Electrical workers face risks every day in their job. One of these risks is injury from an electric arc flash. Arc flashes are sudden and highly unstable energy discharges that often occur due to improper work techniques and abnormal conditions in energized electrical equipment. Enertia Engineering Ltd., with the support of ESPS Electrical Safety Program Solutions INC. (ESPS), has made it their mission to increase the safety of electrical and non-electrical workers. Through ESPS’s Electrical Safety Services Consulting (e.g. Electrical Safety Auditing, Electrical Safety Program development, and Workplace Electrical Safety Training) and Enertia Engineering Ltd.’s engineering-based Arc Flash Hazard Analysis and Mitigation services, employers are able to mitigate or minimize the risk of electrical hazard exposure to their workers.

Typically Arcing happens when a current passes through vapour which is between two live conductors.  OK, what causes it and how is it eliminated.
Well,  it could be caused by any number of factors including old plant breaking down, tools accidentally dropped or become a conduit,  insulation breaking down, too much voltage, dust, corrosion, condensation take your pick.
But we have protection so why should we worry,  If there is a problem, then incident energy increases and as the arcing current is smaller than a normal fault due to the vapour acting as impedance the fault current is often lower than the instantaneous trip setting of the protection.  Therefore a lower fault current could be a longer trip time and greater release of energy.  So a lot of may be, might be , could be.  But with very painful results
From an Electrical Safety perspective, its something that needs to be understood and any issues found and fixed.