Module 4 Overhead and Underground Power Lines Overview
- Slides: 26
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 and transmission towers • Power lines can be – Overhead – Underground Utility W
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: When unloading materials, watch out for overhead • Injuries are typically fatal power lines – Electrocution – Electrical shock – Fires – Falls • As a result of contact with electricity Fire may be caused after overhead power lines are hit
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 Maintain a safe distance from power lines the Danger Zone (10 foot radius from the power line)
Operation Clearances for Energized Overhead Lines Nominal Voltage Minimum Required Distance (Feet) 0 to 50, 000 10 Over 50, 000 10+0. 4 inch for each 1, 000 volt “In Transit” Clearances for Energized Overhead Lines Nominal Voltage Minimum Required Distance (Feet) 0 to 50, 000 4 50, 000 to 345, 000 10 Over 345, 000 to 750, 000 16 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 Fire caused by fallen power line • 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
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 l
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 av
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 Tree trimming may be trained personnel 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 • 1926. 416 Electrical Hazards • 1926. 955 Overhead Lines • 1926. 956 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
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