Arc Flash In Data Centers
It only takes a second for an arc flash incident to occur. If the insulation or isolation between electrified conductors cannot withstand the applied voltage, an electrical current passes through the air, resulting in a powerful blast similar to an explosion and producing temperatures up to four times hotter than the surface of the sun. Arc flash wreaks instant havoc on anything and anybody in its path, and can even injure someone standing more than 10 ft from the fault source. It all happens in the blink of an eye, but the resulting consequences are long-lasting, and in some cases, permanent.
The Institute of Electrical and Electronics Engineers (IEEE) reports that 2,000 workers are admitted to burn centers each year for extended injury treatment caused by arc flash, and the National Safety Council reports that electrical hazards like arc flash cause nearly one workplace fatality every day. That’s a price no business can afford to pay.
If an arc flash incident does occur in a mission critical facility, and workers are lucky enough to escape serious injury from the resulting blast, the facility will likely still pay a high price in terms of equipment and facility damage and business disruption. Data centers that experience arc flash incidents may also face legal liability, increased insurance premiums, and hefty regulatory fines.
Clearly, there is a pressing need to prevent arc flash incidents. But in many data centers, that is easier said than done. Greater overall energy usage and higher system voltages and available fault currents have increased the risk of arc flash hazard within data centers and other facilities too. In mission critical facilities in particular, where electrical equipment may not be taken offline for service, the likelihood of such an incident escalates even more.
For these reasons, data center and facility managers must exercise due diligence to protect their people and their businesses. This begins by first identifying where arc flash hazards exist, and then following through with safety-related work practices designed to mitigate those risks.
This article outlines steps that data center managers can take to create an electrically safe work environment that not only protects people and equipment, but also ensures compliance with the latest electrical codes and regulations from organizations such as the Occupational Safety and Health Administration (OSHA) and the National Fire Protection Association (NFPA).
UNCOVERING ARC FLASH HAZARDS IN DATA CENTER INFRASTRUCTURE
The first step to keeping workers safe is determining when and where they are in danger. OSHA makes employers responsible for identifying the different hazards and risks employees face on the job, including arc flash risks. More specifically, NFPA 70E Standard for Electrical Safety in the Workplace© requires facility owners to determine arc flash-specific risks by completing an arc flash risk assessment prior to allowing a worker to perform tasks on or near energized equipment.
The latest version of NFPA 70E clarifies the meaning of risk assessment, defining it as an overall process that:
• Identifies hazards
• Estimates the potential severity of injury or damage to health
• Estimates the likelihood of occurrence of injury or damage to health
• Determines if protective measures are required
Per a major revision to the 2012 version of NFPA 70E, such risk assessments must be conducted, and the arc flash boundary distance determined, for all locations where the voltage is greater than 50 volts and there is a possibility of performing energized work such as maintenance, diagnostics, and testing.
Beyond increasing the scope of arc flash risk assessments, the new versions of the standard also indicate the need to determine the arc flash boundary via engineering analysis, as opposed to using the tables supplied in the standard for such purposes. In fact, the standard specifically limits the use of the tables to cases where both of the following are true:
• The specific task to be performed appears in the supplied tables
• The system meets the listed criteria for short circuit current magnitude and the fault clearing speed of circuit protection devices
In many instances, the table method will not be allowable because the system does not meet the criteria, or because the data center manager does not have access to the data and information needed to use the tables correctly. In these cases, engineering analysis must be performed. While the engineering analysis may be more costly and time consuming to implement, it does generate site-specific results that can ultimately lead to better protection for workers.
MITIGATING ARC FLASH RISKS
Once arc flash risks have been identified and evaluated using either the table method or engineering analysis, data center managers can use the results to create a site-specific arc flash protection plan for at-risk workers. To ensure compliance with OSHA and NFPA standards, such a plan must include arc flash labeling for equipment, personal protective equipment (PPE) requirements, written energized electrical work permits where required, and safety training for employees who work on or near energized electrical equipment.
Arc flash labeling. Arc flash labeling became an NFPA 70E requirement in 2002, and the requirements continue to be updated. The latest version of the standard, NFPA 70E 2015, spells out the types of AC and DC equipment that need to be labeled, including switchboards, switchgear, panel boards, industrial control panels, meter socket enclosures, and motor control panels.
The new standard also clarifies what must be documented on the hazard labels, including results from the arc flash risk assessment, such as nominal system voltage, the arc flash boundary, and information that can help employees choose the right PPE for each task.
The facility owner is responsible for keeping these arc flash labels up to date and must complete label reviews at least every five years, or whenever major changes are made to the electrical distribution system. It is important to keep in mind that even a seemingly small adjustment, such as replacing a fuse, circuit breaker, or protective relay, can affect arc flash analysis and the resulting field label information. Even minor changes may necessitate new calculations and updated labels in order to ensure worker safety and regulatory compliance.
Arc flash PPE. Risk assessment is the key to determining the need for PPE. When an engineering analysis is used to calculate the arc flash boundary, the results are printed on the arc flash equipment label in the form of incident energy (in calories per square centimeter at working distance). This allows workers to choose PPE with an Arc Thermal Performance Value (ATPV) that meets or exceeds the available incident energy. Since ATPV is also rated in calories per square centimeter, this is a simple determination for workers to make.
If the owner chooses to use the table method to determine PPE requirements, the hazard labels must include the arc flash boundary and PPE category shown by the tables. Workers can then look to Table 130.7(C)(16) to find a list of clothing and other equipment required for each PPE category. If the owner chooses this method for equipment labeling, workers must wear all of the PPE specified for the appropriate category.
Energized eletrical work permits. NFPA 70E 2015 requires that electrical equipment must be de-energized and verified safe before any work is performed. However, work may be performed while the equipment remains energized under certain limited conditions that include the following:
• It has been determined that it is infeasible to deenergize the equipment
• It has been determined that the work can be performed safely
• The owner, safety officer and/or other responsible management persons have completed and signed an energized electrical work permit attesting to the above
Specifically, energized electrical work permits are required when work (e.g., repair or replacement of components) is planned within the restricted approach boundary of exposed energized conductors or circuit parts. A work permit is even required when energized conductors or components are not exposed but when the work activity would expose the employee to a greater-than-normal risk of injury due to arc flash.
Safety training. NFPA 70E states that workers must be trained to recognize and avoid electrical hazards. Furthermore, the 2015 version of the standard adds that workers must demonstrate the ability to use (and not just be familiar with) precautionary techniques, PPE, and other protective devices in order to be considered qualified to work on or around energized electrical equipment.
To ensure compliance with the training requirements in the standard, data center managers must:
• Provide training to employees who work around, and not just on, energized electrical equipment
• Provide additional training on minimum approach distances to exposed parts to workers permitted to work within the limited approach boundary of exposed energized electrical conductors and circuit parts operating at 50 volts or more
• Provide retraining for all workers at least every three years
• Audit workers annually to verify the demonstration of necessary skill sets and ensure worker compliance with all safety-related work practices
• Audit safety policies and training programs at least once every three years
• Document all training, as well as worker, safety policy, and training program audits
CALLING IN THE PROFESSIONALS
Clearly, performing arc flash risk assessments and using the results to create site-specific plans for arc flash labeling, training, and PPE is no small task. Nor is it a task to be taken lightly, considering the potentially deadly consequences of an arc flash incident.
While there is no legal requirement for a registered professional engineer to perform arc flash hazard analysis, the expertise offered by such professionals can help streamline the process and improve the quality and accuracy of the results. This not only promotes compliance with all applicable safety standards, it could save a life.
Well-trained, field technicians and engineers certified by the InterNational Electrical Testing Association (NETA) can complete comprehensive site reviews and an assessment of your electrical distribution system to identify potential hazards. They use state-of-the-art software and engineering analysis to perform arc flash risk assessments and required calculations. These experts can also provide invaluable assistance in defining, implementing, reviewing, and documenting your arc flash labeling, PPE, and worker training programs and audits.
COMPLIANCE WITH NFPA 70E IS SMART BUSINESS
While NFPA 70E is not yet an OSHA-enforceable document in its entirety, compliance with the standard’s requirements is the best way to achieve mandatory OSHA compliance and avoid citations with hefty fines. More importantly, it can protect your data center and the people who work in it, creating an environment that is reliable and safe.
Learn more about electrical safety requirements by downloading the “Understanding 2015 Changes to NFPA 70E” white paper from Emerson Network Power.