What is Arc Flash?
Electrical workers are exposed to a number of
hazards whenever they work live, including
electrical shock. But arc flash is another hazard
that can cause serious injury or death - even if
an employee doesn't come into direct contact
with an energized conductor.
What is Arc Flash?
Arc flash is a short circuit through air that
flashes over from one exposed live conductor to
another conductor or to ground. Arc flash
incidents are common and costly, and the
frequency of reported accidents is increasing.
This is why arc flash has become a very hot
topic within OSHA and the safety industry
overall.
What Causes Arc Flash?
Arc flashes can be caused in a variety of ways:
Just coming close to a high-amp source with
a conductive object can cause the electricity to
flash over.
Dropping a tool or otherwise creating a
spark can ignite an arc flash.
Equipment failure due to use of substandard
parts, improper installation, or even normal
wear and tear.
Breaks or gaps in insulation.
Dust, corrosion or other impurities on the
surface of the conductor.
How Common Is Arc Flash?
In the past, if someone suffered burns in an
electrical accident, people thought the burns
were caused by the electrical shock passing
through the body. Electrical shocks can cause
burns. But what research has shown is that
most burns from electrical accidents actually
come from arc flash.
A report compiled by Capelli-Schellpfeffer,
Inc., estimates that five to 10 arc flash
explosions happen in the USA every day,
resulting in 1 to 2 deaths per day.
That figure only in takes into account
incidents where victims were sent to special
burn centers. The number does not include
cases sent to regular hospitals or clinics, nor
unreported cases or near misses.
What Kind of Injuries Can Arch Flash Cause?
What is the impact of these accidents and what
types of injuries can they cause? Injuries from
arc flash accidents tend to be very severe, and
result from two types of hazards: arc flash and
arc blast.
Arc Flash: Electric arcs produce intense heat,
and can heat the air to temperatures as high as
35,000 degrees Fahrenheit. This is 4 times the
surface temperature of the sun. Fatal burns can
occur when the victim is several feet from the
arc. Serious burns are not uncommon even at a
distance of 10 feet. Arc flash can cause the
following injuries:
Skin burns by direct heat exposure
Metal is vaporized at this temperature.
Droplets of molten metal can be
propelled over great distances, causing
serious burns or igniting clothing.
High-intensity flash can also cause
damage to eyesight.
Arc Blast: a high-energy arcing fault can
produce a considerable pressure wave and
sound blast. The intense heat from arc causes
the sudden expansion of air, resulting in a blast.
A 10,000 A arc at 480 volts is equivalent to 800
MW or approximately 8 stick of dynamite.
Pressure on the chest can be as high as 2000
lbs/sq foot, causing lung collapse. In some
cases, the pressure wave has sufficient energy
to snap the heads of 3/8-inch steel bolts and to
knock over construction walls. Moreover, it can
send metal parts flying at speeds over 700 miles
per hour. Arc blast can cause the following
injuries:
Loss of memory or brain function from
concussion
Hearing loss from ruptured eardrums (sound
associated with blast can exceed 160 dB.
Sound of jet engine only 145 db)
Shrapnel wounds from metal parts
Other physical injuries from being blown off
ladders, into walls, etc.
What Are the Costs of Arc Flash Injuries?
Unfortunately, death is a very real possibility
with arc flash. Even if the employee survives,
he or she may face years of skin grafts and
other medical treatment, and may never return
to work or enjoy the same standard of life again.
Costs to your company can also be
significant, with medical treatment running into
the millions of dollars. Your company may be
tied up in expensive lawsuits with victims and
their families. And it's not just people who get
hurt: equipment can be damaged, requiring
repair or replacement, and possibly causing the
line or even the entire plant to shut down for a
period of time.
Your Opportunity to Reduce the Risk
With the rising frequency of reported arc flash
accidents, and the a potential for serious injury
or death, arc flash deserves the concern it is
generating within OSHA and the safety industry.
To increase safety and ensure compliance
throughout your workplace, it is critical to learn
and identify arc flash hazards in your facilities,
train employees in safe work practices, and use
labels and other awareness aids to keep the
message in the forefront and reinforce the
desired behavior.
Arc Flash Labeling Requirements
Arc flash labeling is the responsibility of
the employer, not the manufacturer or
installer of the equipment. The NEC
provides examples of electrical equipment
located that must be field marked with a
warning label:
Switchboards
Panelboards
Industrial control panels
Meter socket enclosures
Motor control centers
This is not an all-inclusive list. Labeling is
required for any electrical equipment that
is likely to require examination,
adjustment, service or maintenance while
energized, where the potential for an arc
flash incident exists. Thus many
employers are labeling bus ducts and
other electrical equipment not specifically
called out in the NEC.
Any modifications or renovations to
electrical equipment will require an
updated arc flash hazard analysis and
label. This shall be reviewed at least
every five years. Equipment installed prior
to the 2002 NEC provision does not
require a label. However, should it be
modified or upgraded in anyway a label
must be affixed. One OSHA representative
has stated that he considers changing a
use or a breaker to be a modification that
would require labeling. More importantly,
from a safety standpoint, the hazard is the
same regardless of when the equipment
was installed. Consequently, most
employers are simply labeling all the
appropriate equipment, regardless of
when it was installed.
The NEC requirement states that the
marking must be located so that it’s
clearly visible to qualified persons before
they begin work. Typically, the label is
placed outside the panel or enclosure
door. In some cases, however, companies
choose to put the label inside the door
(e.g., to protect it from harsh
environments), but this should only be
done if the door must first be opened
(allowing the label to be seen) before the
panel face or enclosure can be removed.
The key point is that the label be easily
noticeable by workers before they may be
exposed to any potentially dangerous live
parts.