Arc-Flash risk

It is the result of an electrical short circuit conducted through the air. It is a violent release of thermal energy from an electrical source, which can cause serious or even fatal burns or injuries. On an electrical panel, the risks of an Arc Flash become a major concern starting at 220 volts AC.

The difference lies in the consequence related to the accident. In the case of electric shock, it refers to injuries caused by an electric current passing through the body, whereas electrocution refers to death resulting from an electric shock.

An Arc Flash can reach up to 18,000°C, which is about three times the heat of the sun’s surface.

The consequences of exposure to an Arc Flash are multiple :

• Burns : The heat and flames from a massive explosion can cause second- and/or third-degree burns. Projections of molten metal can also cause severe burns.
• Hearing loss : The sound wave can reach 165 dB, comparable to that of an aircraft taking off, and can lead to hearing degradation or loss.
• Eye injuries : An intense light flash, with UV radiation, can cause eye injuries.
• Respiratory disorders : Toxic vapors and fumes (such as vaporized copper) can cause damage after inhalation.

An Arc Flash can occur in various environments, whether related to electrical installations or structures, starting from a nominal voltage of 220 Volts AC. Here are some examples :

• Production : Power plants : nuclear, hydroelectric, thermal, or wind.
• Transmission : Medium and high voltage electrical networks, between different substations.
• Electrical substations : High-voltage current transformed into low-voltage current for distribution.
• Electric traction : Railway networks.
• Factories and industrial installations : Significant energy demand for production.
• Distribution : For low-voltage electrical networks.
• Technical rooms and electrical panels : Electrical distribution panels, circuit breakers, control panels.
• Electric mobility : Cars, trucks, forklifts, and other electric or hybrid vehicles.
• Data centres : Large number of servers and electrical installations with high energy demands.

It is crucial to follow safety and maintenance protocols and to wear appropriate PPE to protect users from the consequences of accidents and to minimize Arc Flash risks in these environments.

A Flash Arc can occur when electricity jumps across a gap between two conductors or between a conductor and a conductive surface (such as the ground or a metal enclosure). Several conditions can lead to an Arc Flash :

• Short circuit : A short circuit between two conductors can create an electric arc. This short circuit can be caused by improperly used tools, exposed wires, damaged insulation, or conductive objects falling into electrical equipment.
• Accidental contact : Accidental contact of a tool or another object with live conductors can cause an arc flash (such as the dropping of tools or accidental contact with electrical systems). This can happen during maintenance or repair work. An Arc Flash can occur with or without human presence.
• Insulation failures : Failures or degradation of the insulation around electrical conductors can allow electricity to jump through the air, resulting in an Arc Flash.
• Accumulation of dust or debris : Dust, debris, or metallic contaminants can accumulate on conductive surfaces, creating conductive paths that promote electrical arcs.
• Corrosion : Corrosion of conductors or connections can increase electrical resistance and generate heat, which can trigger an Arc Flash.
• Moisture : Moisture or condensation can create a conductive path between conductors, facilitating the formation of an arc.
• Overvoltage or overcurrent : Surges or excessive currents, due to equipment failure or lightning, for example, can cause an arc flash by overheating components and creating short circuits.
• Improper handling of equipment : Incorrect opening or closing of switches, breakers, or other energized equipment can generate arcs.

From 220 Volts.

One might think that in LV, there is no exposure to an Electrical Arc,, but that is false ! Even in ELV, the risk is present.

The determining factor is the current intensity, more than the network voltage.

There are several :

• The intensity of the electrical arc, taking into account :
  • Network voltage
  • Current intensity / Amperage
  • Inter-electrode gap
  • Confined environment
• The duration of the electrical arc : or the exposure time
• Working distance : proximity to the source of the Flash Arc
• Improperly worn PPE : improper use of PPE can exacerbate the risks

It is necessary for several reasons, as follows :

• It helps define the protection level of the garment
• It helps define the protection class (4KA, 7KA, etc.)
• It determines the ATPV level for a given electrical installation

Only a notified laboratory or authorized personnel are allowed to carry out the risk analysis.

The unit of measurement used is Cal/cm².

No, there is no formula or normative text on the subject.

Méthode OPEN ARC : EC 61482-1-1

Détermination des indices ATPV et ELIM des EPI en calories/cm² (principe américain).

Méthode d'essai la plus représentative et la plus proche de la réalité. Il s'agit de la simulation des effets thermiques sur le corps, traduits en cal/cm².

Correspondant à de nombreux niveaux d'énergie incidents différents.

Méthode BOX TEST : IEC 61482-1-2

Détermination en deux classes de protection de l’EPI, en fonction du niveau d'intensité de l'installation électrique (principe européen) :

• APC* 1 : 4 kA pendant 0,5 s à 30 cm
• APC* 2 : 7 kA pendant 0,5 s à 30 cm

Test concernant la densité/intensité du courant électrique, qualifiant les EPI en deux classes et jusqu'à 7kA seulement. Ne convient pas au-delà de 7 kA pour l’installation électrique.

NB : Il ne représente pas les effets thermiques effectifs sur le corps. S'applique uniquement aux installations électriques.

*Arc Protection Class

Oui, il existe un lien car ces deux valeurs sont obtenues par la même méthode de test mais elles sont deux interprétations différentes du résultat.

• ATPV = Arc Thermal Performance Value (Valeur de performance thermique de l'arc)

→ L'énergie thermique maximale que l’EPI peut supporter avec une probabilité de brûlures au 2nd degré de 50%. Exprimée en cal/cm².

• ELIM = Incident Energy Limit (Limite d'énergie incidente)

→ L'énergie thermique maximale que l’EPI peut supporter avec une probabilité de brûlure au deuxième degré de 1 % seulement. Exprimée en cal/cm².

Il faut suivre les recommandations de la notice d’utilisation, propre à chaque produit.