Five considerations for choosing an arc flash hazard analysis

One of the critical steps to comply with NFPA 70E 2004 is commissioning a flash hazard analysis for your facility. This requirement affects almost all existing facilities that have electrical distribution systems that operate at 50 V or greater, which at some time may require maintenance or even a lockout/tagout procedure while the equipment is energized.

05/15/2007


One of the critical steps to comply with NFPA 70E 2004 is commissioning a flash hazard analysis for your facility. This requirement affects almost all existing facilities that have electrical distribution systems that operate at 50 V or greater, which at some time may require maintenance or even a lockout/tagout procedure while the equipment is energized.

The methods for calculating arc flash hazard (see IEEE 1584) have been available only since the late 1990s, and the requirement for a flash hazard analysis has been in the electrical safety standards for a relatively short time as well. Since the market demand for this work is so large, with a relatively small number of engineers that are experienced and qualified to do the work properly, this creates potential for concern for individual facilities that are attempting to comply with these relatively new requirements.

 

Flash hazard analyses should be performed by only licensed professional electrical engineers that have experience with power system design, the calculation methods and the software that is used. Such an analysis requires considerable knowledge and judgment on the part of the person performing the study, and that is gained only through education and experience.
While some facilities may have internal engineering resources that are capable of performing these calculations, the majority of companies do not have these resources available. What’s more, facilities that are faced with the prospect of purchasing a flash hazard analysis often do not fully understand what differentiates a high quality service from the rest.

 

The result of a poorly executed flash hazard analysis can in some respects be worse that none at all, since the output of the study will determine the level of personal protective equipment that a worker must use to protect him or herself from the potential arc flash hazards (Fig. 1). Incorrect values can either suggest levels of PPE that will overprotect or underprotect the worker.



Fig. 1. Among the questions facility owners and managers should ask prospective vendors before contracting with them to provide an arc flash hazard analysis is whether they offer electrical safety training for plant workers that is required for them to be considered‘qualified persons’ by the NFPA 70E 2004 definition. Note that while this training is not part of the arc flash hazard analysis, it is a critical requirement for compliance to the safety standards. Photo copyright Oberon Company 2005

A flash hazard analysis is really a composite of three analyses: Short-circuit analysis %%MDASSML%% The first is the short circuit analysis, which determines the maximum amount of available fault current at the line terminals of each piece of electrical equipment in the facility. Protective device time-current coordination analysis %%MDASSML%% The second element is the protective device time-current coordination analysis, which determines the proper settings of each overcurrent protective device in the system, so that faults are cleared selectively by the upstream overcurrent protective device that is closest to the fault itself, whenever possible. The coordination study is a critical element of the flash hazard analysis because the results of it may be useful to mitigate or reduce the incident energy that results from an arcing condition in the system. Flash hazard analysis %%MDASSML%% The third and final analysis is the flash hazard analysis itself.
If a facility has completely accurate and up-to-date single line diagrams, along with short circuit and coordination studies, the process of completing the flash hazard analysis is relatively straightforward and inexpensive. However, most existing facilities do not have this information available in an accurate form, and this system documentation must then be reconstructed before the flash hazard analysis can be completed. This reconstruction of the facility system documentation is a large part of the cost and effort required to complete the flash hazard analysis.

Questions to ask
Following are five key questions you should ask prospective vendors before contracting with them to provide an arc flash hazard analysis. The answers to these questions will help avoid common mistakes in making this important procurement decision.

Vendor qualifications %%MDASSML%% What qualifications does your company have to provide this analysis? Can you provide a list of similar studies that you have done recently for other companies like mine, and provide a list of references? The report should have prioritized recommendations for correcting high incident energy conditions, code violations (if any) and should note any over-dutied equipment found. Scope of work %%MDASSML%% Will your company include the protective device time coordination study as part of the arc flash hazard analysis? Note that many vendors do not include this in their scope of work, in an effort to make their pricing more competitive. The lack of this information will make it impossible to ascertain how to reduce any high incident energy conditions that will be found. Reducing high incident energy conditions %%MDASSML%% Will your report suggest other ways to reduce high incident energy conditions using engineering controls, such as modifying the existing system to reduce existing hazard levels where those conditions are found to be unacceptable? Note that many vendors lack the ability to suggest changes to the system that can reduce hazard levels. It is common to find a few areas in the system where unacceptably high incident energy conditions exist. The capability to mitigate these conditions is very important. Equipment labeling %%MDASSML%% Does your company offer a custom labeling option for equipment that shows the values obtained via the arc flash hazard analysis? Note that the National Electrical Code (Article 110.16) requires application of only a generic hazard warning label, not specific values from the analysis. Many companies are choosing the option to have the supplier of the arc flash hazard analysis generate and affix custom labels that show the details obtained from the analysis (Fig. 2).



Fig. 2. The current requirement for application of hazard warning labels on electrical equipment (National Electrical Code 2005) requires only a generic hazard warning message to the worker. However, many plant engineers have decided to exceed the requirements in NEC 2005 and provide more detailed information on labels, such as the flash protection boundary in inches in the label shown here.

Worker training %%MDASSML%% Does your company offer electrical safety training for our workers that is required for them to be considered‘qualified persons’ by the NFPA 70E 2004 definition? Note that while this training is not part of the arc flash hazard analysis, it is a critical requirement for compliance to the safety standards.

Making the choice
Since an arc flash hazard analysis is so critical for the safety of your personnel, it should be done carefully and with the same due diligence applied in the vendor qualification process. There are many commercial resources available that are well qualified to do this work, along with some that are not capable of performing these system studies well. Since this choice will determine the future safety of your electrical workers, this must be approached carefully and with a thorough understanding of what you expect to receive for your company’s investment.

Joseph Weigel is a product manager for Square D Services marketing. He has been very involved in the development of the Arc Flash Safety program for Schneider Electric. He is also a member of the National Fire Protection Association (NFPA) and the Institute of Electrical and Electronics Engineers, Inc. (IEEE).





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