Arc Flash

An arc flash is an explosive electric shock. The initial heat produced by an arc flash may burn hotter than the surface of the sun (10,000 degrees Fahrenheit).

An arc flash event involves several dangerous conditions that occur simultaneously. These can include a bright flash, an explosive expansion of molten metal, a loud concussive blast, thermal radiation, and an intense flow of electric current.

Arc flashes and electrical incidents generally result from three common root causes:

• Working on unsafe equipment and installations
• Working in an unsafe manner
• Working in unsafe environments

The term "arc blast" is sometimes used specifically to discuss the concussive pressure wave that occurs during an arc flash. An arc flash's explosion is extremely loud.

The concussion that occurs during an arc flash is very hazardous to the human body. In 1996, the Institute of Electrical and Electronics Engineers (IEEE) conducted a test using a dummy to measure the various conditions at play in an arc flash. The pressure sensors measured pressures of 2,160 pounds per square inch (psi), and the audio sensors measured 141.5 decibels at a two-foot distance, both of which were values well above the thresholds for permanent injury to the human body.

The pressures involved in an arc flash are huge and sufficient to collapse the lungs of those in close proximity. Nearby workers can be propelled into other objects in the area, causing blunt-force injuries.

Permanent hearing loss can also result from the volume of the blast, and disorientation can lead to a worker encountering other hazardous conditions. Note that standard hearing plugs do not provide sufficient protection to prevent hearing loss at the noise volume generated by arc flashes.

To learn more about MSHA Part 48 training requirements visit our MSHA Part 48 Subpart B Surface Mining Online Training web page.