An arc flash is a phenomenon where an electric current leaves its intended path and travels through the air from one conductor to another or to the ground. The results can be violent, and when a person is nearby, serious injury or even death can occur.

In the United States, an estimated five to 10 arc flash incidents occur daily, amounting to roughly 30,000 incidents annually. These result in approximately 7,000 burn injuries, 2,000 hospitalizations, and 400 fatalities, according to NIOSH.

NFPA 70E Safety Standards
NFPA 70E is a national consensus safety standard that outlines safe work practices to protect workers from electrical hazards. It specifies that only trained and qualified employees may work on or near exposed energized electrical parts, and they must supervise unqualified personnel nearby. As stated in the standard: “This standard addresses safety of workers whose job responsibilities entail interaction with electrical equipment and systems with potential exposure to energized electrical equipment and circuit parts.”

Causes of Arc Flash
Arc flashes can result from:

  • Dust
  • Dropped tools
  • Accidental contact
  • Condensation
  • Material failure
  • Corrosion
  • Faulty installation

Factors Determining Arc Flash Injury Severity
The severity of an arc flash injury depends on:

  1. Proximity of the worker to the hazard
  2. Temperature
  3. Circuit-break time

Due to the violent nature of arc flash incidents, injuries are often severe, sometimes resulting in death or lifelong consequences for the injured worker.

Results of an Arc Flash
An arc flash can produce:

  • Burns (non-FR clothing can melt onto the skin)
  • Fires (which can spread rapidly)
  • Flying objects (e.g., molten metal)
  • Blast pressure (up to 2,000 lbs/sq.ft)
  • Sound blasts (as loud as 140 dB – comparable to a gunshot)
  • Extreme heat (up to 35,000°F)

Key facts:

  • Arc flashes can reach temperatures over 35,000°F (the Sun is only 9,000°F)
  • Arcs can vaporize metal to 67,000 times its original volume
  • Arc flashes are more likely to occur at voltages above 480V but can happen at any voltage

Protecting Workers
Both qualified and non-qualified employees can be protected using these methods:

  • De-energize circuits
  • Safe work practices
  • Insulation
  • Guarding
  • Barricades
  • Ground Fault Circuit Interrupters (GFCI)
  • Grounding

Additional tips:

  • Only trained and qualified employees should work on electrical equipment
  • De-energize, ground, and verify circuits before starting work
  • When working on live circuits, use proper PPE, insulated tools, and a safety plan, and conduct a briefing beforehand

Working on Energized Equipment
If de-energizing is not feasible, the employer must enforce safety-related work practices to prevent electric shock or injury. These practices should align with the associated electrical hazards and include:

  • Energized Electrical Work Permits
  • Personal Protective Equipment (PPE)
  • Insulated tools
  • Written safety programs
  • Job briefings

Arc Flash Warning Labels

Electrical equipment operating at 50 volts or higher must be evaluated for arc flash and shock hazards. This evaluation determines boundaries (e.g., prohibited, limited, restricted) and specifies the required PPE. After evaluation, Arc Flash Hazard warning labels must be affixed to the equipment and readily accessible to employees working on it.

Don’t Become a Statistic! De-energize, Lock Out, and Verify. Until next time…Work Safe & Be Safe!

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