15 July 2025
how to read arc flash labels
Whether you know them as arc flash warning labels or arc flash and shock hazard labels, they’re not just stickers. They’re essential warnings that help protect workers from thermal burns, blast injuries, and even fatal electrocution. Correctly reading and understanding arc flash labels is essential to making safe decisions on site.
Below, we cover what each section of an arc flash label means, how to interpret arc flash PPE categories and incident energy levels, the arc flash boundary, arc flash label requirements, and the UK regulations and guidelines that underpin them. Whether you're a safety manager, procurement lead or facilities engineer responsible for a large electrical safety and compliance programme.
what is an arc flash label?
An arc flash label is a safety label fixed to electrical equipment to communicate information about the arc flash hazard present. Sometimes it might also be referred to as an arc flash warning label, equipment label, or arc flash and shock hazard label.
It typically states the incident energy level, the arc flash boundary, and the minimum arc-rated PPE required to work on or near that equipment safely.
Arc flash labels are produced as part of a formal arc flash study, in which an engineer calculates the prospective arc flash energy at each piece of equipment on the electrical network. The label translates the results of that study into clear, actionable information for anyone who may need to work on the equipment—from in-house maintenance teams to external contractors. For large facilities with hundreds of distribution boards and switchgear panels, consistent labelling is critical to ensuring every worker has access to the same safety data, regardless of which part of the site they’re operating in.
the arc flash hazard symbol
The arc flash symbol used on labels and safety signage is defined in ISO 7010 as symbol W042. It depicts a person being struck by an electrical arc and serves as a pictographic warning of the hazard. In the UK, safety signs and labels should comply with the Health and Safety (Safety Signs and Signals) Regulations 1996, which govern the use of warning signs in the workplace.
You’ll typically see the arc flash hazard symbol in the upper portion of an arc flash label, often accompanied by the word “WARNING” or “DANGER” depending on the severity of the hazard. Some labels also include the electrical shock hazard symbol alongside it, particularly where both arc flash and shock risks are present. Understanding what these symbols mean is an important part of reading the label correctly—especially for non-electrical workers or contractors who may be less familiar with the specific hazards.
understanding incident energy
One of the most important figures on any arc flash warning label is the incident energy level, usually expressed in calories per square centimetre (cal/cm²). This number estimates the thermal energy that a worker could be exposed to at a given distance from an arc flash. The higher the value, the more severe the potential injury.
Incident energy informs the minimum protective workwear requirements. For example, anything over 1.2 cal/cm² typically requires arc-rated clothing. Above 8 cal/cm², heavier protection such as layered gear or arc flash suits may be needed. Workers should never perform tasks without workwear arc-rated for the listed energy level.
arc flash PPE categories and levels
One of the most practical pieces of information on an arc flash label is the PPE category or arc flash category level. Based on either NFPA 70E tables or a site-specific incident energy analysis, arc flash categories define the minimum level of arc-rated protective equipment a worker must wear. There are four main arc flash PPE categories:
arc flash boundary
The arc flash boundary is another vital part of the label. It defines the minimum distance from the equipment at which incident energy equals 1.2 cal/cm². This is the threshold at which unprotected skin could receive a second-degree burn if an arc flash occurs. This distance is calculated as part of an arc flash study and is specific to each piece of equipment. Anyone entering this boundary must wear appropriate arc-rated clothing.
This isn’t just about those performing hands-on work. Even support staff or bystanders need protection within the boundary. In some environments, remote working tools or barriers are used to keep people outside the arc flash zone. Labels allow teams to clearly identify and respect these limits.
shock hazard information
Some arc flash labels also include shock hazard data. This may cover the system voltage, approach boundaries for shock protection (limited and restricted), and required insulation tools or gloves. Electrical shock is often overlooked in arc flash risk assessments, but it remains a leading cause of serious workplace incidents.
Understanding both arc and shock risks ensures workers take the right precautions, whether that means de-energising systems, using insulated equipment, or enforcing tighter control of access to hazardous zones.
label layout and customisation
Arc flash labels must be clear, consistent and easy to read. Many companies use colour-coded or icon-based designs to aid quick understanding. Labels may also feature the equipment ID, date of assessment, and the name of the engineer who carried out the calculation.
The equipment ID should match the reference on your energised work permits and single-line diagrams. Always check this before beginning work to confirm you're looking at the correct label for the correct piece of equipment. The study date tells you when the arc flash analysis was last performed; if it predates any significant changes to the electrical system, the data on the label may no longer be accurate.
An outdated or damaged label can result in poor workwear selection or exposure to unknown hazards, so make sure all personnel are trained to interpret the label style your site uses.
UK regulations and guidelines for arc flash labels
There is no single standalone UK law dedicated to arc flash labels. Instead, several health and safety regulations collectively require employers to assess, control, and communicate electrical hazards, including arc flash. Arc flash labels are one practical measure to meet these legal duties.
Key legislation and guidelines relevant to arc flash labelling include:
when are arc flash labels required?
Arc flash labels are required whenever a risk assessment identifies potential exposure to arc flash energy that could result in injury. This typically applies to any electrical equipment operating at 50 volts or more that is likely to require inspection, maintenance, or adjustment while energised. In practice, that includes control panels, switchboards, motor control centres and panelboards. The requirement is based on standards such as NFPA 70E and supported by UK regulations.
The arc flash protection requirements that apply to your facility will depend on the results of this risk assessment, including incident energy calculations, the equipment involved, and the tasks being performed. Labels must be in place before live work begins and must reflect up-to-date arc flash analysis data.
arc flash label requirements
The arc flash label requirements that apply in practice will depend on the standards your organisation follows. Under NFPA 70E Article 130.5(H), a label must include the nominal system voltage, the arc flash boundary, and at least one of the following: the incident energy and working distance, the minimum arc rating of clothing, or a site-specific PPE level. In the UK, while there is no single prescriptive format, labels must be clear, consistent and provided in accordance with the Health and Safety (Safety Signs and Signals) Regulations 1996.
Arc flash labels should be placed on all equipment where an arc flash hazard exists and where workers may interact with energised parts. This includes main switchboards, panelboards, transformers, disconnect switches, and motor control centres. Any location where live work could occur, either by intention or due to system design, should be labelled clearly and visibly. Labels should be affixed directly to the panel or enclosure door at eye level to be more easily read.
when to update arc flash labels
Ultimately, the accuracy of the arc flash warning label depends on the data it’s based on. If equipment is modified, added, or repositioned, the incident energy levels may change, and the old label becomes dangerously misleading. Updates should follow any significant system change, including breaker swaps, fuse upgrades, load increases, or reconfiguration of switchgear. Even routine maintenance that alters protective device settings can shift arc flash boundaries.
frequently asked questions
There is no standalone UK law that mandates arc flash labels by name. However, the Electricity at Work Regulations 1989 and the Health and Safety (Safety Signs and Signals) Regulations 1996 collectively require employers to assess arc flash risks and provide appropriate safety signage where a residual hazard exists. Most UK electrical safety programmes include arc flash labelling as a core part of compliance. It is also increasingly expected by insurers and auditors as evidence that risks have been properly communicated.
The duty holder—typically the employer or facility owner—is responsible for ensuring arc flash labels are in place, accurate and up to date. In large organisations this often sits with the electrical safety manager or facilities engineering team, but procurement leads should also be aware of labelling obligations when specifying new equipment or onboarding contractors who will work on energised systems.
These are two approaches to determining what arc-rated PPE a worker needs. The incident energy method uses a site-specific calculation (in cal/cm²) for each piece of equipment, and the worker's PPE must have an arc rating equal to or greater than that figure. The PPE category method uses lookup tables in NFPA 70E to assign a category (1–4) based on the type of equipment and task, without calculating a specific energy value. The incident energy method is more precise and is generally preferred for large or complex electrical systems, while the category method can be simpler to implement where equipment falls neatly into the standard table parameters.
The arc flash boundary tells you how far back from the equipment unprotected people need to stay. If the label states a boundary of 1.5 metres, for example, anyone closer than that distance must be wearing arc-rated PPE appropriate to the incident energy level shown. It's also the distance at which barriers or exclusion zones should be set up to keep bystanders and non-essential personnel clear during energised work.
No. Arc flash incident energy depends on the specific electrical configuration at each location, including supply fault levels, protective device settings and cable lengths. Two identical panels fed from different sources can have very different incident energy values. Each piece of equipment needs its own arc flash study and its own label, which is why large multi-site organisations should factor site-specific studies into their procurement and commissioning process rather than assuming labels are transferable.
trust alsico for arc-rated workwear
Understanding arc flash labels is the first step. Ensuring your workforce has the right arc-rated workwear to match is the next. alsico supplies arc flash protective clothing to some of the UK’s largest utilities, manufacturing and infrastructure organisations, with garments independently tested to IEC 61482 and certified to meet the protection levels outlined on your equipment labels.
If you're reviewing your facility's arc flash PPE programme, our technical team can help you match label data to the right workwear specification across your entire workforce. That includes arc flash PPE guidance, sizing for men and women, and volume supply for multi-site operations.
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