Ien brief:
- While the threat of shock and electrocution from inadvertent contact with energized parts has long been recognized, the arc flash and arc blast hazards have only fairly recently been incorporated into the electrical safety standards.
- 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.
- Conduct an electrical system study to determine the degree of arc flash hazard.
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.
[pullquote]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.
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.
Ensure the proper tools are on hand for safe electrical work. In addition to PPE, the standards require the employer to furnish other tools for safe electrical work. This includes insulated voltage-rated hand tools and insulated voltage-sensing devices that are properly rated for the voltage application of the equipment to be tested.
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.
Worker protection
Figure 2. Electrical distribution systems contain active components such as circuit breakers that help protect the system in the event an electrical fault occurs.
Maintain all electrical distribution system components. All electrical distribution systems contain active components such as fuses, circuit breakers, and protective relays that help protect the system in the event an electrical fault occurs (Figure 2). These components, called over-current protective devices, have a critical role in protecting the system but are also crucial when it comes to protecting workers from the hazards of arc flash and arc blast. Modern, properly adjusted over-current protective devices that have been well-maintained are able to detect an arcing condition almost instantaneously and clear the fault quickly. This always results in significantly reducing the amount of incident energy that is released.
Many existing electrical distribution systems have old components that have not been well-maintained over long periods of time. In actual field testing of these devices, it is often apparent that their ability to react to an arcing event is much slower than would be the case with a modern, well-maintained device. Unless the protective device optimally reduces the time to clear the fault, the hazard to a worker standing within the flash protection boundary can dramatically increase. In the past, attention to maintenance and condition of these devices in many facilities has not been a primary concern for most facility owners, as in many cases it was not clearly understood that poor condition or inadequate maintenance of the devices presents an elevated safety hazard for workers.
With the current focus on workplace hazards and electrical safety, companies will be more vigilant when it comes to the condition and maintenance of their electrical systems. Chapter 2 of NFPA 70E – 2012 provides a set of requirements for maintenance of electrical distribution equipment. The allocation of a specific chapter to these requirements indicates the importance of electrical equipment maintenance for worker safety.
Changes in NFPA 70E-2012
Several important changes were introduced in the 2012 version of NFPA70E. Employees exposed to shock hazard or those responsible for taking action in case of an emergency must now be trained in the use of automatic external defibrillator (AED) in addition to CPR training. Such training must be certified by the employer on an annual basis. Additionally, the employer shall determine through regular supervision or through inspections conducted on at least an annual basis that each employee is complying with the safety-related work practices. Retraining of workers shall be performed at intervals not to exceed three years.
The requirements for the electrical safety program are bolstered to include electrical safety auditing. The electrical safety program must be audited on a frequency of at least every three years to establish that the principles and procedures of the program are in compliance with the latest standards. Further, field work must be audited to verify the requirements are followed. When the auditing determines that the principles and procedures of the program are not being followed, appropriate revisions to the program or procedures must be made.
One major change to the Hazard Risk Category (Task) Tables 130.7(C)(15) in the 2012 revision of the standard is the relocation of the maximum short circuit current and the fault clearing time of the overcurrent protective device from the table footnotes to the body of the tables. This change was made to emphasize the importance of these limitations on the use of the tables.
Best practices
Appoint an electrical safety program manager. Identify a safety professional from your organization who has vast knowledge and experience within the electrical industry. This should be a well-organized, responsible individual who will take the position seriously. Having a single individual who is familiar with electrical code requirements and other safety issues will pay off.
| Reza Tajali, a registered electrical engineer in several states, is a manager of engineering for Schneider Electric Engineering Services (www.schneider-electric.com). Contact him at [email protected]. |
Maintain and update electrical distribution documentation. Electrical distribution system documentation is another important area that has not been well-managed in many facilities. Documents such as the electrical one-line diagram (essential to safety when performing the lock out/tag out process), short circuit and coordination studies, and other critical documents often are not well-maintained. When system components change due to revisions or facility expansions, this documentation is often not updated to reflect these changes. Lack of attention to documentation management makes the cost and work scope of providing accurate arc flash hazard analysis much greater. Since these documents are such a critical part of electrical safe work practices, lack of attention creates additional legal liability if an accident does occur.
Electrical hazards are a significant safety and financial risk for electrical workers and their employers. While the threat of shock and electrocution from inadvertent contact with energized parts has long been recognized, the arc flash and arc blast hazards have only fairly recently been incorporated into the electrical safety standards. The recent focus on and awareness of arc flash and arc blast hazards will play a critical role in reducing the incidence and severity of electrical accidents over time.