By Sara Sankowich
When it comes to working near power lines, tree workers must always use extreme caution. Utilities recommend treating all wires as if they are energized and dangerous, yet accidents involving tree workers and power lines occur every year. Armed with a basic understanding of electricity and simple precautions, tree workers can reduce some risk of serious injury when operating around electrified lines. However, extensive training — including information not covered here — is needed to teach tree workers how to identify voltage and wire types and qualify them to work in this and other high-risk environments.
How electricity travels
It is important for workers to understand how electricity travels in order to stay safe. Electricity travels in stages from a power station to homes and businesses, with voltage strength typically decreasing at each stage. From the power plant, electricity is sent through transformers that first increase the voltage to help it travel long distances. Then the charge travels across transmission lines to substations. At a substation, the voltage is lowered so the charge can be sent across smaller distribution lines through cities and towns, where it is lowered again before finally connecting to homes and businesses. Most of the time, the thin top wire at the top of the utility pole is electrified. Lower wires typically are communication wires, but this is not a hard-and-fast rule. Never assume a wire is safe to touch.
Electricity always flows to the ground via the path of least resistance. The human body is mostly water and is an easy path for electricity to flow through. Workers never want to become that path! When the system is operating normally, electricity flows through wires and safely into buildings. But when that system is disrupted, electricity can travel through a tree branch, a person, or another object that enters its path.
When an energized line falls and makes contact with ground, the earth becomes energized and the voltage dissipates in the ground. As you move farther away from the initial contact point, the voltage changes and decreases. This change can be represented as concentric rings — as when a rock is thrown into a pond and the ripples flow outward. Each unseen “ring” of electricity in the ground has a different voltage. Workers need to be aware of “step potential,” or the voltage value change from ring to ring that can occur when someone takes a step on energized ground. Once a worker has his or her feet in two different voltage zones, he or she is facing a “step potential hazard” and can receive a powerful or deadly electric shock, as the body becomes the path of least resistance for the flow of electricity. Voltage values that equal one another (two feet next to each other on the same “ring”) are of the same potential and put a worker in the same position as a bird on the wire — safe. Workers near potentially energized ground should always keep their feet at the same step potential by hopping or shuffling to safety.
Assume every wire is energized
Just because a wire is down or sits innocently on the ground, it does not mean it is safe. A downed wire is often still energized, especially if the other end remains connected to the source of power. Wires are not insulated like the cords attached to lights, appliances, and other electric devices in our homes. They may have a protective coating, but this will not protect an object or person that comes in contact with the wire.
Workers can come in contact with electric lines through direct or indirect contact. Direct contact means that the worker’s body touches the wires. Indirect contact is when a conductive object (such as an uninsulated tool, rope, tree limb, or branch) that is touching the wires then touches the worker. In both cases, the worker becomes part of the electricity’s path to ground.
While no single practice or piece of safety equipment can fully protect against an incident, tree workers can reduce their risk of injury by taking several precautions on the job site.
First, workers should assess each site by looking for electric wires. They can follow wires from a known location (such as where they attach to a house) out to the road or sometimes to where they disappear into foliage. It is important to identify the path of the wire and keep it in mind when considering the risks of working in a tree (including whether it is safe to climb and work in).
Once in the tree or working aloft, a worker should always have a spotter on the ground who, in addition to watching for other dangers, is aware of identified electric lines and their proximity to ongoing work. All workers must know and use clear communication signals for when to stop working if danger is present.
The climber or bucket operator should be aware of the wires at all times and where they are in relation to their own bodies or equipment. They also need to consider not just their own body and equipment position, but the location of the limbs and branches on which they are working — and, more important, whether these branches might come in contact with an electric line if they are cut and fall in an unexpected direction. A climber should also climb on the side of the tree opposite to conductors when possible, and create a tie-in position that takes the potential for swing into the conductors — if a fall should occur — into account.
Trees and the environment are unpredictable, and this unpredictability is the greatest threat to a worker. Unexpected weights, defects, and movements of limbs from a gust of wind can quickly create a hazardous situation. Making small, controllable cuts can help workers manage tree limbs and better anticipate where they may fall, which can lower the risk of a limb landing on a live wire if it goes the wrong way. The use of ropes and other devices can help workers safely move pieces to a landing zone on the ground without contacting wires.
On any job site, tree workers should make sure they know their exact location, including the town and the nearest cross street. If an accident occurs, this information will be vital to emergency personnel. Additionally, should a worker receive an electric shock and be unresponsive, after first calling 911, other crew members must be sure the accident victim is clear of any electric danger before attempting to perform an aerial rescue; if not, do not attempt a rescue. Rushing to try to save someone could create multiple victims. Emergency first responders will also need to keep in mind that the source of electricity could still be present. It is critical for all involved at the scene to continue to use the utmost caution and ensure additional workers are not put in harm’s way.
The American National Standards Institute (ANSI) guidelines on Safety Requirements for Arboricultural Operations, Z133, addresses electrical hazards and provides the minimum approach distances for qualified persons other than qualified line-clearance arborists.
Remember: tree workers should assume all wires are energized, non line-clearance qualified arborists should maintain at least a 10-foot clearance from overhead wires, and everyone should remain at least 30 feet from downed wires.
Special issues: Storm cleanup and line clearance qualified workers
Tree workers performing town or residential cleanup after a storm event face additional safety considerations. Electric utility customers may be dealing with power outages in the area and workers must make sure no wires are present in a felled tree area. If wires are present, workers need confirmation from the utility that the customer’s service line has been disconnected until repairs have been made and it can be safely reattached. Workers additionally must be cautious that downed trees are not leaning on an electric service wire (a customer may still have power at his or her home, but downed trees in contact with wires remain hazardous to workers).
Utility storm tree cleanup is performed by line clearance qualified workers hired directly by the electric utility. Line clearance qualified workers have specialized training that allows them to prune or remove vegetation within 10 feet of energized power lines. They often wear special gear, including “EH” (electrical hazard) rated safety shoes designed to impede the flow of electricity through the shoe to the ground, which reduces — but does not eliminate — the possibility of electrocution. There is no shoe, glove, or apparel item that negates the risk of electric shock.
After a storm event, all workers should be aware of the potential for electrical hazards created by improper generator hookup. If a homeowner’s generator is hooked up improperly, it can back-feed into the electrical grid and cause otherwise de-energized lines to become energized. This is another reason to always treat all electric wires as hot.
The bottom line
Regardless of their qualification level, tree workers working around electric wires must stay alert at all times, and not become so preoccupied with cutting that they don’t see potential dangers. If nothing else, workers should remember to stay 30 feet from downed wires, at least 10 feet from overhead wires, and always assume a wire is hot.
Sara Sankowich is system arborist at Unitil, a public utility holding company, headquartered in Hampton, New Hampshire, that provides electric and natural gas distribution services in New England.