Right in front of you on the switchboard, a bright orange label reads: “WARNING Arc Flash Hazard, Appropriate PPE Required.” As you look closer at the label, you also see: “6.5 cal/cm2 at a working distance of 18 inches.”
This is all part of your company’s recently updated electrical safety practices. Based on the calculated incident energy in calories per centimeter squared (cal/cm2) at the equipment location, you are now required to wear flame-retardant clothing and related personal protective equipment (PPE) anytime an arc flash hazard exists. Like many people, you are probably thinking, “We never had to do this before. Besides, I am always careful. Is this really necessary?”
The official answer
The National Fire Protection Association (NFPA) 70E Standard for Electrical Safety in the Workplace offers the official answer to that question. NFPA 70E 130.3 Arc Flash Hazard Analysis provides the detailed requirements for proper selection and use of flame retardent clothing and PPE. There’s another answer based on a tragic event that happened many years ago.
My unofficial answer
In the early 1990s, I was performing consulting engineering services for a medium-sized manufacturing company. During that time, I got to know the company’s chief maintenance person rather well. Henry was one of those very upbeat people that others enjoyed being around.
At home on a Sunday, the telephone rang. It was the company’s plant manager. This call was strange because I never get calls from clients at home, especially on Sunday. My brain raced with a million thoughts, all of them bad!
He told me that Henry had been involved in an electrical explosion the day before, and he was in pretty bad condition. He used the term “electrical explosion” because the phrase “arc flash” was not yet established.
I can talk for hours during my electrical training programs. However, this time, I was completely speechless. They asked if I could meet them Monday morning to begin the forensic investigation. Although I had performed similar investigations in the past, this one remains the most vivid because I knew the victim personally.
The company was located in an older high-bay manufacturing building with an upper-level catwalk and mezzanine about 12 feet above the main floor. I learned that Henry had been making a few voltage measurements on Saturday, during the light load weekend period. One of his measurements was on the secondary side of a dry-type transformer on the mezzanine. After removing the transformer’s cover, he reached in with the voltage probes to measure across the 480-volt secondary terminals, except he accidentally made contact with the 4,160-volt primary terminals. Since the test instrument was only rated for a maximum of 1,000 volts, it instantaneously failed, launching a fireball directly at him.
People working below recalled hearing a loud noise and seeing a lot of arcing in the distance. Not knowing what was happening, they assumed Henry must have been doing some pretty serious arc welding. At about that moment, Henry jumped up with his clothing on fire. He ran down the catwalk and slid down the ladder. People working on the ground floor ran toward him, extinguished the flames and called 911. Somewhere between 45 and 60 seconds likely had passed between the time of the arc flash and the time his burning clothing was extinguished.
At the hospital, medical personnel determined he sustained third-degree burns over a large portion of his body, and his chances of survival were not good.
About a week later, I received the call that informed me Henry died.
In the early ’90s, most people did not wear flame-retardant clothing. In fact, most were unaware of the dangers associated with arc flashes. NFPA 70E has changed all of that.
Statistics and phone calls
Various accident statistics routinely are waved around in safety training programs. However, every statistic has a name, friends and family. Requiring people to wear appropriate flame-retardant clothing and PPE when an arc flash hazard is present is one way to ensure you and those you know never become one of the statistics. I cannot imagine making the call to say someone has just been severely injured or killed by an arc flash. Receiving that kind of phone call? I know that one all too well.
So, is this really necessary? Yes, and it is long overdue.
PHILLIPS, founder of www.brainfiller.com and www.ArcFlashForum.com, is an internationally known educator on electrical power systems. His experience includes industrial, commercial and utility systems, and he is a member of the IEEE 1584 Arc Flash Working Group. Reach him at firstname.lastname@example.org.