Editor's Note: At the time of this article's publication, the current edition of the NFPA 70E Standard was the 2009 edition. The 2012 edition is now the most current. See "What is NFPA 70E?" for more information.
According to Wikipedia, "an arc flash (or arc blast) event is a type of electrical explosion that results from a low impedance connection to ground or another voltage phase in an electrical system". The temperature of an arc flash can reach 35,000 degrees Fahrenheit - about four times as hot as the surface of the sun. An electric arc flash can occur if a conductive object gets too close to a high-amp current source or by equipment failure (for instance, while opening or closing disconnects). The arc can heat the air to temperatures as high as 35,000 F, and vaporize metal in the equipment. The arc flash can cause severe skin burns by direct heat exposure and by igniting clothing. The heating of the air and vaporization of metal creates a pressure wave that can damage hearing and cause memory loss (from concussion) and other injuries up to and including death.
A hazardous arc flash can occur in any electrical device, regardless of voltage, in which the energy is high enough to sustain an arc. This would include, Panel Boards, Switch Gear, Transformers, any place that could have equipment failure. Some of the most dangerous tasks include, removing or installing circuit breakers, working on control circuits with energized parts exposed, applying safety grounds, removing panel covers, and performing Low voltage testing and diagnostics.
How do you protect yourself or your employees from this potentially deadly hazard? You follow the guidelines set out in NFPA 70E 2009 Standard for Electrical Safety in the Workplace, 2009 Edition. But what does OSHA say? OSHA recommends referencing NFPA 70E for electrical safety.
NFPA 70E 2009 Standard for Electrical Safety in the Workplace is a general consensus standard that establishes safe electrical work practices. It includes lists of typical electrical job tasks and classifies these jobs into five categories based on hazard level/risk, with charts detailing the personal protective equipment (PPE) needed to protect to the level of the hazard for each category. According to the National Safety Council "Both the Hazard/Risk category classifications and the PPE requirements, as well as the simplified two-category approach, have been widely used. This is due in part to their ease in helping determine what level of PPE is required to protect workers from the hazard potential of the tasks or jobs in each of the hazard risk categories. The simplified two-step approach requires a minimum arc rating - also known as an ATPV - of 8 for "everyday work clothing" and 40 for "switching clothing." All flame-resistant fabrics are, or can be, tested to measure the amount of incident energy required (in cal/cm2) to predictably cause second-degree burns under the fabric.
So what's hot in 2009? An Arc Flash, and what do you wear? You wear the clothing that the arc flash hazard analysis conducted in accordance with the requirements of NFPA 70E 2009 deems appropriate.
Article generously provided by James Norton, President of the JHN Group. He can be contacted regarding Machine Safety Consulting at jamesnorton@jhngroup.com.