Arc flash safety: A comprehensive approach to risk management
HazardEx | June 2015 | Pages 35-37
Arc flash can occur at a wide range of installations, and can cause severe damage to electrical systems and injuries or death to personnel. Paul Welford of GSE Systems highlights the importance of risk management and mitigation to protect systems and staff.
When an electric arc flash occurs, large amounts of energy can be dissipated in a very short time. This energy causes the ionisation and vaporisation of the conductive metal materials (highly conductive plasma). This, coupled with the heating of the ambient air, creates a rapid volumetric expansion, known as arc blast, and consequently an explosion [1, 2].
An arcing fault usually occurs between phase bus bars or from phase to neutral or ground. During this event, current is conducted through the plasma, and the major factor that affects the current magnitude is the impedance of the arc. Intense light, sound waves, shrapnel, molten metal, toxic gases and smoke are all components of the arc flash. Due to the aforementioned hazards, human and business consequences can be severe. Personnel exposed to arc flash can suffer severe burns, lung damage, vision loss, eardrum ruptures and even death [3-6].
The duration and current magnitude of an arcing fault can vary widely. An arc can be initiated by a flashover due to a failure such as breakdown in insulation or by the introduction of a conducting object that accidentally bridges the insulation. Under certain conditions that sustain the arc, faults develop into dangerous arc flash incidents. Generally, systems with voltage magnitudes lower than 120 V AC or 50 V DC cannot sustain an electrical arc.
Within an arc flash safety assessment, a hazard analysis is crucial in evaluating the risk and deciding which mitigation techniques are appropriate to control it. There are ongoing efforts to improve codes, standards and regulations for arc flash so that they include state-of-the art methods to provide better electrical safety and performance .
Risk Management Process
Risk management is an iterative and continuous process that aims to reduce the risk and incorporate best practices . Risk assessment involves identification, analysis and evaluation of the arc flash. Risk analysis is performed to estimate the likelihood of an arc flash incident and the severity of electrical flash hazards. Likelihood is generally affected by two main factors: the number of interactions with energised electrical equipment and the condition of electrical equipment. Severity is the degree of harm that results from the exposure. Risk can be high even in cases of high likelihood, in cases of high severity or both.
Risk evaluation should be conducted to determine if the risk is acceptable or manageable to protect equipment and operators. If not, risk treatment, risk control and mitigation procedures are required to reduce arc flash risk and hazard. Selection of personal protective equipment (PPE), placement of warning labels indicating the hazards, and training of operators are also essential parts of risk management and this should always be combined with mitigation measures to improve efficacy.
Available techniques for reduction of hazard levels in existing systems, including replacement or addition of equipment, are limited  but regularly developing. For new installations, innovative equipment and design methods are constantly being developed. Before implementing any method, its applicability to the specific electrical system must be considered  along with the nature and magnitude of the potential arc hazard. Read More
HazardEx | June 2015 | Pages 35-37
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