Electricity and the apparatus that supports its generation, distribution and use are commonplace in modern society. All arborists must work around these facilities. Yes, line clearance crews have the job to remove tree and shrub disruptions from service corridors. However, even residential arborists must work around communication lines, service drops, streetlight wires and homeowner-installed conductors, just to name a few.
In the terminology of workplace hazards, electrocution and incidents that involve electricity are considered exposure to harmful environment. These types of incidents account for up to one-third of arborist on-the-job injuries and fatalities. Having a firm knowledge of how to work safely around wires and what to avoid, as well as how close a worker can safely approach a conductor, is vital for safe tree care operations.
Electrical systems and facilities differ from region to region, as do laws and standards. Be sure to familiarize yourself with all your local and regional regulations. However, there are some commonalities in work practices we can discuss that will help keep arborists safe.
The first and often most important step in working safely around wires is to recognize the hazard. A thorough job briefing is necessary for any job before work begins. Make sure it includes inspection for any electrical hazards. For a line clearance crew, the wires are there by definition; the proximity of the work to them guaranteed. For residential crews the hazards may exist in many less obvious forms.
Inspect for overhead wires, but also look for buried utilities. Service drops or communication lines may also be present and can carry enough voltage and amps to injure or kill. Be aware of anything the homeowner may have installed, as these may not be to code, well maintained or expected.
In incident reports after electrocution it’s often noted that the crew and/or victim did not see the electrical hazard. While job sites can be complex, and the number of variables vast, electrical hazards can’t be seen unless you look for them. Make sure your crew is taking the time to look for them, identify them, and develop a plan for safe work.
After electrical conductors have been noted, the crew must now ascertain the nominal voltage they carry. As stated earlier, company and regional differences abound in electrical facilities. Be sure to know your area’s quirks and norms. However, there are some basic similarities that can be used to allow tree crews to determine how best to deal with electrical conductors.
First, it is important to remember that we are talking about nominal voltages only. This is the load that the system or hardware is designed to carry. The actual voltage may be lower or higher depending on many factors, from time of day to number of users on the grid. Identifying the nominal voltage allows us to make certain judgements about safe work distances and practices. Two easy ways for arborists to identify nominal voltage is height of wire and size of insulator.
As a general rule, the higher the conductor from the ground, the higher the nominal voltage. This is due to the fact that as the electrical load a conductor is capable of carrying increases, so does its field of induction. This is the area surrounding the conductor within which electricity could “jump” from the conductor to something else.
Another general rule, the larger the insulator the higher the voltage. The insulator (glass or ceramic) holds the wire at a specified distance from other system parts. This makes sense when we remember the ability of electricity to jump from one area to another area with a different electrical potential. Higher voltages will do this more readily and for a greater distance, hence they must be further away from the pole. Most systems will have a ground wire that is also capable of carrying the system voltage and is included in the induction zone.
Be sure your crew can identify your area’s nominal voltages by identifying system height and size of insulators. Also be able to identify various hardware such as transformers.
Because of electricity’s induction field, or ability to jump, arborists must maintain certain distances from systems to work safely. The main factors that affect the minimum approach distances (MAD) are nominal system voltage and altitude above sea level. Distances increase when altitude goes above 5,000 feet in elevation. If you work in elevated areas, be aware of these changes.
Once the nominal voltage is identified the crew can determine how close they can safely approach the conductors. Here we can only speak in generalities, but for residential arborists the minimum approach distance for a conductor 7.6 kilovolts (kV) is 10 feet. Again, generally speaking, in most systems if a conductor is capable of carrying 7.6 kV, it is on an insulator. Lower voltages are protected from induction through other means.
Having said all that, we can infer that if a conductor is on an insulator, the residential arborist can safely approach or work on trees 10 feet or further away from the system. This includes approach by tools and equipment. As the size of the insulator increases and the wires get higher, identify the nominal voltage and check the MAD. Remember, MAD will increase with nominal voltage.
Other systems with lower nominal voltages, such as communication wires and service drops, can still carry fatal voltages and must be treated and worked around with respect. However, arborists with proper training can work closer than 10 feet safely using proper protocol and personal protective equipment (PPE). Familiarity with electrical systems and proper work techniques around them is still a must, regardless of the nominal voltage. Make sure you and your crew are prepared and properly trained.
Working around electrical conductors requires much the same PPE as regular tree work with a few exceptions. Rated eye protection and/or hearing protection remain the same. However, a Class E rated helmet is necessary. These helmets have no holes or metal hardware that could allow electricity to pass. Be aware that helmets with manufactured holes that are plugged will not suffice. Many line clearance arborists and linemen are required to wear flame-retardant clothing as well. This may or not be required in your area. Rubber gloves and insulated poles should not be regarded as offering any greater level of safety for arborists. In general, we are not trained in the necessary inspection, storage and use of these tools.
Electricity and the systems that transport it are a part of our lives and environment. The ability to identify, ascertain nominal voltage and determine proper MADs are skills all residential arborists should hone through training and experience. Knowing safe distances and proper procedures for working around conductors is also a skill set to be developed and perfected by all residential arborists. Electricity and electrical systems can be worked around safely, it just takes knowledge, skill, practice and attention to detail.