San Bernard Electric Cooperative, Inc.

San Bernard Electric Cooperative, Inc.

Arc Flash Assessment

What Is An Arc Flash?• An Arc Flash is the result of a rapid release of

energy due to an arcing short circuit between two or more adjacent conductors.

• The cause of the short normally burns away during the initial flash, and the arc fault is then sustained by the establishment of a highly-conductive plasma.

• The plasma will conduct as much energy as is available and is only limited by the impedance of the arc.

•Electric arcs produce the highest temperatures on earth –up to 35,000 degrees Fahrenheit

•The intense heat from arc causes the sudden expansion of air that results in a blast with very strong air pressure (Lightning is a natural arc).

•All known materials are vaporized at this temperature. (Copper expands 67,000 times, Water 1670 times).

•Arcs in enclosures, such as a Motor Control Centers (MCCs) or switchgear, magnify blast and energy transmitted as the blast is forced to the open side of the enclosure.

• Arcs spray droplets of molten metal at high-speed (700 mph) pressure. Blast shrapnel can penetrate the body.

•Blast pressure waves have thrown workers across rooms and knocked them off ladders. Pressure on the chest can be higher than 2000 lbs/ sq. ft.

•Clothing can be ignited several feet away unless flame-resistant clothing is used. Arc Flashes have caused death as far away as 10 ft.

•Hearing loss from sound blast. The sound can have a magnitude as high as 160 dB.

Why all the interest ?Federal Law• OSHA 1910, 1926

National Consensus Standards• NFPA 70 – National Electric Code• NFPA 70E – Standard for Safety in the Workplace• NESC – National Electric Safety Code• IEEE 1584 – Guide for Arc Flash Hazard Analysis

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Consensus Standards• NFPA-70 - Generally applies to construction &

installation• OSHA requested NFPA to create a standard to address

worker safety …. result was NFPA-70E• Arc flash appeared in NFPA-70E as a “recognized

hazard” in 1995. NFPA-70E excludes “utilities” {90.1(5)}• NESC identified arc flash as a “recognized hazard“ in

2007 and closed the utility loop-hole {410.A.3}• IEEE 1584 created to develop a standard for quantifying

the dangers associated w/ arc flash

OSHA – General Duty Clause

“Each employer shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to employees.”

Law or not??

2007 NESC Rule 410.A.3• Effective as of January 1, 2009, the employer shall

ensure that an assessment is performed to determine potential exposure to an electrical arc for employees who work on or near energized parts or equipment. If the assessment determines a potential exposure greater than 2 cal/cm2 exists (see Neal, Bingham, and Doughty [B53]), the employer shall require employees to wear clothing or a clothing system that has an effective arc rating at least equal to the anticipated level of arc energy.

Adopted by State of Texas

How do you protect workers?

• Work on equipment only after being placed in an electrically safe condition.

• If the equipment must be worked live:PPEProper safety training / proceduresMaximize working distanceMinimize fault clearing time

PPE

• PPE is intended to reduce skin damage to second degree burns only. Second degree burns are considered to be “just curable”.

• 1.2 Calories / cm2 is generally considered to be threshold of a second degree burn.

• Workers can still be burned by following the rules and using the “correct” PPE.

• Is FR equipment considered PPE?

Arc Flash Energy

Contributing Factors Include:• Available fault current• Distance to arc flash• Time exposed to arc flash• Location (open-air, enclosure, etc)• System grounding• System voltage / conductor gap

Personal Protective Clothing

Examples of PPE

Hazard Risk Category 1

Hazard Risk Category 2

Hazard Risk Category 3

Hazard Risk Category 4Hazard Risk

Category 0

2012 NESC Rule 410.A.3If the assessment determines a potential employee exposure greater than 2 cal/cm2 exists, the employer shall:b. Require employees to wear clothing or a clothing system with an effective arc rating not less than the anticipated level of arc energy.EXCEPTION 1: If the clothing required by this rule has the potential to create additional and greater hazards than the possible exposure to the heat energy of the electric arc, then clothing with an arc rating or arc thermal performance value (ATPV) less than that required by the rule can be worn.

2007 NESC Rule 410.A (cont.)4. Employers shall utilize positive procedures to

secure compliance with these rules. Cases may arise where the strict enforcement of a particular rule could seriously impede the safe progress of the work; in such cases the employee in charge of the work should make a temporary modification to the particular rule so the work can be accomplished without increasing the hazard.

5. If a difference of opinion arises with respect to the application of these rules, the decision of the employer or the employer’s authorized agent shall be final. This decision shall not result in any employee performing work in a manner that is unduly hazardous to the employee or to other workers.