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Arc Flash Basics

TRAINING

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Electrical Hazards

(A) Touch Potential (B) Step Potential (C and D) Touch / Step Potential

• Shock

• Arc Flash

• Arc Blast

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Arc Flash & Arc Blast

• Arc Flash

– Heat

– Fire

• Arc Blast

– Pressure

– Shrapnel

– Sound

Example of an arcing fault

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Arc Flash

• As much as 80% of all electrical injuries are burns resulting from an arc flash and ignition of flammable clothing

• 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

• Over 2000 people are admitted into burn centers each year with severe electrical burns

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Arc Blast

• An arc fault develops a “pressure wave”

• Sources of this blast include:– Copper expands 67,000 times its original volume when

vaporized

– Heat from the arc, causes rapid air expansion

• This may result in a violent explosion of circuit components and thrown shrapnel

• The blast can destroy structures, knock workers from ladders, or across the room

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Arcing Fault - Effects

Copper Vapor:Solid to Vapor

Expands by67,000 times

Intense Light

Hot Air-Rapid Expansion

35,000 F

Pressure Waves

Sound Waves

Molten Metal

Shrapnel

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Arc Flash Hazard

• Energy of Arc Flash determined by:– Arcing fault duration or time to clear

• Speed of the overcurrent protective device

– Arcing fault current magnitude• Available fault current

• Current-limitation can reduce

– Distance to Arcing Fault

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Test 4 Still Photo Before

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Test 4 Still Photo INITIAL

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Test 4 Still Photo DURING

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Test 4 Still Photo FINAL

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Test 4 RESULTS

• Burns

– 3rd Degree at Neck and Hands

– Shirt did not ignite and reduced to below 2nd degree burn

• Sound – 141.5 db

• Pressure – Collapsed Lungs

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NFPA 70E 110.8(B)(1)

– Requires an electrical hazard analysis if working on or near exposed conductors or circuit parts• Shock Hazard Analysis

– “Approach Boundaries”

• Flash Hazard Analysis – Flash Protection Boundary

– Incident Energy / PPE

NFPA70E - Electrical Hazard Analysis

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Shock Hazard Analysis

• NFPA 70E 130.2(A)

• A shock hazard analysis shall determine:– The voltage to which exposed

– The boundary requirements

– The personal protective equipment necessary in order to minimize the possibility of electric shock to personnel

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Shock Protection Boundaries

• NFPA 70E 130.2(B)

• The shock protection boundaries identified

– Limited Approach: Qualified persons and unqualified if accompanied by qualified person

– Restricted Approach: Qualified persons only

– Prohibited Approach: Qualified persons only –PPE as if in direct contact with live part

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NFPA 70E Table 130.2(C)

Shock Protection Boundaries

Column Number (1) (2) (3) (4) (5)

Nominal System

Voltage Range

Limited approach Boundary Restricted

Approach

Boundary

Prohibited

Approach

Boundary

Exposed

Movable

Conductor

Exposed

Fixed

Circuit Part

Includes

Inadvertent

Movement

Adder

Includes

Reduced

Inadvertent

Movement

Adder

Phase-to-Phase

Energized Part to Employee - Distance in feet - Inches

Less than 50 V Not Specified Not Specified Not Specified Not Specified

50 V to 300 V 10 ft. 0 in. 3 ft. 6 in. Avoid Contact Avoid Contact

301V to 750 V 10 ft. 0 in. 3 ft. 6 in. 1 ft. 0 in. 0 ft. 1 in.

751 V to 15 kV 10 ft. 0 in. 5 ft. 0 in. 2 ft. 2 in. 0 ft. 7 in.

15.1 kV to 36 kV 10 ft. 0 in. 6 ft. 0 in. 2 ft. 7 in. 0 ft. 10 in.

Column Number (1) (2) (3) (4) (5)

Nominal System

Voltage Range

Limited approach Boundary Restricted

Approach

Boundary

Prohibited

Approach

Boundary

Exposed

Movable

Conductor

Exposed

Fixed

Circuit Part

Includes

Inadvertent

Movement

Adder

Includes

Reduced

Inadvertent

Movement

Adder

Phase-to-Phase

Energized Part to Employee - Distance in feet - Inches

Less than 50 V Not Specified Not Specified Not Specified Not Specified

50 V to 300 V 10 ft. 0 in. 3 ft. 6 in. Avoid Contact Avoid Contact

301V to 750 V 10 ft. 0 in. 3 ft. 6 in. 1 ft. 0 in. 0 ft. 1 in.

751 V to 15 kV 10 ft. 0 in. 5 ft. 0 in. 2 ft. 2 in. 0 ft. 7 in.

15.1 kV to 36 kV 10 ft. 0 in. 6 ft. 0 in. 2 ft. 7 in. 0 ft. 10 in.

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Flash Hazard Analysis

• NFPA 70E 130.3 Flash Hazard Analysis: Flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash. …”

• What is required?

– Determine Flash Protection Boundary

– Determine the personnel protective equipment (incident energy determination)

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Flash Protection Boundary

Linear distance from exposed live parts within which a person could receive second degree burns (1.2 cal/cm2) resulting from an arc flash

480V

MCC

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Flash Hazard Analysis

Three common methods (600V or less):1) Default FPB and task-hazard/ PPE tables

• Qualifiers and limitations

2) Utilize NFPA 70E equations• Incident energy – select PPE

• FPB

3) IEEE1584: equations or calculator • Incident energy – select PPE

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Flash Hazard Analysis

• NFPA 70E 130.7(C)(10) Protective Clothing and Personal Protective Equipment Matrix– Determine after calculating the incident energy

of the arc

– Hazard Risk Category• HRC 0: 0-1.2 cal/cm²

• HRC 1: 1.2-4 cal/cm²

• HRC 2: 4-8 cal/cm²

• HRC 3: 8-25 cal/cm²

• HRC 4: 25-40 cal/cm²

• DANGEROUS: > 40 cal/cm²

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Flash Protection Boundary (FPB)

Must wear appropriate PPE

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NFPA70E - Electrical Hazard Analysis

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LIMITEDRESTRICTEDPROHIBITED

Arc Flash PPE

Shock PPE