An Arc Flash happens during a fault of a short circuit situation that passes through an arc gap. This perilous condition is linked to the release of energy caused by an electrical arc. An electrical arc, on the other hand, occurs when there is loss of insulation between two conductive items at ample potential (voltage). The short circuit power available near high power electrical equipment like service entrance switchgear or transformers is high similar to the energy connected with the electrical arc when a fault occurs. An Arc Flash can be formed through incidental contact which is undervalued for the available short-circuit current, tracking over insulated surfaces and corrosion or degradation of equipment.
Many faults occur during manual operation or switchgear maintenance. Under such circumstances, not only are staff in front of the switchgear and accordingly likely to be deluged by the electrical arc but the fault is typically caused by activities carried out. Such operations include dropping a gadget on live bus bars or closing a circuit breaker under short circuit among others.
The occurrence of an Arc Flash can emit large quantities of deadly energy. The energy expelled by the arc as a result of a fault causes a rise in temperature and pressure in the nearby location. The arc brings about an ionization of the air and the arc flash temperatures become very high, hotter than the surface of the earth. This results in thermal and mechanical stress to adjacent equipment and creates the likelihood of severe injuries within the locality.
The faults that may happen in electrical switchgear are typically;
i. Phase-to-ground fault
ii. Phase-to-phase fault
It is uncommon for a three-phase fault to occur but remember that both phase-to-ground and phase-to-phase faults can quickly result in a three-phase fault. The two faults can be created by accidental contact of equipment or a person with live parts.
Arc Flash Risks and Hazards
The physical effects of an arc flash include:
i. Heating of materials coming into contact with the arc flash
ii. Pressure wave in the surrounding where the arc is created
iii. Possible hazardous sound and light
The main personnel hazards that may arise due to the release of energy created by an arc include:
The kind of temperature produced by the gases of an electrical arc and the emission of burning metal elements can cause severe burns. The heat causes severe burns in humans rapidly within the vicinity of the event. Flames can result in all kinds of burns even carbonization; the incandescent metal fragments can lead to third-degree burns. Flash temperatures liquefy metal parts like aluminum conductors, copper or steel equipment parts. Excessively heated steam results in burns similar to hot liquids and the blazing heat cause less severe burns.
ii. Potential Harmful Sound
The vaporized materials rapidly expand in volumes as it transforms state from solid to vapor generating explosive pressure and sound waves. The electrical arc is a real explosion, and its sound blast makes eardrums to break causing temporary or permanent hearing loss.
iii. Injuries as a Result of Emitted Objects
The electrical arc ejects molten metal or other loose objects that are sprayed by the explosion in the surrounding. Loose objects and metal debris can be deadly objects and can penetrate the cornea. The extent of the abrasions is dependent on the creatures and the kinetic energy of the materials. The area of the eye like the retina and cornea can sustain contusions to the mucosa due to the gases emitted by the arc and release of infrared and ultraviolet rays. The bright flash of the occurrence can cause temporary or permanent blindness. These impacts result in personnel lesions or even worse, death.
iv. Inhalation of Noxious Gases
The fumes created by combusted insulating objects and vaporized metals can be poisonous. The fumes produced are as a result of incomplete combustion and are formed by carbon compounds and other solid substances eliminated in the air.
Arc Flash Hazards is a topic that is undergoing a lot of discussion and investigation in the current safety responsive environment. The essence of the standards is to offer an increased level of protection for electrical workers. There are particular approach boundaries tailored to protect staff while working on or near energized equipment. These limits are:
i. Flash Protection Boundary
ii. Limited Approach
iii. Restricted Approach
iv. Prohibited Approach
There are several ways to protect employees from the risk of electrical hazards. Employees should adhere to the Arc Flash Hazard Label by wearing proper personnel protective equipment (PPE); utilize insulated equipment among other safety-related precautions. This includes not operating on or near circuits unless you are a qualified worker. Other safety standards include the use of arc detection and reduction systems, IP codes and ways of separation, internal arc proof switchgear, and safe work practices.