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Electrical Safety - Construction OSHA Office of Training & Education 1 Electricity - The Dangers • About 5 workers are electrocuted every week • Causes 12% of young worker workplace deaths • Takes very little electricity to cause harm • Significant risk of causing fires OSHA Office of Training & Education 2 SUBPART K Electrical Safety Take Electricity Seriously • Electricity is the second leading cause of death in construction. • Electrocutions make up 12% of construction fatalities annually. • Over 30,000 non-fatal shocks occur each year. • Over 600 deaths occur annually due to electrocution. OSHA Office of Training & Education 3 SUBPART K Electrical Safety Electrical Accidents • Leading Causes of Electrical Accidents: Drilling and cutting through cables Using defective tools, cables and equipment Failure to maintain clearance distances Failure to de-energize circuits and follow Lockout/Tagout procedures Failure to guard live parts from accidental worker contact Unqualified personnel working with electricity Improper installation/use of temporary electrical systems and equipment By-passing electrical protective devices OSHA Office of Training & Education 4 SUBPART K Electrical Safety Harmful Effects of Electricity • Shock – Most common and possibly causing electrocution or muscle contraction leading to secondary injury • Burns – Resistance causes heat • Fires – Enough heat or spark can ignite combustible materials • Explosions – Electrical spark can ignite vapors in air OSHA Office of Training & Education 5 Electricity – How it Works • Electricity is the flow of energy from one place to another • Requires a source of power: usually a generating station • A flow of electrons (current) travels through a conductor • Travels in a closed circuit OSHA Office of Training & Education 6 Electrical Terms • Current -- electrical movement (measured in amps) • Circuit -- complete path of the current. Includes electricity source, a conductor, and the output device or load (such as a lamp, tool, or heater) • Resistance -- restriction to electrical flow • Conductors – substances, like metals, with little resistance to electricity that allow electricity to flow • Grounding – a conductive connection to the earth which acts as a protective measure • Insulators -- substances with high resistance to electricity like glass, porcelain, plastic, and dry wood that prevent electricity from getting to unwanted areas OSHA Office of Training & Education 7 Electrical Injuries There are four main types of electrical injuries: • Direct: Electrocution or death due to electrical shock Electrical shock Burns • Indirect - Falls OSHA Office of Training & Education 8 Electrical Shock An electrical shock is received when electrical current passes through the body. You will get an electrical shock if a part of your body completes an electrical circuit by… • Touching a live wire and an electrical ground, or • Touching a live wire and another wire at a different voltage. OSHA Office of Training & Education 9 Shock Severity • Severity of the shock depends on: Path of current through the body Amount of current flowing through the body (amps) Duration of the shocking current through the body, • LOW VOLTAGE DOES NOT MEAN LOW HAZARD OSHA Office of Training & Education 10 Dangers of Electrical Shock • Currents above 10 mA* can paralyze or “freeze” muscles. • Currents more than 75 mA can cause a rapid, ineffective heartbeat -- death will occur in a few minutes unless a defibrillator is used • 75 mA is not much current – a small power drill uses 30 times as much Defibrillator in use * mA = milliampere = 1/1,000 of an ampere OSHA Office of Training & Education 11 Burns • Most common shock-related injury • Occurs when you touch electrical wiring or equipment that is improperly used or maintained • Typically occurs on hands • Very serious injury that needs immediate attention OSHA Office of Training & Education 12 Falls • Electric shock can also cause indirect injuries • Workers in elevated locations who experience a shock may fall, resulting in serious injury or death OSHA Office of Training & Education 13 Electrical Hazards and How to Control Them Electrical accidents are caused by a combination of three factors: Unsafe equipment and/or installation, Workplaces made unsafe by the environment, and Unsafe work practices. OSHA Office of Training & Education 14 Hazard – Exposed Electrical Parts Cover removed from wiring or breaker box OSHA Office of Training & Education 15 Control – Isolate Electrical Parts • Use guards or barriers • Replace covers Guard live parts of electric equipment operating at 50 volts or more against accidental contact OSHA Office of Training & Education 16 Control – Isolate Electrical Parts Cabinets, Boxes & Fittings Conductors going into them must be protected, and unused openings must be closed OSHA Office of Training & Education 17 Control – Close Openings • Junction boxes, pull boxes and fittings must have approved covers • Unused openings in cabinets, boxes and fittings must be closed (no missing knockouts) Photo shows violations of these two requirements OSHA Office of Training & Education 18 Hazard - Overhead Power Lines • Usually not insulated • Examples of equipment that can contact power lines: Crane Ladder Scaffold Backhoe Scissors lift Raised dump truck bed Aluminum paint roller OSHA Office of Training & Education 19 Control - Overhead Power Lines • Stay at least 10 feet away • Post warning signs • Assume that lines are energized • Use wood or fiberglass ladders, not metal • Power line workers need special training & PPE OSHA Office of Training & Education 20 Hazard - Inadequate Wiring • Hazard - wire too small for the current • Example - portable tool with an extension cord that has a wire too small for the tool The tool will draw more current than Wire Gauge the cord can handle, causing overheating and a possible fire without tripping the circuit breaker WIRE The circuit breaker could be the right Wire gauge measures size for the circuit but not for the wires ranging in size from number 36 to 0 American smaller-wire extension cord wire gauge (AWG) OSHA Office of Training & Education 21 Control – Use the Correct Wire • Wire used depends on operation, building materials, electrical load, and environmental factors • Use fixed cords rather than flexible cords • Use the correct extension cord Must be 3-wire type and designed for hard or extra-hard use OSHA Office of Training & Education 22 Hazard – Defective Cords & Wires • Plastic or rubber covering is missing • Damaged extension cords & tools OSHA Office of Training & Education 23 Hazard – Damaged Cords • Cords can be damaged by: Aging Door or window edges Staples or fastenings Abrasion from adjacent materials Activity in the area • Improper use can cause shocks, burns or fire OSHA Office of Training & Education 24 OSHA Office of Training & Education 25 SUBPART K Electrical Safety Defective Cord Incident • Attempting to climb scaffold with electric drill. • Drill’s cord was worn open. • The wire contacted the scaffolding. • The worker died! OSHA Office of Training & Education 26 Control – Cords & Wires • • • • Insulate live wires Check before use Use only cords that are 3-wire type Use only cords marked for hard or extra-hard usage • Use only cords, connection devices, and fittings equipped with strain relief • Remove cords by pulling on the plugs, not the cords • Cords not marked for hard or extrahard use, or which have been modified, must be taken out of service immediately OSHA Office of Training & Education 27 Permissible Use of Flexible Cords DO NOT use flexible wiring where frequent inspection would be difficult or where damage would be likely. Flexible cords must not be . . . • run through holes in walls, ceilings, or floors; • run through doorways, windows, or similar openings (unless physically protected); • hidden in walls, ceilings, floors, conduit or other raceways. Stationary equipment-to facilitate interchange OSHA Office of Training & Education 28 Grounding Grounding creates a lowresistance path from a tool to the earth to disperse unwanted current. When a short or lightning occurs, energy flows to the ground, protecting you from electrical shock, injury and death. OSHA Office of Training & Education 29 Hazard – Improper Grounding • Tools plugged into improperly grounded circuits may become energized • Broken wire or plug on extension cord • Some of the most frequently violated OSHA standards OSHA Office of Training & Education 30 SUBPART K Electrical Safety Can You Rely on Grounding? • Grounding will not work if the electricity can flow through you more easily than the ground. This can happen when: Your tool doesn’t have a ground pin. You’re working in water. You’re touching a metal object. OSHA Office of Training & Education 31 Control – Ground Tools & Equipment • Ground power supply systems, electrical circuits, and electrical equipment • Frequently inspect electrical systems to insure path to ground is continuous • Inspect electrical equipment before use • Don’t remove ground prongs from tools or extension cords • Ground exposed metal parts of equipment OSHA Office of Training & Education 32 SUBPART K Electrical Safety Do Not Eliminate the Ground! You become the next-best path for current! OSHA Office of Training & Education 33 Control – Use GFCI (ground-fault circuit interrupter) • Protects you from shock • Detects difference in current between the black and white wires • If ground fault detected, GFCI shuts off electricity in 1/40th of a second • Use GFCI’s on all 120-volt, singlephase, 15- and 20-ampere receptacles, or have an assured equipment grounding conductor program. OSHA Office of Training & Education 34 SUBPART K Electrical Safety Circuit Protective Devices • Circuit Breakers and Fuses Only protect the building, equipment, and tools from heat build-up! Never depend on circuit breakers or fuses to prevent shocks! • Ground Fault Circuit Interrupter (GFCI) Is the only device which will protect the worker from shock and electrocution! OSHA Office of Training & Education 35 SUBPART K Electrical Safety Types of GFCI Protection OSHA Office of Training & Education 36 SUBPART K Electrical Safety GFCI Protection All temporary circuits are required to have GFCI protection or: Equipment & cords must be included in an Assured Equipment Grounding Conductor Program An extension cord is a temporary circuit (attach GFCI to front, not end of cord). Types: receptacle, circuit breaker and portable Must be wired correctly and tested. OSHA Office of Training & Education 37 SUBPART K Electrical Safety GFCI Testers OSHA Office of Training & Education 38 Control - Assured Equipment Grounding Conductor Program Program must cover: All cord sets Receptacles not part of a building or structure Equipment connected by plug and cord Program requirements include: Specific procedures adopted by the employer Competent person to implement the program Visual inspection for damage of equipment connected by cord and plug OSHA Office of Training & Education 39 Hazard – Overloaded Circuits Hazards may result from: • Too many devices plugged into a circuit, causing heated wires and possibly a fire • Damaged tools overheating • Lack of overcurrent protection • Wire insulation melting, which may cause arcing and a fire in the area where the overload exists, even inside a wall OSHA Office of Training & Education 40 Control - Electrical Protective Devices • Automatically opens circuit if excess current from overload or ground-fault is detected – shutting off electricity • Includes GFCI’s, fuses, and circuit breakers • Fuses and circuit breakers are overcurrent devices. When too much current: Fuses melt Circuit breakers trip open OSHA Office of Training & Education 41 Power Tool Requirements • Have a three-wire cord with ground plugged into a grounded receptacle, or • Be double insulated, or • Be powered by a low-voltage isolation transformer OSHA Office of Training & Education 42 Tool Safety Tips • • • • • • • • • Use gloves and appropriate footwear Store in dry place when not using Don’t use in wet/damp conditions Keep working areas well lit Ensure not a tripping hazard Don’t carry a tool by the cord Don’t yank the cord to disconnect it Keep cords away from heat, oil, & sharp edges Disconnect when not in use and when changing accessories such as blades & bits • Remove damaged tools from use OSHA Office of Training & Education 43 Preventing Electrical Hazards - Tools • Inspect tools before use • Use the right tool correctly • Protect your tools • Use double insulated tools Double Insulated marking OSHA Office of Training & Education 44 Temporary Lights Protect from contact and damage, and don’t suspend by cords unless designed to do so. OSHA Office of Training & Education 45 SUBPART K Electrical Safety Temporary Lighting • All bulbs must be guarded • No broken bulbs or empty sockets • Not suspended by conductors • Low voltage for wet locations OSHA Office of Training & Education 46 Clues that Electrical Hazards Exist • Tripped circuit breakers or blown fuses • Warm tools, wires, cords, connections, or junction boxes • GFCI that shuts off a circuit • Worn or frayed insulation around wire or connection OSHA Office of Training & Education 47 SUBPART K Electrical Safety Permanent Equipment in Temporary Use What is wrong with using this as a ‘splitter’? OSHA Office of Training & Education 48 Lockout and Tagging of Circuits • Apply locks to power source after deenergizing • Tag deactivated controls • Tag de-energized equipment and circuits at all points where they can be energized • Tags must identify equipment or circuits being worked on OSHA Office of Training & Education 49 Safety-Related Work Practices To protect workers from electrical shock: Use barriers and guards to prevent passage through areas of exposed energized equipment Pre-plan work, post hazard warnings and use protective measures Keep working spaces and walkways clear of cords OSHA Office of Training & Education 50 Safety-Related Work Practices • Use special insulated tools when working on fuses with energized terminals • Don’t use worn or frayed cords and cables • Don’t fasten extension cords with staples, hang from nails, or suspend by wire. OSHA Office of Training & Education 51 SUBPART K Electrical Safety Clever? Or Foolish? OSHA Office of Training & Education 52 Avoid Wet Conditions • If you touch a live wire or other electrical component while standing in even a small puddle of water you’ll get a shock. • Damaged insulation, equipment, or tools can expose you to live electrical parts. • Improperly grounded metal switch plates & ceiling lights are especially hazardous in wet conditions. • Wet clothing, high humidity, and perspiration increase your chances of being electrocuted. OSHA Office of Training & Education 53 Preventing Electrical Hazards - PPE • Proper foot protection (not tennis shoes) • Rubber insulating gloves, hoods, sleeves, matting, and blankets • Hard hat (insulated nonconductive) OSHA Office of Training & Education 54 Preventing Electrical Hazards – Proper Wiring and Connectors • Use and test GFCI’s • Check switches and insulation • Use three prong plugs • Use extension cords only when necessary & assure in proper condition and right type for job • Use correct connectors OSHA Office of Training & Education 55 SUBPART K Electrical Safety Safe Work Practices • No metal ladders for or near electrical work. • No wet hands when plugging or unplugging. • No raising or lowering tools by the cords. • Unless equipment designed for, cannot be used in damp and wet locations, or in extremely hot or chemically destructive work environments. OSHA Office of Training & Education 56 Training Train employees working with electric equipment in safe work practices, including: • Deenergize electric equipment before inspecting or repairing • Using cords, cables, and electric tools that are in good repair • Lockout / Tagout recognition and procedures • Use appropriate protective equipment OSHA Office of Training & Education 57 Summary – Hazards & Protections Hazards • Inadequate wiring • Exposed electrical parts • Wires with bad insulation • Ungrounded electrical systems and tools • Overloaded circuits • Damaged power tools and equipment • Using the wrong PPE and tools • Overhead powerlines • All hazards are made worse in wet conditions Protective Measures • Proper grounding • Use GFCI’s • Use fuses and circuit breakers • Guard live parts • Lockout/Tagout • Proper use of flexible cords • Close electric panels • Training OSHA Office of Training & Education 58 Summary Electrical equipment must be: Listed and labeled Free from hazards Used in the proper manner If you use electrical tools you must be: Protected from electrical shock Provided necessary safety equipment OSHA Office of Training & Education 59