Arc-Flash Hazard Analysis
'Putting the Pieces of the Puzzle Together'

John Lane, PE
Electrical Safety Engineer
AVO Training Institute

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Introduction
Two industrial electricians began work in the basement electrical room one day. They wanted to take some physical measurements and knew the switchgear was energized but were in a hurry to get started. As they were taking measurements on the bus with a wooden ruler the metal tip of the ruler made contact with the bus and caused a massive electric arc. The arc-flash only lasted a fraction of a second. Although no one was electrocuted, one man died instantly from the arc-flash and the other man was badly burned. The man that died was within 24 inches of the bus while the other man was about ten feet away.

The objective of OSHA, NFPA, ASTM, IEEE, and others is to protect the worker from electrical hazards. Potential hazards from electricity include shock, arc-flash, and arc blast. This paper will focus on arc-flash and its analysis. When the insulation medium, between phases or phase and ground, whether air, porcelain, polymer, or other medium can no longer support the applied voltage an electrical arc is formed. A short circuit or insulation breakdown is a switching action that creates a bypass around a circuit which involves either phase-to-phase or phase-to-ground or a combination. The heat generated by the high current flow may melt or vaporize the material and create an arc. This arc-flash creates a brilliant flash, intense heat, and a fast moving pressure wave that propels the arcing products.

While commercial electricity has been around for over 100 years, the most common hazard of electricity has been electric shock or electrocution. As commercial electric systems grew, other hazardous effects such as arc-flash and arc-blast began to surface. The initiation, escalation, effects, and prevention of electrical arcs have been analyzed and researched since the early 1960's. Human errors and equipment malfunctions contribute to the initiation of an electrical arc. Engineering design and construction of arc resistant equipment as well as requirements for safe work practices are continuing to target the risk of electrical arc-flash hazard. As the demand for electricity increases, transmission and distribution utility systems are being upgraded. Transformers are being upgraded or replaced with higher KVA ratings and lower impedances at both the utility and industrial/commercial level. Also, as the demand for higher reliability also increases, transformers are being operated in parallel by closing a tie breaker. All of these modifications to the system can cause dramatic increases in the available fault current. More electrical energy throughput is a result of these modifications; however the downside is an increase in the electrical current to feed a fault to existing equipment in industrial and commercial facilities that may now be under-rated to interrupt available fault current. This increase in available fault current can wreak havoc on under-rated and/or improperly maintained equipment.

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