Electrical Safety - Construction

Electrical Safety 

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

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

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

Electrical Injuries

There are four main types of electrical injuries:
Direct:
Electrocution or death due to electrical shock
Electrical shock
Burns
Indirect - Falls

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.

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

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

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

Falls

Electric shock can also cause indirect injuries 
Workers in elevated locations who experience a shock may fall, resulting in serious injury or death

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.

Hazard – Exposed Electrical Parts

Cover removed from wiring or breaker box 

Control – Isolate Electrical Parts

Use guards or barriers
Replace covers

Control – Isolate Electrical Parts  - Cabinets, Boxes & Fittings

    Conductors going into them must be protected, and unused openings must be closed

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)

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

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

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 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

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

Hazard – Defective Cords & Wires

Plastic or rubber covering is missing

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Damaged extension cords & tools 

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

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 extra-hard use, or which have been modified, must be taken out of service immediately

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 

 Grounding

-Grounding creates a low-resistance 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. 

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

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

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, single-phase, 15- and 20-ampere receptacles, or have an 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

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

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

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

Tool Safety Tip

-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 

Preventing Electrical Hazards - Tools

-Inspect tools before use

-Use the right tool correctly

-Protect your tools

-Use double insulated tools 

Temporary Lights

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

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

Lockout and Tagging of Circuits

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

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
-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.

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

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.

Preventing Electrical Hazards - PPE

-Proper foot protection (not tennis shoes)

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

-Hard hat (insulated - nonconductive) 

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 

Training

-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

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
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