2-�

Chapter 2: Electrical HazardsLearning ObjectivesIn this chapter you will learn to:

discuss the effects of electrical current on the human body;detect electrical hazards, determine which OSHA standards apply, achieve the appropriate standards, and achieve the appropriate protection; anddiscuss safe electrical work practices.

••

•

2-2

True / False QuizThis exercise shows how much you already know about electrical hazards at construction renovation sites. It is not a test, and scores will not be recorded. The only purpose of this quiz is to give you an idea of what you need to learn to stay safe on the job. Please take a few minutes to read the statements, then circle T for “True” and F for “False.” Your instructor will go over the answers when everyone in the class finishes the exercise.

When one of your co-workers is in contact with an electrical circuit and being shocked, you should grab him or her and break their connection with the electrical current as quickly as possible. T F

All electricity is looking for ground. T F

Ground fault circuit interrupters (GFCI) should be used at construction sites in addition to regular grounding and insulation. T F

When you install temporary wiring at a construction site, always disconnect it within the same workday. T F

Before working on electrical circuits, shut off all power at the disconnect (i.e., circuit breaker or fusible switch) and install a lockout/tagout system. T F

During renovations, you can plug your extension cords into the existing building power outlets without any additional equipment. T F

1.

2.

3.

4.

5.

6.

2-�

Basics of Electricity

How serious a workplace hazard is electricity?Very serious. Workers who misuse electricity may suffer injury or death from electrical shock, electrocution, burns, fires and explosions. In 1999 alone, 278 workers in this country died from electrocutions on the job—or almost 5 percent of all recorded U.S. workplace deaths. Most of these fatalities could have been easily avoided. In addition, there are approximately 30,000 electrical shock accidents in this country each year.

How do different materials affect the flow of electricity?A “conductor” is a material that electricity flows through easily. Conductors include metals, air, and even the earth itself. “Insulator” materials slow or stop the flow of electricity and include materials such as glass, plastic, porcelain, clay, pottery, and dry wood.

Workers should avoid contact with known, uninsulated conductors of electricity and be careful in coming close to supposedly poor conductors. Insulating materials can become conductors in some cases. For example, pure water is a poor conductor of electricity, but the addition of small amounts of impurities in water, such as salt, acid, solvents or other materials, can make water a conductor of electricity. When insulating materials, such as dry wood or dry human skin, become wet with water, they can become effective conductors of electricity.

What causes electrical shocks, and what hazards do these pose?Electricity travels in a defined path (or circuit), usually through a conducting material. A person’s body is a good conductor of electricity and accidentally can become a part of the circuit. When this happens, the person may suffer an electrical shock.

Many common materials can become conductors of electricity.

Source Load

+

2-�

Electrical shocks can affect the person in a variety of ways, from a slight tingling sensation to a full heart attack. The most

common injury is electrical burns. The severity of a shock depends on the:amount of current passing through the person’s body;path the current takes through the body;length of time the body remains part of the electrical circuit; and

frequency of the current.Depending upon the path that the current takes, if the shock passes through the middle of the body, it may severely burn and injure the internal organs.

Electrical shocks cause other hazards that also can injure people. For example, electrical arcs can:

start fires;send metal from damaged equipment flying in every direction; andcause violent explosions that release toxic or flammable gases into the air near workers.

Why do people “freeze” when they are shocked, and what should their co-workers do to help them?When people suffer from electrical shock, their muscles severely tighten, and they often cannot break free from the electrical circuit they are contacting. This situation is very dangerous, because it increases the period of electrical shock. The longer a person is exposed to a current, the greater the risk they face of

serious injury or death.

If a co-worker is “frozen” by contact with an electrical circuit, shut off the electricity at once. If this is not possible, pull or push the person away from the electrical source with boards, poles or sticks made of wood or another non-conducting material. Do not touch the person, or you may become part of the

circuit and be injured.

Remember: you must act quickly to help a victim of electrical shock, but protect your own safety by avoiding contact with the electrical circuit through your endangered co-worker.

•••

•

••

•

Injury from electricity depends on current, path, and time.

Act quickly, but protect your own safety when helping a victim of electrical shock.

2-�

How do you know when a person has received a severe electrical shock?It is not always apparent. Shock victims suffer injuries that are often not visible, including:

severe burns and internal bleeding;tissue, nerve or muscle damage; andkidney and other organ damage.

A medical doctor should treat all victims of electrical shock.

What is static electricity, and why is it dangerous?Static electricity occurs when a charge builds up on the surface of an object. People can be shocked when they touch an object with static and the electrical build-up is discharged. A good example of a static electrical discharge is when a person grasps a metal doorknob on a cold, dry day. In this case, the victim only suffers minor discomfort, but static electrical discharges are often more dangerous—for instance, when friction produces the build-up of a high level of static electricity at a specific spot on an object and the discharge ignites flammable or combustible substances nearby.

This can occur when you fill up your truck on a cold, dry winter day. If you do not ground yourself and the gas pump nozzle to your gas port opening, a static discharge can occur and start a fire. Static electricity can also occur when flammable liquids are poured without properly bonding the containers together. This condition can cause fire and explosions.

Basic Electrical Safety Work PracticesMost electrical injuries happen because of unsafe equipment or equipment installations, an unsafe environment, or unsafe work practices. You can protect yourself and others from such accidents with insulation, guarding, grounding, electrical

•••

Static discharge will ignite flammable vapors.

2-�

protective devices, and safe work practices. Let’s discuss some of the basic electrical safe work practices.

What are general safety guidelines to follow when you’re working on or near electrical hazards?You must receive training and be qualified to work on electrical circuits. Unqualified workers should stay away from live electrical wiring.

Before starting work, find (or ask your employer to find) any exposed or concealed hot electric power circuits on your work site. If you are digging, operating a jack hammer, or performing demo work, always wear appropriate voltage rated gloves until you know the exact location of utilities. Always

call before you dig!Your employer must determine if you are qualified through training and experience to work on or near hot electrical equipment. It is up to your employer to decide if you are qualified to do the work. The most important step that you can take to protect yourself is to turn off all electrically powered equipment.

All equipment should be locked and tagged out. To do a lockout and tagout, an authorized person must locate the switch or circuit breaker, shut off all power, and install a lockout device with a tag to identify the person that put on the lock. All locks must be used with tags.Never assume that electrical equipment has been disconnected. You must always act as if all electric circuits are hot until a qualified person makes sure that the energy has been disconnected.Remove all conductive clothing and jewelry such as rings, watches, wrist and neck chains, metal buttons, and metal writing pens. Do not wear synthetic fiber clothing (polyester or other material) because electricity can melt it.

•

•

•

•

•

•

Know and use safe electrical work practices!

ON

OFF

DANGER

DO NOTOPERATE

2-�

Use recommended personal protective equipment, shields, and/or barriers that insulate you from contact with electric circuits. These items include electrically (voltage) rated insulated gloves, aprons, eye protection such as safety glasses and face shields, rubber-soled shoes, insulated shields, and insulated tools.Avoid working in poorly lit areas where hot electric equipment is located. If you must work in these areas, use supplemental lighting. Do not reach into areas with exposed electric components if your view is partially or fully obstructed. Make sure you have sufficient light to see in and around any electrical components or equipment.Do not enter a confined space with exposed electric parts, unless you’re qualified, authorized and wearing adequately rated protective clothing or are using proper barriers, shields or equipment.Do not use areas where exposed electrical equipment is kept as shortcuts or passageways.Make sure that ladders, scaffolds, or any other equipment and materials that you use on the job never come within 10 feet of an overhead electric high voltage power line. If working at heights or handling long objects, make sure there aren’t any overhead wires close enough to touch by accident. Know the voltage of any power lines on your project. You may be required to stay more than 10 feet away depending on the voltage. This includes working in equipment such as scissors lifts and aerial lifts or on scaffolds or any other raised platform.Do not bypass any protective system or device designed to protect employees from

•

•

•

•

•

•

•

Maintain all electrical tools and equipment in safe condition and check them regularly for defects.

2-�

contact with electricity. Do not enter any barricaded electrical hazard area unless you are authorized

to do so.If an there is an electrical fire, use a Class C fire extinguisher to fight the fire.

What are some key guidelines to follow in using power tools?Always have any underground utility, especially underground electrical services properly located.Always wear insulated protective gloves when using

jackhammers or hand tools if the location of underground power lines is unknown. If you are using these type insulated

gloves, they must be inspected prior to each use and must also be tested at least twice each year to ensure that they are providing the proper

insulation. (This is not something you, a worker, does; your employer will send the gloves to a testing

laboratory qualified to do this.)Do not use any frayed, worn or otherwise defective electrical cords or cables.Use only hard duty or extra hard duty 3-wire type extension cords. You can identify 3-wire cords by the lettering usually found on them: S, ST, SO, STO, SJ, SJT, SJO, or SJTO.Maintain all electrical tools and equipment in safe

condition and check them regularly for defects.Tag any defective electrical equipment “Defective—Do Not Use” or remove the tool from the site. Do not store electrical conductors or equipment in damp or wet conditions; locations exposed to gases, fumes, vapors, liquids or over corroding agents; or locations where they are exposed to high temperatures.Never carry a tool by the cord or hose. This can cause the

•

•

•

•

•

•

•

•

•

Make sure ladders, scaffolds, or equipment never come within 10 feet of a power line.

2-�

electrical insulation to pull away from the equipment and expose the conductor wires.Never yank the cord or hose to disconnect it from the receptacle.Disconnect or unplug tools when they are not in use, before servicing, and when changing implements such as blades, bits and cutters.Wear insulated gloves and safety footwear when using tools.Check all of your electrical power tools to ensure that they are either three wire grounded or double insulated. If they are double insulated, it will be marked on the equipment.Remove broken or damaged tools and equipment from the job site.Ensure that all electrical panels, generators, and welders are properly grounded and also located so that will not be exposed to rising water.

Insulation and Grounding

How do you identify the kind of insulation on an electric wire?Electrical wires are insulated by coating them with a nonconductive material such as plastic. You can often identify insulation by the color of the wire’s covering such as:

green or green with yellow strips (or bare copper wire) for grounding conductors;white or gray for grounded conductors; andblack or red for ungrounded conductors (though they can be any color except green, white or gray).

Although these are the correct colors for these type wires, do not assume that the colors are always correct on all equipment. Always check insulation for any exposed wires before connecting electrical equipment to a power source.

Why is it important to ground electrical equipment and metal housings or enclosures?

•

•

•

•

•

•

•

••

Inspect power and extension cords frequently.

Be familiar with the color code for the wiring on each job.

2-�0

Grounding wires provide a path for siphoning off buildups of excess electrical current from equipment and directing this electricity safely into the earth. For example, a grounding wire may run from electrical equipment to a known ground such as a cold water pipe or a copper rod drove driven into the ground. Electricity is always looking for ground.

Different grounding wires have different purposes: a service or system ground primarily protects machines, tools and insulation. An equipment grounding wire is designed to protect equipment operators. Make sure that the ground wire is sufficient in size to provide a proper ground.

What are the limitations of insulation and grounding?Insulation may be damaged by aging, heavy usage, or abuse of the equipment. If workers aren’t observant, they may become exposed to electrical shocks, burns or fires when working with wires they think are well insulated. Double insulation can provide additional protection, but it cannot protect against defective cords and plugs or against very moist operating conditions.

Grounding reduces the chances of a serious electrical injury, but it doesn’t guarantee that workers won’t get shocked. Users may not know when a grounding system is malfunctioning.

A qualified worker should test all newly installed receptacles to ensure the equipment is properly wired. If the receptacle was not wired properly, you may create dangerous conditions such as an open ground. The user of the equipment may think the receptacle is grounded, but the ground wire may not be hooked up in the circuit.

Proper grounding condition can be checking with a simple, inexpensive circuit tester than can be purchased at any hardware or construction materials supplier. If one isn’t available on the job site, ask your employer for one. You must be trained and qualified to test electrical circuits.

In what cases is it important to use ground fault circuit interrupters?

2-��

Insulation and grounding usually provide protection from electrical-related injuries, but these methods do not solve all problems. On construction sites, common residential circuit breakers do not provide enough protection to prevent injuries. Circuit breakers work when the electrical current flowing is too great due to fault causing the breaker to “heat up” and the breaker to “open.” A ground fault circuit interrupter (GFCI) works differently by measuring whether there’s a dangerous situation by comparing the amount of electrical current going into equipment with the amount of current returning from it. If the difference is too great, then the device automatically trips a circuit breaker or blows a fuse, shutting off power. Because of this design, GFCIs are fast-acting circuit breakers which can interrupt the flow of electricity in as little as 1/40 of a second. Use GFCI devices for all construction site equipment. If you are plugging into the existing buildings’ power (not equipped with GFCI) you must use a GFCI cord set (commonly referred to as a “pigtail” or a temporary GFCI device) between the existing power and your equipment. Always plug the pigtail into the outlet before your extension card or equipment plug. Do not plug the pigtail into the user end of the extension cord!

All temporary 120 volt, 15 and 20 amp receptacles must be protected by a ground fault circuit interrupter. You may plug the power cord of your tool directly into an existing permanent receptacle on the construction site, if you are not in a wet or damp location. It is a best practice to always use ground fault circuit interrupters.

Electrical Requirements: Portable Equipment

What must you do to protect your safety while running portable equipment?Construction workers frequently use portable tools, which

Use GFCI’s on all jobs. It could save your life!

RESET

TEST

2-�2

require flexible extension cords. As a general rule, flexible cords are easier to damage than fixed wiring because they are often stretched, twisted and yanked.

To protect workplace safety, you must inspect the tools before each day of use to ensure the cord and plug are not damaged. If the tool is damaged, take it out of service immediately by tagging it and putting in a secured location. On construction sites, the insulation of cords is sometimes cracked or torn away, exposing workers to hot electricity. These electrical currents often are strong enough that workers shocked by them may fall or suffer other potentially fatal injuries.

All portable tools must either be grounded or double insulated. Double insulated tools have their electrical parts isolated from the tool case. They typically have either a symbol or will show that double insulation is present on the equipment.

Portable tools and the cords connecting them to power sources should be protected with ground fault circuit interrupters (GFCIs)—grounding devices that trip circuits very rapidly when they detect dangerous electric discharges.

Temporary Wiring Requirements

What are the general requirements for temporary wiring?Temporary wiring is often necessary on construction sites. Here are some important safety guidelines to follow:

use GFCI devices on all temporary power sources (including extension cords);choose only grounding-type receptacles;ground metal-case sockets;never suspend temporary lights by their electric cords unless cords and lights are designed for this means of suspension; and

•

•••

Double insulation symbol

2-��

remove temporary wiring immediately after completion of construction or the purpose for which the wiring was installed.

Portable Generators

What are the electrical hazards of power generators?During power loss or until temporary power is established, it is a common practice to produce electricity with portable generators. Before starting any generator, make sure to turn off the main circuit breaker and lock it out. Otherwise, power lines may become re-energized (hot) with electricity inadvertently back-fed from the generator. In these cases, utility workers face possible electrocution while they work on power lines.

Always ensure that temporary generators are properly grounded with a proper ground strap attached to a proper ground source. Additionally, always ensure that the generator is equipped with GFCI or that you use a pigtail at the generator plug-in.

•

2-��

Key Terms to RememberHere are some of the key terms presented in this chapter. Let’s review them one more time to reinforce the lessons you learned about electrical hazards.

Conductor: A “conductor” is a material that electricity flows through easily. Conductors include metals, air, and even the earth itself. “Insulator” materials slow or stop the flow of electricity and include materials such as glass, plastic, porcelain, clay, pottery, and dry wood.

Electrical circuit: A defined path that electricity follows, usually passing through a conducting material. A person’s body is a good conductor of electricity and accidentally can become a part of the circuit.

Electrical shock: An injury that occurs when a person become a part of the circuit. Electrical shocks can affect the person in a variety of ways, from a slight tingling sensation to full cardiac arrest. The most common injury is electrical burns.

Ground fault circuit interrupter (GFCI): GFCIs are fast-acting circuit breakers, which can interrupt the flow of electricity in as little as 1/40 of a second.

GFCI cord set: A cord with an inline ground fault circuit interrupter. Commonly referred to as a “pigtail.”

Grounding: A technique that provides a path (through a grounding wire) for siphoning off buildups of excess electrical current from equipment and directing this electricity safely into the earth.

Insulator: “Insulator” materials slow or stop the flow of electricity and include materials such as glass, plastic, porcelain, clay, pottery, and dry wood.

Pigtail: see GFCI cord set

2-��

Lockout/tagout: This technique helps safeguard employees from hazardous energy, such as electricity while they are performing service or maintenance on machines and equipment. A lockout device is an energy-isolating device that ensures the equipment it controls cannot be operated until the lockout device is removed. A tagout device indicates that equipment being controlled may not be operated until the tagout device is removed.

ON

OFF

DANGER

DO NOTOPERATE

2-��

True / False Quiz RevisitedHere are the answers to the pre-chapter quiz. How did you do?1. A Type C fire extinguisher is the type that works on

electrical fires. TrueIf an there is an electrical fire, use a Type C fire extinguisher.

2. When one of your co-workers is in contact with an electrical circuit and being shocked, you should grab him or her and break their connection with the electrical current as quickly as possible. FalseIf a co-worker is “frozen” by contact with an electrical circuit, shut off the electricity at once. If this is not possible, pull or push the person away from the electrical source with boards, poles or sticks made of wood or another non-conducting material. Do not touch the person or you may become part of the circuit and be injured.

3. All electricity is looking for ground. TrueGrounding wires provide a path for siphoning off buildups of excess electrical current from equipment and directing this electricity safely into the earth. For example, a grounding wire may run from electrical equipment to a known ground such as a cold water pipe or a copper rod drove driven into the ground. Electricity is always looking for ground.

4. Ground fault circuit interrupters (GFCI) should be used at construction sites in addition to regular grounding and insulation. TrueA ground fault circuit interrupter (GFCI) works differently by measuring whether there’s a dangerous situation by comparing the amount of electrical current going into equipment with the amount of current returning from it. If the difference is too great, then the device automatically trips a circuit breaker or blows a fuse, shutting off power. Because of this design, GFCIs are fast-acting circuit breakers which can interrupt the flow of electricity in as little as 1/40 of a second. Use ground fault circuit interrupter (GFCI) devices for all construction site equipment.

2-��

5. When you install temporary wiring at a construction site, always disconnect it within the same workday. FalseRemove temporary wiring immediately after completion of construction or the purpose for which the wiring was installed.

6. Before working on electrical circuits, shut off all power at the disconnect (i.e., circuit breaker or fusible switch) and install a lockout/tagout system. TrueThe most important step that you can take to protect yourself is to turn off all electrically powered equipment. All equipment should be locked and tagged out. To do a lock out and tagout, an authorized person must locate the switch or circuit breaker, shut off all power, and install a lockout device with a tag to identify the person that put on the lock. All locks must be used with tags.

7. During renovations, you can plug your extension cords into the existing building power outlets without any additional equipment. FalseUse ground fault circuit interrupter (GFCI) devices for all construction site equipment. If you are plugging into the existing buildings’ power (not equipped with GFCI) you must use a GFCI cord set (commonly referred to as a “pigtail” or a temporary GFCI device) between the existing power and your equipment.