Arc Flash Hazard 101 “The Basics”

Safety OverviewElectrical safety is one of the most over-looked employee work hazard

432 work related deaths last year* Electrocution ranks 4th in work related fatalities

Majority occurring at 600 volts or less.

Electrical violations 4th most violated standard**7,600 electrical injuries occur in the US each year.

*Bureau Labor Statistics **OSHA

Who’s Responsible?

Employer is responsible for -OSHA complianceElectrical safety programSafety policy & proceduresSafety training

Who’s Responsible?

Employee is responsible for –Implementing & complying with procedures

Owner is responsible for -On-site contractors

What are the Hazards?

Electrical ShockArc FlashArc Blast

Electric ShockCaused by current, not voltage

mA Affect on Person

0.5-3 Tingling sensations

3+ Shock

10+ Muscle contractions & pain

30+ Respiratory paralysis

60+ Heart paralysis (Potentially fatal)

100+ Ventricular fibrillation(Usually fatal)

4+ Amps Heart paralysis

5+ Amps Tissue & organs start to burn

Electric Shock

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

Current passing through the heart and lungs is the most serious

What is Arc Flash?Arc flash occurs when phase conductors are shorted and ionization of the air occurs

Arc faults produce large amounts of heat that can severely burn human skin and even set clothing on fire. Molten metal is blasted from the fault location outward in a radial direction. The arcing faults also produce large shock waves that can blow personnel off their feet.

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

Example of an arcing fault

Arc BlastArc-Blast can cause collateral damage and extreme personal damage

Exploding switchgearSend molten metal at extreme high velocities

What is Incident Energy?Energy per unit area received on a surface located a working distance away from the flash location

“Working distance” is the distance between where the worker stands and the flash.

Approximately 24” for low voltage equipmentThe distance is longer as the voltage increases

What is Incident Energy?

The unit of incident energy is cal/cm²The threshold value of incident energy for 2nd degree burn of human skin is about 1.2 cal/cm²

One cal/cm² is equivalent to the amount of energy produced by a cigarette lighter in one secondIncident energy causes burns to human skin

What causes Arc Flash?

Electrical short circuitsFaults on electrical systems can be in the form of phase-to-ground, double phase-to-ground, and three phase

What causes Arc Flash?

Electrical arcs create plasma, hot vapors, and gases that can rise to 23,000 º F

The heat produced can ignite clothing more than 10 feet away

Flash Protection Boundaries

Protection boundaries developed by NFPA 70E

Based upon the employee's training and personal protective equipment

The Limited Approach, Restricted, and Prohibited boundaries are based on the voltage of the energized equipment

Flash Protection Boundaries

Limited Approach boundary is the minimum distance from the energized item where untrained personnel may safely stand

They are prohibited from crossing this boundary

Flash Protection Boundaries

Restricted Approach boundary is the distance where qualified personnel may not cross without wearing appropriate personal protective equipment

Requires a written, approved plan for the work that they will perform

Flash Protection Boundaries

Prohibited Approach boundary is only accessible to those wearing appropriate personal protective equipment

Crossing this boundary is considered the same as contacting the exposed, energized partPersonnel must obtain a risk assessment before crossing this boundary

Flash Protection Boundaries

Flash Protection boundary is based on-VoltageAvailable fault current Time it takes for the upstream protective device to operate and clear the fault

All Protection Boundaries

The time it takes for the protective device to operate is more important than the amount of available fault current

Longer protective device delay times equate to higher incident energy levels

Principle Regulations that Address Arc Hazards

National Fire Protection Association (NFPA) Standard 70 “The National Electrical Code” (NEC).

By definition the NEC is an installation standard although its requirements impact maintenance and repair.

NFPA 70B 2002 “Recommended Practice for Electrical Equipment Maintenance”

NFPA 70E 2000 “Standard for Electrical Safety Requirements for Employee Workplaces”

Referenced by OSHA and part of its “Safety Related Work Practices”

Principle Regulations

Principle Regulations

Standard number 1910.333 specifically addresses “Standards for Work Practices”

Regulations apply to every worker that may approach or be exposed to electric energy

OSHA Standards 29-CFR, Part 1910Occupational Safety and Health Standards 1910 sub part S (electrical)

Principle Regulations

Three Basic Steps

Arc Flash StudyPersonal Protective EquipmentArch Flash Panel Labels

AssessmentProtectionIdentification

Why do an Arc Flash study?

Government regulationsOSHA enforcing National Fire Protection Association (NFPA) document NFPA70Regulations apply to every worker that may approach or be exposed to energized electrical equipment

Why do an Arc Flash study?

LiabilityFailure to comply can results in employee injuries, fines & expensive lawsuits

Personnel safetyReduce shock hazards & injuries through education and personal protective equipment (PPE)

What is an Arc Flash Study?Analysis and assessment of arc flash and shock hazards at a facility or jobsite

What does an Arc Flash study provide?

Personal Protection Equipment (PPE)

Protects against burns to the body that could cause death

Includes clothing, gloves, tools, face protection & glasses

Personal Protection Equipment (PPE)

Different types of clothing have different ratings

Ex: Gloves

GLOVE CLASS VOLTAGE RATING

00 2.5kV

0 5kV

1 10 kV

2 20kV

3 30kV

4 40kV

Who Needs PPE?

Anyone working with energized circuits of 50 volts or more

Per OSHA NFPA 70E, safety tools and personal protective equipment mandatory

PPE RequirementsIn addition to normally used hard hat, safety shoes, safety glasses & hearing protection, requirements include-

Flame-resistant clothingFlash suits (for high-energy arc exposure)Flash suit hoods

Insulating glovesInsulated tools

PPE Selection Options

Per NFPA 70E – Option 1Conduct Arc Flash hazard analysis & document incident energy exposure

Duke Flux Software (Freeware)ArcPro II SoftwareIEEE 1584 Standard

PPE Selection Options

Per NFPA 70E – Option 2Utilize the “Hazard Risk Category Classifications” table to choose the required PPE

NFPA 70E –

Hazard Risk 2

“Moderate Risk”Examples -

Circuit breaker or fused switch operation with enclosure doors closed when working with 600 V Class Motor Control Centers (MCCs). Work on control circuits with energized parts 120 V or below, exposed when working on Metal Clad Switchgear, 1 kV and above

NFPA 70E –

Hazard Risk 3

“High Risk”Examples –

Insertion or removal of circuit breakers from cubicles, doors open, when working with 600 V Class switchgear (with power circuit breakers or fused switches).Opening hinged covers (to expose bare, energized parts) when working with "Metal Clad Switchgear, 1 kV and above

NFPA 70E –

Hazard Risk 4“Great Risk”

Examples -Removal of bolted covers (to expose bare, energized parts) when working with NEMA E2 (fused contactor) Motor Starters, 2.3 kV through 7.2 kV Opening voltage transformer or control power transformer compartments when working with Metal Clad switchgear, 1kV and above

Arc Flash Clothing

NFPA 70E – 2004 and ASTM F1506 under OSHA 1910.269 1,6,iii require Arc Flash clothing

Shirt jacket, parka jacket, pants, coveralls and overalls with ARC Rating 8 cal/cm2 to 100 cal/cm2 ATPV values

What is an Arc Flash Warning Label?

Identifies switchboards, panel boards, industrial control panels and motor control centers of potential electric arc flash hazards

Per section 110.16 of the NEC 2002 code

Arc Flash LabelsMarkings must be visible to personnel before equipment examination, adjustment, servicing, or maintenance

Basic Definitions & Terms

Arc RatingArc Thermal Protection Value (ATPV )

Protection value assigned to textile materials based on predicting 2nd degree burn injury based on the Stoll Curve.

Basic Definitions & Terms

Arc Flash HazardA dangerous, explosive condition

associated with the release of energy caused by an electric arc

Includes a broad spectrum of electromagnetic energy, plasma, fragments and a spray of molten materials

Basic Definitions & Terms

Arc RatingArc Thermal Protection Value (ATPV )Protection value assigned to textile materials based on predicting 2nd

degree burn injury based on the Stoll Curve

Basic Definitions & Terms

Hazard Risk Category ClassificationDefines typical tasks for electrical workers and assigns Hazard/Risk Category values

Per NFPA 70E table 130.7(C)(9)(a)

Basic Definitions & Terms

Hazard Risk Protection CategoryThe ATPV for each Hazard/Risk Category

Ex: ATPV is 8 for Hazard/Risk Category 2Per NFPA 70E table 130.7(C)(11)

Basic Definitions & Terms

PlasmaSuperheated gas that is created by the arc flash and expands rapidly from the Arc location

Basic Definitions & Terms

Protective clothing and PPE Matrix

NFPA 70E Table 130.7(C)(10) defines the PPE requirements for each Hazard/Risk categoryDetermines when face shields & hoods must be used

Basic Definitions & Terms

Stoll CurveA prediction at which one would expect

to receive a second degree burnBased on a function of time and heat