Electrical Safety. Introduction

Transcription

1 Electrical Safety 1 Introduction There are four main types of electrical injuries: Electrocution (death due to electrical shock) Electrical shock Burns Falls Around 300 workers were electrocuted in 2008 and 220 in UW Environmental Health and Safety 1

2 Electrocution (Image very graphic) 3 Biological Effects of Electrical Hazards The effects can vary depending on -Source characteristics (current, frequency, and voltage). - Body impedance and the current s pathway through the body. - How environmental conditions affect the body s contact resistance. - Duration of the contact. 4 UW Environmental Health and Safety 2

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4 Electrical Burns Most common shock-related, nonfatal injury Occurs when you touch electrical wiring or equipment that is improperly used or maintained Typically occurs on the hands Very serious injury that needs immediate attention 7 8 UW Environmental Health and Safety 4

5 Falls Electric shock can also cause indirect or secondary injuries Workers in elevated locations who experience a shock can fall, resulting in serious injury or death 9 Recognizing Hazards 1. Exposed electrical parts 2. Wires with bad insulation 3. Electrical systems and tools that are not grounded or double insulated 4. Damaged power tools and equipment 5. Inadequate wiring 6. Overload circuits 10 UW Environmental Health and Safety 5

6 Guarding of Live Parts Must guard live parts of electric equipment operating at 50 volts or more against accidental contact by: Approved cabinets/enclosures, or Location or permanent partitions making them accessible only to qualified persons, or Elevation of 8 ft. or more above the floor or working surface Mark entrances to guarded locations with conspicuous warning signs 11 Cabinets, Boxes, and Fittings Junction boxes, pull boxes and fittings must have approved covers Unused openings in cabinets, boxes and fittings must be closed (no missing knockouts) 12 UW Environmental Health and Safety 6

7 Hand-held sander has exposed wires 13 Grounding and Double Insulation Hand-held electric tools pose a potential danger because they make continuous good contact with the hand To protect you from shock, burns, and electrocution, tools must: Have a three-wire cord with ground and be plugged into a grounded receptacle, or Be double insulated 14 UW Environmental Health and Safety 7

8 Equipment without a grounding conductor 15 Equipment with a grounding conductor 16 UW Environmental Health and Safety 8

9 Grounding Path The path to ground from circuits, equipment, and enclosures must be permanent and continuous Violation shown here is an extension cord with a missing grounding prong 17 Ground-Fault Circuit Interrupter This device protects you from dangerous shock The GFCI detects a difference in current between the black and white circuit wires (This could happen when electrical equipment is not working correctly, causing current leakage known as a ground fault.) If a ground fault is detected, the GFCI can shut off electricity flow in as little as 1/40 of a second, protecting you from a dangerous shock 18 UW Environmental Health and Safety 9

10 How GFCI works 19 GFCI 20 UW Environmental Health and Safety 10

11 Inadequate Wiring Hazards A hazard exists when a conductor is too small to safely carry the current Example: using a portable tool with an extension cord that has a wire too small for the tool The tool will draw more current than the cord can handle, causing overheating and a possible fire without tripping the circuit breaker The circuit breaker could be the right size for the circuit but not for the smaller-wire extension cord Wire Gauge WIRE Wire gauge measures wires ranging in size from number 36 to 0 American wire gauge (AWG) 21 Control Inadequate Wiring Hazards The wire must be able to handle the current. Its insulation must be appropriate for the voltage and tough enough for the environment. 22 UW Environmental Health and Safety 11

12 Overload Hazards If too many devices are plugged into a circuit, the current will heat the wires to a very high temperature, which may cause a fire If the wire insulation melts, arcing may occur and cause a fire in the area where the overload exists, even inside a wall UW Environmental Health and Safety 12

13 Electrical Protective Devices Fuses and circuit breakers are overcurrent devices When there is too much current: Fuses melt Circuit breakers trip open 25 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 26 UW Environmental Health and Safety 13

14 Use of Flexible Cords More vulnerable than fixed wiring Do not use if one of the recognized wiring methods can be used instead Flexible cords can be damaged by: Aging Door or window edges Staples or fastenings Abrasion from adjacent materials Activities in the area Improper use of flexible cords can cause shocks, burns or fire 27 Permissible Uses of Flexible Cords Examples Pendant, or Fixture Wiring Portable lamps, tools or appliances Stationary equipmentto facilitate interchange 28 UW Environmental Health and Safety 14

15 Prohibited Uses of Flexible Cords Examples Substitute for fixed wiring Run through walls, ceilings, floors, doors, or windows Concealed behind or attached to building surfaces 29 Energized Work EXEMPTION 1 De-energizing introduces additional or increased hazards. Examples include interruption of life support equipment, deactivation of emergency alarm systems, shutdown of hazardous location ventilation equipment, or removal of illumination for an area. EXEMPTION 2 De-energizing is infeasible due to equipment design or operational limitations. Examples include testing of electrical circuits that can only be performed with the circuit energized, and work on circuits that form an integral part of a continuous industrial process in a chemical plant that would otherwise need to be completely shutdown in order to permit work on one circuit or piece of equipment. EXEMPTION 3 Live parts that operate at less than 50V to ground need not be de-energized if there will be no increased exposure to electrical burns or to explosion due to electric arcs. Explain specifics for this work: UW Environmental Health and Safety 15

16 35,000 F Electric Arc Molten Metal Pressure Waves Sound Waves Copper Vapor: Solid to Vapor Expands by 67,000 times Shrapnel Hot Air-Rapid Expansion Intense Light 32 UW Environmental Health and Safety 16

17 33 Lockout/Tagout (when servicing equipment) (1) Shut down the machine or equipment (2) Completely isolate the machine using the appropriate energy-isolating devices (3) Make sure a lockout or tagouot device is applied for each energy-isolating device and only by the authorized employee doing the service or maintenance (4) Make sure all potentially hazardous stored or residual energy is relieved, disconnected or restrained (5) Notify affected employees 34 UW Environmental Health and Safety 17

18 Summary Hazards Exposed electrical parts Wires with bad insulation Ungrounded electrical systems and tools Damaged power tools and equipment Inadequate wiring Overloaded circuits All hazards are made worse in wet conditions Protective Measures Guarding live parts Proper grounding Using GFCI s Using fuses and circuit breakers Proper use of flexible cords Proper use of PPE Training 35 UW Environmental Health and Safety 18