Historically, the focus of arc-fault testing has been performed to determine if workers in the vicinity of medium-voltage equipment would be subjected to a fire hazard or to flying debris if an internal arc fault were to occur. However, increased awareness of the potential hazards related to electrical arcing faults has prompted the National Electrical Code (NEC), Institute of Electrical and Electronics Engineers (IEEE) and Occupational Safety and Health Administration (OSHA) to impose new requirements on facility owners to determine the likelihood that employees would suffer second-degree burns as a result of an internal arcing fault, and to evaluate their low-voltage and medium-voltage switchgear.
As these standards are employed, facility owners must calculate the amount of energy that employees could be exposed to and provide appropriate personal protective equipment (PPE) that will ensure employees are adequately protected against second-degree burns. These new requirements call for more sophisticated testing and analysis techniques than were previously required to evaluate medium-voltage equipment. As a testing facility, KEMA-Powertest foresees these new requirements presenting an opportunity for it to expand test services to a larger customer base. In addition to the traditional manufacturers of medium-voltage switchgear, we are now beginning to offer test and evaluation services to low-voltage equipment manufacturers, facility owners and the manufacturers of PPE materials and protective garments.
Recent changes to the NFPA 70E “Electrical Safety Requirements for Employee Workplaces” include requirements that facility owners perform a flash-hazard analysis prior to allowing someone to work on energized equipment, to first determine the flash-protection boundary distance and the type of PPE required. There have been reports that OSHA has begun to aggressively monitor compliance with the NFPA 70E requirements, so employers are now developing plans to demonstrate compliance and fit their employees with the appropriate PPE.
We have seen these requirements generating increased interest in evaluating the protection level of clothing offered by the manufacturers of PPE. In the United States, the American Society for Testing and Materials (ASTM) has developed standard F 1959/F 1959M-04 for evaluating the arc rating of the materials used in the manufacture of PPE clothing.
IEEE is also developing the IEEE P1584 Standard Test Method for Arc Flash Hazard Testing. This standard is used to evaluate how much a specific short-circuit protective device, such as a fuse or circuit breaker, limits the amount of incident energy available from a particular circuit. This enables the manufacturers of fuses and circuit breakers to compare their devices with those of their competitors and possibly gain a competitive advantage. Facility owners can reduce their liability and expenditure for PPE by specifying equipment with the lowest incident energy.
KEMA-Powertest has been developing capabilities to perform the testing and evaluations required by these standards to measure the incident thermal energy released from arc faults and the arc thermal performance value (ATPV) of flame-retardant (FR) materials. Our laboratory has recently constructed a special test fixture prescribed by the ASTM standard for evaluating the materials used for the PPE. We also have purchased a high-speed temperature-recording system used to measure the temperatures developed during arcing faults, and have developed new algorithm modeling needed to analyze the results and perform the statistical analysis specified in the standard. Recently, our lab has conducted arc flashes on real equipment with clothed mannequins in typical working positions, including new and unprecedented low-voltage work. These tests, captured on video clips, are being shared at conferences and seminars.
Michael Schacker has been president of KEMA-Powertest Inc., a high-power electrical testing laboratory in Chalfont, Pennsylvania, U.S., since 2004.
At the 2005/2006 IEEE PES Transmission and Distribution Conference and Exposition in May, T&D World staff learned a great deal about the new arc-flash standards that are either being implemented or are in the final wording stage.
These new codes and standards from NEC, IEEE, OSHA and others will affect the personal protective equipment (PPE) that safety-apparel field workers are wearing, and they may change the boundary distances for performing day-to-day tasks where arcing faults could occur. All indications point to the enforcement of additional requirements for facility owners to evaluate each job task where the potential hazards related to electrical arcing faults may occur and determining (calculate) the level of risk to the worker. The installation of additional devices such as fuses and circuit breakers may also be required, most notably in low- and medium-voltage systems. This new focus on low- and medium-voltage arc-flash hazards will not only affect electric utility field operations and trainers, but also the providers of safety apparel, PPE testing labs and the manufacturers of fuses and circuit breakers.
To get an industry reading on this new development in arc-flash protection, Transmission & Distribution World editors talked with stakeholders about how these new standards will impact electric utility field operations.
This past year, Randy Wade represented PECO Energy (Philadelphia, Pennsylvania), a unit of Exelon Energy Delivery Services, at an Edison Electric Institute (EEI) meeting in Atlanta, Georgia. EEI, in partnership with the International Brotherhood of Electrical Workers and OSHA, submitted language that was considered in the proposed CFR 1910.269 (T&D standard) revisions.
The charge of the 20-plus utility representatives at the EEI conference was to review and approve technical language to present to OSHA that would parallel NFPA 70E, but would give utilities more flexibility in the way they protect workers from arc hazards during day-to-day activities.
They proposed that OSHA require utilities to abide by one of two options to prevent a worker from receiving second-degree burns:
Provide employees with guidelines for the use of FR clothing and/or equipment with an arc thermal protection value rated to prevent a second-degree burn; or
Permit the use of approved/accepted programs, such as ARCPRO software, to perform a system analysis. The analysis would include fault current available, arc gap, distance from the arc and breaker-clearing times, to ensure that the total energy available at the work site does not exceed equivalent heat energy greater than 2 cal/cm2.
Wade says one procedure that may change is working on energized lines. Everyone agrees that working on something that has been de-energized is the most desirable option. In the past, with the demand for capacity, utilities have typically tried to avoid de-energizing. Now, with these new standards, utilities may consider de-energizing the circuit as the only option when employees are required to work with extreme energy exposures.
Transmission and distribution business must comply with CFR 1910.269 now, according to Wade. However, T&D is under no obligation to comply with NFPA 70E at this time. But OSHA does have a pending revision in the works for CFR 1910.269 that will contain similar, but not identical language, to NFPA 70E.
In the meantime, Exelon has begun organizing an ARC Hazard Energy Exposure review team with ComEd (Chicago, Illinois), PSE&G (Newark, New Jersey) and PECO. This team will chart every T&D task and establish the energy exposure using ARCPRO. After that, the team will look at what options would be advised for each situation.
As stakeholders revisit arc-flash hazards, the obvious question is, where are the biggest risks? Experts site the removal or installation of circuit breakers or fuses, the racking of circuit breakers in and out of switchgear and the removal of electric equipment panel covers as tasks that have the highest injury rates. Arc flashes can occur almost anywhere an electric utility line worker, trouble-call technician or maintenance worker is working around energized lines. Uninvolved workers and the public may also be at risk when an arc fault occurs. Of special concern are tasks on the system where additional equipment such as switchgear, transformers and fuses are involved. Most interesting is the fact that low-voltage testing and system analysis is a task where high numbers of arc-flash injuries are occurring.
Safety advocates point out that standard NFPA 79E was originally written to protect firefighters, and an arc-flash section happened to be included in the standard. It makes a blanket calculation in setting protective standards, but does not address any work methods or the way an electric system is operated.
PSE&G's Tom Verdecchio is a member of the National Electric Safety Code (NESC) Subcommittee 8, which addresses work methods. He reports that the committee is working on several rule revisions related specifically to arc-flash hazards. NESC codes are revised every five years. New rules will be proposed for the 2007 code stating that employers must perform an arc hazard study on any task exposing workers to an arc flash.
The proposed new rule adds tables to the code, which will allow the employer to choose the right level of protection without having to perform a study or do tedious calculations. These tables, based on fault current and clearing time, are the result of studies being done by utilities like PSE&G and PECO.
PSE&G has spent the past 24 months “engineering out the heat hazards” related to arc flash, says Verdecchio. The utility started with the highest risk areas, for example, linemen gloving on 13 kV. The two-year-old initiative includes analyzing the clearing time and distance to employees for each task.
PSE&G's field studies are showing that by reducing the clearing time of a circuit, the heat that an employee is exposed to will be reduced. In one case, the target was to keep the heat exposure to less then 5 cal/cm2 and less than second-degree burns to expose skin. Several utilities are now expanding the study to other exposure tasks related to arc-flash hazards. They hope to have collaborative results available by September 2006.
Another area where PSE&G is making changes is in FR clothing. For example, the utility has gone to a “Level 2 Clothing” applies to shirts, pants and T-shirts for overhead linemen. The utility is now studying FR levels and other preventative procedures on other tasks where arc flashes may occur.
It is worth repeating that when an arc-flash incident occurs, enormous amounts of concentrated energy explode through the air, through cabinets and circuits, and through anything or anyone in the vicinity. It is often unpredictable, but is always capable of doing serious damage to a person's hearing, eyesight and body. Depending on the voltage level, a ball of combusting heat is dispersed that can melt metal and severely burn a worker or anyone in the area. Pieces of metal and material may also be released like a bullet toward workers close and even not so close to the arc fault. The National Institute for Occupational Safety and Health (NOSH) has reported that from 1992 through 2001, there were 44,363 electrical-related injuries involving days away from work. Of those injuries, 17,101 were caused by electric arc-flash burns.
As we have heard from the industry, the final word on increased standards for arc flash is still being written. Everything from increased labeling requirements to more comprehensive exposure calculating practices may be on the horizon. But one thing everyone is in agreement on: Increasing the awareness and understanding of arc-flash hazards is one of the best ways to prevent arc-flash injuries.