Module 4:Overhead and Underground Power Lines

Overview of Module 4Background on power linesHazards of overhead and underground power linesInjury prevention techniquesSummary

BackgroundPower lines transmit electricityElectrical current exposes workers to serious hazardsMost common hazard is electrocutionMost workers are unaware of potential electrical hazards Power lines can beOverheadUndergroundPower lines and transmission towersUnderground Utility Work

Background (cont)Some activities may cause interference with power linesOverhead power linesOperation of a crane, forklift, and other construction equipmentChanging street lightsTree trimmingUnderground power linesExcavationCaution: Look out for overhead power lines when operating equipment

Types of Electrical LinesElectrical Cables High Voltage, Low VoltageSupervisory and Signaling CablesCathodic protection (cabinets, cables, earthing conductors, cable shrouds)Communication CablesPhone linesCoaxial cables (e.g. data cables)Broadband cablesTram traction cables and trolley wiresRailway supply cables and traction wires

Power Line HazardsWho is at risk?Almost everyone working near power linesCommon hazards:ElectrocutionInjuries are typically fatalElectrical shockFiresFallsAs a result of contact with electricityFire may be caused after overhead power lines are hitWhen unloading materials, watch out for overhead power lines

Common MisconceptionsBirds land on power lines, so they must be safe to touch - NOMain objective of electricity is to reach the ground using the most direct routeBirds do not get electrocuted when they land on wires because they do not represent a path to the groundThe power lines are safe for perching, but not when struck

Common MisconceptionsPower lines are insulated, so they are safe to touch - NOThey are not always insulatedInsulation deals with placing nonconductive material around the wire Insulation is a material that offers high electric resistance making it suitable for covering wires to prevent the possible future contact of adjacent conductors resulting in a short circuitJust because a wire is weather protected does not mean that it is insulatedWeather protection prevents water and snow from reaching the wire (and insulation, if used)

Common Misconceptions (Cont)Nonmetallic ladders are safe around power lines - NOWet ladders can be a conducting medium for electricityIf power lines are not touched, they are safe - NOElectricity can jumpMaintain a safe distance from the Danger Zone (10 foot radius from the power line)

Hazard IdentificationConduct site investigation to identify existing conditions of:Voltages of lines and equipmentPresence of hazardous, induced voltagesPresence and condition of protective grounds and equipment grounding conductorsLocations of electrical circuits and equipment Maximum switching transient voltages

Dump truck operators should use caution when unloading materials near overhead power lines

Injury Prevention TechniquesStay away from power lines while workingMaintain a safe distanceOSHAs 10-Foot Circle of Safety ruleIncrease safe distance near higher voltage power lines

Maintain a safe distance from the Danger Zone (10 foot radius from the power line)

Operation Clearances for Energized Overhead LinesIn Transit Clearances for Energized Overhead LinesSource: OSHA

Nominal VoltageMinimum Required Distance (Feet)0 to 50,00010Over 50,00010+0.4 inch for each 1,000 volt

Nominal VoltageMinimum Required Distance (Feet)0 to 50,000450,000 to 345,00010Over 345,000 to 750,00016

Injury Prevention TechniquesRecognize high voltage power linesIf unknown, the appropriate agency should be contactedInform others about high-voltage power linesBe aware of nearby high-voltage power lines

Injury Prevention TechniquesExamine the site Be mindful of power linesSearch carefully around the siteLook for lines not seen due to obstructionsAlert others at the pre-job briefingAssume all lines are energized and potentially dangerousMake a safety clearance boundaryPortable safety barriers

HAZARD:Safe distance has not been maintained

Injury PreventionUse a spotterEquipment operators have limited visibilityGet spotters help to stay clear of overhead power linesSpotters job should only require spotting and NOT guidingGuiders may be at risk of electrical shockEspecially when using a tag line

A spotter guiding heavy equipment operator

Injury PreventionWhen working with tall and long equipmentCarefully plan and organize work with heavy equipmentKeep vehicles clear of power linesWatch out for long objectsAdjust the position of equipment to maintain a safe distance from power linesWorking with tall equipment

Injury PreventionIn cases of fallen power linesStay awayCall for helpShuffle with your feet together and on the ground to minimize electrical shockEncourage others to do the sameDown power lines are dangerous

Injury PreventionFallen power lines can cause fires

If a co-worker makes contact with a power lineStay awayProtect yourselfYou could be shocked too if you touch someone who is in contact with electricityFire caused by fallen power line

Injury PreventionIf you hit a power lineIn case of no immediate dangerMove the equipment awayHave someone call 911Stay on the equipment until you know it is safe.Warn others to stay awayIf you MUST get off the equipment, jump clearCrane hitting a power line

Underground Power LinesHitting a buried power, gas or communications line can cause InjuryExcessive cost of repairPlan the work aheadCall the utility companyWith proper planning, these types of mistakes can be avoided

Underground Power LinesLocate and mark the perimeter of underground linesExercise caution when excavating near power linesSome manual excavation may be requiredStay away from pad mount transformersGreen metal box

Underground utility line that has been hit

Tree TrimmingTrees that grow into power lines can cause unnecessary power outagesTrees planted under or near power lines are potentially dangerous hazardsBefore tree trimming, check for the power linesUse proper equipment and trained personnelTree trimming may be dangerous if power lines are hidden in the foliage

Applicable Standards29 CFR 1926, Subpart K Electrical 29 CFR 1926, Subpart N Cranes, Derricks29 CFR 1926, Subpart O Motor Vehicles, Mechanized Equipment29 CFR 1926, Subpart P Excavations 1926.416 Electrical Hazards1926.955 Overhead Lines1926.956 Underground Lines

Summary of the ModuleWorking in proximity of overhead and underground power lines is hazardousMost common hazard is electrocutionWorkers should be aware of such hazardsSeveral injury prevention techniques should be exercised to prevent injuries and fatalitiesNeed sufficient training to understand the hazards and practices for injury preventionOne of the best ways of hazard elimination is maintain a minimum safe distanceProperly locate underground power lines before starting of work

In this module several topics related to power lines will be covered including fundamentals and principles on electricity and power transmission, work activities and environments related to power line safety hazards, hazard identification and recognition, injury prevention techniques, and highlights of the salient points to use in construction work activities in order to minimize personal injuries.

Overhead power lines are supported by transmission towers and/or utility poles which carry electricity from the point of generation to individual homes, offices, industries, etc. The utility lines often follow the highway right of way. Thus, they surround many highway construction sites. Electrical current exposes workers to serious occupational hazards. Most members of the workforce may be exposed to electrical current during the performance of their daily duties, and highway construction workers are no exception. Electrocutions can involve workers in various job categories. Most workers are unaware of the potential electrical hazards present in their work environment, which makes them more vulnerable to related dangers. Historic data reveals that electrocution accounts for a significant portion of fatalities in the construction industry, many of which involve contact with overhead power lines. Power lines are located both overhead and underground. High voltage power lines are typically located above ground in the rural areas. However, underground power lines are also common in urban areas.

While working in highway construction projects, activities performed at higher elevations, or those involving heavy equipment may be more susceptible to contact with overhead power lines. Some of these activities include the operation of heavy equipment such as cranes, forklifts, etc., changing street lights, tree trimming and others. The photograph in this slide provides an example of an excavator that is in potential contact with an overhead power line. If direct contact had been made, sparks or flames may result and would be visible in the photograph as well. Equipment operators should be cognizant of the potential danger of power lines and take the necessary precautions to avoid them. Construction activities related to earth work or excavation can cause interference with underground power lines. In most urban areas, utility companies insist on being notified prior to commencing any work so that they can provide the exact locations of the power lines. This helps the construction workers to avoid interfering with the power lines during the construction activities.Power lines typically carry 4,000 to 345,000 volts of electricity that can injure or kill a person on contact. Electrical cables can be high voltage or low voltage, and can be overhead or underground. Those cables that have higher voltages are associated with higher potential danger.Communication cables, such as telephone lines, data cables and broadband cables typically carry lower voltages, and are not necessarily as dangerous as electrical cables. These types of cables may be located overhead or underground. Tram traction cables, trolley wires and railway cables and wires carry higher voltages and are typically located overhead. However, contact with any cable often results in a disruption of service to the users and often have financial implications. In any case, if the voltage of a power line is unknown, it is better to assume that the line has a high voltage, and take the appropriate precautions to avoid any kind of contact.

Almost every worker who is working near overhead or underground power lines may be at risk to potential hazards of power lines including on foot workers, equipment operators, truck drivers, spotters, guiders, and other surrounding workers. Since power and electricity are an integral part of everyday life, people generally feel very comfortable around it and may not be aware of the associated hazards. This may generate a false sense of security related to power lines.Common hazards related to power lines include electrocution (injuries are most often fatal), electrical shock (injuries range from minor to fatal), burns as a result of direct contact with electricity or from an electrical fire, and falls (either as a result of a jolt from electrical shock, or when jumping out of equipment/vehicles).

The main objective of electricity is to reach the ground and it will always try to get to the ground by the easiest, most direct route. Birds do not get electrocuted when they land on the wires because they do not represent a path to the ground. A bird on the wire does not give electricity anywhere to go except to go back to the same wire, so it is easier for current to continue on its path in the wire. However, a ladder, a pole or even something as small as a wet string that comes in contact with a new path to the ground can be dangerous. If someone comes in contact with an object that is somehow touching a power line, then they may become part of the path to the ground and be electrocuted. Many people have the misconception that power lines are insulated, so theyre safe to touch. Power lines are typically NOT insulated and one should always avoid contact with them, in order to eliminate the possibility of being electrocuted.While metal is an excellent conductor of electricity, it is not the only conductor. Water is also a conductor of electricity. If a wooden ladder, or ladder made of any other material is wet, then it can be a conductor of electricity and the person using the ladder can be injured upon the contact with electricity.Everything conducts electricity to some degree. A materials conductivity is measured in terms of resistance, which is typically classified as low, medium or high. Some examples of good conductors include gold, silver, copper, aluminum, steel, mercury, salt water and people. Fair conductors include wet wood, water, soil and tires. Poor conductors include glass, porcelain, plastic, paper, pure rubber, fiberglass and asbestos. The other misconception is that as long as someone does not directly touch an object that has just come in contact with electricity (such as a ladder), then they are safe. This is not true. Electricity can jump to a potential conductor such as a metal ladder, depending on how far away you are from the power lines. The proximity in which electricity can jump depends on the weather conditions, the voltage of the power line, and other factors.

Identifying existing conditions related to power line safety that are associated with specific work activities is extremely important before starting work on or near power lines. This survey will assist in properly planning the work activities and abating potential hazardous actions. In these surveys, the location and voltage of all power lines (above and below ground) should be determined. If and when possible, detailed information related to the power lines should also be obtained in order to assess the extent of possible hazards for a given site and how to minimize potential hazards to workers. Background information on nearby power lines may be obtained from local one-call utility companies, such as MISDIG in Michigan. Every state in the U.S. has its own version of a one-call utility company or center, since a national branch does not exist to govern all such companies. The name of the one-call utility company varies from state to state, however, the general purpose of these companies are to assist anyone who would like to locate or inquire about power lines in an area of a community. One-call utility companies typically stake underground public utility lines and provide overhead electric line support to ensure sufficient clearances are maintained at no charge to individuals or companies who are seeking their assistance. In cases where sufficient clearances cannot be maintained in a work area, the local one-call utility company can arrange for the lines to be de-energized or covered by protective layering in order to improve the safety conditions related to power lines.Overhead power lines are located virtually everywhere, especially nearby roads and highways, since they often follow the public right-of-way. This photograph illustrates materials in close proximity to a power line, which poses potential hazards to the truck driver and nearby on-foot workers.

Power lines carry 4,000 to 345,000 volts of electricity that can injure or kill a worker on contact. A basic rule to prevent injuries associated with power lines is to identify where the power lines are located and to avoid the contact with them.OSHA regulation states that a minimum safe distance of 10 feet should be maintained around power lines. However, for higher voltages, an increased safe distances shall be maintained, as shown on the following slides.

No work shall be performed, no material shall be piled, stored or otherwise handled without maintaining a safe distance from energized power lines. OSHA regulations state that during any operation, clearances of a minimum of 10 feet shall be maintained for overhead power lines of 0 to 50,000 voltage. For voltages over 50,000, an additional 0.4 inch of clearance distance per 1,000 volt shall be maintained. When equipment is in transit with lowered boom and no load, a clearance distance of a minimum of 4 feet shall be maintained for voltages of 0 to 50,000. The minimum clearance distance is increased to 10 feet near power lines with voltages of 50,000 to 345,000; and further increases to 16 feet near power lines with voltages of 345,000 to 750,000. If it is not possible to maintain the minimum clearance distances, due to space constraints within the work area, measures should be taken to de-energize the power lines by contacting a one-call utility company.

High voltage power lines pose severe risk of injury or death if contacted. Thus, extra precautions should be taken to identify their presence and plan the work activities accordingly. On-site supervisors and/or other personnel should determine if any high voltage power lines are located in the vicinity of the work area. Many times, high voltage power lines can be easily identified, either by warning signs posted in the area, or orange spherical line indicators mounted directly on the power line. If the voltages of the power lines around the work area are not marked as high voltage lines, and are otherwise unknown, a representative from the one-call utility company should be contacted to obtain the necessary information. Once the presence of high voltage power lines are confirmed, all workers should be notified of their location, instructed to take additional precautions to avoid them, and cautioned of their potential hazards. For activities that will take place in areas located in relatively closer proximity to the high voltage power lines, specific safety plans should be discussed with the associated workers in order to ensure their safety.Search carefully for overhead power lines, poles and guy wires. Since on-site conditions can change, check the site frequently. Look for lines that may be blocked from view by trees or buildings. If hidden power lines are suspected, contact the local on-call utility company, inspectors and/or experienced colleagues to express your concerns. All workers should be informed about the location of nearby power lines and potential hazards at the pre-job briefing. Regardless of their specific duties, all workers must be aware of power lines, including heavy equipment operators, material loaders, truck drivers, workers using hand-held tools, climbing ladders, etc. In order to ensure safety of workers, it is better to assume that all lines are energized and potentially dangerous, and to maintain a minimum 10-foot clear distance at all times. This includes overhead and underground lines and the service drops that run from utility poles to buildings.Physical safety barriers may be placed underneath the overhead lines in order to designate the area in which workers are to stay clear of. This will minimize the possibility of workers coming in contact with the power lines.

When operating any construction equipment, it may be difficult for the operator to judge the distance between the equipment and the power line, due to limited sight lines. Certain weather conditions and bright or dim lighting conditions can make it even harder to see the power lines and thus, increases the chance of coming in contact with the power lines.Someone trained and on the ground, watching around the operator can have a much better view of the power lines. The equipment/vehicle operators should work with a spotter, whose only job is to watch the operator and the position of the equipment to make sure that the operator is at a safe working distance from overhead lines and other hazards. It is essential that the spotter receive adequate training in order to accurately judge the distances. Guiders assist the movement/placement of objects through the use of a tag line, which helps prevent large objects from swaying. If a crane or other piece of equipment the guider is guiding hits an overhead power line, electricity can travel down the tag line the guider is holding and injure the operator. In the event of power line contact, workers on the ground are in the greatest risk of electrocution.The same person should not be responsible for guiding and spotting at the same time. A spotter should be assigned the task of making sure that the equipment stays clear of power lines. Spotting effectively needs the spotters full attention.The life of the operator can depend on the spotter. Make sure the spotter does only one job, that is spotting.

Careful planning of heavy equipment placement (such as cranes) is required to ensure safety for workers and equipment operators. The contractor should plan the locations of heavy equipment in advance in coordination with the one-call utility company. However, even with proper planning, tall/long equipment and work operations may be located near power lines. In such cases, a spotter should be used to assist the equipment operator. In high risk situations, it may be desirable to have the power lines de-energized.Long-bed dump trucks, concrete pumping rigs and other equipment requiring higher clearances can be in contact with overhead power lines. Make sure the operator knows the safe distance to maintain. Use a spotter to keep equipment clear from power lines.Carry ladders and other long objects parallel to the ground until they are ready to be used. Before adjusting ladders or other long equipment, assess clear height requirements to ensure the total height will remain a safe distance from the overhead lines.Fallen power lines can be dangerous to anyone (road workers, pedestrians, motorists) in the nearby vicinity since they may contain live electricity. Stay away from power lines, even if they are not humming, sparking or dancing. If a fallen power line is detected, one should (a) carefully move away from the line, as well as any object that it has touched, (b) instruct others in the area to do the same and (c) call 911 and/or the electric company to report the fallen line.Fallen lines are most common after storms and high winds. If you are outside after a storm, be alert for lines that may be obscured by streams or standing water.Shuffle, dont run, from a fallen line. The correct technique for moving away from a fallen line is to shuffle with your feet together and on the ground. Fight the urge to run and warn others not to run. This is because when a live wire touches the ground, electricity travels through the ground in all directions. If you run or take large steps, you increase the chance of creating a path for electricity to travel (up one leg and out the other), and you could be electrocuted. Warn others to do the same.

If a tree branch touches a high-voltage power line, electricity from the line can make the branch so hot that it catches on fire. From there the fire can spread to nearby trees, plants and buildings. The photograph illustrates the catastrophic results of such an incident. Stay clear of any person or object that is in contact with a power line. In order to protect yourself, the best thing to do is to stay away. If you touch someone who is in contact with electricity, you could also be electrocuted. You can also be electrocuted if you touch the vehicle or equipment that person is in contact with the tool they are holding. Do not try to rescue a person who is in contact with electricity, as you may also be electrocuted. Instead call 911 and the electric company immediately. Do not try to help the victim until you are sure the power is off.

If you hit a power line while operating equipment, and are in no immediate danger (i.e. no fire, no immediate shock occurred), the following steps should be taken: (1) move the equipment away from the line, if it can be done safely, (2) do not attempt to leave the equipment until told by a rescuer, and (3) advise others to stay away since workers standing on the ground have the greatest risk of being injured. If you must get off the equipment due to fire or other danger, jump clear and try to land far enough away from the equipment and dont touch the equipment and the ground at the same time. Land with your feet together and shuffle away keeping your feet together and on the ground.

The risks of coming in contact with underground power lines are similar to that of overhead lines. Hitting a buried power, gas or communication lines can cause serious injury. In the case an overhead power line is hit, the risk of electrocution exists, while in the case an underground gas line is hit, an explosion or fire may result. In addition to the risk of injuries, hitting underground lines typically result in excessive costs to repair the damages. Underground power lines, communication cables, gas lines, water lines or other utilities may lie at various depths below the surface areas of the road. It is important to be safe before excavating by contacting the local one-call utility company. Be sure to allow enough time for the utility companies to mark the location of their underground facilities before the work activities begin.The locations of underground power lines should be marked before any excavation work begins. This is typically done by the local one-call utility company. Since the locations marked for underground power lines may not be exact, caution should be exercised when excavating in close proximity to these locations. Manual excavation may be necessary in such situations and should be done cautiously and slowly, assuming that workers may be at risk of hitting underground utility lines unexpectedly.Workers should be advised to stay away from pad mount transformers, which are green metal boxes that contain the above-ground portion of an underground electrical installation. These boxes transform high and low voltage electricity which is then carried in insulated underground power lines. If the transformers appear to be damaged in any way, the local one-call utility company should be contacted to take appropriate action.

Trees that grow in close proximity to power lines may cause unnecessary power outages. Trees planted near or under power lines are potentially dangerous. Serious or fatal shocks can occur when working on trees near power lines. Trees that branch into electrical lines can cause momentary short circuits (flickering lights) or major outages when combined with thunderstorms, high winds, sleet and snow.Before trimming any tree, check to make sure that there is no power lines in or near the tree. If you see power lines, STOP.When cutting tree limbs near power lines proper personal protective equipment should be worn and the worker should have received adequate training before beginning the work activities. The photograph on the right shows a worker who is trimming tree branches that are located near overhead power lines, without wearing the necessary personal protective gears.

This module discussed the overview of the electrical power lines (overhead and underground), hazards associated with them and the injury prevention techniques to be exercised while working close to power lines.It is a fact that working near overhead and underground power lines is hazardous since they may cause serious injuries and fatalities to workers if workers come in contact with electricity. Workers should also be aware of the fact that it is not necessary to touch the electricity, rather working very close to electricity can be hazardous if the voltage is higher (electricity can jump). If workers are aware of such hazards, they will be prepared to stay away from such hazards and will exercise the practices to prevent injuries.This module also discussed various injury prevention techniques and explained what to do if you or your coworkers hit a power line. Providing sufficient training to workers about the hazards of electricity and injury prevention techniques allows workers a safe working habit. It should be noted that one of the best ways to eliminate the hazards of power lines is to stay away and maintain a minimum safe distance from the power lines as explained in this module. If the work is to be carried out close to power lines, they should be completely de-energized.Note that properly locating the underground power lines for locations, routes, depths and voltage is extremely important. If workers know the locations of hazards, they may be better prepared to prevent injuries. All buried cables should be considered live and lethal.