He was married, had a very upbeat personality, a good position at the company, and
was pleasant to be around. One day, Henry was trying to track down a low
voltage problem and was conducting voltage measurements on a 4,160V to 480V dry
type transformer on an upper level mezzanine. He took off the transformer
cover, knelt down in front of it with a meter to test the 480V side and got the
4,160V side by mistake. The resulting arc flash explosion sent a fireball
blasting out of the cabinet catching him in the torso and groin before rolling
up his face.

With his clothes burning, Henry managed to make it down the ladder. Coworkers put
out the fire and rushed him to hospital where he was diagnosed with third
degree burns over a large portion of his body. He lingered in the hospital for
an agonizing seven days and then died.

“From that moment, the way I viewed electrical power changed forever,” says Jim Phillips, who was called in to conduct the forensic investigation the next day.
Today, Jim is one of America’s foremost experts on Arc Flash and teaches
numerous seminars on electrical safety through his company T2G Technical Training Group and has written a book on the subject that will be published in the fall. “If you work in this business long enough, you either know an arc flash victim or you know someone that knows a victim.”

According to a report compiled by Capelli-Schellpfeffer, Inc., five to 10 arc flash
explosions happen in the USA every day, resulting in 1 to 2 deaths. Moreover, over the course of a seven-year study tracking electrical accidents conducted by the U.S. Department of Labor’s Bureau of Labor Statistics, 2,576 U.S. workers died and another 32,807 were injured -- losing an average of 13 days away from work -- due to electrical
shock or burn injuries. A second study involving more than 120,000 employees
determined arc flash injuries accounted for 77% of all recorded electrical
injuries.

 

What
is Arc Flash?

As defined by IEEE and the National Fire Prevention Association (NFPA), an Arc Flash is a strong electric current – and often a full-blown explosion – that passes through air when
insulation between electrified conductors is no longer sufficient to contain the voltage within them. This creates a "short cut" that allows electricity to race from conductor-to-conductor… to the extreme detriment of any worker standing nearby.

Arc Flash resembles a lightning bolt-like charge, emitting extreme heat – up to 35,000 degrees Fahrenheit or four times the surface temperature of the sun. Anyone exposed to
the blast or heat without sufficient personal protective equipment (PPE) would
be severely -- and often fatally -- injured.

Arc Flash incidents cause several types of injury. Like Henry, victims may be
burned. They may also be thrown by the force of the explosion sustaining impact
injuries such as concussions and fractures, and/or deafened by the bang, which
can reach 160 decibels – louder than a jet engine. The extreme heat of the
explosion may also melt and shatter metal wiring and equipment and spray it
across the room as projectiles, causing shrapnel wounds, burns and igniting
clothing.

According to most studies, the most common cause of these accidents is human error.
Henry’s tragic mistake in measuring the wrong side of the cabinet is a case in point. But many other factors may trigger an incident. In some cases just coming too close to a high-current source with a conductive object can cause the electricity to flash over. Other causal factors include equipment failure due to use of substandard parts, improper installation, or even normal wear and tear, breaks or gaps in insulation or dust, corrosion or other impurities on the surface of the conductor.

"It’s practically impossible to completely eliminate arc flash incidents," says Greg Richards, an automation consultant with Siemens Energy & Automation. “The best way to avoid an Arc Flash incident is to avoid working on energized equipment, but that’s not always realistic,” adds Richards. “If you are in a continuous process
environment or a facility like an Air Traffic Control tower then you may just
have to deal with it.”

“However, there are a number of ways you can significantly reduce the risk, starting with understanding how dangerous these incidents can be, performing all the proper
groundwork as outlined by IEEE and NFPA regulations (see NFPA 70E “Standard for
Electrical Safety in the Workplace” and IEEE 1584 "IEEE Guide for Performing Arc Flash Calculations") and making sure that when you do work on live equipment you have the appropriate PPE on at all times.”

 

Using TIA to reduce Arc
Flash risk

Richards ...