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Arc Flash Events

 
An arc flash is one of the most dangerous electrical hazards to all employees working within an electrical hazard zone. Unfortunately, they’re also quite common. Five to ten arc flash events occur in the United States on a daily basis, with 30,000 arcs flashes occurring annually. Between their common occurrence and extreme danger levels, arc flashes account for nearly 80 percent of all accidents, incidents and fatalities among even highly trained industry employees — resulting in over 7,000 burn injuries annually, 2,000 of which require hospitalization.

Fortunately, the occurrence of arc flashes and electrical accidents in general has steadily gone down over the past few decades. This is primarily due to improvements in electrical education, more stringent preventative measures and better quality equipment. Today, it’s imperative for every person working in the industrial sector to be aware of the dangers of arc flashes and how they can happen, so they can better prepare for an arc flash event.

What Is an Arc Flash Event?

Essentially, an arc flash is an event where an electric current leaves its path to travel through the air. The stray arc usually passes from one conductor to another or to the ground, taking the path of least resistance. This could mean the current passes through an unintended piece of equipment or even a person, resulting in electrocution. The most problematic side effect of these events, however, is arc flash energy.

Most people have seen an arc flash before, in the form of an incandescent light bulb burning out. When the filament in a bulb breaks, the electricity running through the filament continues running through the air, creating an arc that appears as a blue flash of light. While events like these are very small, other events can be substantially larger, depending on the amount of current. Some industrial settings use huge amounts of current, releasing lethal amounts of energy when an arc flash occurs.

Some events can cause the surrounding air to reach temperatures of up to 35000 degrees Fahrenheit

As an arc flash passes through the air, this huge amount of energy ionizes the surrounding air, causing molecules in the air to energize and produce heat. Some events can cause the surrounding air to reach temperatures of up to 35,000 degrees Fahrenheit, which is actually hotter than the surface of the sun. Those temperatures can set fire to clothing, burn skin, liquefy metals and ignite nearby combustible materials within a second, even from a distance. At exposure under ten feet, such temperatures cause fatal burns and instantly vaporize many materials.

Arc flashes also produce other harmful environmental changes, including the following:

  • Pressure Wave: As the temperature increases around the flash arc event, the molecules in the air and surrounding materials react by heating up and expanding in volume. This change in volume creates a massive wave of pressure, often producing more than 2,000 pounds per square foot. This pressure can be enough to throw objects and people across a room, resulting in equipment damage and injury. It’s even enough to collapse lungs and break bones. Additionally, the pressure can throw melted materials, like molten metal, around the area up to a distance of 10 feet, causing additional damage and injury to people and equipment.
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  • Sound Blasts: The sudden pressure change produced by an arc flash can also result in a sound blast, which can be enough to break glass and damage workers’ ear drums, resulting in hearing loss.
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  • Bursts of Light: The explosion from an arc flash produces light as well as heat. This light is extremely bright, and it is enough to cause temporary blindness by itself.

What Causes an Arc Flash Event?

The cause of an arc flash is usually a short circuit of some kind, also called a fault condition. The cause of such a short can be one of many things. Just a few examples include:

  • Human Error: Many people develop lazy workarounds and habits when they’ve worked a job for a while, bypassing safety standards and procedures for those few seconds of saved time. Still other people get distracted while they work, resulting in forgetfulness or clumsiness. Such habits and mistakes include anything from misplacing or dropping a tool to skipping a maintenance step. When working with electrical devices, such mistakes can be enough to trigger an arc flash or other electrical emergency.
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  • Neglected Maintenance Processes: Too much dust and debris building up on equipment can cause some serious functional problems. The same can be said for corrosion and condensation on electronic components. Failing to maintain electronic equipment in industrial settings can lead to any of these problems, each of which can result in a fault.
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  • Improper Electrical Design: Improper installation is another common problem leading to arc flashes. Such installation issues could be a problem in the design or an old or improperly rated piece of equipment These system design problems increase the chances of a fault occurring, potentially resulting in an arc flash.

The resulting arc flash can vary in size and energy based on numerous variables, like amperage, voltage, the size of the arc gap and the space in which the flash takes place. However, you’ll notice that each one of these arc flash causes is largely avoidable. This is why OSHA and other worker safety programs focus so much on quality electrical hazard training.

What Are the Different Kinds of Arc Flash Events?

Four types of arc flash events are arc in a box, open air arc, ejected arc, tracking arc

Arc flash events have multiple causes and can occur in a wide variety of settings, so it makes sense that arc flashes come in different forms. In fact, there are four specific kinds of arc flash events recognized by professionals in the field. These arc flash types are:

  • Arc in a Box: Also called a confined flash, this type of arc flash is one that comes from a distribution or motor control box. Instead of being open on all sides, the flash is contained on all sides except the front opening. This causes all the energy to escape through the opening of the box. Most arc flash calculations use the arc in a box as a standard model, since control boxes tend to be common sites of arc flash events.
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  • Open Air Arc: The name of this arc type is self-explanatory — an open air arc, or a free arc, is an arc flash that occurs in the open air, exposed on all sides. This is the other most common type of arc flash event, most commonly seen at faulty power lines and cables.
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  • Ejected Arc: An ejected arc occurs when the plasma created by an arc flash ejects from the flash site, hitting a nearby worker or piece of equipment. This type of arc can cause serious burns and damage.
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  • Tracking Arc: This type of arc is most common at high voltages, or when someone comes in contact with the arc. It involves the arc current conducting on skin or through clothing, causing serious electrical burns.

The first two of these electric arc types are the best understood of the four, and they tend to be the ones taken into consideration in safety standards and calculations for protective equipment. Unfortunately, arcs tend to be much more unpredictable in the real world, and an open air arc can quickly turn into an ejected or tracking arc when the current runs 480V or higher. Because calculations only take open air and confined flashes into consideration, many arc hazard assessments and protective equipment designs are under-rated for the potential risks posed by ejected or tracking arcs.

What Is an Arc Flash’s Range of Intensity?

The intensity of a blast is typically measured in incident energy, expressed in calories per centimeter squared, or cal/cm2. This is the energy measured on a surface at a certain working distance from the origin of an arc flash. This incident energy depends on several variables, including the current of the short circuit and the duration of the arc. Incident energy tends to increase as the fault current and blast duration increases. Incident energy also increases the closer the subject is to the source of the blast.

Second degree burns occur when bare skin is exposed to incident energy around 1.2 cal/cm2

Work zones will usually set an outer boundary for all hazardous equipment, also known as the protection boundary. This boundary is the furthest set boundary from a piece of energized equipment, set at the point at which an employee exposed to an arc flash event would sustain no more than a second degree burn. For reference, second degree burns occur when bare skin is exposed to incident energy around 1.2 cal/cm2.

On the other end of the spectrum is the prohibited boundary. At this distance and closer, the employee might as well be touching the source of the arc flash. While most potential arc flash sources have the potential to produce 2.1 cal/cm2 of incident energy, less than one percent of these potential sources can release as much as 205 cal/ cm2. For reference, third degree burns occur at 8 cal/cm2, and PPE 4 only protects against incident energy of up to 40. These amounts of energy are lethal for any worker within this prohibited boundary, and even some working beyond it.

The potential intensity of an arc flash within a particular work zone is usually determined during a flash assessment using a series of calculations. In turn, personnel use these calculations to set the boundary lines for employees working and observing the hazardous zone.

What Is the Arc Flash Hierarchy of Hazard Control?

To minimize the potential danger or arc flashes in work environments, most companies recognize a system more commonly known as the hierarchy of hazard control. This hierarchy is a system of safety measures charted by the National Institute for Occupational Safety and Health and Centers for Disease Control and Prevention. Also known as the hierarchy of controls for risk management, it lists control measures from most effective to least effective. These controls are:

  1. Elimination: This step involves eliminating the hazard. This is an ideal situation, though it is impractical in the case of arc flashes. Eliminating arc flashes means eliminating electrical systems from the workplace.
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  3. Substitution: This option involves substituting the hazard for a safer alternative. For example, in the case of arc flash prevention, this would involve switching out equipment with newer models equipped with more safety measures, reducing the potential for an arc flash event. The only problem with this control method is cost — it’s expensive for companies to switch out their equipment for the newest models.
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  5. Engineering Controls: Engineering controls include physically changing the work process to minimize hazards. This tends to be the most favorable of control measures, as it removes hazards at the source without needing to eliminate or replace primary equipment. One example of an engineering control would be an advanced breaker system that monitors and quickly shuts off a circuit as soon as a fault occurs.
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  7. Administrative Controls: This measure involves personnel training and regulation. Most commonly, companies use administrative controls like training to improve employee knowledge about hazards and prevention methods. Some companies also limit the amount of time employees can be exposed to a hazard, reducing their chances of being present during an arc flash event. This places the majority of hazard control and safety management on employees, rather than the company itself.
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  9. Personal Protective Equipment: This measure involves the use of personal protective equipment, or PPE by employees working around a hazard. This is the last line of defense against a hazard for employees, and the usage of such equipment is the responsibility of the employee, rather than the employer.

Ideally, a company should employ all five controls. By eliminating any unnecessary equipment and replacing older equipment with newer models, employers can reduce the number of hazards their employees face. They can further mitigate any remaining hazards by installing engineering controls and requiring proper training and PPE for all employees working in the environment. In combination, all of these controls can effectively minimize the potential dangers employees encounter during a given workday.

Where Can You Learn More About Arc Flash Events?

These arc flash facts only scratch the surface. From regulations to equipment specifications, the amount of knowledge available on arc flashes and other electrical hazards is massive, and it’s constantly changing as new regulations and discoveries come to light. However, employees working in electrically hazard environments have to know this information — it’s crucial to encourage them to keep up safety procedures and processes as well as help protect themselves and their coworkers from the massive destruction arc flashes can cause. That’s where Technical Skills Development Services can help.

At Technical Skills Developmenbt we specialize inhelping companies of all types meet the latest in OSHA training requirements

At Technical Skills Development, safety training has been our focus for nearly 15 years. We specialize in helping companies of all types meet the latest in OSHA training requirements, and we use OSHA, NFPA 70E and other risk management standards to design our training programs. With our on-site eight-hour training sessions and customized programs, you can rest easy knowing your team of both qualified and unqualified workers is learning everything they need to know about arc flashes and how to prevent them.

Learn how Technical Skills Development can help you meet OSHA standards and contact us today for a free quote.