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 What kind of burns can a shock cause?

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.

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.

Why do people sometimes “freeze” when they are shocked, and what should you do?

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.

What to do If a person is “frozen” to a live electrical contact,

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