An arc flash can be caused a number of ways, including:

• Accidental contact with energized parts
• Inadequate short circuit ratings
• Tracking across insulation surfaces
• Tools dropped on energized parts
• Wiring errors
• Contamination, such as dust on insulating surfaces
• Corrosion of equipment parts and contacts
• Improper work procedures

As you would expect, proper procedures, tools and maintenance can prevent most arc flash situations from occurring.