pe="text/css">

Feasibility Study to Reduce Injuries and Fatalities
Caused by Contact of Cranes, Drill Rigs, and
Haul Trucks with High-Tension Lines
H. Kenneth Sacks, Member, IEEE, James C. Cawley, Senior Member, IEEE, Gerald T. Homce, and
Michael R. Yenchek, Senior Member, IEEE
AbstractOverhead electric study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power lines present a serious
electrocution hazard to personnel in a variety of industries.
Overhead lines, typically uninsulated conductors supported on
towers or poles, are the most common study-to-reduce-injuries-and-fatalities-caused-by-contact-/' class='doin' >means of electric study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power
transmission and distribution, and are exposed to contact by mo-
bile equipment such as cranes and trucks. Equipment contacting
energized overhead lines becomes elevated to a high voltage, and
simultaneous contact by personnel of the hot frame and ground
can cause serious electrical shock and burns. Industries where
risk of these accidents is greatest include construction, mining,
agriculture, and communications/public utilities. An estimated
2300 accidental overhead line contacts occur each year in the U.S.
This paper describes a practical low-cost concept to detect actual
contact of mobile equipment with a high-voltage line and provide
a warning. Accident statistics indicate that more than half of the
fatalities could be prevented by such a device.
Index TermsCrane, electrical shock prevention, engineering
control, mining, mobile equipment, study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power line.
I. I
NTRODUCTION
O
VERHEAD electric study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power lines present a serious elec-
trocution hazard to personnel in a variety of industries.
Overhead lines, typically uninsulated conductors supported on
towers or poles, are the most common study-to-reduce-injuries-and-fatalities-caused-by-contact-/' class='doin' >means of electric study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power
transmission and distribution, and are exposed to contact by
mobile equipment such as cranes and trucks. Equipment con-
tacting energized overhead lines can become elevated to a high
voltage, and simultaneous contact of the "hot" frame and ground
can cause serious electrical shock and burns. Industries where
risk of these accidents is greatest include construction, mining,
agriculture, and communications/public utilities. An estimated
2300 accidental overhead line contacts occur each year in the
U.S. [1].
1
Construction activities present the most obvious potential for
line contact accidents, and a recent study estimated that in
1993






The authors are with the Pittsburgh Research Laboratory, National Institute
for Occupational Safety and Health, Pittsburgh, PA 15236 USA (e-mail:
hes3@cdc.gov; gdh3@cdc.gov; mby5@cdc.gov).

1
The estimate of 2300 line contacts per year was generated from 1994 OSHA
data for all industries, and includes any contact of overhead lines, for example,
direct contact by a person, handheld items, ground ladders, and scaffolding, in
addition to mobile equipment
alone, at least 26 electrocutions in this industry were a result
of heavy equipment or hoisted loads contacting overhead lines.
Mobile cranes (including boom trucks) were involved in most
of these incidents (57%), with drill rigs (8%), dump bed trucks
(7%), and manlifts (7%) also common [2]. It should be noted
that this summary likely understates the extent of the problem,
due to reporting and data collection methods, as well as the
omission of accidents resulting in nonfatal injuries. Detailed
and more comprehensive statistics are available for the mining
industry, which represents a smaller work force than the con-
struction industry, but has a similar electrocution rate, and like
construction uses heavy equipment extensively. From 1980 to
1997, at least 94 mobile equipment overhead line contact acci-
dents were reported in the U.S. mining industry, with 114 in-
juries, 33% of them fatal. Most involved cranes (47%), dump
bed trucks (24%), and drills (14%).
II. B
ACKGROUND
Investigations into possible study-to-reduce-injuries-and-fatalities-caused-by-contact-/' class='doin' >means to prevent injuries caused
by contact between study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power lines and cranes date back at least
28 years. In 1980, the U.S. Bureau of Mines contracted with
the Southwest Research Institute (SWRI), San Antonio, TX
[3], to study commercial devices sold to protect crane operators
from contact with overhead high-voltage lines. SWRI acquired
and tested three commercial devices. The proximity warning
devices, as they were generally known, all purported to warn
against impending contact with study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power lines. The SWRI phase I
report concluded [3, p. 10]:
However, all of the devices tested and, in fact, any prox-
imity warning device based only upon electrostatic field
sensing will fail to alarm reliably under certain configura-
tions of multiple study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power line circuits.
Other common prevention techniques are discussed in 29
CFR 1910.333(c)(3) and 29 CFR 1926.550(a)(15) [4], [5].
These include deenergizing lines, maintaining appropriate
distances from energized lines, use of an observer to warn the
operator of impending contact, and barriers to prevent physical
contact with an energized line [4][6].
One technique, the use of insulating links in the load line, at-
tempts to prevent injury once contact has been made. Analysis
of the properties of these links [7] show they can greatly in-
crease worker safety. However, surface contamination and mois-
ture can reduce their insulation resistance and workers who con-
tact parts of the crane other than the load will not be protected.


Fig. 1.
Schematic of a study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power line contact.
The technical approach in this paper assumes that contact
with a study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power line has occurred. The question was whether or not
electrical currents flowing through a vehicle in contact with a
high-voltage source could be practically detected and trigger an
alarm. The alarm would then warn the operator and bystanders
that the vehicle is a serious electrocution hazard and should not
be approached (or dismounted by the operator). Clearly, victims
in contact with the crane or a conductor electrically connected
to the crane (control pendent or load line) at the instant of con-
tact with the study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power line would not be protected.
Two databases of electrocutions were analyzed. The National
Institute for Occupational Safety and Health (NIOSH) does
detailed investigations of fatal accidents through its Fatal
Assessment and Control Evaluation program (FACE). Forty
accidents involving crane electrocutions were investigated
between 19821994 [8]. Of these fatal incidents, 20% could
have been prevented with a contact alarm system. A second
analysis showed that 55% could have been avoided through a
combination of insulating load link and a contact alarm. The
second database was the Mine Safety and Health Administra-
tions (MSHAs) Part 50 mining injury and illness database.
2
From 1980 to 1997, there were 89 mobile equipment/overhead
line accidents that resulted in injury. Of these, 73 incidents
had sufficient information to evaluate the utility of a contact
alarm. A conservative estimate is that 56% of the victims could
have been saved with such an alarm. Again, a second analysis
showed that the contact alarm coupled with an insulating
link could have saved 77% of the victims. NIOSH [5, p.2]
reports that at least 15 people are electrocuted each year from
contact between cranes or similar vehicles and study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power lines.
The implication is that this device coupled with an insulating
link could save eight or more lives every year.
III. E
XPERIMENTAL
A
PPROACH
Fig. 1 shows that, in the event of line contact, current can
flow from the study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power line through the vehicle to earth, via the
vehicles ground contact, and back to the grounded point of the
2
MSHA is required by law to maintain detailed injury statistics for the mining
industry and publishes its results quarterly as the Mine Injuries and Worktime,
Quarterly
Fig. 2.
Schematic representation of the tests done at LLL.
source transformer feeding the lines. To gauge the feasibility of
a contact alarm, it is necessary to learn more about how the elec-
trical current flows within the vehicle framework from the line
to the earth. Specifically, the question that needs to be answered
is whether a signal derived from the vehicle can be used to alarm
those nearby. A realistic experimental protocol involves the ap-
plication of voltages, of the same order of magnitude as study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power
lines, to vehicles representative of those involved in fatal inci-
dents. Experiments of this nature are potentially hazardous and
must be done at an isolated location. Consequently, all field tests
were conducted at the Lake Lynn facility of the Pittsburgh Re-
search Laboratory (PRL).
The Lake Lynn Laboratory (LLL) [9] is located approxi-
mately 14 miles south of Uniontown, PA, on the border with
West Virginia. It encompasses about 400 acres and a former
limestone mine, now used for fire and explosion research. The
remote surface facility features a variety of test beds at the base
of a highwall including grassy fields, gravel roads, and a quarry
floor. In addition, mobile vehicles similar to those found on
mining and construction sites are available for the tests.
To ensure that test currents through the earth did not pose
a hazard to personnel working nearby, it was necessary to de-
vise a test circuit that was electrically isolated from the utility
distribution at Lake Lynn. This was best accomplished using a
portable gasoline generator as the test study-to-reduce-injuries-and-fatalities-caused-by-contact-/' >power source. As shown
in Fig. 2, this 120-V, 2.3-kVA generator was connected to a vari-
able transformer and a step-up transformer to provide test volt-
ages ranging from 0 to 950 V. In the experiments to follow, this
output was connected to the vehicle under test and to an earth
grounding electrode to simulate the grounded point of a source
transformer. A partially bur