In brief
Arc flash is when an electric current jumps through the air and produces a huge amount of heat, light and a pressure wave in a very short time. It is a separate risk from electric shock and can start with a tool dropped while a panel cover is open or a slipping test probe. The first means of protection is to isolate the energy; for steps that remain live, such as verifying the absence of voltage, arc-rated clothing, face shields and gloves suited to the incident energy are used.
What is arc flash?
Arc flash is a short-circuit event that occurs when an electric current passes through the air between two conductors or between a conductor and earth. The path the current takes consists of ionised gas, that is, plasma. In a fraction of a second, a temperature that can reach tens of thousands of degrees, a blinding light, sound and a pressure wave are produced.
Arc flash is different from electric shock. In a shock, the current passes through the body; in an arc flash, a worker can be injured without ever touching a conductor, simply because they are standing in front of the panel. That is why the thought "I'm wearing insulating gloves, I'm safe" does not address the arc risk.
Typical events that start an arc in panel work are:
- A screwdriver, spanner or bolt dropped in an open panel.
- A probe slipping during voltage measurement, or a multimeter of the wrong measurement category.
- A loose connection, overheated and degraded insulation.
- Conductive dust, moisture or rodents accumulated in the panel.
- Misalignment when racking a withdrawable circuit breaker in or out.
- Opening the cover while live, or switching the wrong circuit.
Electric arc burns and blast effects
In an arc flash, injury comes by several routes at once:
| Effect | Consequence | Protection |
|---|---|---|
| Heat | Second and third degree burns on exposed skin, clothing catching fire | Arc-rated clothing and face protection |
| Melting of synthetic clothing | Melting fabric sticking to the skin and deepening the burn | Avoiding synthetic underwear and outerwear |
| Pressure wave | Eardrum damage, being thrown, falls | Distance, switching with the door closed, earplugs |
| Molten metal and fragments | Penetrating injuries to the skin and eyes | Face shield, closed clothing |
| Intense light | Eye damage | Safety glasses under an arc-rated face shield |
| Metal vapour and smoke | Respiratory irritation | Ventilating the area after the event |
Incident energy is used to quantify the electric arc burn risk. Incident energy is the thermal energy reaching the body surface at a given working distance and is expressed in cal/cm². In international practice, for example in the NFPA 70E standard widely used in the US, the value at which a second degree burn is considered to begin on unprotected skin is 1.2 cal/cm². The distance in front of the panel at which this value is exceeded is called the arc flash boundary.
What does incident energy depend on?
Three quantities determine incident energy:
- Short-circuit current: Depends on the transformer feeding the panel and the cable length.
- Clearing time: How long the arc lasts until the protective device (fuse, circuit breaker or relay) opens the circuit. Incident energy increases roughly in proportion to arc duration.
- Working distance: Incident energy falls rapidly as the worker's face and body move further from the arc point.
Example (with representative values): Suppose that in a calculation for a main distribution panel, with protection clearing in 0.5 seconds, the incident energy at the working distance is found to be 20 cal/cm². If a fast protection setting activated during maintenance reduces the clearing time to 0.1 seconds, the incident energy at the same distance falls to about 4 cal/cm². This directly changes both the class of clothing required and the severity of injury.
The incident energy calculation is carried out by an electrical engineer together with the short-circuit and selectivity study; the IEEE 1584 method is widely used for arc flash calculations. The result of the calculation should be labelled on the panel and entered in the risk assessment. For general safety requirements for panels, see our article on electrical panel safety.
Avoiding live work
The most effective measure against arc flash is not to work on a panel while it is live. Before maintenance and repair, the circuit is isolated, locked against re-energisation, the absence of voltage is verified, it is earthed and short-circuited, and nearby live parts are covered. We explained these steps in our articles on the five safety rules in electrical work and LOTO lockout and tagout.
Design and operating measures that reduce live work:
- Remote switching: Racking withdrawable circuit breakers in and out remotely, and switching with the panel door closed.
- Infrared windows: Allowing thermographic checks to be made without opening covers.
- Arc detection protection: Relays that detect an arc by light and current and open the circuit in a very short time.
- Maintenance mode: A switch that speeds up the protection setting during maintenance.
- Arc-resistant switchgear: In new investments, panel types tested against internal arcs.
If live work really cannot be avoided, the justification is set out in a written work permit, the work is done only by an authorised and trained person, and a second person who can call for help is present. For the permit process see our article on the permit-to-work system, and on authorisation, who can carry out electrical work.
Choosing arc flash protective clothing and face shields
Arc flash protective clothing is clothing that has been tested and classified against incident energy. Workwear that is merely "flame retardant" does not count as arc-rated. In Europe, the requirements for arc protective clothing are set out in IEC 61482-2, and it is classified by two test methods:
- Open arc test (IEC 61482-1-1): Gives the energy the fabric or garment can withstand in cal/cm² (ATPV or EBT value). In selection, this value must not be lower than the calculated incident energy.
- Box test (IEC 61482-1-2): Classifies the garment at a test current of 4 kA (class 1) or 7 kA (class 2).
For panels where the incident energy calculation has not yet been done, the PPE categories of NFPA 70E can be used as an international reference:
| NFPA 70E category | Minimum arc rating | Typical equipment |
|---|---|---|
| 1 | 4 cal/cm² | Arc-rated shirt and trousers or coverall, arc-rated face shield |
| 2 | 8 cal/cm² | Arc-rated clothing, face shield and balaclava |
| 3 | 25 cal/cm² | Arc-rated jacket, trousers and full hood |
| 4 | 40 cal/cm² | Arc-rated jacket, trousers or coverall and full hood |
Items that complete the panel maintenance PPE set:
- Face protection: An arc-rated face shield; at low energy a shield and balaclava, at high energy a full arc hood. Safety glasses are worn under the shield. Assess the choice of shield together with our article on safety glasses and face shields.
- Gloves: Insulating rubber gloves suited to the voltage class, with leather protector gloves over them.
- Underwear: Non-melting fibres such as cotton or wool; synthetic underwear can worsen burns even under arc-rated clothing.
- Hearing protection: Earplugs against the pressure wave.
- Tools: Insulated hand tools and a test instrument with a measurement category suited to the panel.
The Regulation on the Use of Personal Protective Equipment at Workplaces requires suitable PPE to be selected and provided where the risk cannot be prevented at source, and the employee to be trained in the use of this equipment. For the general steps of PPE selection, see our article on how to select PPE.
Training, labels and work instructions
Managing arc flash risk begins with the label on the panel and is completed by the worker reading that label correctly. The panel label should contain at least: the panel voltage, the incident energy at the working distance or the PPE category required, the arc flash boundary and the date of the calculation. When the transformer, cables or protection settings change at the facility, the calculation and label must also be updated.
The training given to electricians who maintain panels should cover the following topics in practice:
- The difference between arc flash and electric shock, and protection against each.
- How to read the label and what to do on an unlabelled panel.
- Correctly putting on, checking and cleaning arc-rated clothing, shields and hoods; taking damaged or contaminated clothing out of use.
- Testing the test instrument first on a known source when verifying the absence of voltage.
- Keeping the panel door closed during switching and operating the switch from the side, without placing the body in front of the panel.
Tie these topics to a written panel maintenance instruction and keep the instruction posted in the electrical room where the panel is located.
First response to arc burns
When an arc flash occurs, the power is cut first and 112 is called; the injured person is not touched until it is certain the power has been cut. Burning clothing is extinguished, the burned area is cooled with clean, cool running water, and clothing stuck to the skin is not pulled off. A worker exposed to the pressure wave should be assessed at a healthcare facility even if there is no visible burn. For details, see our article on burn first aid at work.
Under Annex III of the Work Equipment Regulation, internal electrical installations and earthing are subject to periodic inspection once a year; you can track inspection dates with the OHS calendar. At production facilities in Bursa and the surrounding provinces, we address the risk assessment and maintenance instructions for panel work in our OHS specialist services, and plan periodic inspections through our periodic inspection service delivered with our solution partners.
Frequently Asked Questions
Are arc flash and electric shock the same thing?
No. In an electric shock the current passes through the body; in an arc flash, the arc formed in the air produces heat, light and a pressure wave. A worker can suffer severe burns without touching a conductor.
Does flame-retardant workwear provide arc protection?
Not on its own. Arc protective clothing is clothing that has been arc tested and given a cal/cm² value or a box test class. When buying, look for the arc rating and standard on the label and certificate.
On which panels should an incident energy calculation be carried out?
It is recommended for all distribution panels and motor control centres whose covers are opened for maintenance, measurement or switching. The calculation is carried out by an electrical engineer and the result is labelled on the panel.
Is PPE needed when verifying the absence of voltage?
Yes. Until it is confirmed that the circuit really is isolated, this measurement counts as live work and protective equipment suited to the incident energy is used.
A certified specialist matched to your hazard class: site inspections, approved logbook, training plan, annual plan and report follow-up.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.