Tree-Related Electrical Incidents: Us vs. Them

This article is a continuation of the series “Us Versus Them” (see sidebar), contrasting the nonfatal injuries of arborists and the public that occurred while using common arboricultural tools. Past articles have focused on chain saws, chippers/shredders, hand saws/pole saws and aerial devices/ladders. This is the first in the series to discuss arboricultural operations rather than tools.

The focus here is on incidents along the distribution system – the primaries and secondaries, including house drops – that lace across this country. The data sources for this article have expanded from those used previously in the series. While utilizing many of the same sources cited in previous articles, data also comes from event reports collected by states and utilities on their distribution-system incidents.

“Us vs. Them” Series:

The following articles in this series have appeared in previous issues of TCI Magazine, as noted.
“Nonfatal Incidents Involving Aerial Lifts and Ladders: Us Versus Them,”
December 2022
“Tree Worker Safety Update By the Numbers: Another Us Versus Them,”
February 2022
“Injuries Involving Handsaws and Pole Saws: Another Us Versus Them,”
January 2022
“Chipper Safety – An Analysis of Wood-Chipper Nonfatal Injuries: Us Versus Them,” June 2021
“Chain-Saw Injuries: Us Versus Them,” May 2021

Incidents along distribution systems

There are about 5.5 million miles of distribution lines in the United States. This sampling covered about 340,000 miles of these lines, or about 6% of the system. While it includes incident reports from utility data across the country, it is not a random sampling. This means that the data may not reflect the entire population. Still, it is a good snapshot of the tree-related incidents that occurred on distribution lines by arborists, landscapers, other occupation workers and the public.

This article focuses on incidents along distribution systems, not electrical-contact incidents in buildings or on equipment. There are about 500 to 1,000 electrocutions a year and another 30,000 electrical-shock injuries from all sources, indoors and outdoors. The greatest electrical risk is to those workers involved in the installation, maintenance and repair occupations. Most electrical incidents to both workers and the public are indoors. These incidents range from an electrician working on the main panels in a warehouse to a toddler sticking a paper clip into a home outlet.

Shock injuries to the public

The majority, about 80%, of nonfatal shock injuries are to the public. Children account for about 20% of all electrical-contact injuries. These are usually nonfatal incidents, but do result in burns and other injuries.

The distribution system accounts for many of the outdoor electrical fatal and nonfatal injuries each year. Most of these incidents occurred on overhead power lines, about two-thirds of all incidents on distribution systems. The other third of the incidents occurred on the underground system. Two common incidents on underground utility systems involved excavating equipment striking electrical cables or equipment and vehicle collisions with pad-mounted transformers.

Tan house with a woman standing by a white fence with electrical wires in front.
incidents involving arborists and homeowners occur along the distribution system – the primaries and secondaries, including house drops. Here, branches are growing into the house drop, and a dead branch is hung up in the secondaries by the pole. All images are TCIA staff photos.

Transformer dangers

These pad-mounted transformers that dot the landscape, the visible part of the underground system, are treated too casually by people. While they look like small, benign cabinets, they have been a factor in incidents resulting in electrical injuries and power interruption. In one instance, a child suffered severe burns when they reached inside a transformer. The transformer had a broken lock on the door. Tree workers have dropped branches on them, resulting in loss of service. Treat these transformers with as much respect as those secured to a power pole.

Green electrical box on a large cement pad.
Pad-mounted transformers, the visible part of the underground system, are treated too casually by people. While they look like small, benign cabinets, they have been a factor in incidents resulting in electrical injuries and power interruption.

Injuries differ in the south vs. north

Electrical-contact incidents differ in frequency among utility systems across the U.S. People working in trees account for almost half of all incidents on some systems, whereas in others the percentage is much lower, about one in 10 incidents. While this survey was not a stratified, random sampling of systems across the country, the trend was that southern utilities had more tree-related electrical-injury incidents on their distribution lines than northern ones.

Some southern systems saw about 1.0 tree-related electrical-injury incidents per 10,000 miles of distribution lines per year, while some northern utilities had less than 0.1 incidents per 10,000 miles of lines. There are many variables in considering why this might be the case, but the tree species might be a crucial factor. Palms, obviously not common in the north, were frequently identified as the “tree” (palms are not actually trees) that the injured person was working in when the contact was made.

The reason for palms being identified so often in incident reports may be due to their shape. They tend to be a lollipop, a round canopy of fronds on the end of a tall, single stem. Unlike the broad canopy of many other trees, where a person might be trimming branches 20 feet or more from the lines near the tree, if the line is near the palm, the person is also near the line. There is not much separation between the person in the palm and the wire. The unqualified (electrical) tree worker, as well as the public, should not be in trees, or palms in this case, which are within 10 feet of any overhead power line, including house drops.

Another factor

Another factor may be the growth rate of southern vegetation. A long, warm growing season means there are many fast-growing plants such as bamboo along lines. There were incidents where homeowners were clearing bamboo or other fast-growing shrubs from the ground and the cut plant contacted the conductor while the person was holding the stem. While these incidents can occur with northern small trees and shrubs, woody vegetation is more rampant in the South.

Dangers to homeowners

About one-third of the tree-related electrical-contact incidents occurred to homeowners or the public. Almost half of the contact incidents involving this group were fatal. Most of the fatal incidents were caused by indirect contact with a metal pole, most commonly a pole pruner or saw but sometimes a fruit picker. Many of these contacts occurred as the person was standing on a metal ladder leaning into the tree. There is not a lot of impedance in this fault pathway.

The nonfatal incidents to homeowners and the public also included indirect contact with the conductor through a metal pole. Again, this is usually a pole saw. Many of these occurred while the person was standing on the ground while holding the pole. These accounted for about half of the nonfatal electrical-
contact injuries.

The second-most common, about one-fourth of the incidents, was a cut branch (or frond) in contact with the conductor. The person was injured when either they grabbed the branch to pull it free of the conductor or the branch contacted them and the conductor as it fell. Many of these branches or fronds were small in diameter, less than 3 inches, and the injuries were often not electrical burns but fractures. The fractures are the result of the contact startling the person, and they then fell from the tree or ladder.
The remaining quarter involved a variety of tools. Some occurred when the person was moving the ladder and it contacted the conductor. Other incidents happened when the person made direct contact with the conductor while operating a rental lift.

Lamp post next to an electrical box.
Tree workers have dropped branches on electrical boxes, resulting in loss of service.

Shock and burns

The term “shock” was the most frequent description of these nonfatal contacts. Burns were specifically identified in about a third of the nonfatal incidents. The burns were mostly partial thickness (second-degree) and full thickness (third-degree). These burns can be very painful and may require extensive medical care, including skin grafts. Nonfatal does not mean without consequences.


Fractures also were identified in many of these incidents. Usually these occurred while the person stood on a ladder while holding a metal pole saw. The person was not secured while cutting. Instead the tried to balance an extended pole saw while standing on a ladder rung – not the safest position. When the metal pole, or in some instances a cut branch, the person was holding contacted the conductor, the “tingling” from the contact startled the person – think of touching an electric fence – and they lost their balance and fell. The fractures were either to the lower arm and wrist or to the ankle.

These nonfatal incidents did not differ much from those of tree workers, either arborists or landscapers. Indirect contact through a metal pole saw or cut branch were the most common, though landscapers had more contact through a metal pole saw and arborists through a cut branch. The difference was that these incidents occurred more to climbers and aerial-lift operators than while standing on a ladder.


Trees and overhead power lines often merge, and this commingling of space is a hazard for anyone working in trees. The percentage of incidents from direct or indirect contact while working in or on a tree range from one in 10 to nearly half of the incidents in a distribution system. Homeowners and the public account for about one-third of these incidents.

One of the best means of reducing these incidents is having the unqualified (electrical) arborist and allied workers (landscape, grounds maintenance), as well as the public, not work in or on trees where any part of the canopy is within 10 feet of an energized electrical conductor. But unfortunately, they are not trained to recognize electrical conductors and hardware, nor can they tell the difference between overhead power lines and communication lines. So I say, simply, they should not be working on any tree within 10 feet of any dark line in the sky. This alone would save many lives.

John Ball, Ph.D., Board Certified Master Arborist (BCMA), Certified Treecare Safety Professional (CTSP), A-NREMT (Advanced-National Registry of Emergency Medical Technicians,) is a professor of forestry and TCIA member/student advisor at South Dakota State University, as well as a frequent presenter on industry safety and other topics at industry events throughout the U.S.

Leave a Reply

Your email address will not be published. Required fields are marked *

Click to listen highlighted text!