Arc flash hazard awareness has grown significantly over the last 10 years. And yet, within the IT industry, several trends are increasing the risk of an arc flash in the data center. These trends include the acceleration of digitization and data center growth and the introduction of newer, high-energy equipment.
Data centers have become essential societal infrastructure. Meeting the demands to process more data faster than ever before requires higher data center capacities and more power. When there is a failure within the electrical system, the magnitude of the arc flash hazard can be significant.
The utility energy source for high-capacity data centers can generate significant levels of fault current on the low-voltage side of the medium-voltage transformers. Consequently, the trend toward larger power capacity data centers and the rising capacities of individual rooms can increase the available fault current in the data center and the potential for more severe arc flash hazard incidents.
This article focuses in detail on the risks of an arc flash fault and the impact on employees and business success, as well as regulatory requirements and compliance strategies.
Arc Flash Concerns
An arcing fault is the result of a short circuit in the air from line to line or line to ground conductor. It can result in exposure to extremely high temperatures and concussive forces in a fraction of a second. There is little or no time to move away from the hazard to a safe location. Burns can be severe and concussive forces can cause additional physical injury. Costly equipment damage and interruption of operations can occur.
The magnitude of the arcing fault at each equipment location is a function of the available fault current and interrupting time to clear that fault. A short circuit study calculates available fault current, and a coordination study defines the interrupting time of protective devices as the basis to determine the arc flash incident energy in calories per centimeter squared. This incident energy value will be included on a device-specific equipment label. When it is necessary to work on energized equipment, personnel should know the magnitude of the hazard so they can take appropriate steps to protect themselves with personal protective equipment (PPE) and other safety procedures.
The goal of an arc flash study is twofold: first, to reduce the hazard for workers when working on energized equipment; and second, simultaneously providing selective coordination of electrical system protective devices to minimize interruptions to the operation of the facility electrical infrastructure.
An arc flash incident presents risks to employees, third-party contractors, and the system owner. These can include personal injury, equipment damage, lost revenue, fines, legal liability, and damage to the company’s reputation. Failure to comply with an Occupational Safety and Health Administration (OSHA)-mandated safety program prior to an occurrence can amplify the liabilities. Cumulatively, fines can run into the hundreds of thousands of dollars for repeated violations, up to in excess of $1 million if an incident results in serious injury or death. Establishing an arc flash risk management program is the first step toward mitigating these risks and ensuring worker safety and 24x7 operation.
Arc Flash Management Plans
Components of an arc flash hazard risk management program represent a typical sequence of tasks conducted by the system owner, or in conjunction with a third-party service provider, to implement a personnel safety and system reliability solution.
The process starts with a commitment by the system owner to define, document, and implement safe operating practices. This should include electrical safety and policy procedures. Many of these procedures are defined in the NFPA 70E standard as it relates to electrical safety in the workplace.
Specific locations with electrical infrastructure where hazards may be present need to be identified. Details of the electrical system layout are required as the basis to define a scope of work for a risk management solution.
The user or third-party service provider will verify system data on-site. This data will be used to model an electrical representation of the system in order to perform a short circuit, coordination, and arc flash analysis. The analysis is performed according to industry standards using one of several available software applications.
A knowledgeable professional systems engineer will use the tools in the application software to calculate available fault current and recommend protective device settings that optimize system operation while minimizing the magnitude of the arc flash hazard at equipment locations where work may be performed while systems are energized.
A report is provided to document the results of the study by device, including actions to replace underrated devices that can no longer safely interrupt the available fault current and relay settings to support the approved recommendations of the study.
Once the results of the study are approved by the user, equipment labels are produced that provide all of the necessary information workers will require to wear appropriate PPE and define safe working distances. These labels are then available for installation on the electrical devices as defined in the study.
Labeling equipment is only a part of the overall process of operating safely. There are many safety procedures outlined in OSHA and NFPA 70E. These include a requirement to train personnel who may be working on or near energized equipment. NFPA 70E requires personnel to be trained every three years, and audited for retention of safety policies and procedures each year.
An arc flash analysis documents and analyzes a user’s existing system for what it is. It could be a relatively new, state-of-the-art electrical system with the latest gear, a decades-old system with equipment that is no longer manufactured, or something in between. As a result, there are situations where the ability to reduce the magnitude of arc flash hazards while also providing desired protection device coordination for optimal system operations has its limits.
For example, reducing the magnitude of the hazard to a level where PPE is available to work with energized equipment, or that allows the use of more comfortable PPE work clothing in lieu of an arc flash suit. In those cases, an engineered solution, including equipment changes or modifications, may address some of these limitations.
Finally, an arc flash analysis is essentially a snapshot in time. It documents the user’s electrical system as currently configured. Any changes to the system could invalidate all or a portion of the results provided in the study report. Accordingly, NFPA 70E requires the study to be rerun a minimum of every five years or when major changes have been made to the system. Periodic updates not only keep the study current to retain the benefits of safety and system reliability but, in the long run, make the ongoing implementation of an arc flash safety program less costly and complex.
Arc Flash Training
OSHA1910 and NFPA 70E guidelines for arc flash training are key elements in any data center arc flash risk management program. NFPA 70E states this training must be completed at least every three years and audited every year to verify retention of safety policies and procedures. A training course can be conducted in one day and should, in general, cover codes and standards, safety fundamentals, electric shock, arc flash and blast, safe work practices, and safety-related maintenance requirement.
During OSHA 1910/NFPA 70E safety training, attendees will learn how to interpret the information on an arc flash label for selection of PPE to safely work on or near energized equipment. Whenever possible, it is recommended the arc flash study be completed and approved prior to the training. This allows the instructor to review actual hazards in the facilities where the attendees are working.
Figure 1 shows an example of a label layout that follows the latest guidelines of NFPA 70E. There are variations based on customer preference and historical safety procedures already in place. Changes to the standard in recent years include elimination of the prohibited approach boundary for shock hazard and PPE category 0. PPE category designations of 1-4 are no longer required when the analysis method discussed is being used.
Application of PPE also should be discussed during training. How PPE is applied by a system owner will depend on established safety policies, labeling methodology, and inventory management of the PPE itself.
The incident energy in calories/cm2 on the label provides the information necessary for the selection of PPE to protect the worker from the magnitude of the hazard. When the incident energy values on the label are developed using the analysis method, a table in NFPA 70E defines two PPE groupings.
- The grouping from 1.2 to 12 calories/cm2 is shown in Figure 2 with typical work clothes and a face shield.
- The greater than 12 calories/cm2 grouping is shown in Figure 3 with the arc flash suit and hood.
Energized work generally is not recommended for incident energy greater than 40 calories/cm2 but is no longer a specified limit in the NFPA 70E standard.
As discussed earlier, an existing system configuration can place limits on the amount of arc flash hazard mitigation performed beyond recommendations to replace underrated devices and recommended protective device settings. However, the results of the analysis do provide guidance to consider future modifications in safety procedures, system designs, and equipment changes to further reduce or eliminate the hazard.
Up-To-Date Diagrams / Studies
A current one-line diagram is an NFPA 70E requirement. A single line is provided for devices in the model and included in the final arc flash report. This information also is available in AutoCAD format as shown in Figure 4.
Short circuit, coordination, and arc flash incident energy studies are snapshots in time.
It is important to keep them up to date for several reasons. The studies are required by NFPA 70E for significant system changes or at a minimum every five years. It is not uncommon for equipment to be replaced or upgraded. Relay settings might have been changed to deal with a short-term nuisance outage, or the available fault current and protection scheme from the incoming utility service may have changed. Other parts of the electrical system from the existing study may not have changed. This can reduce the work scope and the cost to perform a five-year update. Incremental updates performed more frequently — quarterly or annually, for example — keep the study current and result in the five-year update being less costly and complex. Finally, the safety of personnel working with energized equipment and the operational integrity of the electrical system are maintained or enhanced.
With respect to arc flash, OSHA 1910, NFPA 70E, and IEEE 1584 are the primary standards that drive arc flash compliance activities. These standards have been developed and refined over time from experience to provide policies and procedures that facilitate electrical safety.
OSHA is the law but refers to NFPA 70E to fulfill the performance-based requirements in its standards. The purpose of NFPA 70E is to provide a working area for employees that is safe from unacceptable risk associated with the use of electricity in the workplace. The IEEE 1584 standard referenced in NFPA 70E provides the mathematical model used as the basis to calculate arc flash incident energy values.
These standards and how they are to be applied should be part of every discussion related to an arc flash implementation program.
In many instances, a third-party service provider can provide assistance with a data center arc flash solution. Make sure the service provider is aware of your requirements and how their approach aligns with those needs. The following list includes some criteria to consider.
Qualified field personnel to perform on-site tasks for single or multiple locations, including data collection, labeling, relay settings, breaker testing, device replacement, and installation of an engineered solution.
Professional engineers to perform system analysis, review results, and provide supporting documentation
Comprehensive training program to educate and measure understanding of safety procedures.
Application engineering capability to develop and implement additional mitigation solutions.
Data center project experience for single- and multi-site implementation.
A process to manage system changes that support ongoing personnel safety and system reliability
Arc flash — in and around a data center — is a potential risk to personnel, system performance, reputation, and the bottom line. System owners must be actively involved in and accountable for risk management. Ignorance of compliance standards is not a defense against negligence and liability, especially with the analysis tools and resources available to reduce these risks. Periodic review to update the electrical system analysis and personnel safety training are a requirement of NFPA 70E because. in the end, it’s all about safety and reliability.