Arc flash

When an uncontrolled arc forms at high voltages, and especially where large supply-wires or high-current conductors are used, arc flashes can produce deafening noises, supersonic concussive-forces, super-heated shrapnel, temperatures far greater than the Sun's surface, and intense, high-energy radiation capable of vaporizing nearby materials.

[3] A typical arc flash incident can be inconsequential but could conceivably easily produce a more severe explosion (see calculation below).

The result of the violent event can cause destruction of equipment involved, fire, and injury not only to an electrical worker but also to bystanders.

Most powerlines use voltages exceeding 1000 volts, and can be an arc-flash hazard to birds, squirrels, people, or equipment such as vehicles or ladders.

[5] High-voltage powerlines often operate in the range of tens to hundreds of kilovolts, which can result in very long arc-flashes, often referred to as a flashover.

Care must usually be taken to ensure that the lines are insulated with a proper "flashover rating" and sufficiently spaced from each other to prevent an arc flash from spontaneously developing.

[citation needed] The character of an arc flash blast is quite different from a chemical explosion (more heat and light, less mechanical shock), but the resulting devastation is comparable.

There are four different arc flash type events to be assessed when designing safety programs: One of the most common causes of arc-flash injuries happens when switching on electrical circuits and, especially, tripped circuit-breakers.

If the voltage is high enough, and the wires leading to the fault are large enough to allow a substantial amount of current, an arc flash can form within the panel when the breaker is turned on.

Motors over two horsepower usually have magnetic starters, to both isolate the operator from the high-energy contacts and to allow disengagement of the contactor if the breaker trips.

Once an arc flash begins in a breaker, it can quickly migrate from a single circuit to the busbars of the panel itself, allowing very high energies to flow.

[8] In addition to the heat, light and concussive forces, an arc flash also produces a cloud of plasma and ionized particles.

The charged plasma may also be attracted to metallic objects worn by people in the vicinity, such as earrings, belt buckles, keys, body jewelry, or the frames of glasses, causing severe localized burns.

[citation needed] Table 130.7(C)(15)(a) lists a number of typical electrical tasks by various voltage levels and recommends the category of PPE that should be worn.

For example, when working on 600 V switchgear and performing a removal of bolted covers to expose bare, energized parts, the table recommends a Category 3 Protective Clothing System.

Various design and equipment configuration choices can be made to affect these factors and in turn reduce the arc flash hazard.

By redirecting the fault current, this action provides robust protection for personnel in close proximity to the arc flash and limits damage to equipment by reducing the exposure time to the high-energy event.

The radiant energy released by an electric arc is capable of permanently injuring or killing a human being at distances of up to 20 feet (6.1 m).

The incident energy of 1.2 cal/cm2 on a bare skin was selected in solving the equation for the arc flash boundary in IEEE 1584.

Remote operators or robots can be used to perform activities that have a high risk for arc flash incidents, such as inserting draw-out circuit breakers on a live electrical bus.

Both the Institute of Electrical and Electronics Engineers (IEEE) and the National Fire Protection Association (NFPA) have joined forces in an initiative to fund and support research and testing to increase the understanding of arc flash.

In a notable industrial accident at an Astoria, Queens Con Edison substation on December 27, 2018 a 138,000 volt coupling capacitor potential device failed which resulted in an arc flash which in turn burned aluminum, lighting up the sky with blue-green spectacle visible for miles around.

The event was extensively covered in social media and LaGuardia Airport temporarily lost power, but there were neither deaths nor injuries.