Arc Flash Boundaries
Ensure Electrical Safety by Following New Arc Flash Guidelines
Written by Jack Rubinger
Arc Flash occurs when an electrical short-circuit produces a high-energy, high-temperature explosion. These occurrences are known to propel molten metal and other debris through the air, endangering anyone nearby. Explosions of this nature can damage a person's eyesight, hearing and even cause severe burning or death.
Arc flash facts are "enlightening":
- Five (5) to ten (10) arc explosions occur in electric equipment every day in the US, according to statistics from CapSchell, Inc.
- Electrical arcs produce some of the highest temperatures known to occur on earth, up to 35,000°F (19,426 °C) – 4x the temperature of the surface of the sun which is about 9000°F (4982°C).
- Arc Flash may be caused by a tool, rodent or other element in a breaker or service area, that could compromise the distance between energized components. Incidents often occur when equipment hasn't been properly de-energized.
There are 8 boundary zones to Arc Flash. The flash protection boundary is an imaginary sphere that surrounds the potential arc point "within which a person could receive a second degree burn if an electrical arc flash were to occur," according to NFPA 70E. This standard also defines the incident energy level as "the amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event."
At the core or center the exposure is the greatest. This is any point on an exposed, energized electrical conductor or circuit part. Moving outward the arc flash boundaries are:Click for larger display
Given the unpredictability of arc flash, having an arc flash safety game plan in place is critical. Put some serious time and thought into who you want to reach and what you want to accomplish. Ensuring that you have the right precautions in place, correct personal protection equipment (PPE) and general awareness of the hazards can be the difference between finishing the job or being involved in an accident.
"Effective electrical safety programs begin with achievable goals. Many organizations pursue safety training, arc flash hazard analysis, PPE selection, labeling and electrical safety program development as independent projects, when for an effective safety program, they are really interdependent. Strategic planning can reduce program investment, implementation time and provide enhanced worker safety," said Gary P. Larkins, APS/PowerSafetyPRO.
A comprehensive arc flash/electrical safety plans must address:
- Tools/equipment, including labeling systems
"Unfortunately, arc flash studies aren't an exact science. They are snapshots, based on current utility information. As the grid fluctuates over time, so does the hazard exposure. A change in a utility substation transformer will change the calculation results for the electrical distribution equipment of a facility," said Dave Hill, Intertek Testing.
Below is an overview of current arc flash information from NFPA, ANSI, IEEE and NEC:
- NFPA 70-2011/NEC is the driving document for all electrical installations. The other NFPA, ANSI/UL, IEEE, NEMA and harmonized IEC documents refer back to the NEC for installation practices.
- NFPA 70-2011/NEC Section 110.16 and the Informational Note reference NFPA 70E for guidance of Arc Flash and PPE as well as ANSI Z535.4 for safety warning signage.
- NFPA 70-2011/NEC Section 670.3(A) requires industrial electrical equipment and control panels to have a permanent label denoting short-circuit current rating of the control panel with references to UL 508A Supplement SB as an example of determining the SCCR. Section 409.22 and 409.110(4) are the references for industrial control panels specifically.
- NFPA code calls for labeling electrical panels, disconnects and access points to inform those servicing equipment of potential arc flash hazards present based on studies of the electrical system feeding each location.
- NFPA 70E requires workers to document arc flash analysis calculations used for electrical equipment labeling. Even though NFPA 70E and IEEE 1584 provide standardized calculations for an arc flash analysis, other methods exist, opening the door for variation. Posting key elements of your analysis on electrical equipment will help you remember the methods used after a job is complete.
NFPA (70E) requires that employers quantify the exposure of employees to arc flash. Labels must specify the actual levels of hazard, boundaries required and the proper PPE.
New industrial labeling systems are mobile, compatible with many types of software and empower end-users to quickly create custom safety, hazard and warning signs and labels on-site, in sequence. Displaying arc flash calculations on an industrial label offers valuable information to electrical workers, inspectors and emergency responders.