(Taken from Construction Safety Magazine, produced by the Construction
Safety Association of Ontario, Vol. 11, No. 1, Spring 2000.)
Association of Ontario
a major cause of deaths in construction. Part of the reason is that at
home and on the job we take electricity for granted. This can lead to
familiarity and a false sense of security. Relying on the benefits of
electricity, we may forget its hazards.
accounts for about 20% of all fatalities in construction. Unfortunately,
last year was no exception. Four of the twenty construction deaths in
1999 were electrocutions. All of the fatalities resulted from overhead
contact with powerlines -- a boom truck in one case, ladders in the other
Some people think
that only cranes are involved in overhead contacts. But backhoes, dump
trucks, and low-tech equipment like ladders and rolling scaffolds have
also been involved. Nor does it take high-tension lines to kill construction
people. Too many fatalities involve residential service.
- Locate and identify
all overhead powerlines. Determine voltage before construction begins.
- Have lines moved,
insulated, or de-energized. In urban areas, insulating or "rubberizing"
powerlines is often most practical. Contact the local utility.
- Use a signaler
whenever a backhoe, crane, or similar device is closer than one boom
length to a live powerline of 750 volts or more.
- The signaler must
warn the operator when any part of the machine or its load approaches
the minimum distances allowed in the construction regulation.
- Never use aluminum
or metal-reinforced ladders near overhead lines or live electrical equipment
or wiring. Even contact with a wooden ladder can be fatal under damp
or wet conditions.
- Never store material
or equipment under overhead powerlines if current is more than 750 volts
and cranes or similar lifting devices will be involved.
- Where material
or equipment must be stored under powerlines, hang warning flags
so that personnel will not use hoisting and lifting equipment.
- Remember that
overhead lines can be struck not only by booms and ladders but also
by long pieces of material being lifted by hand, such as pipe and siding.
- Beware of wind
swaying powerlines into contact with equipment, hoist lines, or loads.
And beware of wind blowing hoist lines or loads into contact with powerlines.
In the event of contact
between equipment and overhead powerlines:
Stay on equipment.
Don't touch equipment and ground at the same time. In fact, touching anything
in contact with the ground can be fatal.
away. Warn everyone not to touch the equipment or its load. That
means buckets, outriggers, load lines, and any other part of the machine.
Beware of time-delayed relays. Even after line damage trips breakers,
relays may still try to restore power. They may reset automatically two
or three times.
If possible, break contact by moving the equipment clear of the wires.
This may not be feasible where contact has welded conductors to equipment,
hoist line, or load.
utility. Get someone to call the local electrical utility for
help. Stay on the equipment until the utility shuts down the line and
confirms that power is off. Report every incident of powerline contact
so that the utility can check for damage that could cause the line to
clear. If an emergency such as fire forces you to leave the equipment,
jump clear. If part of your body contacts the ground while another
part touches the machine, current will travel through you. In cases
of high-voltage contact, jump clear and shuffle away in small steps.
With voltage differential across the ground, one foot may be in a
higher voltage area than the other. The difference could kill you.
A tower crane was
lowering a concrete bucket to be filled by a truck. The wind blew the
hoist line and bucket into overhead powerlines. A worker trying to pull
the bucket back was electrocuted.
worker was changing the bulb in a light fixture that had been incorrectly
wired (polarity was reversed). He inadvertently touched the metal
base of the bulb while it was in contact with the socket. He received
a severe shock and later died in hospital
installing switches, receptacles, fixtures, and other equipment,
be sure to respect the color code in wiring. As always, only
an electrician or person with equivalent qualifications should
install electrical equipment. Otherwise polarity may be reversed
with dangerous results. Switches may remain energized when turned
off, for instance, and GFCIs may not work properly.
have been electrocuted by contacting buried powerlines. One incident involved
using an auger attachment on a Bobcat to drill holes for fence posts.
The auger struck a live underground line, electrocuting a worker who was
standing on the ground and touching the machine. The operator remained
in the cab and was not injured.
- Before construction
begins, ask the local electrical utility to locate and mark all buried
- Indicate underground
lines on all plans and drawings. Post warning signs along their route.
- Ensure that warning
signs remain in place during construction.
Grounding is an essential
concept in electrical safety. It can be intentional and work for you,
or accidental and work against you. Grounding is a connection between
an electrical circuit and the earth or some conducting body that serves
as earth. The point is: you don't want that "body" to be yours.
current from faulty wiring, tools, or equipment to a point where it can
be safely discharged, usually to earth or a conductor touching earth.
Grounded tools and equipment help to prevent you from becoming the means
of channeling electricity back to earth.
- Don't cut off
or bend back the ground pin on a three-prong plug. Don't use a two-prong
cheater or adapter. Don't replace three-wire cord with two-wire cord
on tools and equipment. These practices are dangerous and, in most jurisdictions,
- Check extension
cords and outlets for grounding with a circuit-tester before using.
- Ensure that all
electric hand tools are grounded or double-insulated. Double-insulated
tools are made of non-conducting plastic. External metal parts are insulated
from internal electrified parts. Make sure that casings are not cracked,
broken, or otherwise defective.
- Don't hold onto
a water pipe or other grounded conductor when using an electric tool.
The tool or cord could be defective and you might be electrocuted.
- Use ground fault
circuit interrupters (GFCIs) on all electric tools. Ontario law requires
GFCIs with tools used outdoors and in damp locations. GFCIs detect any
current leaking to ground and shut off power before injury or damage
worker was painting a building from a boom-type powered elevating
work platform. He backed up without checking how close he was to a
powerline. The machine touched the line. Trying to escape from the
bucket he climbed onto the roof and was electrocuted
driver raised the box on his dump truck to spread gravel under a powerline.
When the box contacted the line, he got out of the cab to see what
had happened. His foot touched the ground while his hand was still
holding the door. He was electrocuted instantly
aluminum siding installers were lifting trim for the exterior of a
house. Although aware of nearby powerlines, they failed to allow for
the length or bulkiness of their material. A piece of trim shifted
as it was lifted, struck a line, and one worker was electrocuted
Construction -- Electrocutions in 1999
installer carrying aluminum ladder was electrocuted when it touched
- Worker involved
in residential demolition working from ladder contacted powerline.
- Worker using
boom truck to install hydro pole anchors contacted overhead wires.
- Worker moving
aluminum ladder contacted overhead powerline.
The effect of electric shock on the human body is determined by three
- how much current
is flowing through the body (measured in amperes and determined by voltage
- the path of current
through the body
- how long the
body is in the circuit.
Trip setting for ground fault
Victim cannot let go
Breathing difficult - possible
Heart Stops pumping
Increasing probability of death
Enough current to light
a 100-watt bulb
can range from a tingle to cardiac arrest. There is no exact way to predict
the injury from any given amperage. The table below shows generally how
degree of injury relates to current passing through a body for a few seconds.
This is the third
in a series of articles dealing with the major causes of construction
fatalities. Falls were covered in Volume 10, Number 3 (Autumn 1999) and
traffic in Volume 10, Number 4 (Winter 1999/2000).
This paper appears in the eLCOSH website with the permission of the author
and/or copyright holder and may not be reproduced without their consent.
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