Environmental Risks of Arboricultural Operations: Exposure to Weather and Electricity

While almost all tree workers know of the hazard of touching or even standing near an aerial-lift truck when the knuckle contacts an overhead wire, few know of the risk posed by ropes on wires. Photo courtesy of Richard S. Wolowicz

The previous three articles in this series covered tree-worker incidents within the U.S. Bureau of Labor Statistics event categories of Contact with an Object (divided into the two sub-categories of Struck-by or Caught-in) and Falls. These are three of the four horsemen of the arboricultural apocalypse. This article will cover the event category Harmful Substances and Environments. Combined, these four horsemen account for more than 80% of fatal and nonfatal incidents to tree workers.

The category Exposure to Harmful Substances and Environments includes injuries resulting from a condition or substance in the work environment. Almost all the injuries to tree workers coded to this category are within the subcategory Exposure to Electricity. However, we do have injuries due to Exposure to Temperature Extremes and even Exposure to Oxygen Deficiency (a tree worker drowned when he waded into a stream to buck up a felled tree).

Exposure to Temperature Extremes

Each year, several tree workers die from heat shock and more suffer heat exhaustion. Your body operates at 98 F. While working in hot weather or during vigorous physical activity, the body will shed excess heat by sweating – and the evaporation of sweat – and by dilating the skin’s blood vessels. Usually the body can regulate its temperature, but combine high temperatures (so the body cannot rid heat by radiation), high humidity (so evaporative cooling is reduced) and physical activity, and you have the formula for heat exhaustion or heat stroke.

Heat exhaustion is the result of a break-down in the body’s cooling mechanism, either dehydration, so evaporative cooling from sweating is reduced, or when clothing is preventing the sweating to provide this cooling. High humidity also can be a factor. If the symptoms of heat exhaustion are not recognized – cold and clammy skin, thirst, dizziness, nausea – and corrective action is not taken, such as removing some clothing layers, moving to a cooler location such as a building, drinking water and putting water on skin, the condition can deteriorate to heat stroke. This condition occurs when the body’s cooling mechanism is overwhelmed and the body temperature rises (usually above 104 F). This can result in tissue damage and death.

It is not too surprising that heat-stroke incidents among tree workers occur on days with hot temperatures and high humidity. One of the more common activities with high risk for heat stroke is dragging brush and chipping.


The worker was dragging brush and chipping for several hours. He complained he was not feeling well, so the crew leader told him to sit in the shade for a bit. When a crew member checked on him, he was slumping against the tree and unconscious. He was taken to the hospital by EMS and had a body temperature of 107 F. He died the next day while still unconscious.

The day’s weather conditions should be noted during the job briefing and, if heat advisories are forecast, either the work activities need to be adjusted or careful attention needs to be paid to workers to ensure everyone is staying hydrated. Any worker presenting symptoms of heat exhaustion should immediately be attended to, not left alone, and EMS should be contacted if the worker’s condition does not improve with hydrating and cooling.

Exposure to electricity

Electricity and trees are often intertwined, and this is not a good combination for tree workers. Electricity, while essential for the comfort and convenience of daily life, is unforgiving. Bob Felix, former executive vice president of the National Arborist Association (now the Tree Care Industry Association), wrote back in the 1980s that electricity was the number-one killer of tree workers.

Electrocution, i.e., death from an electric shock, is still one of the most common fatal incidents for tree workers and represents about 16% of all tree-worker deaths. While deaths due to contact with an energized electrical conductor have slightly declined among tree workers, it remains one of our greatest risks.

However, contact with an energized conductor is not one of the most common nonfatal incidents. In fact, electric shock accounts for less than 5% of all nonfatal incidents involving hospitalization. The reason? When you touch an energized electrical conductor, either directly or indirectly, the current passes through the body, and the associated deep thermal burns are serious medical conditions that result more often in death than injuries.

One of the more common activities with high risk for heat stroke is dragging brush and chipping. Photo courtesy of Ivan Petrovsky.

Most contact incidents are indirect, where the worker touches a conductive object that is in contact with the energized conductor. The two most common conductive objects are metal pole pruners and cut branches. A metal pole pruner held by a climber is the most common indirect-contact incident, followed by a climber having a cut branch fall on him or her while also in contact with the conductor.


Climber indirect contact through a pole saw:

A climber was at about 25 feet in a tree and reached up with a pole chain saw to cut a branch over the primary-distribution lines. The pole saw was not insulated. The climber had the pole fully extended and was resting against the branch. When the branch was cut, the saw dropped and touched an overhead wire and the worker was electrocuted.

The majority of our electric-contact incidents occur to unqualified workers, as described in ANSI Z133 – 2017, Section 4.1.7: Arborists not qualified by training and experience to work within 10 feet of electrical conductors [less than 50 kV], or to incidental line-clearance arborists who have training and experience (4.2.4) to work where an electrical hazard exists, but are not working for the purpose of clearing space around the conductor for the utility.

A key paragraph in the requirements for incidental line clearance in the Z is 4.2.5, which states that before work is performed within the minimum approach distance (MAD) without insulated tools, the overhead energized lines shall be de-energized. Too often climbers are electrocuted while attempting to remove a limb that extends close to the wire. The responsibility to make this work safe lies with the owner/ operator of the electrical system. They may decide to do the work themselves or to remove the limb to a distance 10 feet from the wires, or take other measures. The point is, the incidental line-clearance arborist is working for a customer, not the utility, and must work with the system owner/operator to ensure a safe working environment.


Climber indirect contact through a branch:

A climber had ascended to about 25 feet and cut a branch that was about 10 feet long. The cut branch contacted one of the primary-distribution lines as it fell, while the climber was directing the fall with his hand on it. The worker was electrocuted.

The overhead lines were identified during the pre-work inspection but were not discussed at a job briefing or in any communication about how the work should be done.

While climbers holding a saw or branch comprise most of the indirect-contact incidents, we have electrocutions involving ground workers touching an aerial lift that is in contact with a wire and even workers tossing a climbing line over a service drop to flick a fallen branch off the wire.

Responding to a 911 call in 2008, the first Marco Island (Florida) Fire Department unit arrived to observe two workers at the top of a ladder that was against a large palm. It was apparent that one of the workers was in medical distress. They were given a report that one of the workers was electrocuted while trimming the palm when a frond came in contact with a live wire. Photo courtesy of Marco Island Fire Department.

While almost all tree workers know of the hazard of touching or even standing near an aerial-lift truck when the knuckle contacts an overhead wire, few know of the risk of ropes on wires.


Ground worker indirect contact through a rope:

The aerial-lift operator tied off a line on the limb to be cut so the two ground workers could lower it to the ground. The limb was over the primary-distribution lines and, when the limb was cut, it touched one of the wires. The rope held by the ground workers became energized; one worker was electrocuted and the other suffered nonfatal electric-shock injuries.

Aerial-lift operator direct contact

About a fourth of all conductor incidents are direct contact, where a part of the body is touching an energized conductor. The most common direct-contact incident involves aerial-lift operators. These incidents often are due to a falling branch or tree striking the boom and pushing the operator into the phase wires. Another is a ground worker contacting a wire that was pulled from the pole during a felling operation.


The aerial-lift operator was working near a primary-distribution line when a branch got stuck in the controls, causing the bucket to become entangled in the neutral wire. The boom continued to move and the back of the worker’s neck touched the primary as his hand was on the neutral. The operator suffered burns on neck and hand. He was transported to the hospital but later died due to the injuries.

So, how can you avoid the most common incidents in this event category? Here are some key considerations along with the corresponding Z133 paragraphs in parentheses.

Every job, every time

• Assess the work site to determine hazards (3.3.2, 3.4.7).

• Conduct a job briefing before the start of each job for all workers, covering at least the hazards, including electrical, special precautions, work procedures, job assignments and personal protective equipment (PPE) (3.4.3 and Annex A glossary).

• Make sure a command-and-response system is established and reviewed (3.4.4).

• Assure everyone is wearing the appropriate PPE (3.3.1).

Exposure to temperature extremes

Section 3.2.3, under Emergency Procedures and Readiness, notes that instruction in identification, preventative measures and first aid shall be provided for poisonous plants and stinging insects. I suggest the job briefing also address weather issues during hot days, when the risk of heat-related conditions is increased.

Exposure to electricity

Every one of the paragraphs in Z133 Section 4 Electrical Hazards is of critical importance to arboricultural operations. I am only highlighting a few, as there have been numerous articles on the requirements, work procedures and minimum approach distances for unqualified, incidental line-clearance and qualified line-clearance arborists.

However, it’s important to note that if the arborist has the training and experience to work near conductors and is working for the utility or one of its contractors to conduct line-clearance operations, he or she is a line-clearance arborist. If the same arborist is working for Mr. and Ms. Smith to prune their tree, the arborist is not a qualified line-clearance arborist.

So, the qualification follows the work, not necessarily the worker. As an example, let’s say an arborist is working for utility X or its contractor to clear wires from Monday to Thursday (four 10-hour days), and on Friday and Saturday, the same arborist works for a residential tree care company. Monday through Thursday, the worker is a qualified line-clearance arborist, and on Friday and Saturday, he or she is an incidental line-clearance arborist. This means a tree worker may be subject to either the paragraphs under 4.2 Incidental Line Clearance or 4.3 Utility Line Clearance, depending on who they are working for on a given day.

Unqualified workers

The root cause of most electrocutions is an unqualified worker. Lacking the skills and knowledge to appreciate the hazard and know how to work safely around it, they typically bring themselves or their conductive tools or ladders within 10 feet of the conductor, managing to contact it directly or indirectly. If a worker does not have the prerequisite training and experience, he or she may not work in a tree from an elevated position – aerial lift, climbing or even from a ladder – if any part of the tree is within 10 feet of a conductor.

This means if the tip of a branch is within 10 feet of even a service drop, an arborist cannot be in the tree’s canopy unless the arborist is qualified. The tree trimmer cannot even be climbing in a wide-spreading tree, perhaps 30 feet or more from the wire, if a single branch tip is within 10 feet of the conductor. Why? Because the tree is a conductive object.

• 4.1.7 – always maintain the minimum approach distance in Table 1, measured radially.

• 4.1.13– ladders, platforms and aerial devices, including insulated aerial devices, must maintain the appropriate minimum approach distance.

Incidental line clearance

The lowest-voltage range identified for a qualified line-clearance arborist in their MAD chart (Table 3) is 0.050 to 0.300 kV; for the incidental chart (Table 2), it’s stated as 0.300 kV or less. This lowest-voltage range for both workers has the phrase “avoid contact.” This means the worker can get very close to the conductor if contact by their person or a conductive object is avoided – and that means it does not happen, not that you should just try to avoid it. So, for the incidental line-clearance arborist, you cannot even touch a rope over a communication wire to pull it away.

• 4.2.4 – possess the skill and techniques to know the exposed live parts of the electric equipment; be able to determine nominal voltages of exposed live parts and the appropriate minimum approach distance specified in Table 2.

• 4.2.7 – If branches or other parts of the tree within the minimum approach distance have been browned or charred by past contact, climbing should be avoided.


These four articles have been an overview of the major risks during arboricultural operations and note some of the key parts of the Z133 Safety Requirements intended to eliminate, reduce or avoid common hazards. Most of the hazards discussed in this series are well known to tree workers, as well as the means to manage them. A root cause of many incidents is not that the worker did not know what to do, they just didn’t do it. I will close the series with the best guideline I know to avoid this problem.

“The truth of the matter is that you always know the right thing to do. The hard part is doing it.” – Gen. Norman Schwarzkopf, Jr.

About this series

This is the third in a four-part series of articles looking at causes of the majority of incidents in the tree care profession. Part 1, “Avoiding Struckbys,” ran in the April 2019 issue of TCI Magazine. Part 2, “Caught-in or Compressed-by,” ran in May. Part 3, “Falls, Slips and Trips,” ran in June.

Dr. John Ball, CTSP, is professor of forestry at South Dakota State University and a Board Certified Master Arborist. This article is based on his presentation on the same subject at TCI EXPO in Charlotte, North Carolina, last fall. To listen to an audio recording of that presentation, go to this page in the digital version of this issue online, under the Publications tab, and click here.

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