Elaina Harvey, arc flash and Nomex specialist at DuPont discusses the latest innovations and developments in arc flash protective clothing
What is arc flash?
Electrical flashover or ‘arc flash’ is one of the most deadly and least understood hazards of electricity. Each year around 1,000 electrical accidents at work are reported and as many as 25i people die from their injuries. It is widely recognised the higher the voltage of an electrical power system, the greater the risk for people working on or near energised conductors and equipment. However, arc flash can still cause devastating, injuries even at low voltages.
An 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. When this occurs, 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. The risk of injury can extend beyond the immediate area.
Arc flash injury can include external burns to the skin, internal burns from inhaling hot gases and vaporised metal, hearing damage and eye damage such as blindness from the ultraviolet light of the flash.. Depending on the severity of the arc flash, an explosive force known as an arc blast may also occur which can result in pressures of over 100 kilopascal (kpa), launching debris as shrapnel at speeds up to 300 metres per second (a high speed train travels, on average, 85 metres per second).
The risk
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.
Whilst legislation requires businesses to perform risk assessment for all work activities, this particular hazard is often overlooked because most people are unsure how to assess and manage this risk effectively.
Inevitably, the penalties can include HSE investigations resulting in prohibition notices, improvement requests, fines and corporate/individual prosecutions, severe equipment damage, lost production and loss of company reputation.
The need for risk assessment is embodied in European Law through Directive 89/391 (EU Workplace Health and Safety Directive) and the associated guidance which identifies electrical work as a ‘high risk’ activity. 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:
1. 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.
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 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.
Selecting the correct protective clothing
With the danger of counterfeit or poorly manufactured protective garments an ever-present threat, companies are continually looking for reassurance that garments purchased are authentic and are of a high quality.
The DuPont Nomex Partner Program helps to combat this by creating a carefully-selected network of customer-oriented and progressive spinners, weavers and garment manufacturers whose fabrics and garments pass the rigorous quality controls of DuPont. Certified Nomex fabrics are visible to the end-user through the distinctive Nomex labelling programme.
To reinforce the work that DuPont is doing in the field of electric arc flash protection, DuPont Personal Protection, work with a team of experts including DuPont Engineering Technology, DuPont Sustainable Solutions and external independent electrical safety experts , who can help companies understand, assess and reduce the severities and consequences of electrical arc hazards.
Key trends and developments
There are many new key trends and developments within arc flash protective clothing, one being new technological processes and fibres which enable garment layering, providing optimal protection against arc flash. 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. However it is critical that each layer has been tested and qualified as an arc flash protection PPE.
Additionally, the economic crisis has put an emphasis on cost savings on all levels, including protective workwear, and has led safety engineers to look for multi-hazard, one fits all needs garments with maximum wearer comfort. Rather than invest in garments made from FR treated cotton blends, safety engineers can now opt for multi-hazard protection which not only outperform in terms of wearlife costs, but is also lightweight and comfortable. However, different fabrics and levels of body protection are required to protect against specific hazards. In the case of arc flash, multi-hazard garments might need to be layered together to provide the highest arc rating. In the case of workers potentially exposed to a ‘flash fires’, they will require specialist heat and flame protection. In a flash fire, the duration is longer, intensity of heat lower and magnitude different; more convective than radiant, together with a re-ignition potential so premium heat and flame protective garments must be worn. However, in an “arc flash” the duration of an arc is shorter, the intensity of heat is higher, there is more radiant heat and, in addition, molten metal splatter, so the fabrics and garment design must be different.
The innovative Arcban garment range from DuPont Nomex partner J&K Ross (www.arcflashprotection.co.uk) now provides an intelligent layering approach to protection as opposed to using a heavy bulky single layer system or garment.
This multilayer system uses a combination of two fabrics to achieve high arc protection at maximum wearer’s comfort. The e+ARC® 220 is a patented highly durable and breathable fabric made 100% with DuPont Nomex and Kevlar fibres, and the A+Panther fabric made with DuPont Nomex comfort fibre which produces thermal protection garments with a very high level of tactile and thermal comfort.. The Arcban single layer every day wear designed for lower risk environments, comprises of a trouser made from e+AR 220 (9.8 cal/cm?) and a shirt made from A+PANTHER (8.7 cal/cm?). To increase the level of arc protection, workers can layer an Arcban coverall over the top which then provides a minimum of 43.7 cal/cm?. Made from the same fabric as the Arcban trousers, the coverall can be worn alone providing 9.8 cal/cm? protection, however, it is vital that workers select undergarments that will not melt or burn in the event of an arc flash.
For ultimate protection from one garment, the Arcban 40 cal/cm? Kit is a dual layer construction comprising of an e+ARC fabric outer layer stitched to an A+Panther inner layer.
DuPont and partner weavers have launched a range of blends of Nomex for mid-performance protection and performance coupled with high comfort in their secondary ‘orange’ label fabric category. Solutions include globally compliant multi-hazard protection Nomex MHP, Nomex / FR Viscose Diamond, iProtect and A+Panther.