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By Reza Tajali, Schneider Electric
Electrical hazards cause more than 300 deaths and 4,000 injuries in the workplace each year. In fact, electrical accidents rank sixth among all causes of work-related deaths in the United States, according to the Electrical Safety Foundation International (www.esfi.org). The injuries and fatalities that result from arc flash incidents, shock, and electrocution are always devastating to the workers and their families. Additionally, the financial consequences of such events can be very damaging to the employer.
“Many existing electrical distribution systems have old components that have not been well-maintained over long periods of time.”
There are important steps that companies can take to reduce the occurrence of electrical accidents and better protect the worker and the employer from the physical, financial, and statutory consequences of electrical accidents. Following are the required steps for reducing the risk of electrical accidents. These steps are part of the National Fire Protection Association (NFPA) requirements, in its standard 70E 2012, which is a detailed reference for providing electrical workplace safety.
Clearly, the fundamental requirement for electrical safety is always to place electrical equipment in an electrically safe condition whenever possible through a proper lock out/tag out procedure. But NFPA 70E 2012 provides additional best practices for electrical safety, and these are recognized and enforced by OSHA.
Establish an electrical safety program with clearly defined responsibilities. This document is created by the employer and covers all areas of the company’s electrical safety policies. It includes such things as lock out/tag out procedures, safe work practices, and responsibilities for electrical safety.
Figure 1. The incident energy potential will define the hazard/risk category of personal protective equipment that an employee is required to wear.
Conduct an electrical system study to determine the degree of arc flash hazard. This is an electrical system engineering study that is performed by engineers familiar with the power distribution and control equipment and the calculation methods required. The arc flash analysis will determine, among other things, the incident energy potential of each piece of electrical distribution equipment in the facility. This incident energy potential will define the personal protective equipment (PPE) that the employee is required to wear while performing any work when energized parts are exposed (Figure 1). The methodology for conducting these arc flash analyses is outlined in IEEE 1584 Guide for Performing Arc-Flash Hazard Calculations.
One alternative to a detailed arc flash analysis that is permitted in NFPA 70E 2012, Article 130.5 Exception, is to use the task tables in 130.7(C)(15) to determine the required PPE hazard risk category. The tables have usage limitations as is now stated in the body of the tables. These limitations typically specify a range of available fault current and clearing time for the upstream over-current protective device beyond which the tables may not be safely used. Unless a detailed arc flash analysis has been performed, users will usually not know these details, and this commonly leads to misuse of the task tables, which can lead to under-protection for the worker.
The task tables are based on calculated arc flash energy values within the stated limits of fault current and overcurrent protective device opening time. But they also include the probability of causing an arc flash based on the task being performed. This probability factor is highly variable and subjective and can potentially lead to significant under-protection. Relying on a detailed arc flash analysis for PPE selection is always a preferred and more accurate method.
Apply warning labels to all equipment. The current NEC requirement for application of hazard warning labels on electrical equipment, the National Electrical Code (NEC) 2011, doesn’t require that the specific information, such as the PPE hazard/risk category, incident energy, boundary distances, and other data that would be provided by the arc flash hazard analysis, must be included on the label. However, the current NFPA 70E 2012, in Article 130.5(C). has elevated the labeling requirement by stating that the equipment must contain the incident energy, PPE level, or hazard risk category. Additionally, voltage rating and the arc flash boundary must be marked on the label.