How to Analyze Your Arc Flash Risk
Arc energy is a function of the short-circuit current and how quickly it is removed by the protective devices such as relays, breakers and fuses during an arc flash incident. In order to perform an arc flash analysis, the engineer has to determine the available three-phase fault current and the operating characteristics of the protective devices credited with the clearing of the fault that is associated with the arc flash. Therefore, the engineer has to model the electrical power system, input the required system data, and set the over-current relays and protective devices in a software program that is designed for conducting arc flash analysis based on IEEE standard 1584 or NFPA 70E. This process is known as performing short-circuit and coordination studies.
Once these studies are completed, then arc flash analysis can be performed to calculate the various parameters of the arc flash hazard. It should be noted that it takes an experienced engineer who is well-versed in the art of protection and coordination of power systems to implement the above steps correctly. Because this is a complex process that requires expertise and computer modeling capabilities, the studies and analysis should be performed only by a qualified electrical engineer or engineering firm.
The regulations are clear: an employer has an obligation to protect workers from known hazards. An effective arc flash and electrical safety program can save lives and losses that may result from an arc flash or shock event. Prudent building owners, operators and managers should seek guidance on and evaluation of their arc flash hazards risks to avoid penalties for failing to comply with OSHA regulations, costs associated with downtime and repair, and liability resulting from an injury or fatality.
Paul Gill, PE, is president of Electrical Power Technology, LLC, a firm specializing in power system studies and analytics. Gill has 45 years of experience in the utility industry and served for 27 years on the Nuclear Regulatory Commission. He has written three books on power system analysis, testing and maintenance.
Arc Flash Hazard Analysis
An arc flash hazard analysis is performed to calculate the "incident arc energy," or level of risk, at every point in the electrical power system of the building where workers may be required to switch or work on energized equipment. The process includes creation of one-line diagrams to represent the building electrical power system, performance of a short-circuit and coordination study, calculation of arc-fault energy, determination of personal protective equipment (PPE), and labeling of the electrical equipment to bring the facility into compliance with the regulations.
The arc flash analysis itself identifies the incident energy at each point to enable proper labeling of the equipment, which in turn, enables workers to identify approach distances and boundaries and the use of correct PPE to make them safe from an arc flash event.
The arc flash hazard analysis comprises the following steps:
- Collect the system data and build the electrical model
- Determine the system modes of operation
- Calculate the bolted fault currents
- Determine the arcing fault currents
- Determine protective device characteristics and the duration of the arc
- Determine the system voltages and classes of equipment
- Select the working distances
- Determine the incident energy for all equipment
- Determine the flash boundary for all equipment
- Select the PPE Category from NFPA 70E-2009
- Label each piece of equipment with arc flash labels
— Paul Gill