TOOLBOX SAFETY TALKS
What is an Arc Flash/Arc Blast?
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There are three electrical hazards that cause injury and even death while working on or near
electrical equipment. They are:
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•
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Electrical Shock
Arc Flash
Arc Blast
Everyone is aware of the electrical shock hazard, which can ultimately lead to death. In fact, most
people have experienced minor shocks with relatively no consequences. In contrast, few people
have experienced the violent nature of an electrical arc flash/blast and the potential for severe
burns.
What is an arc Flash?
An arc flash is the passage of electric current between two conducting metals through an ionizing
gas or vapor, usually air. It is initiated by a flashover, or from the introduction of some conductive
material such as a screwdriver or bolt. The arc flash results in intense heat and light.
Heat/Fire: A fierce conductive-plasma fireball develops in an arc flash occurring from a fault
current. Arc temperatures can exceed 35,000°F at the arc terminals. Compare this to the surface
of the sun where the temperature is about 9,000°F. Serious or fatal burns can occur at distances
of more than 10 feet from the source of the flash. In addition to burns from the flash, flammable
clothing can ignite. Synthetic fibers such as polyester and rayon blends will melt to the body
increasing the severity of the burn.
Intense Light: Ultraviolet radiation from the flash can severely damage a person’s eyesight. Also,
workers exposed to an arc flash typically develop cataracts up to 2-3 years after the incident.
What is an Arc Blast?
The arc blast is the pressure wave component that occurs from the fault current during the arc
flash. The pressure wave is caused by rapid expansion of air and vaporization of conducting
material from intense heat.
Vaporized Copper and Molten Metal: The intense heat is capable of vaporizing the copper
bus/conductors. Copper expands by a factor of 67,000 times as it vaporizes in the same way that
water expands 1,670 times when it becomes steam. Workers typically breathe in vaporized copper
and molten metal during an arc flash/blast resulting in damaged lungs.
Shrapnel: The pressure wave from the expansion of air and vaporization of conducting material
blows up the electrical equipment with shrapnel striking the worker.
Impact with Objects: The resulting pressure wave from an arc blast is capable of knocking a
person off a ladder or throwing them across the room. A 25KA arc can create as much as 160
lbs.ft² of pressure on a person two feet from the source. This would place 480 lbs of force on the
average person’s body.
Staff Electric Company, Inc.
What is an Arc Flash/Arc Blast (November 2003)
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In addition, nearby equipment and structures may be severely damaged from the pressure wave.
A 100KA, 10KV arc reached a pressure level of 400 lb/ft² at a distance of just over three feet. This
force could easily destroy a conventional wall at a distance up to 40 feet away. A small 25KA arc
blast could destroy a wall or equipment at a distance of nearly 10 feet.
Noise: The pressure wave has also caused ear damage. 140 decibels (dB) was measured two
feet away from an arc source. This compares to 130 dB for a jet engine.
As you see, the consequences of being involved in an arc flash and arc blast are severe,
sometimes resulting in death. Be sure to follow the company’s procedures regarding deenergization of electrical equipment to avoid hot work.
Has anyone ever experienced or witnessed an arc flash?
What were the causes? What injuries occurred?
Temperatures and measurements on the body during an arc flash.
Arc Flash during a non-current limiting staged test.
Staff Electric Company, Inc.
What is an Arc Flash/Arc Blast (November 2003)
Page 2
SIGN-OFF SHEET: What is an Arc Flash/Arc Blast?
This sign-off sheet documents the employees who have participated in a training session on arc
flash/arc blast hazards. Completed sign-off sheets need to be faxed to (262) 790-1044 or mailed
to Kurt Wildner, Safety Director.
Foreman:
Job Location:
Date of Training:
P R I N T Name below:
Staff Electric Company, Inc.
Employee Signature
What is an Arc Flash/Arc Blast (November 2003)
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