Arc Flash
What is an electric arc flash?
Mostly caused by inadvertent contact between an energized conductor with another conductor or an earthed surface, an arc flash short circuit can result in severe injury or even death. The risk is not just for those working on the equipment but also to those in close proximity. A full arc flash will melt the conductors, ionize the air and develop into a conducting plasma fireball. Temperatures within the arc may reach well over 20,000°C.
Arc flash injuries frequently include burns to the skin but also internal burns from inhaling hot gasses and vaporized metal. On top of this there may be damage to hearing and eyesight including blindness from the ultraviolet light. There are many of these devastating injuries recorded every year. More severe arc flash examples also involve an explosive force known as an arc blast. The blast pressure can launch shrapnel at speeds of up to 300 meteres per second and can lead to further injuries. Those who experience an arc flash event and are lucky enough to survive often have horrific injuries which require extensive treatment and rehabilitation. The physical, emotional and financial cost of these injuries can be extreme.
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Shock and electrocution from contact with energized parts have long been recognized as a risk to electrical workers. According to the Electrical Safety Foundation International (ESFI):
Electrical hazards cause more than 300 work-related deaths and 4,000 injuries a year.
Electrical accidents rank sixth among all causes of work-related deaths in the United States.
There are important steps that companies should take to reduce risk and prevent electrical accidents. These steps are required as part of National Fire Protection Association (NFPA) standard 70E®-2012, which provides a detailed reference for facilities to meet electrical workplace safety requirements. A sixth step assists facility owners with fine-tuning the electrical system for safety and operability.
Step 1: Develop and audit an Electrical Safe Work Practices (ESWP) policy.
Step 2: Conduct an electrical system study to determine the present degree of arc flash hazards and label the equipment.
Step 3: Ensure adequate supplies of personal protective equipment (PPE) and proper tools.
Step 4: Conduct regular safety training and employee assessments.
Step 5: Maintain all electrical distribution system components.
Step 6: Follow strategies to reduce and control arc flash hazards.
Often overlooked, Steps 5 and 6 are crucial to optimizing safety and performance of the power system.
NFPA 70E dedicates an entire chapter to the subject of maintenance for electrical safety. All electrical distribution systems contain active components such as fuses, circuit breakers and relays that help protect the system in the event of an electrical fault. These components are also crucial when it comes to protecting workers from arc flash and arc blast hazards. Modern, properly adjusted overcurrent protective devices that have been well maintained are able to detect an arcing condition and clear the fault quickly.
The goal of arc flash mitigation is to reduce the arc flash energy, and thus the PPE, to a level that permits normal tasks to be performed on equipment. The methodologies to reduce arc flash energy or to mitigate its effects fall under two basic categories: A collection of engineering controls to reduce arcing time, and equipment and techniques to remove the worker from the danger zone.
Solutions that lower arc flash energy by reducing the arcing time include:
Over-Current Protective Device (OCPD) coordination studies
Specialized relaying such as light sensing technology
Virtual main relay
Solutions that remove the worker from a dangerous location or place a barrier between the worker and exposed energized parts include:
Wireless temperature monitoring system...More at More Reading
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