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 from 220 volts AC upwards.

The difference lies in the consequence related to the accident. In the case of electric shock, we refer 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 vapours and fumes (such as vaporised 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 requirements.

It is crucial to follow safety and maintenance protocols and to wear suitable PPE to protect users from the consequences of accidents and to minimise 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 AC.

One might think that in LV (Low Voltage), there is no exposure to Arc Flash, but this is false ! Even in ELV (Extra Low Voltage), the risk is present.

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 defines the protection requirements – which means that it :

• Allows the definition of the PPE protection level.
• Allows the definition of the protection class : APC1 (Arc Protection Class 1) or APC2 (Arc Protection Class 2).
• Defines the incident energy level for a given electrical installation (ATPV and/or ELIM value expressed in cal/cm²).

It is important not to forget the notion of responsibility – the employer must request this analysis from qualified individuals or organisations.

Only a recognised organisation or qualified individuals are authorised to carry out the risk analysis. The employer must request the analysis from these bodies to define the protection requirements.

The incident energy related to Arc Flash is expressed in cal/cm² (calories per square centimetre).

No, it is not possible to establish a link between ATPV (Arc Thermal Performance Value) and APC (Arc Protection Class) because they are two distinct test methods (not the same equipment for testing, nor the same units of measurement in the results).

OPEN ARC Method : EC 61482-1-1

Determination of ATPV and ELIM values of PPE in cal/cm² (American-based principle).

This is the most representative test method, and the closest to real-life conditions. It simulates the thermal effects on the human body, expressed in cal/cm².

It corresponds to many different levels of incident energy.

BOX TEST Method : IEC 61482-1-2

Determines two protection classes of PPE, based on the intensity level of the electrical installation (European-based principle) :

APC 1* : 4 kA for 0.5 s at 30 cm
APC 2* : 7 kA for 0.5 s at 30 cm

A test based on the current intensity/density, classifying PPE into two categories, up to 7 kA only. Not suitable for electrical installations above 7 kA.

NB : It does not represent the actual thermal effects on the human body. Applies only to electrical installations.

*Arc Protection Class

Yes, there is a link because both values are obtained using the same test method, but they represent two different interpretations of the result.

• ATPV = Arc Thermal Performance Value

→ The maximum thermal energy that PPE can withstand with a 50 % probability of second-degree burns. Expressed in cal/cm².

• ELIM = Incident Energy Limit

→ The maximum thermal energy that PPE can withstand with only a 1 % probability of second-degree burns. Expressed in cal/cm².

Follow the recommendations in the product-specific instructions for use.