Purpose: This paper reviews arc flash hazards and techniques to mitigate associated personnel risks.
What is an Arc Flash Hazard?
An arc flash is a complex phenomenon gaining increased understanding and attention in electrical safety. Arcs are basically ionized gases caused when electricity travels through air. You may have heard the terms “arc flash”, “arc blast” or “electric arc” which are all different names for the same phenomenon.
There are three primary risks associated with electrical arcs from a personnel safety point of view:
▪ Thermal
▪ Pressure Wave
▪ Current Flow
Electricity begins to travel through air due to a breakdown of insulation, causing the air to ionize, spinning off outer shell electrons. This ionization has two effects: blast and radiation release. The blast is a function of the fault current, container size and other parameters including magnetic forces. The ensuing pressure wave is not as well documented as the thermal effect but can also present personnel risks.1
Example of Arc Blast Radiation Release. Image from www.nopsema.gov.au
Arc Flash Regulations and Standards
To assist OSHA in regulating electrical safety, the National Fire Protection Association developed NFPA 70E: Standard for Electrical Safety in the Workplace. Although not adopted as law under OSHA, NFPA 70E is the standard used in the industry for evaluating and mitigating risks whereas OSHA focuses on safety requirements. Meeting NFPA 70E requires a hazard assessment be conducted for arc flash risks at electrical equipment located in the workplace. Both NFPA 70E and IEEE 1584-2002 – Guide for Performing Arc Flash Hazard Calculations provide methods for performing the calculations and establishing arc flash boundary zones.
Understanding the Arc Flash Boundary
The National Fire Protection Association (NFPA) recommends identifying two boundaries to define the safe working limits for personnel working in an area with shock hazards. Each area is associated with a level of training and PPE. NFPA 70E Tables 130.4(D)(a) (ac voltages) and 130.4(D)(b) are used based on the nominal voltage of the equipment.
The arc flash boundary (AFB) is the minimum ‘safe’ distance from exposed energized conductors or circuit parts that has a potential for an arc fault. It is defined as the distance at which, in the event of an arc flash, a worker would be exposed to a thermal event with incident energy of 1.2 cal/cm² for 1.0 second. With this exposure, a worker may receive the onset of a second degree burn to exposed skin, typically the neck, face and hands. If it is necessary for workers to cross the arc flash boundary, and potentially be exposed to higher incident energies from any arc flash, they must be wearing appropriate personal protective equipment (PPE).
The required arc-rated clothing and PPE increases rapidly as a worker approaches the potential source of an arc flash. Incident energy, the heat generated by an arcing fault, increases by the inverse square of the distance (the Inverse Square Law) as it is approached. More simply stated, the incident energy increases rapidly as the distance decreases. When troubleshooting or performing any other task where there is a potential for an arc flash, workers should always be aware of their body position and working distance.2
Required PPE Categories to Enter the Arc Flash Boundary Zone as Defined by NFPA70E Table 130.7(C)(15)(c)
AWC IntelliPower System – PPE Category 0 (or less)
The above arc flash boundary zone and PPE equipment categories are designed to limit injury in the event of an arc flash incident when personnel are present. If we remove personnel from the arc flash boundary for monitoring and operating equipment, then the likelihood of injury or death approaches ZERO.
The AWC IntelliPower System allows remote connectivity to protective relays in new or existing installations allowing data monitoring and breaker operation outside of the arc flash boundary.
Example of AWC IntelliPower Monitoring and Control System
AWC Support:
For more information, please reach out to the local Power Specialists in your area. You can find them anytime via online chat at www.awc-inc.com or by contacting your local AWC office.
You can also reach out to the AWC Power Distribution and Protection Group at powerdistribution@awc-inc.com.
References:
1. What is an Arc Flash? Retrieved from https://www.e-hazard.com/learn/arc-flash/what-is-arc-flash.php
2. Understanding the Arc Flash Boundary. Retrieved from https://www.fluke.com/en-us/learn/best-practices/safety/arc-flash-and-arc-blast/understanding-the-arc-flash-boundary
