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OSHA Arc Flash

Arc Flash is the result of a rapid release of energy due to an arcing fault between a phase bus bar and another phase bus bar, neutral or a ground. During an arc fault the air is the conductor. Arc faults are generally limited to systems where the bus voltage is in excess of 120 volts. Lower voltage levels normally will not sustain an arc. An arc fault is similar to the arc obtained during electric welding and the fault has to be manually started by something creating the path of conduction or a failure such as a breakdown in insulation.

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. This massive energy discharge burns the bus bars, vaporizing the copper and thus causing an explosive volumetric increase, the arc blast, conservatively estimated, as an expansion of 40,000 to 1. This fiery explosion devastates everything in its path, creating deadly shrapnel as it dissipates.

The arc fault current is usually much less than the available bolted fault current and below the rating of circuit breakers. Unless these devices have been selected to handle the arc fault condition, they will not trip and the full force of an arc flash will occur. The electrical equation for energy is volts x current x time. The transition from arc fault to arc flash takes a finite time, increasing in intensity as the pressure wave develops. The challenge is to sense the arc fault current and shut off the voltage in a timely manner before it develops into a serious arc flash condition.

Why the focus on Arc Flash?

In the early 1980's a paper "The Other Electrical Hazard: Electric Arc Blast Burns" by Ralph Lee was published in the IEEE Transactions on Industrial Applications. The effect of this paper was to realize the need to protect people from the hazards of arc flash. Four separate industry standards concern the prevention of arc flash incidents:

§  OSHA 29 Code of Federal Regulations (CFR) Part 1910 Subpart S.

§  NFPA 70-2002 National Electrical Code.

§  NFPA 70E-2000 Standard for Electrical Safety Requirements for Employee Workplaces.

§  IEEE Standard 1584-2002 Guide for Performing Arc Flash Hazard Calculations.

Compliance with OSHA involves adherence to a six-point plan:

§  A facility must provide, and be able to demonstrate, a safety program with defined responsibilities.

§  Calculations for the degree of arc flash hazard.

§  Correct personal protective equipment (PPE) for workers.

§  Training for workers on the hazards of arc flash.

§  Appropriate tools for safe working.

§  Warning labels on equipment. Note that the labels are provided by the equipment owners, not the manufacturers. It is expected that the next revision of the National Electric Code will require that the labels contain the equipment's flash protection boundary, its incident energy level, and the required personal protective equipment (PPE).

Companies will be cited and fined for not complying with these standards.

Personal Protection Equipment (PPE) Hazard Categories


Required PPE

Min. Arc


·         T-Shirt & Long Pants (natural fibers)

·         Safety Glasses



·         Long sleeve Shirt & Long Pants
(natural fibers)

·         Safety Glasses



·         Fire-Resistant Shirt & Pants
(or Fire-Resistant Coverall)

·         Hard Hat

·         Safety Glasses

·         Leather Gloves & Shoes



·         Cotton Underwear

·         Fire-Resistant Shirt & Pants

·         (or Fire-Resistant Coverall

·         Hard Hat

·         Safety Glasses or Goggles

·         Arc-Rated Face Shield
(or Flash Suit Hood)

·         Hearing Protection

·          Leather Gloves & Shoes




Same as 2 EXCEPT Flash Suit 8 Hood required (no face shield option)



·         Cotton Underwear

·         Fire-Resistant Shirt & Pants (PLUS Fire-Resistant Coverall)

·         Hard Hat

·         Safety Glasses or Goggles

·         Flash Suit Hood

·         Hearing Protection

·         Leather Gloves & Shoes



·         Cotton Underwear

·         Fire-Resistant Shirt & Pants (or Fire-Resistant Coverall)

·         Hard Hat

·         Safety Glasses or Goggles

·         Full Flash Suit with Hood

·         Hearing Protection

·         Leather Gloves & Shoes


Minimum Arc Rating indicates the amount of thermal energy the apparel protects against. It’s critically of arc blast or explosion. De-energizing and locking out equipment is the best way to protect workers. important that workers wear natural fibers and fire resistant clothing, because the most severe burns are caused by ignited or melted clothing. Additional shields and barriers may also be necessary to protect workers. 

Arc flash typically occurs while electrical equipment is being disconnected, inspected or serviced, and can be caused by a variety of factors such as:


    · Accidental contact with live parts

    · Close proximity of a conductive object, like a metal tool, with a high-amp current source

    · Sparks generated from racking in breakers, replacing fuses, or even from dropped tools

    · Over voltage conditions

    · Insulation failure or corrosion buildup on electrical terminals

    · Presence of fumes or chemical vapors that reduce the breakdown voltage of air


Comply with the NEC marking requirement for arc flash hazard protection

·         Hazard warning labels are now required by the 2002 National Electric Code (Article 110.16) to help reduce the occurrences of serious injury or death due to arcing faults to those who work on or near energized electrical equipment

·         Post these durable self-adhesive vinyl labels to switchboards, panel boards, etc. to warn

Introduced in the 2002 Edition of the National Electric Code

 EMPLOYERS, not manufacturers or installers, are responsible for complying with NEC labeling requirements.


Switchboards, panel boards, industrial control panels, and motor control centers must be field marked. Many companies are also marking conduits, disconnect switches, and any other equipment where the risk of arc flash exists.


Any equipment installed after 2002 needs to be labeled. For equipment installed before 2002, labeling must be applied if ANY modifications or upgrades take place. Smart employers are taking the safe, efficient approach of labeling all their electrical equipment, regardless of when it was installed.


OSHA has been working with the National Fire Protection Agency (NFPA), the Institute of Electrical and Electronics Engineers (IEEE) and other organizations to develop a set of regulations that specifically address arc flash.


OSHA does not specifically mention arc flash hazards or requirements in its standards. However, the requirements for protecting employees working on exposed live parts are described in terms general enough to include arc flash hazards, allowing OSHA to cite employers for exposing workers to arc flash hazards.


OSHA 29 CFR 1910.331 - .335, Electrical Safety-Related Work Practices is the main standard defining requirements for protecting workers who may be exposed to electrical hazards. In enforcing worker safety procedures, OSHA cites the NFPA 70E standard as the "how to" source for compliance. NFPA 70E provides guidance on specific steps that must be taken to comply with the more general statements made in the OSHA standards. 

NFPA 70E-2004 Standard For Electrical Safety in the Workplace

NFPA 70E can be considered an offshoot of the National Electric Code. The NEC is concerned mainly with electrical design, construction and inspection. As such, it was hard for employers and employees to understand the electrical safety requirements for working on installed electrical systems in the work place. Using the NEC and other documents as a basis, the NFPA 70E was created to provide clearer instructions for electrical safety in the workplace. As part of the requirements, employers are required to perform an arc flash analysis.


Click here for more detailed information regarding OSHA-arc-flash

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