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.
{mosimage}“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 has his own Arc Flash horror story. Prior to
joining Siemens he worked in a plant where a worker got seriously hurt checking
the voltage on a circuit to make sure it had enough power to drive another
piece of equipment. “He had second and third degree burns from the waist up. He
was in the hospital for nearly a year and needed multiple skin grafts.”
This incident led to the creation of an Arc Flash task
force for the company’s five North American plants. “We started with making
sure we had the right PPE, but then we went looking for ways to eliminate Arc
Flashes altogether.”
Eventually Richards realized that reducing the need to
open the cabinet in the first place was one of the best ways to accomplish that
goal. "People open the cabinet for many reasons, but chief amongst them is
that, typically, they don’t know what’s going on inside," he says.
"They know there’s a problem; they are getting an alarm or a circuit has
tripped or something. But they don’t know exactly what. What if we can get that
information without opening the cabinet?"
By integrating all the relevant equipment, such as the
motors, drives and switchgear, with the communications network in what Siemens
calls a Totally Integrated Automation (TIA) architecture, operators are able to
monitor and pull diagnostic information, perform trend and root cause analysis
and generally better see what the problems are before sending an electrician
into the plant to deal with a problem. Over time Richards found that workers
were going into the electrical cabinet less and less often.
“As we used it more, the guys learned to trust the
information they were getting,” Richards said. “If a breaker tripped, they knew
it. But, before the TIA system, there was nothing to do but reset the breaker.
The TIA diagnostics allowed engineers to go back and trend the data—to perform
and process the diagnostics externally. For example, if I wanted to know what
the drive current was, I could just look that up. As a result, we found that,
over time, people were going into the cabinet less and less.”
Phillips agrees that the TIA approach is solid. “If there
are ways to monitor and control things that keep people from opening the
cabinet then that’s a much better way. The best option is always to avoid the
hazard. Doing this through automation and control is a great approach.”
“Having access to this data does not stop arc flash,”
cautions Richards. “The number one thing you can do to avoid that is to
coordinate your power system and reduce your exposure to a potential incident.
And the more you integrate, the less likely you are to have to open the cabinet
in the first place.”
Arc Flash Resources:
www.SafetyBase.com
Many free articles and downloads - www.brainfiller.com
A global community about arc flash and electrical safety
- www.ArcFlashForum.com
Siemens Arc Flash brochure
Siemens Arc Flash studies
Video of Arc Flash accident