As we know heat from an electric arc is an important hazard that workers need to be protected from. Once end users have carried out their own risk assessment and if they have identified as a result of this to provide their workforce with FR protective clothing, there are new standards and test methods that they can refer to Clothing is subject to draft norm IEC 61482-2. In order to choose adequate protective clothing, the potential incident heat energy (in units of energy per square surface) caused by an electric arc and to which a worker may be exposed, needs to be calculated in this thorough risk assessment.

Within the garment standard, the norm refers to fabrics that can be tested to "open arc", covered by IEC 61482-1 (latest version is IEC 61482-1-1) or "arc in a box" covered by IEC 61482-1-2 / EN 61482-1-2

Quantifying the arc rating of a protective garment
1. The arc rating is most commonly quantified by the ARC THERMAL PERFORMANCE VALUE (ATPV) determined by the open arc test method IEC 61482-1. This test method is currently being revised to IEC 61482-1-1. The ATPV represents the maximum incident thermal energy in units of energy per surface area (e.g. kJ/m2 or cal/cm2) that a fabric can support before the wearer will suffer 2nd degree burns.

The break-open threshold energy (or EBT) is another fabric characteristic. It represents the highest incident energy exposure value on a fabric where the garments do not exhibit break-open. The formation of holes in the fabric caused by break-opne would allow heat or flames to pass through. Workers are assumed safe if the arc rating of their clothing (or ATPV value) exceeds the electric arc incident energy as calculated in the worst case scenario of a risk assessment.

THIS TEST IS SIMILAR TO ASTM F 1959

2. The box test is another way to measure the protective performance of clothing against the thermal effects of an electric arc and is defined in the IEC 61482-1-2 / EN 61482-1-2 test method. In this test, the fabric is exposed to an electric arc confined in a specific box with a specific electrode arrangement.
Class 1
Arc Duration= 0.5s Arc Current = 4kA
Class 2
Arc Duration= 0.5s Arc Current = 7kA

A fabric passes the test:
- if the heat transferred behind the fabric does not cause second degree burn (i.e. is below the Stoll curve)
- if the after flame time is below 5 seconds
- if there is no melting to the inner side of the fabric
- if a hole caused by the arc is not larger than 5 mm in every direction (in the inner most layer).

Test conditions for Class 1 try to simulate typical exposure conditions for a short circuit current of 4 kA protected by devises limited the duration of the arc to 0.5 seconds in confined space, and of 7 kA respectively for Class 2.