Arc flash glossary: ATPV, ELIM, APC and key terms

Fabric designed to dissipate static charge rather than let it build up and discharge. It matters in classified explosive atmospheres, where the wearer's clothing must not become the ignition source. Performance can degrade with washing and wear, so follow the care routine.

APC stands for Arc Protection Class. In the box test (EN 61482-1-2) a garment is exposed to a constrained arc: 4 kA for APC 1 and 7 kA for APC 2. It is a pass or fail result, recorded alongside the garment's cal/cm² rating. Your risk assessment sets which class applies.

A sudden release of energy caused by an electrical fault travelling through the air between conductors. It produces intense heat, light and pressure, at temperatures far above the ignition and melting points of everyday clothing.

The tested arc flash performance of a garment, shown on its label as ATPV or ELIM (or EBT) in cal/cm². Choose garments rated at or above the incident energy from your risk assessment. Ratings belong to individual garments and are not added together when layered.

The incident energy, in cal/cm², at which there is a 50% probability that heat transfer through the fabric would cause a second-degree burn. It comes from the open arc test, EN 61482-1-1.

The layer worn next to the skin. If it is not arc rated, it can melt and bond to the skin under arc flash incident energy and undo the protection of the outer garment, so base layers in arc hazard areas should be arc rated. Some standards accept non-melting natural fibres as a minimum; follow your own risk assessment.

The test in EN 61482-1-2, in which a garment is exposed to a constrained arc under controlled laboratory conditions. The result is an APC class, 1 or 2.

Calories per square centimetre: the unit for incident energy and for arc ratings. A higher figure means more thermal energy. Match the garment's rating to the incident energy in your risk assessment.

Reported instead of ATPV when the fabric breaks open before the ATPV level is reached. It is the incident energy at which there is a 50% probability of break-open in the open arc test.

A more conservative value reported from the same open arc test as ATPV. Where ELIM is lower than ATPV, it is the safer figure to compare against. Which one your specification requires is set by your risk assessment or site standard.

A sudden, short-duration fire caused by the ignition of a flammable gas, vapour or dust cloud. It is a different hazard from arc flash, which is an electrical event, although both can be present on the same site.

Grams per square metre: a measure of fabric weight. Heavier does not automatically mean more protective, because protection comes from the fibre and the fabric construction. Lighter garments are more likely to stay on in hot conditions.

EN ISO 20471 groups hi-vis clothing into Classes 1 to 3, with Class 3 the highest visibility. The class depends on the area of fluorescent and retroreflective material, not just the presence of tape. Always check the label.

The thermal energy that reaches a surface at a given distance from an arc, measured in cal/cm². Your arc flash risk assessment gives a figure for each task, and garments must be rated at or above it.

Protection built into the fibre itself, so it cannot wash out. This differs from treated fabric, where a finish is applied to the surface and can degrade over repeated laundering. Always check the garment label.

Arc ratings are not added together. A base layer rated 8 cal/cm² under a jacket rated 12 cal/cm² is not 20 cal/cm². A combined rating only exists where that exact combination has been tested as a system.

The test method in EN 61482-1-1. Fabric panels are exposed to an open electric arc to produce the ATPV, ELIM and EBT values.

The assessment that works out the incident energy and the protective measures for each electrical task. It sets the minimum garment rating, so start there.