FEATURE ARC FLASH UNEARTHING THE ANSWERS
To assist safety managers and buyers, Elaina Harvey, arc flash and Nomex specialist at DuPont, answers five common questions on arc flash
core of the arc that can reach upwards of 20,000°C. Arc flash injury can include external burns to the skin, internal burns from inhaling hot gasses and vaporised metal, hearing damage and eye damage.
Q2. WHO’S AT RISK? 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.
B
ack in 2007 two technicians were installing a capacitor in a central
London office building in order to help reduce energy consumption. 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 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. However, when it does happen, it’s one of the most deadly and least understood hazards of electricity.
Q1: WHAT IS ARC FLASH? Electric arc flash is usually caused by inadvertent contact between an energised conductor, such as a busbar 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
28 SEPTEMBER 2014 | ELECTRICAL ENGINEERING
amount of ‘incident energy’ that a person working at a given distance away from the arc could receive. 2. Prevent - eliminate the hazard at
its source or mitigate it by change of design or temporary change of protective device settings. 3. Protect - where the risk cannot be controlled by prevention or where there
Below: 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
DuPont Nomex, are used. It is advised that only garments that have been tested as an ensemble are worn so that you can demonstrate that the claimed ATPV (arc thermal performance value) is based on fact.
DuPont
www.dupont.com T: 01483 414 751
Q3. HOW CAN THE RISKS BE REDUCED? 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. The following DuPont ‘4P’ approach can be used to help understand and manage electrical arc hazards: 1. Predict - the severity of the thermal effect of an arc flash by the
Above: Elaina Harvey, arc flash and Nomex specialist at DuPont provides some arc flash answers
is a residual risk of injury then it may be necessary to consider personal protective equipment (PPE) to prevent injury to the worker. 4. Publish - communicate and document results of site arc flash to those who are at risk.
Left: an arc flash accident is a relatively rare phenomenon, but when it does happen, it’s one of the most deadly and least understood hazards of electricity
Q4. WHEN SHOULD PPE BE USED? 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 may 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.
Q5: WHAT PPE WILL BE NEEDED? 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
Enter 211 / ELECTRICALENGINEERING
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64