You have enough to think about when you are focused on the task at hand. Excavating to a deadline, and wishing to maintain your exemplary levels of quality workmanship and safety. This latest job has you working close to power lines and both you and your spotter have been working for the better part of the day. Knowing that these high voltage lines impose yet another additional demand upon your multitasking mind, you begin to juggle priorities, quality, safety, dead lines. This struggle leads you down a dangerous path. As the angle of the sun lowers, it becomes a little more difficult for you to keep one eye on your spotter, and one on the darkening trench before you, then it happens: there is a bright flash out of the corner of your eye, the loud ‘crack’ of a high voltage arc, followed by a heavy transformer type hum, and then quiet. One of the main hydro line breakers has been tripped, but it is on a time delay, and about to automatically reset. Knowing that this is a possibility, you stay put, waving to the others to stay away, and advising them to call the local hydro company. They arrive promptly and disable the automatic reset, allowing you to safely disembark from your equipment.
As with any job, efficiency and safety are crucial. It’s also important to recognize when the number of factors is stacking up against you. Weather conditions, the time of day, aboveground and belowground hazards, time pressures, all of these and others may all begin to stack up, until there is possibly just one too many.
Contact with electricity continues to be a significant cause of fatalities within the construction industry. The US Bureau of Statistics and the Center for Construction Research and Training monitors injuries and fatalities that occur each year, and the number of overall fatalities within the construction industry in the U.S. is considered to be relatively high when compared to other countries. Of the deaths that are related to electrocution, a significant portion is related to equipment contacting high voltage lines. Electrocution continues to be the cause of one in five deaths in the construction industry, and a good number of these are preventable.
Some rules that have been designed to help improve safety include minimum required clearances from power lines. These are stipulated by the U.S. Occupational Safety and Health Administration.
Determine the voltages of the lines you are working in close proximity with (check the pole or poles for a voltage label; if there is none, call the local utility) and have a trained spotter assist you in maintaining these minimum required distances.
If, for example, the spotter becomes distracted by having to clear people out of the area, stop work until his full attention is back on the job. Ensure that both operator and spotter understand, and are working from, the same set of hand signals. Review them prior to commencing work, if necessary.
The spotter should wear visible clothing and be positioned in a way that they are readily visible to the operator. Be aware of the risk of arc flash to overhead lines. Absolute contact my not be necessary under some conditions, such as high humidity, or a damp earth. Both of these factors make your machine a more attractive ground path for high voltage.
Respect the minimum distances, as these have been determined by taking environmental factors into consideration. If work is such that the minimum distances cannot be observed, arrange for the local utility to shut down the power or have the utility add wire insulators in the required locations.
If the power is shut down, the utility will clamp on an auxiliary ground wire which serves two purposes: first, it drains any residual charge, if present, and ensures that no ‘stray’ voltages can be induced into the line; and secondly, it provides an important visual confirmation that the power is off and the line is de-energized.
As excavator work involves loading dump trucks, it is important to inform dump truck drivers of the presence of overhead wires. Numerous fatalities have occurred by an elevated box coming into contact with overhead power lines.
Despite the best preventative measures, accidents unfortunately still happen, and it is important to know what to do in the event of an electrical accident.
If the equipment comes into contact with overhead power lines
If the contact was only momentary, it is still important to report this to the utility so they can check the wire, especially if arcing was observed. A weakened wire could break later on (with increased wind or small amount of freezing rain) creating an unexpected hazard.
If the wire remains in contact with the equipment:
Stay on the equipment. The key is to avoid becoming part of the current path. In most situations the current path is between the power line, the metal part of the equipment and the ground. Avoid touching any metal objects. Keep gloves on. Any added insulation that may reduce possible current flow is a help.
Warn others to stay away. Even if the power seems to have stopped, it could come on again without warning. The earth near the equipment can contain harmful voltages. The equipment and anything in contact with the equipment should not be touched.
Call the local utility. Get someone to call the local electrical utility for you. These are the only people with the equipment and expertise to help you out of your current situation. They will disconnect the power and be able to confirm that it is disconnected. They will advise you when it is safe to disembark.
In case of fire, jump clear! It may be necessary to jump out of the equipment to avoid the hazards of a fire. Jump clear of the equipment and land with both feet together, then shuffle away from the equipment. Potential (voltage) differences can develop in the soil surrounding the machine. Shuffling ensures that the voltage difference between your feet is kept to a minimum. Jumping clear of the equipment ensures that you are not in contact with the equipment and the earth at the same time. Do not climb down. Do not walk or run.
Buried powerlines. Call before you dig (or drill) well in advance to allow time for the utility to come and map out the locations of all of the buried power lines. The locations should be added to the drawings and conspicuously flagged and marked out on the construction site itself. Ensure that these are not removed until the job is done. The metal bucket, or auger, will energize the equipment. Anyone coming in contact with both the equipment and the ground while this is occurring will be electrocuted.
In the event that equipment comes in contact with buried power lines, the same rules apply: Stay in the equipment; keep other people away; and, get someone to call the utility.
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Ross Price is with the engineering team at Spectron Safety Inc., a manufacturer of the Line Defender, helping construction companies safeguard excavating equipment from dangerous overhead wires. For more information and for a free copy of Spectron Safety’s Excavator Safety Guide, visit: www.spectronsafety.com/mcsguide
