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The common misconceptions around Arc Flash

Published: 14 December 2018 - Victoria White

When it comes to industrial safety, all of us understand the importance of wearing a hard hat, protective gloves or steel toe-capped boots. In fact, most employers wouldn’t dream of letting their teams on-site without adequate protection, and workers themselves are more than clued up when it comes to the latest safety requirements. However, the same can’t be said when it comes to the potentially fatal risk posed by Arc Flash – a relatively misunderstood, but extremely common type of electrical explosion facing sectors from industrial electrical, to utilities, civil engineering and rail.

What actually is an Arc Flash?

Hotter than the sun and louder than a bullet, an Arc Flash is when an arcing fault releases dangerous levels of radiant energy, which vaporizes metal that spews from the arc. The air is super-heated causing pressure waves that can throw individuals across rooms and create a deadly molten shrapnel. They can be caused by voltage spikes, worn connections, cable strikes or gaps in insulation, and are a risk even in low-voltage set ups.

It goes without saying; the extreme temperatures of an Arc Flash can burn clothing and human skin within fractions of a second, even if the operative is situated five or six metres away from the Arc Flash event. It can also result in an explosive pressure wave that can throw workers across the room, and a sound blast that can rupture eardrums. An Arc Flash event is also accompanied by a bright flash which can cause temporary or even permanent blindness.

Treatment for those that survive an incident can require years of skin grafts, hospital stays and rehabilitation – they may never recover sufficiently to regain their lifestyle, so it’s safe to say that choosing the appropriate PPE is key when it comes to arc flash safety.

“Outerwear PPE is enough”

The material worn beneath an Arc Flash protective jacket is just as crucial to protecting from the event as outer clothing. While the outer garments are key components for providing protection, they are not enough to match the risk posed to an operative’s safety and effective base layers are needed to defend against the risk of an Arc Flash.

The flames caused by an Arc Flash may not actually come into contact with skin through the protective outer layers, but the extreme heat from the event can melt the materials used to manufacture everyday undergarments, including nylon, cotton, and polypropylene. This will inflict burns on an operative and potentially cause non-Arc Flash protective undergarments to melt into the skin underneath their PPE.

When it comes to layering up, it’s important to ensure you undergarments are also Arc-resistant – including base layer leggings, tops and even underwear!

“FR provides sufficient protection”

While many might think flame retardant PPE can also provide protection in an Arc Flash incident, there are in fact separate safety standards for Arc Flash clothing, which go further than the ones for fire resistance, meaning that the level of protection provided by flame retardant clothing does not match that of Arc resistant PPE.

Arc Flash protective clothing is designed to not only protect you from fire, but from the thermal energy generated by an Arc Flash, which can also cause external and internal burns. In fact, fabric used in Arc resistant garments must meet higher tear resistance and tensile strength than those used for fire-resistant clothing.

While the threads used for the structural seams must be fire-resistant, under IEC 61482, Arc Flash resistant clothing has various standards that separate it from fire-resistant clothing. Each arc-resistant garment must be designed in a way to allow the wearer to quickly remove the item; must always have long sleeves rather than short sleeves; and feature no exposed metal.

Cal ratings – “7+14=21”

While layering Arc-rated garments may have benefits, simply totalling the cal ratings to determine their overall level of protection is too simplistic and could result in extremely dangerous working conditions. For instance, wearing an 8 cal outer coverall over a 4 cal polo shirt, wouldn’t necessarily give you a 12 cal system. In fact, it may only be a tiny fraction better than only wearing the 8 cal outerwear.

On the other hand, in some instances, layering a 7 cal polo shirt with a 14 cal sweatshirt has been shown to achieve a 31 cal overall result – a much greater level of protection than the 21 cal result you might expect by simply adding the individual ratings together.

There are many variables that can affect this, such as the amount of air trapped between the two layers, as well as the tightness of the garments on the wearer. Unfortunately, there are no easy short cuts to working out whether combining garments will result in negligible or substantial improvements to the overall protection level; this can only be determined by rigorously testing the specific garment combinations as a system.

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Source: Industrial Compliance

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-June 2019+