Feature Arc Flash Prevention and protection
Mike Frain, electrical consultant, Electrical Safety UK and Elaina Harvey, DuPont Nomex account manager, offer some advice and guidance on how to alleviate the dangers of arc flash
cially. Whilst legislation requires busi- nesses to perform risk assessments for all work activities, electric arc risk is often overlooked because most people are unsure how to assess and manage this hazard effectively.
Risk assessment A
n arc flash is usually caused by inadvertent contact between an energised conductor such as a busbar or wire with another con- ductor 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°C.
The most common causes of arc flash are accidentally bridged contacts on energised equipment such as switchgear, from tools dropped during maintenance work, or using substandard electrical test equipment. Poorly maintained installations can become hazardous on their own if moisture or dust is allowed to build up on insulating surfaces. Utilities, energy producers and providers, mining, manufacturing companies (particularly those in the food, pharmaceutical and chemical industries), hospitals, large commer- cial organisations, data centres, educa- tion establishments and large leisure facilities are the industries most at risk. It is widely recognised that the higher the voltage of an electrical power system, the greater the risk for people working on or near energised conductors or equipment. However, arc flash can actually be worse and more common at lower voltages.
Consequences
People working on or close to electri- cal equipment are at risk from a variety of serious injuries or even death. 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 300m/s. The cost of injury can be extreme - physically, emotionally and finan-
Electrical Engineering MAY 2013
Although many companies look to implement personal protective equip- ment (PPE) as a first line of defence against arc flash, in truth this should be one of the last steps taken in manag- ing electric arc risks.
The arc flash hazard needs to be determined by risk assessment, out of which the decision to work live or dead and the required precautions will be derived. The need for risk assess- ment 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.
The European Agency for Safety and Health at Work defines risk assessment as the process of evaluating risks to workers’ safety and health from work- place hazards. It is a systematic exami- nation of all aspects of work that considers what could cause injury or harm; whether the hazards could be eliminated and, if not; what preventa- tive or protective measures are, or should be in place to control and miti- gate the risks. However, a risk assessment should provide more information than this. For example, DuPont offer a step by step approach of Predict, Prevent, Protect and Publish that is recom- mended in its DuPont Arc-Guide.
Managing risk
Ensuring that the work is fundamen- tally safe ideally means switching off the power to the equipment and ensur- ing that it is ‘dead’ for as long as the work continues. That means isolating all the sources of power supply, earth- ing the dead circuit conductors (espe- cially on high voltage systems), isolating any nearby live conductors and finally, issuing a permit to who- ever is going to work in the area, con- firming they understand the task and the limits of the safe zone.
If this is not feasible, then the risk of 27
Above: Elaina Harvey, DuPont
Above left and below: people working on or close to electrical
equipment are at risk from a variety of serious injuries or even death
Above: Mike Frain, Electrical Safety UK
electric arc flash should be designed out, which might include replacing old switchgear and control panels where the live components are often exposed with arc protected equipment. Procedures should be introduced to ensure that protection already in place is properly maintained and not compro- mised by alterations.
Protective clothing
It is important to communicate to any one working in high risk environments to always assume that any system is live until you have proven it dead. If there is no avoiding working live, then you need to be sure that the people doing the work are competent and understand the true level of risks. What’s left when you have covered all the other bases of design, engineering controls, operator compe- tence and safe systems, is PPE. The best approach to choosing PPE is to use the arc flash study data to provide exactly the right protection. From here, a layer- ing approach should be taken, which gives the benefit of creating air gaps between the layers, dissipating the energy in the event of an arc flash. Layering is also an easy way of achieving a higher level of protection without becoming too heavy, for example layer- ing thin layers such as a jacket or coverall over a base layer.
DuPont has developed its Arc-Guide in conjunction with independent experts, to help companies better assess the arc flash hazards (with the use of simple calculators) and provide them with the knowledge on how to both reduce the severity and consequences of an arc flash.
DuPont
www.arcguide.dupont.com T: 01438 734 000
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