To cross the boundary into the restricted space while the equipment is still powered, personnel need to have been trained, have a written and approved plan for the work they’ll perform, and be wearing the correct PPE. The Restricted Approach Boundary: This boundary is in close proximity to a shock hazard and may only be crossed by qualified persons. Also, unqualified persons may cross the limited approach boundary if escorted by a qualified person and with appropriate PPE. The distance is based on the voltage of the equipment and can only be crossed by a trained and equipped person if necessary. The Limited Approach Boundary: This is the minimum distance from energized equipment where unqualified and unprotected persons may safely stand. If a worker has to cross the boundary to handle a task, they must wear appropriate personal protective equipment (PPE), such as flame resistant (FR) clothing, to protect them from life-altering injuries. When an arc flash hazard exists, workers must be able to determine their relative risk and a safe distance from the equipment in order to limit injuries to a treatable level. And while second-degree burns are not desirable, they’re treatable, unlike third-degree burns that could be sustained by individuals closer to the source of an arc flash.

In such a case, the Incident Energy value of an arc flash would be 1.2 cal/cm² for 1.0 second. The NFPA 70E shows an Arc Flash Boundary, which determines the distance from the equipment within which a person could receive a second-degree burn in the event of an arc flash. For this reason, NFPA 70E includes a “safe distance” to minimize the risk of burns and other arc flash injuries to individuals in proximity to energized electrical equipment. The extreme, radiant heat given off by an arc spreads out in all direction, getting weaker as it dissipates farther from the source. What is Considered a Safe Distance From an Arc Flash? Arc flashes can destroy property and lead to the death of personnel present within the arc flash boundary. Other arc flash injuries include nerve damage, hearing loss, blindness, and cardiac arrest. Worse, clothing can be ignited and the synthetic fabrics can be melted to skin. The burns are caused by extreme heat and metal molten splatter. Staged tests have shown temperatures of up to 437 degrees F on the hands and neck of an individual standing at a distance of 10 feet from an arc blast. What’s more, the combination of pressure and fire will blow electrical equipment apart, sending blast shrapnel into a worker’s body.Īn arc flash can cause second- and third-degree burns if the victim is several feet from the arc. The explosion has enough force to push a worker off a ladder or throw them across rooms, rupture eardrums, or collapse a worker’s lungs. The intense heat results in a sudden expansion of air, which causes an invisible arc blast with a very high air pressure wave.

Inappropriate operation of a load break switchĪn electrical arc flash can reach temperatures of up to 35,000 degrees F, about four times the temperature of the sun’s surface.

Corrosion on poorly maintained equipment.

when workers carelessly drop tools on live parts or when they fail to ensure that equipment is properly de-energized. Incidents of arc flashes often occur by human error, e.g. The flash is immediate and happens in a fraction of a second, but the consequences can be devastating for anything in its path. The plasma will then conduct energy, resulting in the release of massive energy that burns the bus bars, vaporizes the copper, and causes a fiery explosion.

The cause of the short typically burns away after a few seconds but highly conductive plasma (ionized gases) is established to sustain the arc fault. The term “arc flash” describes an unwanted, rapid, and dangerous electric discharge that travels through the air due to an arcing fault between several electrical conductors. Tags: arc flash safety, preventing arc flash

Arc flash boundaries