Understanding "Arc Flash"

Simply put, an arc flash is a phenomenon where a flashover of electric current leaves its intended path and travels through the air from one conductor to another, or to ground.

The results are often violent and when a human is in close proximity to the arc flash, serious injury and even death can occur.

Arc flash can occur when an employee or vendor is working around electrical boxes or connections and is not qualified for the work or does not follow safe working procedures.  Some of the common conditions that can help with causing an arc flash include:

  • Dust
  • Dropping tools
  • Accidental touching
  • Condensation
  • Material failure
  • Corrosion
  • Faulty Installation

Three factors determine the severity of an arc flash injury:

  • Proximity of the worker to the hazard
  • Temperature
  • Time for circuit to break

Because of the violent nature of an arc flash exposure when an employee is injured, the injury is serious, even resulting in death. It’s not uncommon for an injured employee to never regain their past quality of life. Extended medical care is often required, sometimes costing in excess of $1,000,000.

Typical Results from an Arc Flash:

  • Burns (Non FR clothing can burn onto skin)
  • Fire (could spread rapidly through building)
  • Flying objects (often molten metal)
  • Blast pressure (upwards of 2,000 lbs. / sq. ft.)
  • Sound Blast (noise can reach 140 dB – loud as a gun)
  • Heat (upwards of 35,000 degrees F)

    Ways to Protect the Workers

First, find out what employees are doing around electrical hazard.  We recently found out that a parks supervisor was opening electrical boxes and using an ordinary screw driver to “tighten” live, energized circuit breaker screws.    Apparently this supervisor had gotten “away” with this unsafe act for some time -that is- until the arc flash occurred.  All operations around or in electrical systems have to be reviewed to ensure the employees doing the operations are qualified for the operation, properly trained, following the most up-to-date safety procedures and are equipped with the proper equipment and personal protective equipment (PPE).

Second, protect the workers that are not performing the electrical operations but are in the area.  All electrical equipment should be identified with arc flash warning labels that match the exposure.

Each piece of equipment operating at 50 volts or more and not put into a de-energized state must be evaluated for arc flash and shock protection. This evaluation will determine the actual boundaries (i.e. prohibited, limited, restricted, etc.) and will inform the employee of what PPE must be worn.

Once the evaluation is complete an Arc Flash Hazard warning label must be affixed to the equipment and readily accessible to employees who may work on the energized equipment.

Each employee must follow the requirements of the Arc Flash Hazard label by wearing the proper PPE, use of insulated tools and other safety-related precautions. This includes not working on or near the circuit unless you are a “qualified” worker.

A qualified person is an employee or vendor who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved.  Qualified employees and vendors are those permitted to work on or near exposed energized parts and shall, at a minimum, be trained in and familiar with the following:

  • The skills and techniques necessary to distinguish exposed live parts from other parts of electric equipment.
  • The skills and techniques necessary to determine the nominal voltage of exposed live

    parts, and

  • The clearance distances specified in National Fire Protection Association guidelines and adopted standards and the corresponding voltages to which the qualified person will be exposed.

If you need help with setting up your policies, programs or procedures, contact your local Risk Control Consultant.