What Is an Arc Flash? (FAQs)

What is an Arc Flash?

A dangerous release of energy created by an electrical fault. Release will contain:

• Thermal energy
• Acoustical energy
• Pressure wave
• Debris

What Causes an Arc Flash?

The arc can be generated by:

• Mechanical breakdown / failure
• Current overload
• Accidental contact
• Dirt, Debris, Dust, Ionized Air

Arc Flash Intensity

Variables that effect the size and energy of an electric arc flash are:

• Clearing time
• Available fault current
• Amperage
• Voltage
• Arc Gap
• Distance away from arc
• 3 phase v single phase
• Confined space

What Type of Equipment Can Cause an Arc Flash?

Typical equipment can be:

• Motor Control Centers (MCC's)
• Circuit Breakers
• Disconnects
• Metering Devices (remove - install)
• Panel Boards
• Switchgear (low and high voltage)
• Transformers
• Junction Boxes
• Buss Way
• Any Live Electrical Conductor

What is my risk to being exposed to arc flash?

The exposure to arc flash depends on the following:

• Number of times the workers perform a task involving exposed live equipment.
• Complexity of the task performed; need to use force, available space, safety
• Margins, reach, etc.
• Training, skills, mental and physical agility, coordination with helper
• Tools used
• Condition of equipment

What standards regulate arc flash hazards?

There are four main regulations governing arc flash. They include:

• OSHA Standards 29-CFR, Part 1910Occupational Safety and Health Standards.1910 sub part S (electrical) Standard number 1910.333 specifically addresses Standards for Work Practices and references NFPA 70E.
• The National Fire Protection Association (NFPA) Standard 70 – 2009" The National Electrical Code" (NEC) contains requirements for warning labels.
• NFPA 70E 2000provides guidance on implementing appropriate work practices that are required to safeguard workers from injury while working on or near exposed electrical conductors or circuit parts that could become energized.
• The Institute of Electronics and Electrical Engineers (IEEE) 1584 – 2002Guide to Performing Arc-Flash Hazard Calculations.

What data is required to be on the new arc flash warning labels?

Labels shall include more information on the specific parameters of the hazard including:

• Available Short-Circuit Current
• Flash Protection Boundary
• Incident energy at 18" expressed in cal/cm2
• PPE required
• Voltage shock hazard
• Limited shock approach boundary
• Restricted shock approach boundary
• Prohibited shock approach boundary

Arc Energy Basics

• Exposure energy expressed in cal/cm2
• 1 cal/cm2 = hottest part of the flame from a lighter for 1 sec
• An exposure of only 1-2 calories will cause second degree burn on human skin
• Typical non-FR "workwear" can ignite at energies as low as 2 calories
• Reports indicate that 80-90% of job tasks have hazards with the potential to release up to 8 cal/cm2

Arc Flash Events

• Arc temp can reach 35,000 F
• Copper expands 67,000 times when vaporized
• Fatal burns can and do occur at >10 feet
• Per OHSA, 80% of electrically related accidents, incidents and fatalities among qualified workers are caused by Arc Flash