Electric Arc Flash – Unearthing The Essential Answers

Elaina Harvey, arc flash and Nomex® specialist at DuPont, answers 5 key questions on arc flash

 At an office building in central London in 2007 two technicians were installing a capacitor to help reduce energy consumption at the site. One of the workers was fitting cables in the back of the capacitor, which was positioned above a number of live conductors. The cables came into contact with one of the conductors (Read More)  and caused an electric arc flashover. The worker suffered severe burns to his face and upper body – horrific injuries that have prevented him from returning to work. In the ensuing prosecution, the health and safety manager who had overall responsibility for safety procedures at the site was found guilty of various breaches and fined £2,500 and ordered to pay £5,500 in costs. The company pleaded guilty to similar charges and was fined £25,000.

An arc flash accident is a relatively rare phenomenon, leading some electrical workers to believe that it won’t happen to them. But when it does happen, it’s one of the most deadly and least understood hazards of electricity.

Q 1: What is an arc flash and what can happen?

A: Electric arc flash is usually caused by inadvertent contact between an energised conductor, such as a bus bar or wire, with another conductor or an earthed surface. The resulting short circuit current will melt the conductors, ionise the air and create a conducting plasma fireball with temperatures in the core of the arc that can reach upwards of 20,000 degrees centigrade.  Arc flash injury can include external burns to the skin, internal burns from inhaling hot gasses and vaporised metal, hearing damage and eye damage.

Q 2: Which industries are most at risk?

A: All industries that employ electrical engineers or electrical contractors have a level of risk but there are of course those that carry a higher risk such as utilities, energy producers and providers, mining, manufacturing companies particularly those in the food, pharmaceutical and chemical industries, hospitals, large commercial organisations, data centres, education establishments and large leisure facilities.

Q 3: How can the risk of an arc flash be reduced?

A: In order to really understand the arc flash risk, an arc flash study provides the actual incident energy levels and recommendations to reduce the probability of an arc flash occurring. One can use the following DuPont ‘4 P’ approach to understanding and managing electrical arc hazards:

Predict - the severity of the thermal effect of an arc flash by the amount of ‘incident energy’ that a person working at a given distance away from the arc could receive.
Prevent - eliminate the hazard at its source or mitigate it by change of design or temporary change of protective device settings.
Protect - where the risk cannot be controlled by prevention or where there is a residual risk of injury then it may be necessary to consider personal protective equipment (PPE) to prevent injury to the worker.
Publish - communicate and document results of site arc flash to those who are at risk.

Q 4: At what point should personal protective equipment (PPE) be used?

A: PPE should be used for residual risks that cannot be eliminated through other measures and should be procured through a reputable arc flash clothing specialist. Depending on the outcome of the risk assessment it is recommended that a layering approach is taken. Some clients may want a switching garment (multi-layer garment), whilst others want multiple garments layered. The principle of layering gives the benefit of creating air gaps between the layers, dissipating the energy in the event of an arc flash. It is also an easy way of achieving a higher level of protection without becoming too heavy, for example layering thin layers such as a jacket or coverall over a base layer.

Q 5: What PPE will I need to protect against arc flash risks?

A: Polyester and nylon are flammable fibres and can ignite, melt and drip if exposed to flash fire or electrical arc so these materials are never recommended. It is recommended that garments using inherently flame resistant (i.e. a consequence of the properties of the fibre, rather than through the application of a finish to the fibre or fabric to reduce flammability) fibres, such as DuPont™ Nomex®, are used. It is advised that only garments that have been tested as an ensemble are worn so that you can demonstrate the claimed ATPV (arc thermal performance value) is based on fact.

To find out more about DuPont and its arc flash protective garments, visit:
http://www.arcflashprotection.co.uk.