Your San Francisco electrician has your best interest at heart when it comes to electrical safety. Learn here about a common cause of electrical accidents. And be sure to call your electrician should you need any assistance with electrical repairs or for a technician to perform a safety inspection.
Arc flash is a short circuit through air that flashes over from one exposed live conductor to another conductor or to ground. Arc flash incidents are common and costly, and the frequency of reported accidents is increasing – making arc flash a very hot topic within OSHA and the overall safety industry.
What Causes Arc Flash?
Arc flashes can be caused in a variety of ways:
- Just coming close to a high-amp source with a conductive object can cause the electricity to flash over.
- Dropping a tool or otherwise creating a spark can ignite an arc flash.
- Equipment failure due to use of substandard parts, improper installation, or even normal wear and tear.
- Breaks or gaps in insulation.
- Dust, corrosion or other impurities on the surface of the conductor.
How Common Is Arc Flash?
- In the past, if someone suffered burns in an electrical accident, people thought the burns were caused by the electrical shock passing through the body. Electrical shocks can cause burns. But what research has shown is that most burns from electrical accidents actually come from arc flash.
- According to the NFPA 70E-2004 standard, the majority of hospital admissions due to electrical accidents are from arc flash burns, not from electrical shocks. Of the approximately 350 persons killed in the work place by electricity last year, roughly 50% were related to arc flash
- A report compiled by Capelli-Schellpfeffer, Inc., estimates that five to 10 arc flash explosions happen in the USA every day, resulting in 1 to 2 deaths per day.
- That figure only takes into account incidents where victims were sent to special burn centers. The number does not include cases sent to regular hospitals or clinics, nor unreported cases or near misses.
- NFPA 70E-2012 states that each year more than 2000 people are admitted to burn centers with severe arc flash burns.
Injuries from arc flash accidents tend to be very severe, and result from two types of hazards: arc flash and arc blast.
Arc Flash: Electric arcs produce intense heat, and can heat the air to temperatures as high as 35,000 degrees Fahrenheit. This is 4 times the surface temperature of the sun. Fatal burns can occur when the victim is several feet from the arc. Serious burns and fatalities are not uncommon at a distance of 10 feet. An arc flash will also cause ignition of clothing which will only add to the severity of the skin burns. Arc flash can cause the following injuries:
- Skin burns by direct heat exposure
- Second degree skin burns from exposure of unprotected skin to an electrical arc flash with incident energy above 1.2 cal/cm2
- Metal is vaporized at this temperature. Droplets of molten metal can be propelled over great distances, causing serious burns or igniting clothing.
- High-intensity flash can also cause damage to eyesight.
Arc Blast: A high-energy arcing fault can produce a considerable pressure wave and sound blast. The intense heat from arc causes the sudden expansion of air, resulting in a blast. A 10,000 A arc at 480 volts is equivalent to 800 MW or approximately 8 stick of dynamite. Pressure on the chest can be as high as 2000 lbs/sq foot, causing lung collapse.
In some cases, the pressure wave has sufficient energy to snap the heads of 3/8-inch steel bolts and to knock over construction walls. Moreover, it can send metal parts flying at speeds over 700 miles per hour. Arc blast can cause the following injuries:
- Loss of memory or brain function from concussion
- Hearing loss from ruptured eardrums (The sound associated with blast can exceed 160 dB. The sound of jet engine only 145 db!)
- Shrapnel wounds from metal parts
- Other physical injuries from being blown off ladders, into walls, etc.