15 July 2025

How to read arc flash labels

Arc flash labels provide critical safety information for anyone working on or near electrical systems. They're not just stickers; they’re essential warnings that help protect workers from thermal burns, blast injuries, and even fatal electrocution. That’s why correctly reading and understanding arc flash labels is key to making safe decisions on site. In this guide, we explain the key elements of arc flash labels, arc flash label requirements, what each section means, and why this information matters for electrical safety and compliance.

Learn more: Arc flash PPE: Everything you need to know

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.

workwear category or level

Labels often include a category or arc flash level, based on either NFPA 70E tables or incident energy analysis. These are typically split into four levels:

Category 1: Minimum protection. Single-layer arc-rated shirt and trousers.
Category 2: Enhanced protection. Includes arc-rated face shield and gloves.
Category 3: Higher thermal resistance. Typically requires an arc-rated flash suit.
Category 4: Full-body protection for extreme energy levels, including suit, hood, gloves, and boots.

Understanding these categories helps workers choose the right gear for the task. Workwear that doesn't meet the listed level may leave them exposed to serious arc flash injuries.

arc flash boundary

The arc flash boundary is another vital part of the label. It defines the minimum distance from the equipment within which a person could receive a second-degree burn if an arc flash occurs. 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

There’s no single mandatory format for arc flash labels in the UK, but they 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.

Labelling systems should be updated whenever equipment is changed, or when new risk assessments are completed. 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.

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 like the Electricity at Work Regulations 1989, which mandate risk-informed control measures. Labels must be in place before live work begins and must reflect up-to-date arc flash analysis data.

where are arc flash labels required?

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.

trust alsico for arc-rated workwear

Reading an arc flash label properly can be the difference between safe working and serious injury, but labelling is only as useful as the workwear you’re wearing – if you can’t trust the workwear, you can’t trust the label. So trust alsico for your protection. Explore our arc flash protection range today, or contact our team for more information.