Understanding Arc Flash.pdf

8/11/2019 Understanding Arc Flash.pdf

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S – Stop

top

A – Arcrc

F – Flash

lash

E – Episodes

pisodes

T – Through

hrough

Y – Your Knowledge

our Knowledge

Presented by

resented by

Timothy W. Trotter, P.E., RCDD, LEED AP

imothy W. Trotter, P.E., RCDD, LEED AP

S.A.F.E.T.Y.

.A.F.E.T.Y.

Understanding

nderstanding

Arc Flash

rc Flash

What is Arc Flash?

hat is Arc Flash?

NFPA 70E defines flash hazard as “a

dangerous condition associated with the

release of energy caused by an

electric arc.”



A calorie is the energy required to raise one

gram of water one degree Celsius at one

atmosphere. At 1 second, 1.2 cal/cm

2

of

heat energy can cause a second degree burn.

One cal/cm

2

is equivalent to the amount of

energy produced by a cigarette lighter in

one second.

What is a Calorie?

hat is a Calorie?

Incident Energy

ncident Energy

The incident energy is a measure of

thermal energy at a working distance from

an arc fault. The unit of incident energy is

cal/cm

2

or J/cm

2

.

Arc Flash Incident

rc Flash Incident



Background

ackground

May 2003

Troubleshooting energized outdoor switchgear

Three workers,

all wearing

polyester blend clothing

Voltage = 13,200V

A company security

camera filmed the entire

accident

AF Incident

F Incident

The next scene shows a ball

of flame totally engulfing the

three workers

AF Incident

F Incident

The worker who was standing in front of the equipment

on the left hand side is engulfed in flames

The worker laying in

the cell is propelled

outward in a ball of

flames



AF Incident

F Incident

The worker who was at the bottom of the compartment is

crawling away from the equipment with his clothing on

fire

The worker on the

right lands on his back

with his feet in the air

The worker on the left

is running away

AF Incident

F Incident

State of shock

Panic after the Arc Flash

and Arc Blast

AF Incident

F Incident

The worker on fire is frantically tearing his coveralls from

his body

As he is doing this, we

can see the workpants

he is wearing underneath

his coveralls are on fire



Injuries

njuries

Two workers 2

nd

& 3

rd

degree burns over 60% of the body

Synthetic hair nets and hardhat suspension burned into

scalp

One burn victim in

drug-induced coma

for 6 weeks while

burns being scrubbed

Injuries

njuries

3

rd

worker not burned but suffered neurological damage

from the blast

Note: He weighed

approximately 300 lbs.

and was thrown almost

12 feet backwards

Currently OSHA has

$148,000 in penalties

pending for serious

and willful violations

Injury Facts

njury Facts

Numerous workers are injured or killed each year while

working on energized equipment.

Defining incident energy hazards raises awareness of the

harm to humans that can result from an electric arc.

Injuries often include:

Severe skin burns

Hearing damage

Face and eye injuries

Blast pressure injuries



Skin Damage

kin Damage

Skin damage will occur based on the intensity of the heat

generated by an electrical arc accident. The heat reaching

the skin of the worker is dependent on the following three

factors:

Power of the arc at the arc location

Distance of the worker to the arc

Time duration of the arc exposure

1992

992

-2000 Arc Flash Reports

000 Arc Flash Reports

Nonfatal shock and burn injuries

When is it acceptable to work on

hen is it acceptable to work on

Energized Equipment?

nergized Equipment?

Examples of increased or additional hazards

Interruption of:

Life Support

Emergency alarm systems

Hazardous location ventilation

Examples of unfeasibility:

Start-up testing

Trouble shooting diagnostics

Continuous process segment



Causes of an Electric Arc

auses of an Electric Arc

Inadvertent contact

Loose connections

Insulation failure

Faulty equipment

Voltage transients

Unsuccessful Short Circuit interruption

Animals – squirrels, snakes, etc.

Types of Faults

ypes of Faults

Bolted Faults are characterized by a solidly connected fault

path causing high levels of current to flow through this solid

connection

Arcing Faults differ in the fact that the current actually

flows through ionized air causing an arc.

Major difference between these two types of faults is that

the energy in a bolted fault condition is dissipated in the

faulted equipment while an arcing fault releases energy out

into the surrounding environment.



AF Incident

F Incident

480 Volt System

22,6000 Amp

Symmetrical Fault

Motor Controller

Enclosure

6-Cycle Arcing

Fault (0.1 sec)

Physical Effects of Arc Flash

hysical Effects of Arc Flash

Metal vapor and air expand very rapidly due to arc heating

Pressure wave knocks worker away from arc

Good – removes personnel from heat source

Bad – removes personnel from ladder

Pressure propels molten metal droplets out from arc source

Hot enough to ignite clothing

Structural damage to building

Damaging sound pressure

Eardrum rupture – Blindness - Lung Damage - Death

Arcing Short Circuit

rcing Short Circuit



AF Incident

F Incident

Characteristics of an Electric Arc

haracteristics of an Electric Arc

An electrical arc will oscillate and escalate

if not constrained

A 1-ph arc can engulf a second or third

conductor in two cycles

Arc current propels the arc away from the

power source

Arc Terminals – up to 35,000 degrees F

Why Arc Flash is Dangerous

hy Arc Flash is Dangerous

An arc is a source of intense heat, light, sound & pressure

South Georgia in August: 100° (311k)

Surface of the Sun: 8,540 ° (5,000k)

Arc @ Arc Terminals: 35,540 ° (20,000+k)

Maximum arc power = ½ x bolted fault kW

Heat transfer depends on:

Size of arc (arc power)

Duration of arc

Distance from arc (1/x ^2)

Enclosure (“arc in box” focuses heat in one direction)



How often Arc Flash occurs

ow often Arc Flash occurs

Five to 10 Arc Flash explosions occur in

electric equipment every day in the United

States. This number does not include cases

in which the victim is sent to an ordinary

hospital. Instead, these incidents are so

severe the victims require treatment from a

special burn center.

AF Incident

F Incident

Awareness is on the Rise

wareness is on the Rise

“Arc Flash” is the New Buzzword

Conferences/Seminars/Training

Language added to NFPA-70/70E

Technical Papers

Department of Labor (OSHA) Fines

Codes/Standards



Codesodes

and

nd

Standards

tandards

NEC

EC

™2002 Article 110.16

002 Article 110.16

110.16 Flash Protection.

10.16 Flash Protection. Switchboards, panelboards,

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.

Warning for awareness, to prepare for future work

Field marked – not marked by manufacturer

No mention of values – only warning of hazard

NFPA 70E

FPA 70E

-2004

004

As a result of growing injuries, recent changes/additions

have been incorporated into the National Fire Protection

Association publication number 70E, the most recent

version being NFPA 70E-2004.

1) Work must be performed by a trained individual,

qualified for the work to be conducted (reference:

NFPA 70E-2004 110.6(D)(1)).

2) The best way to determine the potential hazard of

an arc flash is to conduct an arc flash hazard

assessment before work begins (reference: NFPA

70E-2004 130.3).



NFPA 70E

FPA 70E

-2004

004

NFPA 70E: The fifth edition of the NFPA Std 70E Electrical

Safety Requirements for Employee Workplaces, published in

1995, established a flash protection boundary. This edition

gave recognition to the hazard of arc flash and required

employee protection from the flash hazard. The sixth

edition (published in 2000) expanded the requirement for

flash protection boundaries and the use of PPE.

Developments Leading to NFPA 70E

evelopments Leading to NFPA 70E

-2004

004

Large Hydro in Pacific NW

6.9kV Swgr

Racking in Breaker

AF occurred

One worker injured

5+ years

$10+ million



-2004

004





-2004

004

Institute of Electrical and Electronics Engineers (IEEE)

In 1960 an AIEE paper was written that identified the potential for

injury from arching faults caused by such things as tools contacting bare

buses, rodents, dust, insulation failure or loose connections

In 1982, an IEEE paper was written that highlighted the electric

arc flash hazard. The paper described the electric arc blast as the

other electrical hazard

The Petro/Chem Industries Committee of the Industry

Applications Society of IEEE formed a working group to raise

awareness of electrical personnel to the hazards associated with

arching faults

In September 2002, IEEE issued the Guide for Performing Arc-

Flash Hazard Calculations, IEEEE Std P1584 – 2002



-2004

004

The intent of NFPA 70E regarding arc

flash is to provide guidelines which

will limit injury to the onset of

second degree burns.



-2004

004

NFPA 70E and IEEE P1584 joined

forces to do further research on

Arc Flash (Feb 2006)



Occupational Health & Safety Administration

ccupational Health & Safety Administration

On 4 August 1991, OSHA included

language in its Title 29 Code of Federal

Regulations, Subpart S, for the electrical safe

work practices for general industry that

added arc flash as an additional hazard to

the shock hazard

OSHA 29 CFR 1910.333

SHA 29 CFR 1910.333

Safety related work practices shall be employed to prevent electric

shock or other injuries resulting from either direct or indirect

electrical contacts

“Live parts to which an employee may be exposed shall be de-

energized before the employee works on or near them, unless the

employer can demonstrate that de-energizing introduces additional

or increased hazards or is infeasible.”

The fundamental requirements is to de

he fundamental requirements is to de

-energize

nergize

Working on energized equipment is always a risk

orking on energized equipment is always a risk

OSHA 29 CFR 1910.335

SHA 29 CFR 1910.335

Personal Protective Equipment

“Employees working in areas where there are potential electrical

hazards shall be provided with, and shall use, electrical protective

equipment that is appropriate for the specific parts of the body to

be protected and for the work to be performed.”

Notice that OSHA does not specifically mention calculation of NFPA 70E.

However, since NFPA 70E is a recognized, published standard available to the

industry, OSHA will cite using requirements of NFPA 70E.



What can be done

hat can be done

to ensureo ensure

compliance with

ompliance with

these Codes?

hese Codes?

Standards?

tandards?

Arc Flash

rc Flash

Analysis

nalysis

What is Arc Flash Analysis?

hat is Arc Flash Analysis?

A study for the

Investigation of a worker’s potential

exposure to arc flash energy

Prevention of worker injury

Determination of safe work practices

and appropriate levels of Personal

Protective Equipment (PPE)



Coordination Study

oordination Study

Coordination traditionally used for Equipment

Protection and System Reliability

Arc Flash requirements bring new safety focus to

coordination studies looking at minimum faults

and setting faster trip times

Faster trip times may cause more nuisance trips

Alternative protection schemes may gain

popularity

Two Methods

wo Methods

of

f

Analysis

nalysis

NFPA 70E 2

FPA 70E 2

-1.3.3

.3.3

“Flash hazard analysis shall be done before a person approaches any

exposed electrical conductor or circuit part that has not been placed

in an electrically safe work condition.”

IEEE 1584

EEE 1584

-2002

002

“IEEE Guide for Performing Arc Flash Hazard Calculations”

Incorporates results of extensive testing performed by several parties

Provides tools to calculating incident arc flash energy and protection

boundaries

Does not reduce NEC or 70E – instead, works with and alongside of

them

NFPA 70E 2

FPA 70E 2

-1.3.3

.3.3

Calculations for predicting the incident

energy produced by a three phase arc

Equations are complex and not very

intuitive



IEEE 1584

EEE 1584

-2002

002

Provides a method of conducting an arc flash hazard analysis

This method uses equations that were developed using statistical

analysis of data from arc flash testing performed at laboratories

This standard includes a spreadsheet calculator that can be used

to solve the equations

A detailed arc flash hazard analysis using this method requires

the steps shown on the following slide

IEEE 1584

EEE 1584

-2002

002

Step 1: Collect power system data

Step 2: Determine the power system’s modes of operation

Step 3: Determine the bolted fault currents

Step 4: Determine the arc fault currents

Step 5: From the protective device characteristics find the arcing duration

Step 6: Record system voltages and equipment classes

Step 7: Determine working distances

Step 8: Determine incident energy for each work location in the study

Step 9: Determine the flash-protection boundary for each work location

in the study

Arc Flash Boundary

rc Flash Boundary

Distance from exposed live parts within which a person

could receive a second degree burn if electrical arc flash

were to occur.

The onset of second degree burns is at the 1.2 cal/cm

2

(5.0 J/cm

2

) level.

It is assumed that a second-degree burn will be curable

and will not result in death.



Arc Flash Boundary

rc Flash Boundary

Arc Flash Boundary

rc Flash Boundary

Arc Flash Analysis Deliverables

rc Flash Analysis Deliverables

Input

nput - Single-line diagram

Study

tudy

- Short circuit duty assessment

Time-current coordination setting

Output

utput - Equipment labels



Arc Flashrc Flash

Sample Labels

ample Labels

Sample Label

ample Label

Sample Label

ample Label



Sample Label

ample Label

Protective

rotective

Clothing and

lothing and

PPEPE

PPE Categories

PE Categories

Category



The selection of a level of Personal Protective Equipment (PPE)

should be a balance between the calculated incident energy

exposure and the work activity being performed while meeting the

following:

Provide enough protection to limit injury to a second

degree burn in all cases

Avoid having more protection than is needed and the

consequent risk of heat stress, poor visibility, and limited

body movement.

PPE Extent

PE Extent

PPE Rating

PE Rating

Arc Thermal Performance Exposure Value (ATPV)

Minimum incident thermal energy on a fabric or

material that results in sufficient heat transfer through

the fabric or material to cause the onset of a second

degree burn based on the energy transmitted through the

clothing

ATPV is expressed in cal/cm2. This energy is related to

the Stoll curve

The ATPV rating is an average of 20 tests performed

using the ATM F1959-99 standard

PPE ASTM Standard

PE ASTM Standard

ASTM F1506-02a – Standard Performance Specification for

Textile Material for Wearing Apparel for Use by Electrical

Workers Exposed to Momentary Electric Arc and Related

Thermal Hazards 2002a

Developed to give minimum performance specs for

protective clothing

Major requirement being that the fabric is flame

resistant

Results must be reported to the end user as an Arc Rating

on a garment label



PPE Material

PE Material

OSHA requires that the clothing, which an employee wears,

does not contribute to the severity of any injuries he or she

incurs as a result of an electric arc

Includes the use of the prohibited fabrics in any layer of a

multi-layer outfit (inside, middle or outer)

Best to use some type of flame-resistant or flame-retardant (FR)

clothing

Examples include FR cotton and wool. Nomex and PBI/Kevlar

PPE Flame Resistance

PE Flame Resistance

Flame resistance is characteristic of a fabric that causes it to not

burn in air

Often confused with flame retardant which is a term used to

describe a chemical substance that imparts flame resistance on

fabric

Government reports note the majority of severe and fatal burn

injuries are due to clothing igniting and continuing to burn, not

by the exposure itself

PPE Layering

PE Layering

Layering significantly increases the level of protection

Two thin layers are better than one thick layer

Layer of air acts as a “buffer zone” between layers of flame

resistant fabrics

Some multi-layer testing has been done by various fabric

manufacturers and ASTM Task Groups (varies dramatically

with different two-ply systems.)



Protective Clothing and PPE

rotective Clothing and PPE

Multi-layering Testing

PPE Care

PE Care

Expected Lifetime and Effects of Cleaning

Wear life is affected by laundering

Industrial laundering will create more wear on a garment

than home laundering

Garments manufacturer’s provide the expected lifetime

based on use and laundering

Repeated abrasion of any type will shorten wear life in the

area on the garment where the abrasion occurs

PPE Suit Versus Synthetic Blend

PE Suit Versus Synthetic Blend



NFPA 70E Methods for Selecting Protective Clothing & PPE

FPA 70E Methods for Selecting Protective Clothing & PPE

Matrix Approach Using Table 130.7(C) (9)(a) And Table 130.7

(C) (10) From NFPA 70E-2004

Table 130.7(C) (9)(a) from NFPA 70E-2004 lists a number of

common work tasks with the respective Hazard/Risk Category

associated with each task

If the work task is not shown in the table, then a flash hazard

analysis is required

If the work location has greater than assumed short circuit

capacity or longer than assumed fault clearing times as shown

in the notes of the table, then a flash hazard analysis is required

NFPA 70E Methods for Selecting Protective Clothing & PPE

FPA 70E Methods for Selecting Protective Clothing & PPE

IEEE Methods for Selecting Protective Clothing & PPE

EEE Methods for Selecting Protective Clothing & PPE

Takes the NFPA 70E model to the next level

Uses systematic approach to calculations and

PPE selection

Method incorporated into powerful Electrical

analysis software such as SKM PowerTools

™

Produces more accurate results – no longer

relies on table lookup



Ok, we have established the

fact that Arc Flash is not

only dangerous but

potentially

FATAL

ATAL. What

can you do, as an Owner, to

reduce risk for you and your

workers?

Reducing

educing

Arc Flash

rc Flash

Minimize Risk with Good Safety

inimize Risk with Good Safety

Practices

ractices

De-Energize Equipment versus

“Working It Live” unless increased

hazards exist or infeasible due to design

or operational limitations

Switching remotely (if possible)

Closing and tightening door latches or

door bolts before operating a switch

Standing to the side and away as much

as possible during switching operations





Practices

ractices



Practices

ractices

Electrically Safe

lectrically Safe

The following steps must be taken to ensure an electrically safe

work condition

Find all possible sources of supply

Open the disconnecting device for each source

Where possible visually verify the device is open

Apply lock-out/tag-out devices

Test voltage on each conductor to verify that it is de-energized

Apply grounding devices where stored energy or induced volt age could exist

or where de-energized parts could contact live parts

Remember personal protective equipment must be worn when workingwithin the flash

protective boundary until the circuit is verified to be de-energized



Safe Operations

afe Operations

Design Methods for Reducing

esign Methods for Reducing

Incident Energy

ncident Energy

Lower available Fault Current

Faster Tripping Time

Equipment Alternatives


quipment Alternatives

Current-Limiting Breakers/Fuses – Reduces the clearing time

which reduces the incident energy

Metal-Clad Switchgear – Structural design reduces the possibility

of arcing faults within the enclosure

Arc Resistant Switchgear – Structural design includes robust

design and pressure relief vents which re-direct the blast away

from the worker



AF Incident

F Incident

AF Incident

F Incident

AF Incident

F Incident



AF Incident

F Incident

AF Incident

F Incident

AF Incident

F Incident

Same system

Add Current

Limiting Device

with <1/2 cycle

operation (.0083

sec)

Note that Arcing Fault

must be in current

limiting range



AF Incident

F Incident

AF Incident

F Incident

AF Incident

F Incident



AF Incident

F Incident

AF Incident

F Incident


quipment Alternatives

Arc Flash Reduction Maintenance

Switch (ARMS)

Remote Power Racking (RPR)

Zone-Selective Interlocking (ZAI)

Current-Limiting MCCBs




rc Flash Reduction Maintenance

Switch

witch

™ (ARMS) Retrofit of LVPCBs

ARMS) Retrofit of LVPCBs


rc Flash Reduction Maintenance

Switch

witch

™ (ARMS) Retrofit of LVPCBs

ARMS) Retrofit of LVPCBs

An external over-ride switch and circuitry are connected to a

breaker’s trip unit and is adjustable between 2.5x - 10x.

When a person wants to perform maintenance they close the

switch, which automatically over-rides all of the delay functions,

and causes the breaker to trip without any intentional delay

whenever a fault is detected. Use its lockout features for normal

lockout – tag-out procedures

Integral ARMS

ntegral ARMS

Has 5 user-selectable levels of

protection to choose maximum

protection, while avoiding

nuisance tripping

Blue color LED indicating

Maintenance mode

Can be remotely activated

through IR communication with

PDA

Available 3Q 2005



Conclusiononclusion

First line of defense – DEENERGIZE

If Deenergization is not possible, make sure

EVERY feasible effort has been taken to REDUCE

the level of Incident Energy exposure

Develop and Maintain Arc Flash Hazard Analysis

Labels

Proper PPE

Be Prepared for Arc Flash

e Prepared for Arc Flash

This

his

…



Not this

ot this

…

S A F E T Y

A F E T Y

–

Stop Arc Flash Episodes

top Arc Flash Episodes

Through Your Knowledge

hrough Your Knowledge

information gleaned from

nformation gleaned from

presentations by:

resentations by:

Questions?uestions?



Thank youhank you

Timothy W. Trotter, P.E., RCDD, LEED AP

imothy W. Trotter, P.E., RCDD, LEED AP

[email protected]

[email protected]

Understanding Arc Flash.pdf

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