Module 4: Overhead and Underground Power Lines

Overview of Module 4 Background on power lines Hazards of overhead and underground power lines Injury prevention techniques Summary

Background Power lines transmit electricity Electrical current exposes workers to serious hazards –Most common hazard is electrocution –Most workers are unaware of potential electrical hazards Power lines can be –Overhead –Underground Power lines and transmission towers Underground Utility Work

Background (cont) Some activities may cause interference with power lines –Overhead power lines Operation of a crane, forklift, and other construction equipment Changing street lights Tree trimming –Underground power lines Excavation Caution: Look out for overhead power lines when operating equipment

Types of Electrical Lines Electrical Cables –High Voltage, Low Voltage –Supervisory and Signaling Cables –Cathodic protection (cabinets, cables, earthing conductors, cable shrouds) Communication Cables –Phone lines –Coaxial cables (e.g. data cables) –Broadband cables –Tram traction cables and trolley wires –Railway supply cables and traction wires

Power Line Hazards Who is at risk? Almost everyone working near power lines Common hazards: –Electrocution Injuries are typically fatal –Electrical shock –Fires –Falls As a result of contact with electricity Fire may be caused after overhead power lines are hit When unloading materials, watch out for overhead power lines

Common Misconceptions Birds land on power lines, so they must be safe to touch - NO –Main objective of electricity is to reach the ground using the most direct route –Birds do not get electrocuted when they land on wires because they do not represent a path to the ground The power lines are safe for perching, but not when struck

Common Misconceptions Power lines are insulated, so they are safe to touch - NO –They are not always insulated Insulation 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 circuit –Just because a wire is weather protected does not mean that it is insulated Weather protection prevents water and snow from reaching the wire (and insulation, if used)

Common Misconceptions (Cont) Nonmetallic ladders are safe around power lines - NO –Wet ladders can be a conducting medium for electricity If power lines are not touched, they are safe - NO –Electricity can jump Maintain a safe distance from the Danger Zone (10 foot radius from the power line)

Hazard Identification Conduct site investigation to identify existing conditions of: –Voltages of lines and equipment –Presence of hazardous, induced voltages –Presence and condition of protective grounds and equipment grounding conductors –Locations of electrical circuits and equipment –Maximum switching transient voltages

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

Injury Prevention Techniques Stay away from power lines while working Maintain a safe distance –OSHA’s “10-Foot Circle of Safety” rule –Increase safe distance near higher voltage power lines Maintain a safe distance from the Danger Zone (10 foot radius from the power line)

Nominal VoltageMinimum Required Distance (Feet) 0 to 50,00010 Over 50, inch for each 1,000 volt Operation Clearances for Energized Overhead Lines Nominal VoltageMinimum Required Distance (Feet) 0 to 50, ,000 to 345,00010 Over 345,000 to 750, “In Transit” Clearances for Energized Overhead Lines Source: OSHA

Injury Prevention Techniques Recognize high voltage power lines –If unknown, the appropriate agency should be contacted Inform others about high-voltage power lines Be aware of nearby high- voltage power lines

Injury Prevention Techniques Examine the site – Be mindful of power lines Search carefully around the site Look for lines not seen due to obstructions Alert others at the pre-job briefing Assume all lines are energized and potentially dangerous Make a safety clearance boundary –Portable safety barriers HAZARD: Safe distance has not been maintained

Injury Prevention Use a spotter –Equipment operators have limited visibility –Get spotter’s help to stay clear of overhead power lines Spotter’s job should only require spotting and NOT guiding –Guiders may be at risk of electrical shock Especially when using a tag line A spotter guiding heavy equipment operator

Injury Prevention When working with tall and long equipment –Carefully plan and organize work with heavy equipment –Keep vehicles clear of power lines –Watch out for long objects –Adjust the position of equipment to maintain a safe distance from power lines Working with tall equipment

Injury Prevention In cases of fallen power lines –Stay away –Call for help –Shuffle with your feet together and on the ground to minimize electrical shock –Encourage others to do the same Down power lines are dangerous

Injury Prevention Fallen power lines can cause fires If a co-worker makes contact with a power line –Stay away –Protect yourself You could be shocked too if you touch someone who is in contact with electricity Fire caused by fallen power line

Injury Prevention If you hit a power line –In case of no immediate danger Move the equipment away Have someone call 911 Stay on the equipment until you know it is safe. Warn others to stay away –If you MUST get off the equipment, jump clear Crane hitting a power line

Underground Power Lines Hitting a buried power, gas or communications line can cause – Injury –Excessive cost of repair Plan the work ahead Call the utility company With proper planning, these types of mistakes can be avoided

Underground Power Lines Locate and mark the perimeter of underground lines Exercise caution when excavating near power lines  Some manual excavation may be required Stay away from pad mount transformers –Green metal box Underground utility line that has been hit

Tree Trimming Trees that grow into power lines can cause unnecessary power outages Trees planted under or near power lines are potentially dangerous hazards Before tree trimming, check for the power lines Use proper equipment and trained personnel Tree trimming may be dangerous if power lines are hidden in the foliage

Applicable Standards 29 CFR 1926, Subpart K – Electrical 29 CFR 1926, Subpart N – Cranes, Derricks 29 CFR 1926, Subpart O – Motor Vehicles, Mechanized Equipment 29 CFR 1926, Subpart P – Excavations Electrical Hazards Overhead Lines Underground Lines

Summary of the Module Working in proximity of overhead and underground power lines is hazardous –Most common hazard is electrocution Workers should be aware of such hazards Several injury prevention techniques should be exercised to prevent injuries and fatalities –Need sufficient training to understand the hazards and practices for injury prevention –One of the best ways of hazard elimination is maintain a minimum safe distance Properly locate underground power lines before starting of work