Understanding the Dangers of Arc Flash
Electricians face many hazards on a regular basis. In fact, working with or near electricity presents the risk of electrical events, which can severely injure or even kill workers. Arc flash is a dangerous instantaneous electrical event that occurs often. According to the National Institute for Occupational Safety and Health (NIOSH), 5 to 10 arc flash incidents occur each day in the U.S. Arc flash is extremely dangerous because it can produce some of the highest temperatures known to occur on earth, up to 35,000 degrees Fahrenheit, which is four times the temperature of the surface of the sun!
OSHA defines arc flash as “a phenomenon where a flashover of electric current leaves its
intended path and travels through the air from one conductor to another, or to ground.” According to a study conducted for NIOSH, arc flash can be spontaneous or result from inadvertently bridging electrical contacts with a conducting object. They can also be caused by many factors including:
- Dropping tools
- Accidental touching
- Material failure
- Faulty Installation
According to the same study for NIOSH, typical results from an arc flash include:
- Burns (Non flame-resistant clothing can burn onto skin)
- Flying objects (often molten metal shrapnel)
- Blast pressure (upwards of 2,000 pounds per square foot)
- Sound Blast (noise can reach 140 decibels—as loud as a gun)
- Heat (upwards of 35,000 degrees Fahrenheit)
Because of the danger and frequency of arc flash events, standard organizations, such as OSHA and the National Fire Protection Association (NFPA), are updating their regulations. In April 2014, OSHA issued a final rule on electric power generation, transmission, and distribution that includes new or revised requirements for fall protection, minimum approach distances, and arc-flash protection. The final rule also includes requirements for electrical protective equipment. OSHA anticipates that the new rule will help prevent almost 20 deaths and 118 serious injuries annually.
Although OSHA sets the requirements for arc flash prevention and other electric safety issues, the NFPA’s standard outlines how to be safe while meeting those requirements. NFPA 70E assists companies to comply with OSHA’s 1910 Subpart S and 1926 Subpart K. The latest NFPA standard has changed its terminology from “arc flash hazard analysis” to “arc flash risk assessment.” Experts say that this change puts emphasis on equipment evaluation instead of simple equipment selection.
According to Safety + Health Magazine, a task group from the NFPA 70E committee have been considering if the NFPA standard should include requirements for certified personal protective equipment, such as arc flash rated clothing, rubber gloves, and insulated tools. In addition, the NFPA and Institute of Electrical and Electronics Engineers (IEEE) are collaborating on an arc flash research project. Both organizations hope to provide improved safety guidance by better understanding arc flash and its hazards. NFPA will update its 70E standard based on the results of the experiments conducted during the study.
Although there are several methods to protect against arc flash, such as insulation and guarding, the best way to protect against arc flash is to deenergize the circuit. Additionally, NFPA 70E recommends creating an “electrically safe work condition” by:
- Identifying all power sources,
- Interrupting the load and disconnecting power,
- Visually verifying that a disconnect has opened the circuit,
- Locking out and tagging the circuit,
- Testing for voltage, and
- Grounding all power conductors.
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