Crane
Training Power Line Clearances
WARNING!
Crane operators and crew members may be electrocuted when they
work near overhead power lines.
The National Institute for Occupational Safety and Health (NIOSH)
requests assistance in preventing electrocutions of crane operators
and crew members working near overhead power lines. Recent NIOSH
investigations suggest that employers, supervisors, and workers
may not be fully aware of the hazards of operating cranes near overhead
power lines or may not implement the proper safety procedures for
controlling these hazards. This Alert describes five cases (six
electrocutions) that resulted from such hazards and makes recommendations
for preventing similar incidents. The Alert updates a previous NIOSH
Alert published in July 1985 [NIOSH 1985].
The recommendations in this Alert should be followed by all employers,
managers, supervisors, and workers in companies that use cranes
or similar boomed vehicles. NIOSH requests that the following individuals
and organizations bring this Alert to the attention of workers who
are at risk: editors of trade journals, safety and health officials,
construction companies, unions, suppliers and manufacturers of building
materials, crane manufacturers, electric utilities, and others who
use cranes or boomed vehicles.
Workers are killed each year when cranes contact overhead power
lines.
BACKGROUND
NTOF Data
Data from the NIOSH National Traumatic Occupational Fatalities
(NTOF) Surveillance System indicate that electrocutions accounted
for approximately 450 (7%) of the 6,400 work-related deaths from
injury that occurred annually in the United States during the period
1980-89 [NIOSH 1993a]. Each year an average of 15 electrocutions
were caused by contact between cranes or similar boomed vehicles
and energized, overhead power lines. The actual number of workers
who died from crane contact with energized power lines is higher
than reported by NTOF because methods for collecting and reporting
these data tend to underestimate the total number of deaths [NIOSH
1993a]. More than half of these crane-related electrocutions occurred
in the construction industry.
FACE Data
From 1982 through 1994, NIOSH conducted 226 onsite investigations
of work-related electrocutions under the Fatality Assessment and
Control Evaluation (FACE) Program. Twenty-nine (13%) of these incidents
(which resulted in 31 fatalities) involved crane contact with overhead
power lines. Nearly half of the incidents occurred in the construction
industry. Because the FACE investigations were conducted in only
16 states, these fatalities represent only a portion of the crane-related
electrocutions during the period 1982-94.
OSHA Data
A study conducted by the Occupational Safety and Health Administration
(OSHA) showed that 377 (65%) of 580 work-related electrocutions
occurred in the construction industry during the period 1985-89
[OSHA 1990]. Nearly 30% (113) of these electrocutions involved cranes.
CURRENT STANDARDS
OSHA Regulations
Current OSHA regulations require employers to take precautions when
cranes and boomed vehicles are operated near overhead power lines.
Any overhead power line shall be considered energized unless the
owner of the line or the electric utility company indicates that
it has been de-energized and it is visibly grounded [29 CFR 1926.550
(a)(15)(vi)]. The OSHA regulations are summarized as follows:
Employers shall ensure that overhead power lines are de-energized
or separated from the crane and its load by implementing one or
more of the following procedures:
—De-energize and visibly ground electrical distribution
and
transmission lines [29 CFR 1910.333(c)(3); 29 CFR 1926.550(a)(15)]
—Use independent insulated barriers to prevent physical contact
with
the power lines [29 CFR 1910.333(c)(3); 29 CFR 1926. 550(a)(15)]
—Maintain minimum clearance between energized power lines
and the
crane and its load [29 CFR 1910.333(c)(3)(iii); 29 CFR
1926.550(a)(15)(i), (ii), (iii)].
Where it is difficult for the crane operator to maintain clearance
by visual means, a person shall be designated to observe the clearance
between the energized power lines and the crane and its load [29
CFR 1926.550(a)(15)(iv)].
The use of cage-type boom guards, insulating links, or proximity
warning devices shall not alter the need to follow required precautions
[29 CFR 1926.550 (a)(15)(v)]. These devices are not a substitute
for de-energizing and grounding lines or maintaining safe line clearances.
ANSI Standard
The American National Standards Institute (ANSI) has published
a standard for mobile and locomotive cranes that includes operation
near overhead power lines [ANSI 1994]. This consensus standard (B30.5-1994)
contains guidelines for preventing contact between cranes and electrical
energy. The standard addresses the following issues:
Considering any overhead wire to be energized unless and until
the person owning the line or the utility authorities verify that
the line is not energized
De-energizing power lines before work begins, erecting insulated
barriers to prevent physical contact with the energized lines, or
maintaining safe clearance between the energized lines and boomed
equipment
Limitations of cage-type boom guards, insulating links, and proximity
warning devices
Notifying line owners before work is performed near power lines
Posting warnings on cranes cautioning the operators to maintain
safe clearance between energized power lines and their equipment
CSA Recommendations
The Construction Safety Association of Ontario, Canada (CSA) recommends
safe work practices in addition to those addressed in the OSHA and
ANSI standards [CSA 1982]. These recommendations include the following.
Work Practices
Operate the crane at a slower-than-normal rate in the vicinity of
power lines.
Exercise caution near long spans of overhead power lines, since
wind can cause the power lines to sway laterally and reduce the
clearance between the crane and the power line.
Mark safe routes where cranes must repeatedly travel beneath power
lines.
Exercise caution when travelling over uneven ground that could cause
the crane to weave or bob into power lines.
Keep all personnel well away from the crane whenever it is close
to power lines.
Prohibit persons from touching the crane or its load until a signal
person indicates that it is safe to do so.
The CSA recommendations also address the limitations of proximity
warning devices, hook insulators, insulating boom guards, swing
limit stops, nonconductive taglines, ground rods, and similar devices
for protection against electrical hazards.
Procedures to Follow
If Contact Occurs
To protect against electrical shock injury in the event of contact
between a crane and an energized line, the CSA recommends the following:
The crane operator should remain inside the cab.
All other personnel should keep away from the crane, ropes, and
load, since the ground around the machine might be energized.
The crane operator should try to remove the crane from contact by
moving it in the reverse direction from that which caused the contact.
If the crane cannot be moved away from contact, the operator should
remain inside cab until the lines have been de-ener gized.
CASE REPORTS
The five cases presented here were investigated by the NIOSH FACE
Program between March 1990 and March 1993.
Case No. 1--One Death
On March 1, 1990, a 29-year-old worker was electrocuted when he
pushed the crane cable on a 1-yard cement bucket into a 7,200-volt
power line. The victim was a member of a crew that was constructing
the back concrete wall of an underground water-holding tank at a
sewage treatment plant. Before work on the tank began, the company
safety director made sure that insulated line hoses were placed
over sections of the power line near the jobsite and that a safe
clearance zone was marked off for arriving cement trucks to use
for loading their cement buckets.
After the wall was poured, the driver of the cement truck cleaned
the loading chute on his truck with a water hose mounted on the
truck. As he began to pull away, the crew supervisor yelled to him,
asking if the crew could use his water hose to wash out the cement
bucket suspended from the crane. The driver stopped the truck under
the power line and the crane operator (not realizing that the truck
had been moved) swung the boom to position the bucket behind the
truck. The victim grasped the handle of the bucket door and pushed
down to open it, bringing the crane cable into contact with the
power line. The victim provided a path to ground and was electrocuted
[NIOSH 1990b].
Case No. 2--One Death
On August 11, 1990, a 33-year-old well driller was electrocuted
when a metal pipe lifted by a truck-mounted crane contacted a 12,000-volt
overhead power line. The victim and a coworker were repairing a
submersible pump for a water well at a private residence. The well
was located in a pasture with three parallel power lines overhead.
One of the power lines passed directly over the well (32 feet above
the ground). On the day of the incident, the victim positioned the
truck-mounted crane beneath the power line. Using a handheld remote-control
pendant, the victim fully extended the end of the boom 36 feet above
the ground. The crane cable was attached to a 1-inch-diameter galvanized
pipe that ran to the pump inside the well. As the victim raised
the pipe, it contacted the power line directly above the well, energizing
the crane and the handheld remote-control pendant. The victim provided
a path to ground and was electrocuted [NIOSH 1990c].
Case No. 3--One Death
On August 22, 1990, a 24-year-old foreman for a telecommunications
company was electrocuted when he grabbed the door handle on a truck-mounted
crane whose boom was in contact with a 7,200-volt overhead power
line. The foreman and three other workers (a lineman, a cable splicer,
and a laborer) were attempting to remove four poles that had supported
a billboard. The poles stood 20 feet high and were buried 5 feet
in the ground. They were located 15 feet away from (and parallel
to) the power line. To remove the poles, the lineman positioned
the crane directly under the power line. He controlled the crane
boom while standing on the ground using rubber-coated hand controls
mounted on the back of the truck. The poles were removed by hooking
the crane boom cable around the middle of each pole and vertically
pulling each pole out of the ground. While the workers were pulling
out the third pole, the end of the boom contacted the overhead power
line. The laborer (who was working in the back of the truck) noticed
that the lineman was being shocked and was unable to let go of the
hand control. The laborer kicked the lineman in the chest and the
lineman fell unconscious to the ground. He revived without assistance
about 3 minutes later with electrical burns to his left hand. However,
the crane boom remained in contact with the power line, the truck
tires ignited, and the truck began to burn. When the foreman noticed
that the boom remained in contact with the power line, he tried
to open one of the truck doors (presumably to move the truck). When
his hand contacted the door handle, he provided a path to ground
and was electrocuted [NIOSH 1990a].
Case No. 4--One Death
On June 24, 1991, a 37-year-old construction laborer was electrocuted
while pulling a wire rope attached to a crane cable toward a load.
The choker was to be connected to a steel roof joist that was to
be lifted 150 feet across the roof of a one-story school and set
in place. The cab of the crane was positioned 11 feet 6 inches from
a 7200-volt power line. After a previous roof joist had been set
in place, the crane operator swung the crane boom and cable back
toward the victim, who grabbed the choker in his left hand. With
his right hand, he held onto a steel rod that had been driven into
the ground nearby. At this point, the momentum of the swinging crane
apparently caused the crane cable to contact the power line. The
electrical current passed across the victim's chest and through
the steel rod to ground, causing his electrocution [NIOSH 1991].
Case No. 5--Two Deaths
On March 31, 1993, a 20-year-old male truck driver and his 70-year-old
male employer (the company president) were electrocuted when the
boom of a truck-mounted crane contacted a 7,200-volt conductor of
an overhead power line. The incident occurred while the driver was
unloading concrete blocks at a residential construction site. The
driver had backed the truck up the steeply sloped driveway under
a power line at the site and was using the crane to unload a cube
of concrete blocks. The company president and a masonry contractor
watched as the driver operated the crane by a handheld remote-control
unit. The driver was having difficulty unloading the blocks because
the truck was parked at a steep angle. While all three men watched
the blocks, the tip of the crane boom contacted a conductor of the
overhead power line and completed a path to ground through the truck,
the remote control unit, and the driver. The company president attempted
to render assistance and apparently contacted the truck, completing
a path to ground through his body. He died on the scene. The truck
driver was airlifted to a nearby burn center where he later died
as a result of electrical burns [NIOSH 1993b].
CONCLUSIONS
These case reports indicate that some crane operators, their employers
and supervisors, and others who work around cranes may not be fully
aware of the hazards of operating cranes near overhead power lines
or may not implement the proper safety procedures for controlling
these hazards.
RECOMMENDATIONS
NIOSH recommends that employers take the following measures to
protect workers and operators of cranes and other boomed vehicles
from contacting energized overhead power lines.
Comply with OSHA Regulations
Train workers to comply with current OSHA regulations. These regulations
require workers and employers to consider all overhead power lines
to be energized until (1) the owner of the lines or the electric
utility indicates that they are not energized, and (2) they have
been visibly grounded [29 CFR 1910.333 (c)(3); 29 CFR 1926.550(a)(15)].
Employers shall ensure that overhead power lines are de-energized
or separated from the crane and its load by implementing one or
more of the following [29 CFR 1910.333(c)(3); 29 CFR 1926.550(a)(15)]:
—De-energize and visibly ground electrical distribution and
transmission lines at the point of work
—Use insulated barriers that are not a part of the crane to
prevent
contact with the lines
—If the power lines are not de-energized, operate cranes in
the area
ONLY if a safe minimum clearance is maintained as follows:
At least 10 feet for lines rated 50 kilovolts or below
At least 10 feet plus 0.4 inch for each kilovolt above 50
kilovolts; or maintain twice the length of the line
insulator (but never less than 10 feet)
Where it is difficult for the crane operator to maintain safe clearance
by visual means, designate a person to observe the clearance and
to give immediate warning when the crane approaches the limits of
safe clearance [29 CFR 1926.550(a) (15)(iv)].
Do not use cage-type boom guards, insulating links, or proximity
warning devices as a substitute for de-energizing and grounding
lines or maintaining safe clearance [29 CFR 1926.550(a)(15)(v)].
Follow ANSI Guidelines
Train workers to follow ANSI guidelines for operating cranes near
overhead power lines (ANSI Standard B30.5-1994, 5-3.4.5)[ANSI 1994].
These guidelines recommend posting signs at the operator's station
and on the outside of the crane warning that electrocution may occur
if workers do not maintain safe minimum clearance that equals or
exceeds OSHA requirements as follows:
--------------------------------------------------------------------------------
Power line voltage Minimum safe
phase to phase (kV) clearance (feet)
--------------------------------------------------------------------------------
50 or below 10
Above 50 to 200 15
Above 200 to 350 20
Above 350 to 500 25
Above 500 to 750 35
Above 750 to 1,000 45
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Notify Power Line Owners
Before beginning operations near electrical lines, notify the owners
of the lines or their authorized representatives and provide them
with all pertinent information: type of equipment (including length
of boom) and date, time, and type of work involved. Request the
cooperation of the owner to de-energize and ground the lines or
to help provide insulated barriers. NIOSH encourages employers to
consider de-energization (where possible) as the primary means of
preventing injury from contact between cranes and power lines.
Develop Safety Programs
Develop and implement written safety programs to help workers recognize
and control the hazards of crane contact with overhead power lines.
Evaluate Jobsites
Evaluate jobsites before beginning work to determine the safest
areas for material storage, the best placement for machinery during
operations, and the size and type of machinery to be used.
Know the location and voltage of all overhead power lines at the
jobsite before operating or working with any crane.
Research has shown that it is difficult to judge accurately the
distance to an overhead object such as a power line [Middendorf
1978]. Therefore, NIOSH recommends that no other duties or responsibilities
be assigned when workers are designated to observe clearance during
crane movement or operation.
Evaluate Alternative
Work Methods
Evaluate alternative work methods that do not require the use of
cranes. For example, it may be possible to use concrete pumping
trucks instead of crane-suspended buckets for placing concrete near
overhead power lines. Alternative methods should be carefully evaluated
to ensure that they do not introduce new hazards into the workplace.
Train Workers
Ensure that workers assigned to operate cranes and other boomed
vehicles are specifically trained in safe operating procedures.
Also ensure that workers are trained (1) to understand the limitations
of such devices as boom guards, insulated lines, ground rods, nonconductive
links, and proximity warning devices, and (2) to recognize that
these devices are not substitutes for de-energizing and grounding
lines or maintaining safe clearance. Workers should also be trained
to recognize the hazards and use proper techniques when rescuing
coworkers or recovering equipment in contact with electrical energy.
CSA guidelines list techniques that can be used when equipment contacts
energized power lines [CSA 1982] (see Current Standards in this
Alert).
All employers and workers should be trained in cardiopulmonary resuscitation
(CPR).
Call for Help
Ensure that workers are provided with a quick means of summoning
assistance when an emergency occurs.
Develop Safer Equipment
Encourage the manufacturers of cranes and other boomed vehicles
to consider developing truck-mounted cranes with electrically isolated
crane control systems, such as those that use fiber optic conductors
to transmit control signals.
ACKNOWLEDGMENTS
The principal contributor to this Alert is Paul H. Moore, Division
of Safety Research. Please direct any comments, questions, or requests
for additional information to the following:
Director
Division of Safety Research
National Institute for Occupational Safety and Health
1095 Willowdale Road
Morgantown, WV 26505-2888
Telephone, (304) 285-5894; or call 1-800-35-NIOSH (1-800-356-4674).
We greatly appreciate your assistance in protecting the health of
U.S. workers.
Linda Rosenstock, M.D., M.P.H.
Director, National Institute for
Occupational Safety and Health
Centers for Disease Control and Prevention
REFERENCES
ANSI [1994]. American national standard for mobile and locomotive
cranes. New York, NY: American National Standards Institute, ANSI
B30.5-1994.
CFR. Code of Federal regulations. Washington, DC: U.S. Government
Printing Office, Office of the Federal Register.
CSA (Construction Safety Association) [1982]. Mobile crane manual.
Toronto, Ontario, Canada: Construction Safety Association of Ontario.
Middendorf L [1978]. Judging clearance distances near overhead power
lines. In: Proceedings of the Human Factors Society, 22nd annual
meeting. Santa Monica, CA: Human Factors Society, Inc.
NIOSH [1985]. NIOSH Alert: request for assistance in preventing
electrocutions from contact between cranes and power lines. Cincinnati,
OH: U.S. Department of Health and Human Services, Public Health
Service, Centers for Disease Control, National Institute for Occupational
Safety and Health, DHHS (NIOSH) Publication No. 85-111.
NIOSH [1990a]. Foreman electrocuted and lineman injured after truck-mounted
crane boom contacts 7,200-volt overhead power line in Virginia.
Morgantown, WV: U.S. Department of Health and Human Services, Public
Health Service, Centers for Disease Control, National Institute
for Occupational Safety and Health, Fatal Accident Circumstances
and Epidemiology (FACE) Report No. 90-39.
NIOSH [1990b]. Laborer touching suspended cement bucket electrocuted
when crane cable contacts 7,200-volt power line in North Carolina.
Morgantown, WV: U.S. Department of Health and Human Services, Public
Health Service, Centers for Disease Control, National Institute
for Occupa- tional Safety and Health, Fatal Accident Circumstances
and Epidemiology (FACE) Report No. 90-29.
NIOSH [1990c]. Well driller electrocuted when pipe on crane cable
contacts 12,000-volt overhead power line in Virginia. Morgantown,
WV: U.S. Department of Health and Human Services, Public Health
Service, Centers for Disease Control, National Institute for Occupational
Safety and Health, Fatal Accident Circumstances and Epidemiology
(FACE) Report No. 90-38.
NIOSH [1991]. Construction laborer is electrocuted when crane boom
contacts overhead 7,200-volt power line in Kentucky. Morgantown,
WV: U.S. Department of Health and Human Services, Public Health
Service, Centers for Disease Control, National Institute for Occupational
Safety and Health, Fatal Accident Circumstances and Epidemiology
(FACE) Report No. 91-21.
NIOSH [1993a]. Fatal Injuries to workers in the United States, 1980-1989:
a decade of surveillance. Cincinnati, OH: U.S. Department of Health
and Human Services, Public Health Service, Centers for Disease Control
and Prevention, National Institute for Occupational Safety and Health,
DHHS (NIOSH) Publication No. 93-108.
NIOSH [1993b]. Truck driver and company president electrocuted after
crane boom contacts power line--West Virginia. Morgantown, WV: U.S.
Department of Health and Human Services, Public Health Service,
Centers for Disease Control and Prevention, National Institute for
Occupational Safety and Health, Fatality Assessment and Control
Evaluation (FACE) Report No. 93-14.
OSHA [1990]. Analysis of construction fatalities--the OSHA database
1985-1989. Washington, DC: U.S. Department of Labor, Occupational
Safety and Health Administration.
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Crane Alert--DHHS (NIOSH) Publication No. 95-108
Crane operator
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