Understanding “Arc Flash”
Simply put, an arc flash is a phenomenon where a flash over of electric current leaves its intended path and travels through the air from one conductor to another, or to ground. The results are often violent and when a human is in close proximity to the arc flash, serious injury and even death can occur.
Arc flash can be caused by many things including:
– Dropping tools
– Accidental touching
– Material failure
– Faulty Installation
Three factors determine the severity of an arc flash injury:
1. Proximity of the worker to the hazard
3. Time for circuit to break
Because of the violent nature of an arc flash exposure when an employee is injured, the injury is serious – even resulting in death. It’s not uncommon for an injured employee to never regain their past quality of life. Extended medical care is often required.
Typical Results from an Arc Flash:
– Burns (Non FR clothing can burn onto skin)
– Fire (could spread rapidly through building)
– Flying objects (often molten metal)
– Blast pressure (upwards of 2,000 lbs. / sq.ft)
– Sound Blast (noise can reach 140 dB – loud as a gun)
– Heat (upwards of 35,000 degrees F)
The four types of electric arcs:
1.Open air arc – The primary arc used in arc testing
2.Arc-in-a-box – Used in one form for arc testing in the EU
3.Ejected Arc – When arc plasma hits the worker
4.A tracking arc – Most common at higher voltages, arc plasma conducts on skin or through clothing
Only the first two are considered in the calculations and standards. The open air arc is well understood.
In lab testing, we control movement of the arc for the sake of repeatability, but in real life from 480V higher the open air arc can quickly turn into an ejected arc or a tracking arc. The tracking arc is most common at very high voltages or during an electrical contact.