Lecture 8 -_electrical_hazard


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Lecture 8 -_electrical_hazard

  1. 1. Topic 7 : Electrical hazard Topic Learning outcome : 1) Describe the definition of Electrical hazard 2) Explain the possible source of electrical hazard. 3) Describe the identifying and assessing technique of electrical hazard. 4) Describe the electrical hazard control and prevention strategies.
  2. 2. ElectricalHazarddefinition: • A dangerous condition such that contact or equipment failure can result in electric shock, arc-flash burn, thermal burn, or blast. • How much Electricity is Dangerous?
  3. 3. ElectricalHazarddefinition: Electricity – related hazards; 1) Electric shock • Direct contact with energized electrical conductors 50V or more can lead to injury. • 3 factors involved in electric shock: a) Resistance – the lower resistance of human body, the greater potential of electrical shock occur. b) Voltage – the higher voltage, the greater potential of electrical shock occur. Voltage exceed 50V is dangerous. c) Current – the higher current, the greater potential of electrical shock. Current exceed 5mA is dangerous.
  4. 4. ElectricalHazarddefinition: Electricity – related hazards; 2) Arc-flash burn • Contact with live conductor. • At entry and exit points of electrical current flowing through the body. • Electrical current with arc example flash, spark. 3) Thermal Burn • Electricity is a common cause of many fires. • The cause of the electrical ignition covers : a) spark between a conductor b) Arc- discharge from greater electric power c) Short circuit
  5. 5. ElectricalHazarddefinition: Electricity – related hazards; 4) Blast • Caused by short circuit or spark from electrical connection • Example : Short circuit during maintenance job. 5) Electrostatic/ Static electricity • Effect generates by electrical charge that trapped in the insulation. • Source of electrostatic discharge include following; a) Moving large sheets of plastic which may discharge sparks. b) Vehicle tires rolling across a road surface. c) Friction between a flowing liquid and a solid surface
  6. 6. The major causes of electrical hazard, e.g. electrical shock : • Contact with a bare wire carrying current. The bare wire may have deteriorated insulation or be normally bare. • Working with electrical equipment that lacks the UL label for safety inspections. • Electrical equipment that has not properly grounded. • Working with electrical equipment on damps floors or other sources of wetness. • Static electricity discharge • Using metal ladder to work on electrical equipment. These ladders can provide a direct line from the power source to the ground, again causing a shock • Working on electrical equipment without ensuring that the power has been shut off • Lightning strikes. SourceofElectricalHazard:
  7. 7.  Performing the Electrical Hazards Analysis is vital to the safety of personnel who are or may be exposed to live parts operating at 50 volts or more that are not placed in an electrically safe work condition. Shock Hazard Analysis  Shock hazard analysis determines the system voltage to which personnel can be exposed, the protection boundary requirements and identifies PPE required to minimize shock hazard.  In order to appropriately assess the electrical shock hazard associated with any type of maintenance or repair work it is necessary to evaluate the procedures or work practices that will be involved. These practices should be evaluated against both regulatory and consensus standards requirements as well as recognized good practice within the industry. Identifyingandassessingelectricalhazard:
  8. 8. Identifyingandassessingelectricalhazard: Shock Protection Boundary
  9. 9. FLASH Hazard Analysis  The Flash Hazard Analysis is performed in order to protect personnel from the possibility of being injured by an arc-flash.  The analysis also determines the Flash Protection Boundary and the personal protective equipment that personnel working within this boundary must use.  The analysis required the available fault current to calculated and documented at every point in the electrical system  Table A provides a basic formula for calculating the flash protection boundary. Identifyingandassessingelectricalhazard:
  10. 10. There are various ways of protecting people from the hazards caused by electricity. These include: insulation, guarding, grounding, electrical protective devices, and safe work practices. Insulation • One way to safeguard individuals from electrically energized wires and parts is through insulation. An insulator is any material with high resistance to electric current. • Insulators-such as glass, mica, rubber, and plastic-are put on conductors to prevent shock, fires, and short circuits. Before employees prepare to work with electric equipment, it is always a good idea for them to check the insulation before making a connection to a power source to be sure there are no exposed wires. ElectricalhazardControl&PreventionStrategies
  11. 11. Guarding Live parts of electric equipment operating at 50 volts or more must be guarded against accidental contact. Guarding of live parts may be accomplished by: • location in a room, vault, or similar enclosure accessible only to qualified persons; • use of permanent, substantial partitions or screens to exclude unqualified persons; Indoor electric wiring more than 600 volts and that is open to unqualified persons must be made with metal-enclosed equipment or enclosed in a vault or area controlled by a lock. In addition, equipment must be marked with appropriate caution signs. ElectricalhazardControl&PreventionStrategies
  12. 12. Grounding • Grounding is another method of protecting employees from electric shock; however, it is normally a secondary protective measure. • The "ground" refers to a conductive body, usually the earth, and means a conductive connection, whether intentional or accidental, by which an electric circuit or equipment is connected to earth or the ground plane. • By "grounding" a tool or electrical system, a low-resistance path to the earth is intentionally created. When properly done, this path offers sufficiently low resistance and has sufficient current carrying capacity to prevent the buildup of voltages that may result in a personnel hazard. ElectricalhazardControl&PreventionStrategies
  13. 13. Circuit Protection Devices • Circuit protection devices are designed to automatically limit or shut off the flow of electricity in the event of a ground-fault, overload, or short circuit in the wiring system. Fuses, circuit breakers, and ground-fault circuit interrupters are three well- known examples of such devices. Safe work practice • These include: de energizing electric equipment before inspecting or making repairs, using electric tools that are in good repair, using good judgment when working near energized lines, and using appropriate protective equipment. ElectricalhazardControl&PreventionStrategies
  14. 14. Training • To ensure that they use safe work practices, employees must be aware of the electrical hazards to which they will be exposed. Employees must be trained in safety-related work practices as well as any other procedures necessary for safety from electrical hazards. -END- ElectricalhazardControl&PreventionStrategies