Arc Flash Training
What is an Arc Flash?
An arc flash blast is an explosive electrical arc that is powered with enough energy to cause fire, injury, death, or property damage, resulting from the insulation failure or accidental short-circuiting of an electric current between the air and uncontrolled conduction between ground, and different phases in an electrical system. These flashes can exceed temperatures of over 30,000 degrees Fahrenheit at the faults in their terminals, and vaporizes the metal and even ionizes the air within its circuit path, creating super-heated and expanding lava-like plasma that can move at high speed and force.
Normally, an arc flash does no major damage because high voltage fuses will open the circuit and eliminate electrical current, but any number of factors can create a potential for destruction and even death, if people are near the explosion. In some cases, the fuses in some instances cannot physically blow fast enough to completely isolate all electrical current from the short circuit, and the copper conductors in the bus bars will change from solid to plasma in an instant—but their conductive properties don’t change until the plasma has completely dissipated from the area.
This essentially creates an area of air that can conduct the electrical current that is now free to follow the path of least resistance. Obviously, since that path is so open and vague, the electrical current creates an arc that is represented by an explosive fireball cloud that can reach temperatures four times the temperature of the sun, and creating shrapnel and shock waves that can blow a person off of their feet and burn their skin, blind their eyes, potentially cause severe neural damage, or even death if they aren’t properly protected with the appropriately rated arc flash personal protective equipment (PPE).
Arc Flash Examples
An electrical utility worker was working on the electrical panels in a high-rise apartment building and opened up a panel to conduct an inspection. Unbeknownst to her, a previous worker had absent-mindedly left a wrench on top of the panel after closing it, and it fell into the panel when she opened it. The wrench landed on one of the bus terminals and caused a short, ultimately creating an arc fault. The arc flash blasted the woman directly in the face and physically threw her across the room, into the front of another electrical panel. She was hospitalized with severe burns, shock, and some neural damage.
According to the Department of Labor’s own Occupational Safety and Health Administration’s (OSHA) website, arc flash negligence is a danger and punishable under the law:
“The U.S. Department of Labor's Occupational Safety and Health Administration has cited Heartland Refinery in Columbus with one alleged serious safety violation for failing to control the release of flammable liquids and vapors resulting in a July 17, 2010, fire at the facility. The refinery also has been cited with two repeat violations for problems that existed in March 2010 and were found in July 2010 not to have been corrected, as well as one failure-to-abate violation first brought to the company's attention by OSHA in 2009. Proposed penalties total $68,900.
"Failing to follow proper procedures to prevent the unintentional release of flammable vapors and liquids in an area where a known ignition source exists creates a serious safety risk to workers, and as this case shows, a high risk of fire in the workplace," said OSHA Area Director Deborah Zubaty in Columbus. "There is no excuse for this type of complacency, and OSHA will do all it can to protect employees in the workplace."
Focus on Personal Safety
First off, in order to sufficiently train personnel in proper safety techniques and to explore various methods of arc flash prevention, all levels of management and employees must embrace the need for safety—if not for solely for personnel safety, then for legal and insurance purposes.
There are several ways to protect personnel from arc flash hazards. The first way is to de-energize the electrical component or panel before personnel must open and work on it. This isn’t always practical, and sometimes, as in the case of thermographic arc flash surveys, the panel must be in operation while the inspection is underway. Another safety option is to keep personnel as far away as possible, using remote racking systems to carry out electrical panel work without having a service person working within the arc flash hazard zone.
When neither of these options is possible, and personnel must work directly on energized panels, it is absolutely mandatory that those workers wear PPE-rated at or higher than the arc flash category of that particular panel or transformer energy levels. This usually means referring to the NFPA 70e-established arc flash hazard risk categories on the electrical appliance and wearing PPE that correlates with the expectations of that category. Whenever working in an arc flash rated zone, it is almost always mandatory that personnel use a face shield or “beekeeper hood” (which includes a filtered protective coating, safety glasses, and thick leather work boots. Depending on the arc rating, which the NFPA 70e document defines as “A value of the energy necessary to pass through any given fabric to cause with 50% probability a second or third degree burn. This value is measured in calories/cm2. The necessary Arc Rating for an article of clothing is determined by a Hazard/Risk Assessment and the resulting HRC,” protective clothing that has the ability to protect a body from intense heat, shock, and fire with varying arc thermal protective values are expected to be worn, including arc thermal gloves, which require a layer of leather to cover an insulating rubber base, so the rubber doesn’t burn onto the person’s skin below.
Prevention by Design
Much like the necessity of PPE for workers, the need for designing effective arc flash reduction devices has prompted electrical supply companies to add arc elimination relays, low amperage fuses, grounding resistors, and circuit breakers that can open a circuit before a full fault or arc flash can happen. As mentioned above, a remote racking system, or remote.
Arc Flash Standards and Codes
In an effort to protect people from possible arc flash hazards, the Institute of Electrical and Electronic Engineers (IEEE) developed a Guide for Performing Arc-Flash Hazard Calculations, or IEEE Std 1584-2002. This gives personnel some ballpark idea of the kind of PPE they should wear to work on an energized electrical box.
Perhaps one of the best sources for arc flash protective standards and work practices for personnel to safely service exposed conductors and energized circuit components, the National Fire Prevention Association’s National Electrical Code (NEC), or NFPA 70e, sanctioned the necessity of conducting arc flash and short-circuit analyses on all appliances conducting 50V or higher and affixing those units with a label that indicates all electrical information along with its arc rating and all appropriate PPE expectations.
Along with the NFPA and IEEE, the Occupational Safety and Health Administration’s OSHA 29 Code of Federal Regulations (CFR) plays a major role in enforcing that acceptable safety measures are enacted and readily-displayed and will even fine manufacturing and other production facilities not in compliance with those standards.