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By Steven Maling, Schneider Electric
Five to 10 times per day in the United States, a worker is severely injured or killed in an electrical arc flash accident. Other electrical incidents can also injure workers; these typically involve accidental contacts with energized parts that result in shock and electrocution. The injuries and fatalities that result from these accidents are always devastating to the workers and their families. Additionally, the financial consequences of such events can be very damaging to the employer.
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. Many of these steps are required as part of the National Fire Protection Association (NFPA), in its standard 70E 2009, which provides a detailed reference for facilities to meet the requirements of electrical workplace safety. Additional steps are recommended and considered best practices for improving overall safety within a facility.
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 2009 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 is a written document created by the employer that covers all areas of the company’s electrical safety policies and includes such things as lock out/tag out procedures, internal safety policies, 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 hazard/risk category of 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 2009, Article 130.3 Exception Number 2, is to use the task tables in 130.7(C)(9) to determine the required PPE hazard risk category. The tables have usage limitations as stated in the footnotes. The footnotes 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 some calculated values within the limits of the stated footnotes but 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. Since NFPA 70E 2009, Article 130.3(C), now requires the equipment be labeled with either the incident energy in calories per square centimeter or the PPE hazard risk category, using the tables creates a problem with labeling, as well. Relying on a detailed arc flash analysis for PPE selection is always a preferred and more accurate method.
Conduct safety training for all workers. NFPA 70E defines a qualified person as “one who has skills and knowledge related to the construction and operation of the electrical equipment and systems, and has received safety training to recognize and avoid the hazards involved.” This training requirement means that the employee must have received safety training specific to the hazards of arc flash, arc blast, shock, and electrocution. Electrical workers are not considered to be qualified by OSHA until they have received this specific training.
Ensure there is adequate personal protective clothing and equipment on hand. Employees working in areas where there are potential electrical hazards shall be provided with electrical protective equipment that is appropriate for the specific parts of the body to be protected and for the work to be performed. This can include fire-resistant shirt, pants or coveralls, or a multi-layer flash suit.