Understanding Arc Flash jargon can help you save lives

Let’s start with the most important and the one everyone needs to know -

Arc Flash:  Simply put, this is when an arcing fault releases dangerous levels of radiant energy, which vaporises 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.

With temperatures of up to 35,000ºF – more than four times hotter than the surface of the sun – has the potential to burn an operative’s skin within fractions of a second. In fact, combined with the blast pressure waves it can ignite clothes on a worker 10 feet away. 

Arc numbers: a method to rate and assess Arc Flash protection provided by a garment. The National Fire Protection Association (NFPA) has identified four risk category levels, ascending 1 to 4; with Arc 1 requiring a 4cal rating, Arc 2 an 8cal, Arc 3 a 25cal, and Arc 4 a 40cal rating.

IEC 61482: a standard that covers PPE (personal protection equipment) against the thermal dangers of Arc Flash. Within this, the IEC 61482-2 standard covers various aspects of the garment design and is an EU requirement for Arc Flash PPE garments.

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 garment must allow the wearer to quickly remove the item; must always have long sleeves; and feature no exposed metal.

ELIM: a new, more rigorous method for calculating arc ratings. Previously, these have been measured using ATPV values, calculated from a prediction of the incident energy level of an Arc Flash, at which there’s a 50% probability that the heat transfer will cause material to break open and expose the operative. ELIM rating will be measured to ensure a 0% probability.

With temperatures four times hotter than the surface of the sun,arc flash has the potential to burn an operative’s skin within fractions of a second

An Arc Flash garment could have a lower ELIM rating compared with its ATPV rating. This means that, to achieve 8cal ELIM protection, wearers may be required to wear Arc Flash base layers underneath their outer PPE or wear a heavier garment.

Treated fabrics: made from fibres which are not flame retardant by nature but have undergone a chemical process to add a fire resistance quality to them.

Inherent fibres: has fire retardant properties as part of its natural make-up and needn’t undergo a chemical process to become flame-retardant. Offers higher protection but is more expensive than treated fabrics.

Thermal energy; While most PPE is designed to be flame retardant, Arc Flash protective clothing however needs to also be designed to withstand the intense heat generated by thermal energy, which can cause both internal and external burns.

Incident energy: a measurement of the amount of thermal energy that a worker would encounter at a given distance from an arc fault, measured in calories/cm2 and calculated from the available bolted fault current, system voltage, the clearing times of the associated over-current protective devices and the individual parameters of the electrical distribution system. Helps assess clothing has a sufficient level of Arc Flash protection.

Electric arc/arc discharge: breakdown of a gas that produces a prolonged electrical discharge, occurs when an electrical discharge or short circuit moves through the air.

Mark Lant is senior technical sales manager at ProGARM