The Hazards of Electricity – Do You Know What They Are?
The three main hazards of electricity are electric shock, electrical arc-flash, and electrical arc-blast. OSHA statistics show that several hundred deaths occur annually as a result of electric shock. This number has come way down since the introduction of GFCIs but is still a tragedy on an enormous scale. Studies also show that 10-15 employees are hospitalized every day with arc-flash burns. It is for these reasons that it is important that everyone understands the hazards of electricity.
Electric Shock
Electric shock occurs when a person’s body completes the current path between two energized conductors of an electrical circuit or between an energized conductor and a grounded surface or object.
Electrical Arc-Flash
There seems to be a serious misconception in the industry that electrical arcs are a product of only high voltage. Actually, electrical arc-flash is not voltage sensitive but is more a product of short-circuit current and clearing time or arc duration. In some cases, it is possible to generate higher arc energy from a low-voltage source than from a high-voltage source. The amount of energy will in turn determine the temperature of the arc, which can reach 20,000°K (Kelvin) or about 35,540°F.
Electrical Arc-Blast
According to studies on the subject, the pressures from an arc are developed from two sources, the expansion of metal in boiling and vaporizing, and the heating of air by passage of the arc through it. Copper expands by a factor of 67,000 times when it vaporizes. This accounts for the expulsion of near-vaporized droplets of molten metal from an arc. These droplets can be propelled for distances of up to 10 feet (3 m). Plasma (ionized vapor) is also generated outward from the arc for a distance proportional to the arc power. One inch³ (16.39 cm³) of copper vaporizes into 1.44 yards³ (1.098 m³) of vapor. The air in the arc stream expands in warming up from its ambient temperature to that of the arc, or about 20,000°K (35,540°F). The arc-blast created by the heating of the air is similar in nature to the generation of thunder by the passage of lightning through it.
Go to the following link to read the full report presented at the 2006 IEEE IAS Electrical Safety Workshop, February 7-10, 2006, Philadelphia, Pennsylvania.
http://www.ewh.ieee.org/cmte/ias-esw/pdfs/Hazards_of_Electricity.pdf
Edited By
David Herres
Wildernesslight1@aol.com
http://www.electriciansparadise.com.
Herres Construction Co.
Balsams Grand Resort Hotel
