General Electrical Safety

General Electrical Safety

Agenda • Electrical Injuries • Classification of Exposure • Electrical Hazards • Electrical Hazard Control

Electrical Injuries Electrocutions: • 1970s: 600-700 per year • 1990s: 300-400 per year (NIOSH, 1998) 5th leading cause of occupational fatalities. • 7% of total deaths, ranked after motor vehicle crashes, homicide, falls, and mechanical trauma. • Each year, electrical accidents cause as many as 165,380 electrical fires and 7,000 injuries.

Classification of Exposure High Voltage • >600 volts: typically associated with “outdoor” electrical transmission. Accounts for 60% of electrocutions (OSHA). Note: some people classify >480 volts as high voltage. Low Voltage: • <600 volts: typically associated with “indoor” electrical service. Accounts for 32% of electrocutions (OSHA). Low voltage does not imply safe voltage.

Electrical Hazards • Shock :Conductors vs. Resistors :Grounding :The Ground Fault Accident :GFCIs • Burns • Falls • Fire

Electrical HazardsElectrical Shock • Shock occurs when current passes through the body. • Severity of the shock depends on: – Path of current – Amount and type of current – Duration of exposure • Electrocution is a fatal electrical injury.

Electrical HazardsConductors vs. Resistors • All materials exhibit some resistance to electrical current. • Materials with low resistance are called conductors (ex. copper, aluminum, gold, water). • Materials with high resistance are called resistors (ex. rubber, glass, air, most plastics).

Electrical HazardsConductors vs. Resistors continued… • Electricity wants to find the path of least resistance to the ground. • Human tissues and body fluids are relatively good conductors because of high water content. • So if a person touches an energized bare wire or faulty equipment while grounded, electricity will instantly pass through the body to the ground, causing a harmful, potentially fatal, shock.

Electrical HazardsGrounding • Grounding is a method of protecting employees from electric shock. • By grounding an electrical system, a low-resistance path to earth through a ground connection is intentionally created. • This path offers low resistance and has sufficient current-carrying capacity to prevent the build-up of hazardous voltages. • A three pronged cord offers a grounding connection.

Electrical HazardsGrounding continued… • White wire (neutral or common wire), returns the power. • Black wire (hot wire), is connected to the switch and fuse and carries the power. • Green (or ground wire). • Three wires for each cord and terminal. • A two prong plug has a hot prong and a return prong, no ground prong. • In any case, never remove the third (grounding) prong from any three-prong piece of equipment.

Electrical HazardsThe “Ground Fault” Accident • A ground fault accident occurs when a person touches or grasps an electrically energized object while the feet or other body parts are in contact with the ground or a grounded surface. • In some cases a ground fault accident occurs when the opposite hand touches the ground or a grounded object.

Electrical Hazards Ground Fault Accident Example A woman was putting up her Christmas tree. When she went to plug in the strands of lights, her finger was touching the metal prong on the plug. Her other hand was touching a metal coffee table leg for support. The current went through her body as a result, causing cardiac arrest and death.

Electrical HazardsElectrical Shock Example A worker came out of the bathroom with her hands dripping wet, and reached down to plug in a lamp. She got a shock but survived. The same worker was cleaning walls with a sponge and a bucket of soapy water. Not paying attention she washed over an outlet, which also gave her a shock. The shock was intensive enough to stop her breathing. She survived this time as well.

GFCI’s are to be used when using electrical equipment in a wet environment. GFCI’s are designed to detect any leakage of current in an electrical circuit. GFCI’s turn off or “trip” the circuit whenever the leakage is greater than 5/1000 of an ampere. For comparison two 60 Watt light bulbs draw a total of 1 ampere of current. Electrical HazardsGround-Fault Circuit-Interrupters (GFCI’s)

Electrical HazardsGround-Fault Circuit-Interrupters (GFCI’s) • Three types of GFCI’s • A GFCI receptacle used in place of standard receptacle. • A portable GFCI plugs into a standard receptacle. • A GFCI circuit breaker combines leakage current detection with the function of a circuit breaker. • Whenever working in a wet area, or outdoors, employees should use one of these types of GFCI’s.

Electrical HazardsElectrical Burns • Most common nonfatal electrical injury. • Types: – Internal: “deep tissue”. – Skin: “entry” and “exit” points. – Arc: “flash” burns from heat and radiant energy. • Common sites of visible skin burns are the hands and feet.

Electrical HazardsElectrical Burns continued… • Circuits may produce electrical burns with relatively massive amounts of tissue destruction by heating the tissues. • This is due to the physical property of friction from the passage of electrons and by destruction of cell membranes by producing holes in the membranes.

Electrical HazardsElectrical Burns Example A worker was mounting a large mirror onto the wall of an office. He was using a metal power tool which accidentally severed a wire causing a shock and massive burns. The victim exhibited deep tissue destruction along the entire current path, along with surface tissue damage at the point of entry and exit.

Electrical HazardsFalls • Involuntary muscle contractions can “throw” workers and cause falls. • If working at elevation, the fall may cause serious injury or death.

Electrical HazardsFire • In the United States 25% of fires are caused by electricity. • A build-up of dust, trash and spider webs increases the potential for fire to start in the electrical system. • Unprotected light bulbs in work areas are another potential hazard. They can be hit, broken and cause a fire. • Electrical wiring can be hit when drilling holes or driving nails in walls causing a fire.

Electrical HazardsFires continued… • Many fires result from defects in, or misuse of the power delivery system. • Wiring often fails due to faulty installation, overloading, physical damage, aging and deterioration by chemical action, heat, moisture and weather. • Such wiring should be replaced and new circuits installed.

Electrical HazardsFires continued… • Typical home and office electrical systems run like this: • The electrical service enters the house and connects to a main electrical panel. • From the main electrical panel, wires run in different directions throughout the house/building to power lights, outlets, ceiling fans, air conditioners, and various other direct-wired electrical appliances.

Electrical HazardsFires continued… • When electricity flows through a wire, the wire heats up because of its resistance to the flow of electrical current. • Both the size of the wire and how many electrical devices on the circuit are drawing electricity affect the amount of heat generated in the wire. • This is why electrical fuses or circuit breakers are used in the main electrical panel. Their function is to sense the overloading of circuits (and short circuits) and shut off power to that branch circuit before the wires get too hot and start a fire.

Electrical HazardsFires continued… • To keep the wire from getting too hot and starting a fire, circuit wiring attempts to contain the amount of electrical load on the branch circuit by limiting the number of potential electrical appliances that can be running at the same time on that circuit. • For example, only so many outlets are put on one branch circuit or larger pieces of electrical equipment are put on circuits dedicated to that equipment only. • The homeowner or worker can plug in and run too many appliances on the same circuit at one time and overload the circuit.

Electrical HazardsFires continued… • Each circuit must be protected by a fuse or circuit breaker that will blow or “trip” when its safe carrying capacity is surpassed. • If a fuse blows or circuit breaker trips repeatedly while in normal use (not overloaded), check for shorts and other faults in the line or devices. • Do not resume use until the trouble is fixed.

Electrical HazardsFires continued… • It is hazardous to overload electrical circuits by using extension cords and multi-plug outlets. • Use extension cords only when necessary and make sure they are heavy enough for the job. • Avoid creating an “octopus” by inserting several plugs into a multi-plug outlet connected to a single wall outlet. (CDC)

Electrical HazardsFires continued… • Dimmed lights, reduced output from heaters and poor television pictures are all symptoms of an overloaded circuit. • Keep the total load at any one time safely below maximum capacity. • When using a high wattage device such as a heater, iron or power tool, turn off all unnecessary lights and devices. • Try to connect into a circuit with little electrical power demand.

Electrical HazardsFire continued… • Property damage is a primary event resulting from fire. • Injuries and fatalities may result from fire (secondary events).

Electrical Hazards Electrical Fire Example at B.G.S.U. In McDonald North, a fire broke out in a student dorm room. A drop cord was found to be the cause. The cord had been damaged by the bed post, leaving frayed wires. The power ran through a spare breaker because the circuit was very hot. The fire was detected by the smoke and heat detectors and help arrived in time for the fire to be extinguished. No injuries, but damage to the wall and carpet.

Electrical Hazard Control • Extension cords should only be used on a temporary basis in situations where fixed wiring is not feasible. • DO NOT use extension cords as permanent wiring. They may not be able to carry the load. • However, if it is necessary to use an extension cord, never run it across walkways or aisles. • It causes a potential tripping hazard. • It wears down the insulation.

Electrical Hazard Control continued… • Wall receptacles should be designed and installed so that no current-carrying parts will be exposed, and outlet plates should be kept tight to eliminate the possibility of shock. • Replace or repair electrical appliances that over heated, sparked, shorted out, smoked or have damaged cords or cracked equipment.

Electrical Hazard Control continued… • If wires are exposed, they may cause a shock to a worker comes into contact with them. • Cords should not be hung on nails, run over or wrapped around objects, knotted or twisted. This may break the wire or insulation. • Short circuits are usually caused by bare wires touching due to breakdown of insulation. • Electrical tape or any other kind of tape is not adequate! • Cords in areas of water or other conductive liquid must be approved for those locations.

Electrical Hazard Control continued… • When the outer jacket of a cord is damaged, the cord may no longer be water-resistant. • The insulation can absorb moisture, which may then result in a short circuit or excessive current leakage to the ground. • These cords should be replaced immediately. • Electric cords should be examined on a routine basis for fraying and exposed wiring.

Electrical Hazard Control continued… • Electrical cords should be examined visually before use on any shift for external defects such as: • fraying and exposed wiring • loose parts • deformed or missing parts • damage to outer jacket or insulation • evidence of internal damage such as pinched or crushed outer jacket • If any defects are found the electric cords should be removed from service immediately.

Electrical Hazard Control continued… • Pull the plug not the cord. Pulling the cord could break a wire, causing a short circuit.

Electrical Hazard Control continued… • Plug your microwave or any other large appliances into an outlet that is not shared with other appliances. • Do not tamper with fuses as this is a potential fire hazard. • Do not overload circuits as this may cause the wires to heat and ignite insulation or other combustibles.

Electrical Hazard Control continued… • Keep office equipment properly cleaned and maintained. • Ensure lamps are free from contact with flammable material. • Always use lights bulbs with the recommended wattage for your lamp and ceiling fixtures. • Be aware of the odor of burning plastic or wire.

Electrical Hazard Control continued… • ALWAYS follow the manufacturer recommendations when using or installing new office equipment. • Wiring installations should always be made by a licensed electrician or other qualified person. • All electrical appliances should have the label of a testing laboratory.

Water is VERY conductive! Reference: http://www.safteng.net

Overloading! Reference: http://www.safteng.net

Missing grounding prong! Reference: http://www.safteng.net

Missing outlet cover! Reference: http://www.safteng.net

Electrical tape is not a fix! Reference: http://www.safteng.net

Pinched cord!

Damaged casing! Reference: http://www.safteng.net

Any Questions?

Where to Get More Information • http://www.osha.gov. Occupational Safety and Health Administration.

General Electrical Safety