POWER ARC

Characteristics of an Arc
Electrical workers are frequently in close proximity to energized parts where power arcs can occur. It is
not necessary to touch an energized conductor to receive an electrical shock. Anyone who has rubbed
their feet across a carpeted room and reached for a metal doorknob can attest to that. High voltage may
cause current flow through the air from one conductive surface to another if the voltage is great enough
and conditions are right.
A lightning strike, which might have an electrical potential of millions of volts, is an electrical arc that
could span miles. Similarly, in electrical work, when there is a difference of potential between two
points, an arc can occur under the right set of conditions. Not only could an electrical arc jump from a
conductor to a person and give them a shock but arcing can result in serious burns and explosive blasts.
Typically, arcing distances are rather small. Safe approach distances should include a safety factor to
the arcing distances in order to account for such things as inadvertent movement and variable work
conditions.
Workers should always be aware of the arcing hazard when handling tools and equipment near
energized electrical conductors. Personal Protective Equipment (PPE) may be required in certain
situations depending on the amount of energy available at the source.
The power arc is a discharge of electricity through a combination of ionized air and vaporized conductor
material. The conductive material is vaporized by temperatures in an arc which can be as high as 35,000
degrees Fahrenheit.
Burns associated with high energy arcs can be fatal even if the victim is several feet from the arc, and
severe burns at distances up to ten feet are common. Clothing may also be ignited at distances of
several feet. This may also be fatal, because the clothing cannot be removed or extinguished quickly
enough to prevent serious burns over much of the body's skin.

The following table,  gives several examples of the increased temperature of human skin
above normal when exposed to power arcs of varying lengths.

Electrical Arc Blasts
In addition to an electrical shock and burns, another hazard to employees is the blast effect that can
result from arcing. If the current involved is great enough, these arcs can cause injury and start fires.
Extremely high-energy arcs can damage equipment causing fragmented metal to fly in all directions.
Low-energy arcs can cause violent explosions or blasts in atmospheres containing explosive gases,
vapors or combustible dusts.
The hot vaporized metal from the arc blast will combine with oxygen and become an oxide of the metal
of the arc. These molten particles will stick to almost anything actually melting into many surfaces.
Clothing may ignite as a result of contact with this molten material and a victim may receive serious
burns. Also, your body has an instinctive reaction when you are suddenly startled to breath in heavy or
gasp. Inhaling the hot vaporized particles will cause serious damage to your respiratory system by
burning the lungs, throat and esophagus.
There is no equipment available to completely protect electrical workers from the effects of blast.
However, safe practices, such as standing to the hinged side of a cubicle door when operating a breaker,
and other precautions listed below can be taken to minimize the effect of a blast. The main protections
against arc blasts are listed in the following chart.

Exposure Limitation
The amount of time you spend around high
energy equipment; don't loiter.
Distance
 Always stay as far away as possible from
high energy equipment unless you have a
need to be there.
Mass
 Try to keep some type of sturdy material
between you and a potential blast.
Protective Clothing
 Flash suits may offer some protection to
minimize burns resulting from blasts.

If an arcing fault occurs while a worker is in close proximity, the survivability of the worker is mostly
dependent upon system design aspects, such as characteristics of the over-current protective device and
precautions the worker has taken prior to the event, such as wearing personal protective equipment
appropriate for the hazard.