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Electrical Safety - Construction. Subpart K 1926.400-449. Electricity - The Dangers. 5 workers electrocuted every week Causes 12% of young worker workplace deaths Very little electricity to cause harm Significant risk of fires. Electricity – How it Works.

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Electrical safety construction

Electrical Safety - Construction

Subpart K

1926.400-449

OSHA Office of Training & Education


Electricity the dangers

Electricity - The Dangers

  • 5 workers electrocuted every week

  • Causes 12% of young worker workplace deaths

  • Very little electricity to cause harm

  • Significant risk of fires

OSHA Office of Training & Education


Electricity how it works

Electricity – How it Works

  • The flow of energy from one place to another

  • Source of power: usually a generating station

  • Electrons (current) travels through a conductor

  • Travels in a closed circuit

OSHA Office of Training & Education


Electrical terms

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


Electrical injuries

Electrical Injuries

2 categories & 4 types of electrical injuries:

  • Direct:

    • Electrocution or death due to electrical shock

    • Electrical shock

    • Burns

  • Indirect

    • Falls

  • OSHA Office of Training & Education


    Electrical shock

    Electrical Shock

    An electrical shock is received when electrical

    current passes through the body.

    When 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


    Shock severity

    Shock Severity

    • SEVERITY 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


    Electricity the human body

    Electricity &the Human Body

    • Effects are dependent on current & voltage

    • Currentflowing through the body has the most detrimental affects

    • 10 mA can produce painful to severe shock

    • 15 mAis the “let-go threshold”

    • 100to200 mA: ventricular fibrillation

    • Electrical resistance of human body affected by:

      • skin moisture / contact pressure / contact area

    OSHA Office of Training & Education


    How electric shock affects you

    100-200mA

    >200mA

    30-50mA

    9mA

    6mA

    3mA

    1mA

    Respiratory Paralysis - Imminent Death

    Local Muscle Contractions - Freezing

    .1mA

    Perceptible Shock w Reflex

    1/4+ sec. Can Cause Fibrillation

    No Let-Go Current for Women

    No Let-Go Current for Men

    Painful Shock

    No Sensation

    How Electric Shock Affects You

    OSHA Office of Training & Education


    Electrocution threshold seconds

    50 mA

    60 mA

    80 mA

    120 mA

    150 mA

    240 mA

    Electrocution Threshold: Seconds

    So…for the typical adult, how many seconds till fibrillation starts?

    6

    4

    2

    1

    .50

    .25

    OSHA Office of Training & Education


    Dangerous paths thru the body

    Dangerous Paths Thru the Body

    • Hand to Hand

    Through the chest cavity being the most dangerous path !!!

    OSHA Office of Training & Education


    Dangerous paths thru the body1

    Dangerous Paths Thru the Body

    Head to Toe Toe to Head

    OSHA Office of Training & Education


    Dangerous paths thru the body2

    Dangerous Paths Thru the Body

    Left Arm to Feet

    Why the left arm?

    OSHA Office of Training & Education


    Dangers of electrical shock

    Dangers of Electrical Shock

    • 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


    Burns

    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


    Falls

    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


    Electrical hazards and how to control them

    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


    Hazard exposed electrical parts

    Hazard – Exposed Electrical Parts

    Cover removed from wiring or breaker box

    OSHA Office of Training & Education


    Control isolate electrical parts

    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


    Control isolate electrical parts cabinets boxes fittings

    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


    Control close openings

    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


    Hazard overhead power lines

    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


    Control overhead power lines

    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


    Hazard inadequate wiring

    Wire Gauge

    WIRE

    Hazard - Inadequate Wiring

    • Hazard - wire too small for the current

    • Example - portable tool with an extension cord that has a WIRE GAUGE 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 measures wires ranging in size from number 36 to 0 American wire gauge (AWG)

    OSHA Office of Training & Education


    Control use the correct wire

    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


    Hazard defective cords wires

    Hazard – Defective Cords & Wires

    • Plastic or rubber covering is missing

    • Damaged extension cords & tools

    OSHA Office of Training & Education


    Hazard damaged cords

    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


    Control cords wires

    Control – Cords & 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, & fittings equipped with strain relief

    • Remove cords by pulling on the plugs, not the cords

    • Cords not marked for hard or extra-hard use, or which have been modified, must be taken out of service immediately

    OSHA Office of Training & Education


    Improper use of flexible cords

    Improper 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


    Grounding ground fault

    Grounding/ Ground Fault

    • Creates a low-resistance path from tool to 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


    Normal circuit

    Normal Circuit

    OSHA Office of Training & Education


    Ground fault loop

    Ground Fault Loop

    Green wireprovides the ground-fault path

    OSHA Office of Training & Education


    Equipment grounding conductor incomplete

    Equipment Grounding Conductor Incomplete

    Path to ground

    DANGER:CB does not trip when ground-fault occurs

    OSHA Office of Training & Education


    Hazard improper grounding

    Hazard – Improper Grounding

    • Tools plugged into improperly grounded circuits may become energized

    • Broken wire or plug on extension cord

    • One of the most frequently violated OSHA standards

    OSHA Office of Training & Education


    Control ground tools equipment

    Control – Ground Tools & Equipment

    • Ground power supply systems, electrical circuits, and electrical equipment

    • Frequently inspect to insure path to ground is continuous

    • Inspect equipment before use

    • Don’t remove ground prongs Ground exposed metal parts of equipment

    OSHA Office of Training & Education


    Ground fault circuit interrupters

    A GFCIis the only protective device whose sole purpose is to protect people

    Useful when

    working in high moisture or wet conditions

    around bathroom / kitchen sinks

    using extension cords exposed to physical damage

    Valuable when insulation or grounding can not provide adequate protection

    Ground-Fault Circuit-Interrupters

    OSHA Office of Training & Education


    Control use gfci ground fault circuit interrupter

    Control – Use GFCI(Ground-Fault Circuit Interrupter)

    • Detects difference in current between the black (hot) and white (neutral) conductors

    • Senses a 5 mA (+/- 1) difference (below “let-go threshold), GFCI shuts off electricity in 1/40th of a second

    • Use GFCI’s on all 120-volt, single-phase, 15- and 20-ampere receptacles, or have an assured equipment grounding conductor program.

    OSHA Office of Training & Education


    Control assured equipment grounding conductor program

    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


    Hazard overloaded circuits

    Hazard – Overloaded Circuits

    • Too many devices plugged into a circuit

      • causing heated wires and possibly a fire

    • Damaged tools overheating

    • Lack of overcurrent protection

    • Wire insulation melting

    OSHA Office of Training & Education


    Control electrical protective devices

    ControlElectrical Protective Devices

    • These 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


    Power tool requirements

    Power Tool Requirements

    On jobsites, must:

    • 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


    Preventing electrical hazards tools

    Preventing Electrical Hazards - Tools

    • Inspect before use

    • Use the right tool correctly

    • Protect your tools

    • Use double insulated tools

    Double Insulated marking

    OSHA Office of Training & Education


    Temporary lights

    Temporary Lights

    Protect from contact and damage, and don’t suspend by cords unless designed to do so.

    OSHA Office of Training & Education


    Clues that electrical hazards exist

    Clues that Electrical Hazards Exist

    • Tripped circuit breakers

    • Blown fuses

    • Warm tools, wires, cords, connections, or junction boxes

    • GFCI that shuts off

    • Worn, frayed, melted insulation around wire or connection

    OSHA Office of Training & Education


    Lockout tagging of circuits 1926 417

    Lockout & Tagging of Circuits(1926.417)

    • Apply locks to power source after de-energizing

    • 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

    Reference: See 1910.147 (LOTO)

    OSHA Office of Training & Education


    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

    Safety-Related Work Practices

    OSHA Office of Training & Education


    Safety related work practices1

    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


    Preventing electrical hazards planning

    Preventing Electrical Hazards - Planning

    • Plan your work with others

    • Plan to avoid falls

    • Plan to lock-out and tag-out equipment

    • Remove jewelry

    • Avoid wet conditions and overhead power lines

    OSHA Office of Training & Education


    Preventing electrical hazards ppe

    Preventing Electrical Hazards - PPE

    • Avoid wet conditions

    • Proper foot protection (not tennis shoes)

    • Rubber insulating gloves, hoods, sleeves, matting, and blankets

    • Hard hat (insulated - nonconductive)

    OSHA Office of Training & Education


    Preventing electrical hazards proper wiring and connectors

    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


    Tool safety tips

    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


    Training

    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


    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

    Summary – Hazards & Protections

    OSHA Office of Training & Education


    Summary

    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


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