Electrical Workplace Safety

Electrical Safe Work Practices
Including NFPA 70E

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

Introduction
There are four main types of electrical injuries:
Electrocution (death due to electrical shock)
Electrical shock
Burns
Falls

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 Terminology
Current – the movement of electrical charge
Resistance – opposition to current flow
Voltage – a measure of electrical force
Conductors – substances, such as metals, that have little resistance to electricity
Insulators – substances, such as wood, rubber, glass, and bakelite, that have high resistance to electricity
Grounding – a conductive connection to the earth which acts as a protective measure

Electrical Shock
Received when current passes through the body
Severity of the shock depends on:
Path of current through the body
Amount of current flowing through the body
Length of time the body is in the circuit
LOW VOLTAGE DOES NOT MEAN LOW HAZARD

Dangers of Electrical Shock
Currents above 10 mA* can paralyze or “freeze” muscles
Currents greater than 75 mA* can cause ventricular fibrillation (rapid, ineffective heartbeat)
Will cause death in a few minutes unless a defibrillator is used
75 mA is not much current – a small power drill uses 30 times as much
* mA = milliampere = 1/1,000 of an ampere Defibrillator in use

How is an electrical shock received?
When two wires have different potential differences (voltages), current will flow if they are connected together
In most household wiring, the black wires are at 110 volts relative to ground
The white wires are at zero volts because they are connected to ground
If you come into contact with an energized (live) black wire, and you are also in contact with the white grounded wire, current will pass through your body and YOU WILL RECEIVE A SHOCK

How is an electrical shock received? (cont’d)
If you are in contact with an energized wire or any energized electrical component, and also with any grounded object, YOU WILL RECEIVE A SHOCK
You can even receive a shock when you are not in contact with a ground
If you contact both wires of a 240-volt cable, YOU WILL RECEIVE A SHOCK and possibly be electrocuted

Electrical Burns
Most common shock-related, nonfatal injury
Occurs when you touch electrical wiring or equipment that is improperly used or maintained and which may produce Arc Flash
Typically occurs on the hands
Very serious injury that needs immediate attention
More on Arc Flash later!

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

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.

Overload Hazards
If too many devices are connected 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
IR picture of overloaded panel

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

Control- Electrical Protective Devices
Automatically opens circuit if excess current from overload or ground-fault is detected – shutting off electricity
Include fuses, circuit breakers, and ground-fault circuit-interrupters (GFCI’s)
Fuses and circuit breakers are overcurrent devices
When there is too much current:
Fuses melt
Circuit breakers trip open

Grounding Hazards
Some of the most frequently violated OSHA standards
Metal parts of an electrical wiring system that we touch (switch plates, ceiling light fixtures, conduit, etc.) should be at zero volts relative to ground
Housings of motors, appliances or tools that are plugged into improperly grounded circuits may become energized
If you come into contact with an improperly grounded electrical device, YOU WILL BE SHOCKED

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

Ground fault video

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 1/40 th 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 – Exposed Electrical Parts
Cover removed from wiring or breaker box

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

Control – Isolate Electrical Parts - Cabinets, Boxes & Fittings
Conductors going into them must be protected, and unused openings must be closed

Guarding of Live Parts
Must enclose or guard electric equipment in locations where it would be exposed to physical damage
Violation shown here is physical damage to conduit

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)
Photo shows violations of these two requirements

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

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

Hand-Held Electric Tools
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, or
Be powered by a low-voltage isolation transformer

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

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
Use of Flexible Cords

Flexible cord
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.

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
Wire gauge measures wires ranging in size from number 36 to 0 American wire gauge (AWG) Wire Gauge 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

Hazard – Defective Cords & Wires
Plastic or rubber covering is missing
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

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.

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

Training
Deenergizing electric equipment before inspecting or making repairs
Using electric tools that are in good repair
Using good judgment when working near energized lines
Using appropriate protective equipment
Train employees working with electric equipment in safe work practices, including:

Recent Changes
Attention to Personnel Protection (PPE)
Recognition of Unsafe Work Practices
Impact to Business and Medical Costs
Changes to NFPA 70E & NEC
IEEE Standard for Arc Flash Analysis
Requirements of OSHA 1910, Subpart S applies when contractors are connecting to existing circuits

What Does OSHA Say? NEC & NFPA must be followed!
29 CFR 1910.333
Live electrical parts that an employee may be exposed shall be de-energized unless additional or greater hazards are introduced. (NFPA 70E 130.1)
29 CFR 1910.335
Employees working in areas where potential electrical hazards (including shock and arc flash) exist shall be provided with and shall use personal protective equipment. Written permit also required.
(NEC 110.16 & NFPA 130.1(A)(1))

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

Industry Standards and Regulations
OSHA 29 CFR 1910 & 1926
OSHA & Code inspectors enforce NEC 110.16 & NFPA 70E
NFPA 70E-2004
Requires de-energizing circuit unless infeasible
When circuit worked on is energized, permit required
Requires shock and arc flash boundaries
Requires specific personal protective equipment
NEC 110.16-2005
Requires NFPA 70E markings warning of ARC Flash

NEC 2005
110.16 Flash Protection. Switchboards, panel boards, industrial control panels, and motor control centers in other than dwelling occupancies, that are likely to require examination, adjustment, servicing, or maintenance while energized, shall be field marked to warn qualified persons of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.

Sample NEC Warning Article 110.16

Energized Electrical Work Written Permit REQUIRED ELEMENTS*
A description of the circuit and equipment to be worked on and their location
Justification for why the work must be performed in an energized condition (130.1)
A description of the safe work practices to be employed
Results of the shock hazard analysis
Determination of shock protection boundaries [130.2(B) and Table 130.2(C)]
Results of the flash hazard analysis (130.3)
The Flash Protection Boundary [130.3(A)]
The necessary personal protective equipment to safely perform the assigned task [130.3(B), 130.7(C)(9), and Table 130.7(C)(9)(a)]
Means employed to restrict the access of unqualified persons from the work area [110.8(A)(2)]
Evidence of completion of a job briefing, including a discussion of any job-specific hazards [110.7(G)]
Energized work approval (authorizing or responsible management, safety officer, or owner, etc.) signature!
*requirements are found in referenced sections of NFPA 2004

Exemptions to Work Permit
Work performed on or near live parts by qualified persons related to tasks such as testing, troubleshooting, voltage measuring, etc., shall be permitted to be performed without an energized electrical work permit, provided appropriate safe work practices and personal protective equipment in accordance with NFPA 70E Chapter 1 are provided and used.

Why is ARC-FLASH Protection such an issue?
As much as 80% of all electrical injuries are burns resulting from an arc-flash and ignition of flammable clothing.
OSHA estimates between 5 and 10 persons per day are electrically burned severe enough to require treatment at special burn centers!
Arc temperature can reach 35,000°F - this is four times hotter than the surface of the sun
Fatal burns can occur at distances over 10 ft .

ARC EXPOSURE ENERGY BASICS
Exposure Energy is Expressed in cal/cm 2 /0.1sec
The calorie (symbol: cal) is the amount of heat (energy) required to raise the temperature of one gram of water by 1 °C .
1 cal/cm 2 Equals the Exposure on the tip of a finger by a Cigarette Lighter in One Second
An Exposure Energy of Only One or Two cal/cm 2 Will Cause a 2nd Degree Burn on Human Skin

ARC Flash Analysis
OSHA 1910.132, .145,.303,.335, 1926.95, .403, .404, .405
Where work will be performed within the flash protection boundary, the flash hazard analysis shall determine, and the employer shall document, the incident energy exposure to the worker which shall determine the level of Flame resistant (FR) clothing and PPE to be used by the employee based upon the incident energy exposure associated with the specific task.
As an alternative, PPE requirements of NFPA 70E Part II 3-3.9 may be used in lieu of a detailed flash hazard analysis.

Hazard Risk Category Classification
NFPA 70E – Hazard Risk 0
This hazard risk category poses minimal risk.
This hazard risk category poses some risk.
This hazard risk category involves tasks that pose a moderate risk.
This hazard risk category involves tasks that pose a high risk.
This hazard risk category represents tasks that pose the greatest risk.

Hazard Risk Category Tables Table 130.7(C)(9)

PPE Matrix based upon Hazard Risk Category Table 130.7(C)(10)

Preventing Electrical Hazards - PPE
Proper foot protection (not tennis shoes)
Rubber insulating gloves, hoods, sleeves, matting, and blankets
Hard hat (insulated - nonconductive)
FR clothing

What are the shock approach and flash protection boundaries?

Flash Protection Boundary (FPB)
The safe approach distance from energized equipment or parts
4 feet for low voltage ( < 600V ) systems
FPB to be calculated which may decrease the boundary distance
crossing into FPB requires wearing the appropriate PPE
A qualified person must accompany unqualified persons
Defined as the distance at which the worker is exposed to 1.2 cal/cm2 for 0.1 second
IEEE Std 1584 - 2002 details the procedure and needed equations for arc flash calculations. The equations are used to calculate the incident energy and flash boundary. The IEEE procedure is valid for voltages ranging from 208V volts to 15kV with gap ranges between 3 mm. and 153 mm .

Limited Approach Boundary
A shock protection boundary to be crossed by only qualified persons
Unqualified persons must be escorted by a qualified person
Minimum distance from energized item allowed for unqualified personnel
Determined by NFPA 70E Table 130.2(C) based on voltage of equipment
Qualified persons must use the appropriate PPE
Qualified persons must be trained to perform the required work

Restricted Approach Boundary
A shock protection boundary to be crossed by only qualified persons
Requires use of shock protection techniques & equipment when crossed
Qualified persons must use the appropriate PPE
Qualified persons must be trained to perform the required work
Must have a written approved plan for the work that they will perform
Must plan the work to keep all parts of the body out of the Prohibited Space
Determined by NFPA 70E Table 130.2(C) based on voltage of equipment

Prohibited Approach Boundary
Considered the same as making contact with exposed energized parts therefore must do the following:
Have specified training to work on energized conductors or parts
Have a documented plan justifying the need to work that close
Perform a risk analysis
Have (2) and (3) approved by authorized management
Use appropriate personal protective equipment rated for the voltage and energy level involved

Approach Boundaries Table 130.2(C) 3 ft. 1 in. 3 ft. 7 in. 10 ft.0 in. 11 ft. 0 in. 138 – 145 kV 2 ft. 8 in. 3 ft. 3 in. 8 ft.0 in. 10 ft. 8 in. 72.6 – 121 kV 2 ft. 1 in. 3 ft. 3 in. 8 ft.0 in. 10 ft. 0 in. 46.1 – 72.5 kV 1 ft. 5 in. 2 ft. 10 in. 8 ft.0 in. 10 ft. 0 in. 36.1 – 46 kV 0 ft. 10 in. 2 ft. 7 in. 6 ft.0 in. 10 ft. 0 in. 15.1 – 36 kV 0 ft. 7 in. 2 ft. 2 in. 5 ft.0 in. 10 ft. 0 in. 751V - 15 kV 0 ft. 1 in. 1 ft. 0 in. 3 ft.6 in. 10 ft. 0 in. 301 - 750 Avoid contact Avoid contact 3 ft.6 in. 10 ft. 0 in. 51 - 300 Not specified Not specified Not specified Not specified 0 - 50 Includes Inadvertent Movement Adder Exposed Fixed Circuit Part Exposed Moveable Conductor Phase-to-Phase Prohibited Approach Boundary Restricted Approach Boundary Limited Approach Boundary Nominal System Voltage Range

Preventing Electrical Hazards - Summary
Plan your work with others
Plan to avoid falls
Plan to lock-out and tag-out equipment
Follow NFPA 70E
Remove jewelry
Avoid wet conditions and overhead power lines

Safe Distance Equations
The short-circuit symmetrical ampacity from a bolted 3-phase fault at the transformer terminals is calculated with the following formula:
I SC = {[MVA Base x 10 6 ] ÷ [1.732 x V]} x {100 ÷ %Z}
where I SC is in amperes, V is in volts, and % Z is based on the transformer MVA .
A typical value for the maximum power (in MW) in a 3-phase arc can be calculated using the following formula:
P = [ Maximum bolted fault MVA bf ] x 0.707 2
The Flash Protection Boundary distance is calculated in accordance with the following formula:

Methods of Reducing Hazard Risk
Specifying Current Limiting Fuses on Low Voltage Switchgear Breakers
Specifying ARC Resistance Medium Voltage Switchgear
Remote Control of Switchgear Breakers
High Resistance Grounding on Low Voltage and Medium Voltage (15kV and below) Systems

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Electrical Workplace Safety

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Electrical Workplace Safety Presentation Transcript