Download Electrical Safety CBT Script Welcome / Splash Screen

Electrical Safety CBT Script
Welcome / Splash Screen
Welcome to the Florida Department of Transportation’s computer-based training series
on OSHA Construction Awareness Training. This is Chapter 4, Electrical Safety. To
begin, select the start button or press Shift+N on your keyboard.
Welcome
A Help button is located at the top of each page in this course. Selecting this button will
bring up a PDF file with information on how to navigate and use this course.
You may select the Help button now if you would like to review this useful information
before you begin the course.
Introduction
Electricity has long been recognized as a serious workplace hazard, exposing
employees to electric shock, electrocution, burns, fires, and explosions. On average,
approximately 300 workers per year die as a direct result of contact with electric current;
more still succumb to injuries sustained in falls or fires resulting from electrical mishaps.
In 2004, 253 people died from electrocution on the job, according to the Bureau of
Labor Statistics.
While that number is lower than the average, there is still plenty of room for
improvement – as witnessed by the fact that “only” 246 workers died in 2003. What
makes these statistics tragic is that most of these fatalities could have been easily
avoided. OSHA’s goal for worker safety training is to work toward the day when
electrocution is no longer a rampant danger in any workplace.
FDOT employees face many electrical dangers in their daily work. Electrical shock
from tools, overhead power lines and lightening are just some of the threats faced by
FDOT workers while out in the field. This course will help you recognize these dangers
and teach you valuable information to help prevent on the job electrical accidents.
Electricity: The Basics
What affects 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 strike.
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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. Anyone working with electricity in a damp or
wet environment needs to exercise extra caution to prevent electrical hazards.
What causes shocks?
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. When a person receives a shock,
electricity flows between parts of the body or through the body to a ground or the earth.
Shocks occur when a person’s body completes the current path with:
both wires of an electric circuit;
one wire of an energized circuit and the ground;
a metal part that accidentally becomes energized due, for example, to a break in its
insulation; or
another “conductor” that is carrying a current.
What effect do shocks have 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:
the amount of current flowing through the body,
the current’s path through the body,
the length of time the body remains in the circuit, and the current’s frequency.
Physical Dangers
The chart below gives the effects of several different levels of current on the human
body.
Electrical burns are the most common shock-related, nonfatal injury. They usually occur
on the hands and should be treated immediately.
Electric shock can also cause indirect or secondary injuries. If you are working in an
elevated location, on a bridge or elevated roadway for example, and you experience a
shock, you might fall and experience a serious injury like broken bones, or even death.
Physical electric shock dangers to FDOT workers might come from a variety of sources:
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Power tool usage
Working around or near overhead power lines
Lightning
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.
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.
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.
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 in this module. 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.
The two best means of preventing injuries from electrical equipment are insulation and
grounding.
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Insulation is placing nonconductive material, like rubber or plastic, around a
conductor.
Grounding is usually accomplished with a direct connection to a known ground
such as a metal pipe.
For example, motor housings and electrical junction boxes made of metal help protect
equipment from dirt and moisture. Unfortunately, a malfunction within the equipment such as deteriorated insulation - can create a shock hazard. Most metal enclosures are
connected to a ground, which reduces or eliminates the hazard to workers.
Insulation & Grounding
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.
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.
Insulation may be damaged by hard usage on the job, or simply by aging. If the damage
exposes the conductors, then you have all the ingredients for shocks, burns, or fire.
“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 module.
A service or system ground is designed primarily to protect machines, tools, and
insulation against damage. One wire, called the “neutral” or “grounded” conductor, is
grounded. In an ordinary low-voltage circuit, the white or gray wire is grounded at the
generator or transformer and at the building’s service entrance.
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.
If a “hot” wire contacts a grounded enclosure, a condition called a ground fault results,
which normally trips circuit breakers and blows fuses in the circuit. Metal enclosures
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and containers, along with most portable tools and appliances, are usually grounded by
connecting them with a wire, called an equipment grounding conductor, which goes
to ground. The disadvantage to this system is that a break in the grounding system
can happen without anyone’s knowledge.
Any time you touch any part of an electrical circuit, the danger of a shock exists if your
body is the easiest path to ground. In the case of tools, the dangerous situation is
when the conductor which grounds the tool has a high resistance, or comes into contact
with your body.
If this should ever occur, a device called a ground fault circuit interrupter, or GFCI, can
interrupt the circuit and prevent a serious shock. The OSHA standard for the
construction industry requires GFCIs to be used. This requirement helps reduce the
number of injuries and accidents from electrical hazards, keeping work disruptions to a
minimum, and requires very little inspection and maintenance time.
Insulation and Grounding
CASE STUDY
Interchange of I-275 and I-4
In 2002, the Florida DOT began a 2.7-mile project to make improvements at the
interchange of I-4 and I-275 in Hillsborough County, including a new bridge deck over
Columbus Drive in 2003. The bridge deck was poured at night, and portable lighting
was used in many places. Portable lighting devices are common on night construction
sites, are as vulnerable as any tool to ground faults, and are often clamped to other
metal structures (like the metal scaffolding in this image). Without GFCI devices in the
circuit, a single fault in a high- voltage portable lamp could shock anyone in contact with
the structure. Ground faults can be a dangerous jobsite hazard, but they are also
entirely preventable.
© Florida Dept. of Transportation (5/8/03)
Concrete is placed at night for a new bridge deck over Columbus Drive in Tampa, FL.
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It is important to note that while proper grounding will prevent many accidents, it
cannot replace the importance of training and care for workers that use electrical
equipment or install wiring.
Standard 120-volt circuits, which are the household standard in the US, usually
have two wires; the black wire is “hot” and carries 120 volts, and the white (very
occasionally green) wire is neutral and connected to ground. Touching the black
wire will cause a shock in almost every case.
240-volt circuits, which are common in some construction tasks, usually have
two wires. One carries an electrical potential of +120 volts, and the other is at 120 volts. Touching both of these wires at once will cause a potentially fatal
shock.
GFCI: The Basics
A GFCI is a fast-acting circuit breaker that can sense small imbalances in the
circuit, like those caused by a tiny leak through a tool operator, and shut off the
flow of electricity in a fraction of a second.
The GFCI continually matches the amount of current going to an electrical
device against the amount of current returning from the device along the
electrical path. Whenever the amount “going” differs from the amount “returning”
by 5 milliamps or so, the GFCI interrupts the electric power within as little as
1/40 of a second.
GFCI’s can be used successfully to reduce (but not eliminate) electrical hazards
on construction sites.
A GFCI won’t protect against “line-to-line” contacts, where instead of providing a
path to ground you place yourself into the circuit. This could happen if you
accidentally touched two “hot” conductors at the same time, or touched a hot
conductor and a neutral one.
Ground faults are much more common, however, GFCIs can protect against
fires, overheating, and destruction of insulation on wiring caused by ground
faults.
When a GFCI interrupts the flow of electrical current, or trips, wet electrical
connectors or tools can be the cause. It is good practice to limit exposure of
connectors and tools to excessive moisture by using watertight or sealable
connectors.
GFCI Protection Types
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Receptacle
Receptacles are available that include a GFCI device. These are becoming
common in homes and businesses, because they are inexpensive and easy to
install, but are rare at most FDOT construction sites.
Cord-Connected
This GFCI device has a female socket at one end and a male plug at the other,
allowing it to function as an extension cord. Any device plugged in to the
socket is protected by the GFCI. Cord-connected GFCIs include the standard
test and reset buttons, as well as a no-voltage release similar to those on
portable GFCIs.
Portable
Portable GFCIs come in several styles, all of which are designed for easy
transport. Some plug into existing non- GFCI power outlets, and some connect
with a cord and plug arrangement.
Most portable GFCIs also incorporate a no-voltage release device that will
disconnect power to the outlets if any supply conductor is open - in other words,
the device won’t work unless they are attached to a complete, safe electrical
circuit.
On a job site, the best choice is portable GFCIs in waterproof housings. These
units are portable, can make use of existing outlets and some generators, and
can generally stand up to the conditions of the construction environment.
Protect Yourself
Due to the dynamic, rugged nature of FDOT construction work, normal use of
electrical equipment at your site causes wear and tear that results in insulation
breaks, short-circuits, and exposed wires. Training like this helps build your
awareness of the potential dangers you may face.
You need to take measures to protect yourself. To avoid hazards, remember
to:
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Use ground-fault circuit interrupters (GFCIs) on all 120-volt, single-phase,
15- and 20- ampere receptacles.
Follow manufacturers' recommended testing procedure to insure GFCI is
working correctly.
Use double-insulated tools and equipment, distinctively marked.
To avoid hazards, remember to (continued):

Use tools and equipment according to the instructions included in their
listing, labeling or certification.
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Visually inspect all electrical equipment before use. Remove from service
any equipment with frayed cords, missing ground prongs, cracked tool
casings, etc. Apply a warning tag to any defective tool and do not use it
until the problem has been corrected.
To reduce hazards, flexible cords must connect to devices and to fittings
in ways that prevent tension at joints and terminal screws.
Flexible cord may be damaged in many ways including abrasion from adjacent
materials and aging. If the electrical conductors become exposed, there is a
danger of shocks, burns, or fire.
CASE STUDY
Interchange of I-75 and Florida State Road 60
In March of 2003, the Florida DOT finished improving the interchange of FL SR60 and I-75. The improvements included adding a turn lane, extending a right
turn lane, and directing traffic to intersections with traffic signals. In a project
like this, if a sidewalk needs to be removed, there may be no room for heavy
equipment - or budget considerations might cause the project manager to direct
that hand-held tools, like an electric jackhammer, be used. Consider the
following questions:
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•
•
What electrical hazards might a jackhammer present?
For maximum safety from ground faults, what surfaces on the
jackhammer should be insulated?
If a portable generator is used to power the jackhammer, where in the
circuit should a GFCI be placed?
FDOT employees often find themselves working near potentially dangerous
overhead powerlines while in the field. These guidelines will help you protect
yourself while working in the vicinity of overhead powerlines.
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Never get closer than 10 feet to an overhead power line!
Consider all overhead lines as energized until the electric utility indicates
otherwise, or an electrician verifies that the line is not energized and has
been grounded.
If overhead lines are present, call the utility company and find out what
voltage is on the lines. Ask if the utility company can shut off the lines
while you are working near them. If overhead lines cannot be shut down,
ask the utility company if they can install insulation over the lines during
the time you will be working near them.
Living in Florida, FDOT workers must be prepared to work after major storms
and hurricanes. The following guidelines will keep you safe from downed
powerlines while assessing damage after a storm.
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Never drive over downed power lines. Assume that they are energized.
And, even if they are not, downed lines can become entangled in your
equipment or vehicle.
Never go near a downed or fallen electric power line. Always assume that
it is energized. Touching it could be fatal.
Low-hanging wires still have voltage potential even if they are not
touching the ground. So, “don’t touch them.” Everything is energized
until tested to be de- energized.
If contact is made with an energized power line while you are in a vehicle,
remain calm and do not get out unless the vehicle is on fire. If possible,
call for help.
If you must exit any equipment because of fire or other safety reasons, try
to jump completely clear, making sure that you do not touch the
equipment and the ground at the same time. Land with both feet together
and shuffle away in small steps to minimize the path of electric current
and avoid electrical shock. Be careful to maintain your balance.
CASE STUDY
Transportation Employee Dies from Electrical Injuries Resulting from
Contact with Overhead Powerline
On November 5, 1984, a 49-year-old crew leader for a state department of
transportation was measuring the amount of asphalt in a 10,000 gallon storage
tank. As he removed the 12' 8" iron measuring rod from this tank, the rod came
in contact with a nearby overhead powerline (7200 volts). The crew leader
sustained severe electrical burns to the hands, arms, axilla, back and thighs. He
was taken by the local emergency medical service to the nearest hospital and
transferred later that day to a hospital burn unit. On November 25, 1984, while
still a patient in the burn unit, the worker died due to pulmonary emboli resulting
from the electrical burn injuries.
The full report of this incident can be found at the following link: Powerline
Dangers.
Lighting Strike
The highest death rates from lightning in the United States are in Florida, which
is known as the lightning capital of the country. From 1959 to 2003 lightning
killed 3,696 people in the United States. Of those, 425 were in the Sunshine
State. FDOT employees should be aware of what to do should lightning activity
threaten a job-site.
•
If you hear thunder and see lightning, act right away – especially if you
count 30 seconds or less between the thunder and lightning. If the
thunder gets louder or you see the lightning more often, the storm is
getting closer. (Sometimes lightning will strike out of a sunny sky 10 miles
or more from a storm.)
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•
If you are out in the open and have nowhere to go, squat down with your
feet together and only let your feet touch the ground. That way, you are so
low the lightning may hit something else. And by not touching much of the
ground, you have less chance that the lightning will move across the
ground to you. Do not lie flat on the ground.
Lighting Strike
If a storm is near Do NOT:
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•
•
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Be the tallest object in an area.
Stand out in the open.
Stand under a tree.
Stand next to metal objects
Stay next to water
If a storm is near DO:
•
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Get into an enclosed building - like a house or shopping center or school or
office building.
Get into a car, van, truck, or bus with the windows closed all the way. Do
not touch the doors or other metal inside.
Conclusion
In an era with the technology to produce GFCIs, there’s less reason than ever to
suffer the consequences of a severe shock. Be sure to check for the presence
and integrity of these life-saving devices when you’re working with electricity on
the job, and ensure you’re not at risk to become the “easiest path to ground.”
Exam
You are about to begin a 10 question exam on the material that was presented
in this module. You must pass this exam with a score of 70% to receive credit
for this course.
You may take this exam as many times as necessary. Feel free to review the
material if you feel you are not ready to proceed.
You must agree to the following affidavit before you can begin to the exam.
AFFIDAVIT
By entering my name in the field below, I hereby declare, warrant and confirm,
under penalty of perjury, that I have not misrepresented my identity, and I intend
to personally take and complete the following exam.
Please enter your name: ________________
Press the "next" button to begin after you have signed the affidavit.
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