Arc Flash Protection: Risk Assessment, PPE Categories & Prevention

Incident Energy Reference Levels

• Below 1.2 cal/cm² — onset of second-degree burns on exposed skin. This is the threshold at which arc flash begins to cause burn injuries. Even at this level, the intense light can cause temporary blindness and the blast can cause hearing damage.
• 1.2 to 4 cal/cm² — second-degree burns likely on exposed skin. Category 1 arc-rated PPE provides protection at this level. Typical of some domestic and light commercial installations at close working distances.
• 4 to 8 cal/cm² — serious burns through ordinary clothing. Non-flame-resistant clothing can ignite. Category 2 arc-rated PPE required. Typical of commercial distribution boards with moderate fault currents.
• 8 to 25 cal/cm² — severe, potentially life-threatening burns even through standard work clothing. Category 3 arc-rated PPE required. Typical of larger commercial and industrial switchgear.
• 25 to 40 cal/cm² — extreme thermal hazard. Category 4 arc flash PPE required (full arc flash suit, balaclava, face shield, arc-rated gloves). Typical of large industrial switchgear, motor control centres, and some high-voltage equipment.
• Above 40 cal/cm² — exceeds the protection capability of commercially available PPE. Work must not be performed at this incident energy level without additional engineering controls to reduce the incident energy (remote switching, fault current limiting, zone selective interlocking).

• Arc flash boundary — the distance at which the incident energy equals 1.2 cal/cm² (the onset of second-degree burns on bare skin). Anyone working inside this boundary must wear arc-rated PPE appropriate to the calculated incident energy at their working distance. The arc flash boundary varies depending on the available fault current and protective device clearing time — for a typical domestic consumer unit it may be less than half a metre, while for industrial switchgear it can extend to several metres.
• Limited approach boundary — the distance from exposed live parts at which a shock hazard exists. Only qualified persons (those trained and competent to work on or near electrical equipment) may enter this boundary. For 230V systems, this is typically 1.0 metre; for higher voltages, it increases accordingly.
• Restricted approach boundary — a closer boundary within which there is an increased risk of shock due to arc-over combined with involuntary movement. Work within this boundary requires specific training, supervision, and appropriate insulated tools and PPE.
• Prohibited approach boundary — the closest boundary to exposed live parts. Working within this distance is considered equivalent to direct contact with live conductors and requires the same protective measures as live working — including arc-rated PPE, insulated tools, and a detailed method statement for the specific task.

• Identify the arc flash hazard — determine whether electricians or other workers will be working on or near energised electrical equipment where an arc flash could occur. This includes switchgear, distribution boards, motor control centres, bus duct systems, and any equipment with exposed live conductors.
• Determine the available fault current — obtain or calculate the prospective short-circuit current (PSCC) at the point of work (as required by BS 7671 Reg 643.7.3.201 for initial verification). This data may come from the DNO, from loop impedance measurements, from design calculations, or from the installation records. The higher the fault current, the greater the potential arc energy.
• Determine the protective device clearing time — identify the upstream protective device (fuse, MCB, MCCB) and determine its clearing time at the calculated fault current. Faster clearing times mean lower incident energy. Current-limiting devices (such as HRC fuses and Class 3 MCBs) significantly reduce arc energy.
• Estimate the incident energy — using the fault current, clearing time, working distance, and electrode configuration, calculate or estimate the incident energy in cal/cm². IEEE 1584 provides the standard calculation method. Simplified lookup tables are available for common installation types.
• Select the appropriate PPE category — based on the calculated incident energy, determine the required arc flash PPE category (1, 2, 3, or 4). If the incident energy exceeds 40 cal/cm², additional engineering controls are needed before work can proceed.
• Document and communicate — record the findings, label the equipment with arc flash warning labels (showing the incident energy, required PPE category, and boundary distances), and ensure all workers are informed of the arc flash hazard and the required protective measures.

• Electricity at Work Regulations 1989 — Regulation 4(1) requires that all electrical systems shall at all times be of such construction as to prevent, so far as is reasonably practicable, danger. Regulation 4(2) requires that, as necessary to prevent danger, all systems shall be maintained so as to prevent, so far as is reasonably practicable, such danger. Regulation 14 addresses working on live equipment. These regulations collectively require arc flash risk to be assessed and managed.
• Management of Health and Safety at Work Regulations 1999 — Regulation 3 requires a suitable and sufficient risk assessment of all workplace hazards, which includes arc flash. The assessment must identify the hazard, evaluate the risk, and determine appropriate control measures.
• Personal Protective Equipment at Work Regulations 2022 — require employers to assess the need for PPE, provide suitable PPE (including arc-rated PPE where the risk assessment identifies an arc flash hazard), ensure it is maintained, and train workers in its use.
• BS 7671:2018+A4:2026 — the IET Wiring Regulations address the design and installation of electrical systems to minimise the risk of faults that could cause arc flash. Requirements for protective device selection, fault current rating, and safe isolation all contribute to arc flash risk management.
• IEEE 1584 (Guide for Performing Arc Flash Hazard Calculations) — while an American standard, IEEE 1584 is widely used in the UK as the reference method for calculating incident energy and arc flash boundaries. Many UK electrical engineers and safety consultants use IEEE 1584 calculations as the basis for arc flash risk assessments.
• IEC 61482-1-1 and IEC 61482-1-2 — the international standards for testing arc-rated clothing. IEC 61482-1-1 (open arc test) determines the ATPV rating. IEC 61482-1-2 (box test, also known as the European test) classifies clothing as Class 1 (4 kA) or Class 2 (7 kA). Both test methods are recognised in the UK.

• Eliminate — de-energise before working — the most effective control measure. Proper safe isolation and lock off/tagout eliminates the arc flash hazard entirely. If the circuit is dead, there is no energy to create an arc. This should always be the first option considered.
• Substitute — use remote operation — where switchgear must be operated while energised, use remote operating mechanisms to keep the operator outside the arc flash boundary. Remote racking systems for draw-out circuit breakers and remote-controlled switches reduce operator exposure.
• Engineering controls — reduce incident energy — use current-limiting protective devices (HRC fuses, current-limiting MCBs) that clear faults faster and reduce arc duration. Install arc-resistant switchgear that channels arc energy away from the operator. Implement bus differential protection and zone selective interlocking (ZSI) to reduce clearing times.
• Administrative controls — safe systems of work — establish clear procedures for working on or near energised equipment. Use permit to work systems. Maintain equipment regularly to prevent insulation degradation and loose connections. Provide training on arc flash awareness and safe working practices. Conduct regular thermographic surveys to identify hot spots and potential fault points before they escalate.
• PPE — arc-rated personal protective equipment — when residual arc flash risk remains after applying higher-level controls, provide arc-rated PPE matched to the calculated incident energy. This includes arc-rated clothing, face shields, balaclavas, gloves, and hearing protection. Ensure all layers of clothing are arc-rated — non-arc-rated garments worn over or under arc-rated clothing can melt and increase injury severity.