• Three families will never be the same again.
Post evaluation • No hazard analysis. • Workers could not cite the three hazards in the workplace. • Workers were not properly trained. • Workers were wearing polyblend clothing. • All three workers were within the flash protection boundary.
End results • Lost three long term employees • OSHA citaƟon and fine • NegaƟve publicity • LiƟgaƟon
4. ARC BLAST A release of mechanical, acoustical, thermal, and optical energy from an electric arc.
The Electrical Arc Blast • The air contains chemical property can expand several thousand times than its normal volume when heated to high temperatures. • When the air within an electrical equipment room is superheated to more than 10,000 ºF ~ 5530⁰C in less than 1 second, the air rapidly expands, generating a pressure wave that pushes outward from the arc source. • This pressure wave is experienced as an explosion and is recognized in electrical vernacular as an arc blast.
The arc blast presents three principle dangers to humans: 1) The concussive force of the blast can directly cause physical trauma similar to that caused by any type of explosion. Studies have shown that pressure can build to more than 15,000 times atmospheric pressure within the first 5 ms of arc initiation (Wactor, Miller, Bowen, et al., 2000). Pressure of this magnitude can easily exceed the structural strength limits of metal enclosures and cause injury to anyone in the vicinity of the arc blast. 2) The blast provides the propellant for projectiles (e.g., partially melted metal parts, broken insulators) that present a serious hazard to anyone in the vicinity. 3) The blast can blow the enclosure doors open, releasing hot gases and molten metal into the area near the electrical equipment. These hot gases and molten metal present significant burn hazards to those in the vicinity.
Some arc blast facts to think about • An arc blast can be 35,000° F, which is hotter than the surface of the sun. • The force of an arc blast can splat you against a wall 10 feet away. • The intense light and sound of an arc blast can destroy your vision and hearing instantly. • The average cost of a major arc flash incident with personal injury is 25 million dollars.
Three primary hazards associated with an arc-blast. (1) Burn • Arcing gives off thermal radiation (heat) and intense light, which can cause burns. • Several factors affect the degree of injury - skin color, area of skin exposed, and type of clothing worn. • Proper clothing, work distances, and overcurrent protection can reduce the risk of such a burn. (2) Explosion • A high-voltage arc can produce a considerable pressure wave blast. • A person 2 feet away from a 25,000-amp arc feels a force of about 480 pounds on the front of the body.
- Winter '17
- Alternating Current, electrical shock, arc flash