Introduction

The discovery of electricity and subsequent knowledge of how to use it is one of the most significant discoveries by man, only second to our ability to make and use fire. Without electricity, our society cannot function. But just as there are downsides to the use of fire, electricity also has many inherent risks.

In industrial settings, electrical distribution and lighting equipment is by far the number one cause of fires, accounting for almost one in four.[1] On the home front, electricity is also a risk, being the third leading cause of house fires (behind cooking and heating).[2]

There are several ways that fires can originate from some type of electrical fault. Overloaded plugs, extension cords, and/or breakers can overheat; lightning can strike; or outdated equipment can fail. In the industrial setting, arcing is the second leading cause of electrical fires, only slightly behind overheated electrical equipment.[3]

When arcing is discussed, there are many types to consider. One type is the arcing that occurs in wiring or equipment that can eventually heat up adjacent combustibles until they reach their ignition temperature.

Another type of arc incident is an arc flash/arc blast. An arc flash is a sudden and large release of electrical energy in the form of heat and light as it strays from its intended path.[4] Arc blast is the pressure wave component of an arc flash.[5] As we will discuss, arc flashes are often the result of human error and, consequently, it is frequently the associated person who is injured or killed.

Electrical Arcs

Electrical arcs are produced “when an electric current flows through the air from one conductive point to another.”[6] In this air gap is where the arc is visible (think sparkplug) and where heat and energy are released. In most instances, arcing is to be avoided. But when the physics of arcing is harnessed, it can be used beneficially for everyday purposes such as arc welding. This process uses the heat produced by the arc to melt welding rods or wire and to fuse metal together.

The difference between an arc that causes an electrical panel to overheat and one that creates an explosion has to do with the amount of energy that is being released and the time within which it is released—but the mechanism is the same.[7]

In appliances, electrical panels, and wiring, arcing can be caused by:

Arcing causes fires because it is extremely hot— think surface-of-the-sun hot. Actually, the surface of the sun is a cool respite comparatively speaking, as arcs can achieve temperatures of up to 35,000°F.[9] The sun’s surface is a mere 10,000°F in comparison.[10]

The reason that arcing does not start a fire every time it occurs is that frequently the arc occurs over too brief of an interval to ignite surrounding combustibles.[11] Further, the surroundings of the arc also play a major role. When the arc only contacts non-combustibles, then there isn’t anything to catch fire.

If the arcing only occurs intermittently, it may do this over many episodes before it ignites its surroundings. And during this course, the user may have no idea that anything is amiss. Then, on one of these occasions, everything lines up just right and the arc starts a fire. This is why electrical fires are so sinister, they often give no warning before ignition.

Of course, there are the occasions where fire ensues immediately following the arcing. These more high-energy arcs cause the notorious arc flashes and arc blasts. Arc flash incidents can have devastating consequences on any personnel present, as well as cause severe thermal and mechanical damage to the surrounding structure.

Arc Flash and Arc Blast

A simple way to differentiate arc flash and arc blast is to think of thunder and lightning. In this scenario, arc flash is the lightning and arc blast is the thunder. All arcs have a flash, but it is those accompanied by a damaging pressure wave that are referred to as a blast.

Arc flash incidents are a real thing in industry. Studies estimate that there are as many as ten arc flash incidents every day in the U.S. resulting in thousands of injuries and hundreds of fatalities. OSHA findings reveal that arc flash burns are in the top three hazards when working with energized electrical equipment.[12]

Arc flashes are typically associated with working on or around high voltage equipment, although they are very possible and dangerous with low voltage equipment as well.[13] Frequently, arc flashes occur in industry when technicians are working on energized electrical equipment. A common theme in arc flash incidents is the involvement of kV-rated switchgears.

There are a number of causes for an arc flash, but most of them can be attributed to human error in some form. These can include:

The release of energy from an arc flash/blast can be tremendous. In an instant, the space is filled with fire and electrical energy. This is often accompanied by a pressure wave which causes additional extensive damage to both the worker and the surrounding structure.

The injuries from an arc flash can be horrific. They are frequently disabling and require long-term care and rehabilitation. Second- and third-degree burns are common, as are amputations from where the current literally blows off digits and limbs. There are also other injuries possible from flying shrapnel, as well as broken bones from the blast wave.

Arc flashes/blasts can be so violent that they have been known to kill workers ten feet away from the actual flash.[14] It is estimated that 80% of the fatalities from arc flash incidents are due to extensive burns rather than electrocution.[15]

In addition to the safety risk to workers and bystanders, there is a high probability that the arc flash will propagate fire to its enclosure. It is hot enough to vaporize copper which, upon condensing on other components, can cause additional electrical faults. Plus, unless the worker is wearing arc flash-rated clothing, his/her clothes are sure to catch fire; in addition to severely burning the worker, this can cause the fire to spread to the adjacent structure.

This short video illustrates the terrible consequences of an arc flash in slow motion. (NOTE: The video is a safety presentation; no one gets hurt.)

Safety Precautions

The best way to deal with arcing and arc flashes is to prevent them. Arcing occurring in wiring and appliances that can lead to a fire may be avoided through:

The risk of arc flashes can be minimized by following all of the above steps in addition to:

If an arc flash does occur, it is vitally important to quickly extinguish the ensuing fire. This is a life safety measure, as personnel are often present for the arc flash. Unless they are wearing appropriately-rated clothing, their clothing will likely be on fire. And a quick-acting fire suppression system is crucial to save their lives.

A Stat-X® total flooding fire suppression system is ideal to protect areas with arc flash potential. When connected to a fire or arc flash detector, the system quickly discharges, filling the space with a fire-suppressing aerosol agent that can reduce the size of the arc flash fireball. It also goes on to extinguish any secondary fires that may result. Most importantly, the Stat-X system extinguishes any ignited clothing on the worker(s). As we noted earlier, 80% of the deaths in an arc flash are due to burns.
. . .
Electrical fires are the number one cause of fire in the industrial setting and number three in house fires. Arcing that causes a fire and arc flash/blast are two electrical faults that significantly contribute to these rankings. As with everything in the safety arena, the best approach is to prevent the incidents from happening through effective training, maintenance, and work procedures. Even when these steps are taken, it pays to be prepared with an automatic fire protection system that is rated for quick knockdown of electrical fires.

[1]osIndustrial.pdf (nfpa.org)
[2]Home fires report (nfpa.org)
[3]osIndustrial.pdf (nfpa.org)
[4]Microsoft Word – HANDOUT Arc Flash.doc (osha.gov)
[5]https://www.cedtechnologies.com/arc-flash-arc-blast/
[6]What is Arcing? – Definition from Safeopedia
[7]https://elecsafety.co.uk/what-is-arc-flash/
[8]What is Arcing? – Definition from Safeopedia
[9]Microsoft Word – HANDOUT Arc Flash.doc (osha.gov)
[10]https://www.space.com/17137-how-hot-is-the-sun.html
[11]Electricity and Fire – NFPA 921 (interfire.org)
[12]https://www.ishn.com/articles/112500-in-a-flash-take-steps-to-protect-workers-from-hazards
[13]https://elecsafety.co.uk/what-is-arc-flash/
[14]https://www.ishn.com/articles/112500-in-a-flash-take-steps-to-protect-workers-from-hazards
[15]https://www.ishn.com/articles/96001-arc-flash-statistics
[16]https://energytoday.biz/blog/do-surge-protectors-wear-out

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