Download Electrical Hazards in Construction

Electrical Hazards in Construction
Applicable Regulations
OSHA’s regulations directly applicable to electricity in construction are generally technical in
nature, relating more to what electricians do than what other construction workers do.
The regulation is found at 29 CFR 1926, Subpart K.
In addition, as with any worksite, OSHA may apply its “General Duty” clause. The clause, Section
5(a)(1) of the Occupational Safety and Health Act, requires an employer to furnish to its employees
“employment and a place of employment which are free from recognized hazards that are causing or are
likely to cause death or serious physical harm to employees ….”
It is important to note that the General Duty clause cuts both ways—it also requires employees to
comply with occupational safety and health standards and all rules, regulations and orders issued
pursuant to the OSH Act that are applicable to their own actions and conduct.
Introduction/Overview
Electricity is dangerous at any worksite, but at construction sites, it's particularly dangerous. This is
true for several reasons:
• There are a lot of different workers on the site who don't know one another and who are not
familiar with each other's systems and protocols.
• Many structures and installations and hookups are temporary, and may change as the project
continues.
•
The electricity on construction sites is often at a higher voltage than normal household current.
So it is worthwhile for every construction worker to become familiar with basic guidelines for
avoiding electrical accidents on the worksite.
Your Body the Conductor
Let's talk a bit about your body and how electricity can be hazardous to it.
First of all, one widely held fiction is that low-voltage electricity is not dangerous. Actually, the fact
is that most injuries involving electricity are from low-voltage power sources.
The amount of current flowing at any given voltage depends upon the resistance of the material
through which it flows—including any human body that becomes part of the circuit.
Metals such as copper, iron, and aluminum offer low resistance, so they are good conductors.
Materials like rubber, ceramics, and dry wood (among others) offer high resistance to the flow of
current, making them poor conductors but good insulators.
The human body can act as either a poor conductor or a good one, depending on various factors:
•
The health of the individual
•
The duration of contact with the flow of current
•
The area of contact
•
The condition of the skin (wet, dry, greasy, etc.)
Electricity seeks an uninterrupted path, or circuit, to follow. If your body becomes part of that
circuit, electricity will pass through it.
Even with "household" voltage, if your body’s resistance to the flow is reduced—by wet hands or
feet, for example—enough electrical energy can flow through your body to kill you. This is especially
true if the electricity passes through vital organs, such as the heart or lungs.
If you were to measure your body's resistance to the flow of current from one arm to the other on a
warm day on which you were perspiring freely, the resistance could be low enough that 25 volts would
produce enough current to kill you.
There are cases of deaths caused by 32-volt farm lighting systems, yet, under favorable conditions,
the body's resistance may be such that a 120-volt house lighting system might cause only a slight
tingling shock.
And, of course, on many construction sites, there are higher voltages, which make the danger all the
worse.
Ground Takes the Current
Electricity always follows the path of least resistance. That’s why it is so important to provide an
easy path for the current to follow that is not your body. This is called a ground.
For example, let’s say you are holding a drill that has developed a short. Your hands are dry and you
are standing on a dry surface, so your body is not a good conductor. The drill has a ground wire. This
means the current from the short will follow the ground wire, not you.
Although dry hands and feet offer considerable resistance to household current, the resistance drops
rapidly in the presence of moisture. In the same scenario, if you are perspiring and standing in pool of
water, the current might choose you instead of the ground wire.
Keeping this in mind, let’s take a look at some of the common electrical hazards that construction
workers face.
Specific Electrical Hazards in Construction
As you will see below, there are a number of situations in which construction workers must be
especially careful of electrical hazards. We'll discuss them and show you how to avoid the danger.
Carrying Conductive Materials
On construction sites, workers often carry long items that could conduct electricity, for example,
metal ladders, piping, rebar, corner bead, pike, or a host of other items. If you are not thinking about
where the far end of the piece is, it is easy for it to contact an energized source of current.
Whenever carrying such materials, check out the path over which you must pass. Look for overhead
wires, junction boxes, etc., and take pains to keep your load far away. Also be aware of electrical
installations in walls or on the ground. It is easy for the material you are carrying to come into contact
when you turn or look around.
If you are working around overhead lines, the lines should:
•
Be de-energized and grounded by the appropriate organization, or
• Have protective measures—such as guarding, isolating, or insulating—in place before work
starts.
There are also limits on how close workers—and the longest conductive objects they hold—can
come to an energized line. The minimum is 10 feet for an unqualified worker. "Qualified" workers can
get closer depending on the line's voltage and the protection provided.
Vehicles also can't get closer than 10 feet to an energized overhead line, unless:
•
The elevating structure is lowered on a moving vehicle.
•
Insulating barriers, separate from the vehicle, prevent contact with the lines.
•
Protections on the vehicle, the employee, and the equipment prevent contact.
Barricades, insulation, or other protections are also required to protect employees working on the
ground when a vehicle or equipment may be elevated near energized lines.
Remember to allow for swaying or sagging of electrical lines.
Reaching into Enclosed Spaces
Many workers have found a nasty electrical surprise when they reach into boxes or other enclosures
whose contents are not visible.
Don't reach blindly into areas that may contain wiring or energized parts. Find out what is inside any
enclosed area before reaching into it or probing it with a metal tool.
Such areas should be protected but, especially during construction, they may not be.
Using Portable Tools
Portable electric power hand tools are used for many different kinds of work. Unless you are using
an acceptable double-insulated electric power tool, you must be absolutely sure that the noncurrentcarrying parts are properly grounded.
Usually a three-prong plug in a three-hole outlet provides a proper ground. However, if you are not
sure that the ground is effective, have it tested.
Attaching the third wire to a pipe that does not go to the ground or to a nonconductor is not an
effective means of grounding; you might as well not have it at all.
For your safety:
• Don’t attempt to make electrical tool repairs yourself; it’s better to send a defective tool back to
the manufacturer. This is especially true of double-insulated tools, which must be repaired by the
manufacturer.
•
If you have wet hands or are standing in water, don’t use an electric tool.
•
Always disconnect the tool before cleaning or adjusting it.
Using Extension Cords
Using portable power tools usually means using extension cords, which have their own set of
problems.
[Note: It will be helpful to have with you samples of the different kinds of cords, lamps, and
accessories that may be used in your operations.]
Here are some tips for safe use of extension cords:
• Always use the right cord for the circumstances. (All cords should be UL-approved and meet
electrical code specifications for outdoor use.)
•
Plastic covers of some sort are recommended for use around solvents or oils.
• Jacketed cords are the proper type for use with portable electric tools or extension lamps
intended for work in boilers, tanks, and other grounded enclosures.
•
Other types of cords are specially designed to resist moisture, heat, or chemicals.
• Check to be sure that electrical cords are in good condition, not kinked, cracked, punctured, or
frayed.
• Disconnect cords by gripping the plug, not pulling on the wire. Jerking on the cord can cause
serious damage.
•
Use one long cord instead of several shorter cords. A longer cord should have a larger diameter.
•
If using a cord outdoors, plug it into ground fault circuit interrupter (GFCI).
•
Don't overload cords. Multiplug devices should contain an integral circuit breaker.
•
Never splice or tap an extension cord.
•
Be sure that cords are not pinched in doors, drawers, equipment, or anything else.
• Use products that have grounded three-pronged plugs or the new polarized plugs with one blade
slightly wider than the other.
•
Never bend prongs or force a three-pronged cord into a two-pronged outlet.
• For extension lamps, porcelain, composition, or rubber sockets are recommended. The handles
should be made of nonconductive material, and there should be no metallic connection between the lamp
guard and socket shell.
Trips and falls may not always be as life-threatening as electric shocks, but they can have serious
effects—and they are probably the most common hazard associated with extension cords. Try to avoid
letting extension cords cross aisles or other areas where pedestrians can trip over them.
If a cord must be laid on the floor, placing a board on either side of it can protect it—and make it
more visible to workers in the area. So can taping it to the floor or carpet at intervals—a bright-color
tape helps.
Coping with Static Electricity
We are all familiar with the static electrical charge that bites the fingers when we turn on the light
after stroking the cat or slide across the car seat to open the door, but we may realize that in the
workplace, static electricity can be more than a nuisance. It can be a danger.
A single static spark in a workshop where there are flammable materials can ignite a cloud of
propane, powdered aluminum, flour, or paint, causing an explosion or serious fire.
Static electricity is generated by vehicles or equipment in motion (such as a conveyor belt or a belt
running over a pulley); moving liquids (such as solvents discharged from a hose or transferred from
container to container); or various granulated, powdered, or pulverized materials.
The key to coping with static is to minimize the amount that is stored. This means making sure
static is conducted away from the area where it accumulates. Removing static from a charged object is
accomplished through bonding and grounding. Bonding is the connection of two or more conductive
objects together with a conductor so that a spark cannot occur. The bonded elements are then connected
to the ground. This is called grounding.
Be aware in a worksite that has the potential to produce static electricity, that all equipment must be
bonded and grounded. Observe the "make before break" rule. If you have to ground an item to a
different location from the one where it is currently grounded, be sure to make the new ground
connection before you break the existing one.
Make your ground connections far from the hazard, not at it. This is especially important if you
know that the item to be grounded is already carrying a static charge. And don’t let conductive mats,
floors, shoes, and wheels fool you into thinking they will ground you safely. A film of dirt, dust, or wax
may ruin their conductivity.
Understanding Lockout/Tagout
Lockout/Tagout is the system for de-energizing equipment and securing it so that it cannot be
energized during clearing, repair, maintenance, or when working nearby.
Any powered machinery or electrical equipment that could move in a way that would put people in
danger is a hazard that can be prevented by lockout/tagout. You also have to be alert to equipment that
could roll, fall, or move onto a person after it's shut down.
The most important rules for workers are:
1) Never try to start or activate a piece of equipment that is locked or tagged out.
2) Do not attempt to reach into or enter a piece of equipment that could cause harm if energized until
it is locked out. Normally, each of the workers involved will separately lock the piece of equipment out.
That way, each must be all clear before the equipment may be restarted or reenergized.
If you are involved with equipment that needs lockout, you will receive separate training on that.
There is a carefully worked out six-step shutdown procedure that involves checks to be sure that all
energy is released and all involved workers have attached their locks.
Then there is a five-step procedure for coming out of the lockout mode. It is designed to make sure
that the equipment is ready to operate and that all personnel are clear before reenergizing.
Special circumstances may apply during shift changes and when an employee who placed a lock or
tag is not available to remove it. For safety, follow your company's procedures in these situations.
Avoiding Fire and Explosion
Electricity, particularly sparks, can cause fires or explosions, especially in areas with flammables in
the air. If you have any suspicion that there might be an explosive atmosphere or fire danger, don't turn
on your electrical equipment—first find out from your supervisor what dangers might be present.
Take precautions such as ventilation and removal of combustible dust.
Should you start or encounter an electrical fire start, don’t try to use water to put it out.
Charging Batteries
Batteries and the act of battery charging can be hazardous. If you work around batteries or are
involved in charging them, you will receive specialized training.
Otherwise, remember that battery contents are hazardous and that batteries may create an explosive
situation if improperly managed.
Misusing Equipment
If electrical equipment is used in ways for which it is not designed, you can no longer depend on
safety features built in by the manufacturer. This may damage your equipment and cause employee
injuries. Here are some common examples of misuse:
• Using multi-receptacle boxes designed to be mounted by fitting them with a power cord and
placing them on the floor.
•
Fabricating extension cords with ROMEX® wire.
•
Using equipment outdoors that is labeled for use only in dry, indoor locations.
•
Attaching ungrounded, two-prong adapter plugs to three-prong cords and tools.
• Using circuit breakers or fuses with the wrong rating for over-current protection, e.g., using a 30amp breaker in a system with 15- or 20-amp receptacles. Protection is lost because the breaker will not
trip when the system's load has been exceeded.
Using Defective Equipment
On the construction site, equipment can get pretty banged up. So take precautions:
• Inspect electrical equipment before using it; look for broken or bent plugs, frayed cords, bare
wires, smoke, sparks from switches or controls, liquids spilled in or on equipment, or erratic operation.
If you notice any of these defects, or if you feel a tingle when you touch controls, do not use the
equipment; tag it and send it for repair. In addition to being a shock hazard, defective equipment can
cause fires. Equipment should be inspected regularly by electricians.
• Never place electrical appliances like radios or coffeepots near sinks where they may fall in and
injure people using the sinks.
About Fuse Boxes, Circuit Breakers, and GFCIs
Fuses and circuit breakers are devices that are deliberately designed as a weak spot in an electrical
circuit that will give way and break the flow of current if the circuit is overloaded. The fuse and circuit
breakers are also used to break the circuit when work must be done on it.
Serious trouble will most certainly result if you attempt to keep a circuit operating by installing a
fuse of heavier amperage or by inserting a metal connector between the two contacts of the fuse.
Remember: The fact that a fuse or circuit breaker of the proper amperage fails is a sign that
something is wrong with the circuit, and continuing to operate it will produce a significant and
dangerous overload. What you need to do is look for the short circuit or overload that caused the fuse to
fail.
Ground fault circuit interrupters (GFCIs) are also widely used to prevent accidental shock. They are
basically very sensitive circuit breakers that detect shorts and break the circuit very quickly—fast
enough to avoid a lethal shock. If you can plug your tools into a GFCI-protected receptacle, do so.
Helping a Victim
An important part of electrical safety is knowing how to help a victim of electrical shock. First, stop
the current flowing from the circuit through the victim’s body. Often, particularly in cases of low
voltage shock, victims are unable to pull away from the course of current. In this case, disconnect or deenergize the circuit, if possible. If you can't, get a nonconductive item, such as dry clothing, dry rope, or
a dry stick, and remove the victim from the source of the current. Never use your bare hands—touching
the person may pass the current through you.
Then call or send for help. If the victim’s heart or breathing has stopped, give needed first aid until
professional help arrives.
Wrap-Up
Here is a safe conclusion about electricity and the most important fact to remember: If you know
little or nothing about it, leave it alone! Conditions can vary so greatly that without knowledge of all the
facts—and what they mean—you are sure to make an error. In working with electricity, however, there
is no margin for error: Make an unwise decision, and you may be saying "Sayonara."