Arc Flash

What is an Arc Flash? 

An arc flash, also known as an electrical flashover, is a hazardous electrical event characterised by a rapid release of energy due to an electric arc.

An electric arc occurs when electrical current flows across a gap between electrical conductors or one electrical conductor and ground. Typically, the gap is filled with air and provided that there is sufficient voltage to ionise it, thereby creating a conductive path, an electrical current will flow and energy in the form of heat will be released.

Expand the follow sections to learn more about the characteristics, effects, and potential causes of an arc flash.

Characteristics of an arc flash
◾ Extremely high temperatures (which can reach 20,000°C)
◾ Intense light
◾ Arc blast / electric arc explosion (i.e. pressure waves)
◾ Sound blast
◾ Ultra-violet light from blast
◾ Vaporisation of conductor materials
◾ Propulsion of molten metals and equipment parts
Effects of an arc flash
◾ Fire
◾ Equipment damage
◾ Severe burns
◾ Hearing damage
◾ Lung damage
◾ Eye damage
◾ Fatality
Potential causes of an arc flash
◾ Improper installation of equipment
◾ Equipment failure
◾ Poorly maintained equipment
◾ Insulation breakdown
◾ Live work on damaged or poorly maintained equipment
◾ Operation of equipment during electrical fault conditions.
◾ Accidental contact with live electrical components (e.g. dropping uninsulated tools or conductive objects)
◾ Build-up of dust
◾ Moisture or vapour
◾ Animal contact (e.g. rodents)
◾ Human error (e.g. distractions, tiredness, haste, complacency)
◾ Lack of training (e.g. ignorance or lack of competence)

Why are Arc Flash Studies important?

Arc flash studies allow one to predict/quantify/estimate the severity of the potential risk presented by an arc flash hazard, specifically the thermal effects of the hazard.

An incident energy analysis is performed using electrical power system analysis software to determine  the Estimated Incident Energy (1), and a corresponding  Arc Flash Boundary (2) at each location in an electrical network.

Arc flash hazard warning labels can then be produced and affixed to equipment to show the level of risk and the required level of arc-rated clothing and personal protective equipment (PPE) that should be worn by electrical workers working on or in the vicinity of the equipment.

It should be noted that PPE recommendations based on incident energy analysis are the last line of defence against arc flash hazards. Other mitigation measures provide the first line of defence and should be employed in the first instance, such as;

  • Engineering controls
    • De-energise electrical equipment before working on or near it.
    • Keeping workers at a safe distance from live equipment (e.g. installing remote operating devices to reduce the need to operate switches whilst close to equipment).
    • Installing arc-resistant switchgear or equipment designed to redirect, contain or extinguish an electrical arc.
    • Using fast operating protective devices to reduce fault clearance times.
    • Using current-limiting fuses to reduce the energy releases during an arcing fault.
  • Administrative controls
    • Developing and enforcing electrical safety policies, procedures and protocols for conducting work on or near energised equipment, including risk assessments and work permits.
    • Providing comprehensive training for workers.
  • Regular inspection, testing and maintenance of electrical equipment


Key Challenges Involved in Arc Flash Studies 

  • Collecting requisite data – some equipment data can be difficult to obtain and therefore engineering judgement is needed to employ appropriate assumptions.

  • Modelling complexity – meshed networks consisting of multiple electrical sources and the various operating scenarios of networks can add to the complexity of arc flash hazard analysis. Engineering expertise is needed to select scenarios which represent the largest potential incident energy exposure. A thorough knowledge of protection co-ordination schemes is required.

  • Dynamic operating conditions – capturing dynamic operating conditions (e.g. loading changes, switching operations and transient events) in arc flash studies entails detailed modelling and analysis.

  • Arc flash calculation – calculating arcing current and incident energy involves complex equations that depend upon equipment characteristics, fault current levels, system impedance and protective device coordination. Power engineering expertise is essential in ensuring careful consideration of the many assumptions and parameters involved in this process.

  • Accessing equipment – accessing electrical equipment for data collection, testing or maintenance can pose safety risks.

  • Regulatory compliance – thoroughly understanding the requirements of the relevant standards and regulations and adhering to best practices is essential.

  • Skills and resources – arc flash hazard analysis requires specialist engineering expertise and knowledge, modelling software and potentially equipment testing capabilities.


View industry standards on our Standards, Regulations and Resources page.

1. Estimated Incident Energy is the thermal energy, measured in calories per square centimetre or Joules per square centimetre, that a worker could potentially be exposed to at a given distance from the source of an arc flash.

2. Arc Flash Boundary is a distance from an arc source at which incident energy is calculated to be 1.2 cal/cm2 or 5.0 J/cm2, the threshold for a second-degree burn.

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