Across many different industries personal protective equipment (PPE) is considered to be the last line of defence, and the difference between a near miss and serious, even fatal, injury. Depending on the situation, employers are required to provide their workers with a minimum level of PPE to ensure they remain safe at all times.
In order to make sure that the right type of PPE is issued to staff, it is important to understand the different Arc Flash PPE categories and the clothing requirements for each one of them.
How is Arc Flash Clothing calculated?
The categories start at HRC 0, which offers virtually no protection, up to CAT 4, which is the highest level of protection. The different categories are broken down based on the minimum arc rating of the PPE in calories per centimetre squared.
HRC 0 (0 cal/cm²) – this is basically any type of generic clothing/workwear, including items such as trousers, long sleeve shirts, safety glasses, hearing protection etc. Protection provided is from 0 cal/cm², so this type of clothing will not keep workers sufficiently safe from any type of arc flash event.
ARC CAT 1 (4 - 7cal/cm²) – this includes garments such as flame resistant trousers and shirts, or an arc rated fire resistant coverall. To protect the head, a face shield or Arc hood is required. Finally, for the hands, heavy-duty leather gloves need to be worn. It is made up of a single layer of true PPE and is rated to provide arc rating of 4 cal/cm².
ARC CAT 2 (8 - 24cal/cm²) – consisting of the same type of PPE as CAT 1, in this category, garments are better made for additional protection or an extra layer will be worn. This provides protection of 8 cal/cm². There may be additional items of PPE needed, including leather footwear, eye protection, and / or an arc rated jackets to be worn on top of arc rated shirts, arc long sleeve t-shirts or arc polo shirts.
ARC CAT 3 (25 - 39cal/cm²) – this category includes the same garments as CAT 2 but also with an arc flash suit that meets the minimum arc rating requirements. This will be made up of either two or three layers of protection. Additionally, rubber insulating gloves and leather protectors are required. There may also be a need for additional PPE, such as a hard hat, eye protection, hearing protection, and leather footwear. For this category, the minimum arc rating is 25 cal/cm² of protection.
- ARC CAT 4 (40+ cal/cm²) – here it is the same items as CAT 3 but with greater quality and levels of protection. There should be either three or four separate layers being worn by a worker to provide them with at least 40 cal/cm² of protection. There may also be the need to wear Cotton under garments plus arc shirts and arc pants plus multilayer arc flash suit (3 or more layers).
How is Arc Flash clothing tested?
When looking at an arc rated item of clothing, the rating you should see included on a label is the arc thermal performance value (ATPV) of the fabric which is measured in cal/cm². The ATPV identifies the point at which 1.2 cal/cm² of incident energy is transferred through the fabric and is the point at which a second-degree burn can be expected.
The cal/cm² rating of a particular fabric is determined be using either the open arc testing method or the arc in a box testing method.
Open arc testing:
Open arc testing determines the arc rating of a material by exposing it to an open arc under controlled laboratory conditions. The results are evaluated against a second-degree burn curve to calculate the probability of burn injury at various incident energies. The arc rating of the material is determined as the incident energy measured in cal/cm2 that has a 50% probability of causing a second-degree burn through it.
Arc in a box testing:
Arc in a box testing is performed on both fabric and finished garments. It stimulates exposure to service or maintenance situations, applying to low voltage systems like distribution boxes, distributions boards, and switchboards