Arc Flash Hazards and Electrical Safety Program Implementation

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Arc Flash Hazards and Electrical Safety Program Implementation

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    Arc Flash Hazards and Electrical Safety Program Implementation

    Copyright Material IEEE Paper No. IAS54p2

    H. Landis Floyd, P.E. Daniel R Doan, P.E. C T Wu Susan L Lovasic Fellow, IEEE Senior Member, IEEE DuPont DuPont DuPont DuPont PO Box 80723 PO Box 80723 Cheng Kung Road PO Box 27001 Wilmington, DE 19880 Wilmington, DE 19880 Kuan Yin, Tao-Yuan Hsien Richmond, VA 23261 USA USA Taiwan USA Abstract Electrical Arc Flash is a significant hazard associated with electrical power systems. Understanding of this hazard is developing, and the electrical hazards our workers encounter can be reduced with proper design and work practice management. This paper provides an introduction to the electrical arc flash hazard, and description of a comprehensive arc flash management program that includes analysis, electrical system design, and work practices and protective clothing plans. A case history of an industrial site's arc flash hazard mitigation program is included.

    Index Terms arc flash, electrical safety, electrical

    hazards, hazard reduction, protective clothing.

    I. INTRODUCTION

    Beginning in the 1980s, with the formation of the IEEE Standard P902[1] working group, several technical committees in the IEEE Industry Applications Society led efforts to advance standards, regulations, and technology to reduce workplace electrical injuries. This work has significantly increased understanding of burn injuries caused by exposure to arcing faults in electric power distribution systems. Most importantly, cost effective techniques to eliminate or mitigate arc flash hazards have been developed. This includes arc flash hazard analysis tools and techniques, equipment and system design methods to reduce or eliminate personnel exposure to arcing faults, work practices to reduce risk of exposure to potential arcing faults, and the development of personal protective equipment and clothing to minimize injury if workers are in proximity to an arcing fault.

    As noted by Doan, Floyd and Neal[2], a comprehensive arc flash hazards management program that includes arc flash hazard analysis to identify and quantify hazardous exposures and to assure proper selection of personal protective equipment and clothing, the application of engineering design solutions to reduce frequency and magnitude of arcing faults, and improved safe work practices can be cost effective.

    II. ELECTRICAL ARC FLASH INJURIES

    An arcing fault involves an intense transfer of energy from

    the power system to the environment surrounding the fault. The energy of an arc flash can cause burn injury on bare skin and possibly cause ignition of conventional clothing. The burn injury sustained can be more severe if the workers clothing catches fire or melts as a result of this thermal threat. Burn injuries can be avoided or at least minimized by the identification of job tasks and work areas where electric arc

    flashes can occur, quantification of the expected thermal hazard, and selection and use of the last line of defense personal protective equipment (PPE). In the U.S. alone, an estimated 2000 workers are seriously injured with arc flash burns each year. Hospitalization and rehabilitation costs are estimated to exceed $US 1 billion annually. The life-altering affect to burn injury survivors including lost work time due to hospitalization and rehabilitation, disfigurement, and reconstructive surgeries can be avoided or at least minimized by implementation of a comprehensive electric arc hazard safety program as illustrated in Figure 1.

    Figure 1. A comprehensive arc hazard safety program.

    III. ANALYZING THE HAZARDS

    A. Methods of Analysis Research into the nature and hazard of the electrical arc

    flash has been published in many papers in recent years. Lee published an early paper describing this hazard and providing a theoretical incident energy equation [3]. Subsequent papers by Doughty, Neal and others [4][5][6] have discussed protective clothing testing and methods for estimating the arc flash incident thermal energy that is present in a system.

    In 2002, an IEEE standards working group gathered test data, performed further testing on the arc flash hazard, and published IEEE-1584 Guide for Performing Arc Flash Hazard Calculations [7]. The development of the Guide was described in a paper given at the IEEE/IAS/PCIC conference, and was published in the IEEE Industry Applications Magazine [8]. The equations published in IEEE-1584 provide a method for estimating the thermal incident energy hazard

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  • for workers who are exposed to electrical power systems and equipment. These equations have been accepted by local and national codes and standards bodies (such as NFPA 70E, Standard for Electrical Safety in the Workplace [9]) as one of the permissible means of assessing arc flash hazards.

    There are other hazard exposures during an electrical arc flash, such as blast, pressure wave, and shrapnel. Some papers have been published on these subjects [10][11][12], and more testing is required to determine the extent of these hazards. The thermal hazard is generally accepted as the most significant hazard from arc flash, since documented arc flash injuries are predominantly burn injuries[13].

    Further research into the arc flash hazard has been published recently which points out the high variability of the arc flash hazard, depending on design of the equipment. In particular, Stokes and Sweeting[14] have shown that horizontal bus bars, pointing at the worker, can have very high incident energy exposures, since the plasma in the arc can be pushed off the ends of the bus bars, toward the worker. In equipment with this geometry, such as the end section of a bus compartment with the end plates removed, special safety procedures should be in place to ensure that the worker is not exposed to the arc plasma during an incident. B. Results of Typical Industrial Site Analysis

    A summary of the arc flash hazard analysis for a typical industrial company was published as a recent paper [15]. The hazard analysis data for 9 660 pieces of equipment, and over 1 000 000 annual exposures was evaluated for incident energy, type of equipment, and type of work being done. A summary of the results for incident energy is shown in Figure 2. Incident thermal energy can be measured in calories per square centimeter (cal/sqcm) or joules per square centimeter (J/sqcm). One cal/sqcm is equivalent to 4.18 J/sqcm.

    0%

    10%

    20%

    30%

    40%

    50%

    < 1.2 1.2 - 4 4 - 20 20 - 40 > 40

    Incident Energy in cal/sqcm

    Figure 2. Percent of annual exposures by incident energy. Nearly 75% of the exposures can be protected by a single

    layer of flame-resistant fabric. Many manufacturers make garments such as shirt and pants or coveralls that have an arc rating of at least 4 cal/sqcm. At a minimum, all electrical workers should be wearing garments of this type that have been tested and approved for arc flash exposure. Also, other workers who operate electrical equipment should also be protected. For this industrial company, everyday protective clothing (pants and shirt) or coveralls of this fabric can be a simple and effective means of protection from 75% of the arc flash exposures during work. See section V below.

    The exposures over 40 cal/sqcm are of particular concern, since these high energy exposures can bring significant injury to the worker. Injuries to the ears through the loud noise, and to the body through blast effects and shrapnel, are difficult to quantify for these high-energy exposures. The hazards should be reduced by careful attention to design, over-current protection, and safety practices.

    IV. REDUCING THE HAZARDS

    The data from an arc flash hazards analysis provides the

    basis for identifying opportunities to eliminate or reduce hazardous exposures. Often thermal energy exposures can be lowered by an order of magnitude by making changes in protective relay and circuit breaker settings or selection, often at little or no cost. For fuse applications, the substitution of a faster current limiting fuse can be a low cost solution to reduce arcing fault current and/or fault duration. Switchgear designs that contain or direct arcing fault energy away from workers are also an option.

    Motor control centers and switchgear, employing smart technology or sensors and measuring devices, enable shifting some maintenance and trouble-shooting tasks to the safer environment of a remote computer screen.

    The data from the arc flash study can also be used in redesigning administrative controls to reduce the frequency of hazardous situations, and limit their time exposure. The redesign of a routine switching procedure to isolate an industrial unit substation is an example of applying enhancements to administrative controls. A typical unit substation may have one or two primary switches or circuit breakers and 10-15 secondary circuit breakers. Depending on the switching sequence employed, the task to isolate the substation may require a workers hazard exposure of 5 minutes minimum to 45 minutes maximum. Our goal when planning a switching sequence should be to minimize hazardous switching operations.

    Other administrative and engineering controls include designing procedures or methods that place workers at a greater distance from potential exposure. Examples include remote switching and remote racking of drawout circuit breakers.

    V. PROTECTING AGAINST THERMAL HAZARDS

    A. Evolution of Arc Protective Clothing and Standards

    Use of flame resistant clothing to protect workers from the intense heat of an electric arc flash has been used by some employers in the chemical industry and electrical utility sector since the 1980s. However until the mid 1990s, their ability to select the most appropriate arc flash protective garments was limited. The development of an industry recognized test method (ASTM F-1959[16]) to assess the protective qualities of flame resistant fabrics to the unique thermal hazards associated with an arc flash has greatly aided efforts to protect workers from burn injury. Additionally, updating of a key industry standard for electrical workplace safety (NFPA 70E [9]) along with the development of improved methods to conduct workplace hazard assessments (IEEE 1584[7]) have also helped put the pieces together. Employers have increased awareness regarding the need to protect their workers from the hazards of electrical arc flashes. Employers

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  • have additional means to conduct assessments of their workplace hazards, and once they have quantified the level of hazard associated with particular workplace activities, they can seek out appropriate flame and arc resistant clothing and other PPE to match these hazards. B. Steps To Implement An Arc Protective Clothing Program

    Once the arc flash protection boundary and arc energy hazard level has been determined for the various work tasks, then the next step is to match these identified arc hazard levels with the corresponding protective clothing and PPE. Note that the appropriate PPE will likely include protection for the workers body (flame resistant clothing) as well as protective items for the workers eyes, head, hands, and feet, as illustrated in Figure 3.

    Figure 3. Example of Arc Flash Hazard PPE.

    In the case of protective clothing, the arc rating (expressed

    in cal/sqcm) of the clothing system should meet or exceed the arc energy level determined by the hazard analysis. Look for the arc rating provided in the label of the protective garment. Also be sure that the garment is compliant with the appropriate performance standards. One key standard for clothing is ASTM F-1506[17]. Other specialized standards also exist. These include ASTM F-1891[18] for flame resistant rainwear and ASTM F-2178[19] for face shields and hoods.

    For simplicity, the employer might choose to group together tasks with similar arc protection requirements and create a few levels of protection that meet their particular needs. This approach would cluster similar arc energy levels to simplify the number of clothing ensembles to be purchased. The approach will also increase the likelihood that all workers required to wear the arc protective clothing will understand which level of clothing they must wear for a particular assignment. It is important to note that if the employer chooses to cluster the work tasks, that the task with the highest arc hazard will set the minimum requirement for the arc protective clothing at that level.

    For many higher energy arc hazards (e.g. those 15 cal/sqcm), layering of two flame resistant garments should be considered. This approach would permit the worker to wear a lightweight base flame resistant garment to meet work tasks expected to have lower energy hazards while providing added thermal protection due to the second flame resistant

    garment worn over the base garment for specific tasks. For example, a single layer 6 oz/sqyd aramid fabric garment such as a shirt and pant combination would provide an arc rating of approximately 6 cal/sqcm. If another 6 oz/sqyd aramid fabric garment, such as a coverall, were worn over this shirt and pant combination, the combined arc rating for this two- layer system would be approximately 20 cal/sqcm. This layering approach can improve worker comfort since it only requires the use of heavier weight flame resistant garment systems for specific tasks.

    In addition to identifying and providing flame resistant clothing with the appropriate arc rating for the work tasks, the employer must also ensure that any garments worn over the designated arc resistant clothing (e.g. rainwear, jackets, sweat shirts) are also flame resistant. As for underlayers, meltable fibers such as nylon and polyester must not be worn next to the skin. These materials could increase skin burn injury even if worn under flame resistant clothing. The use of non-meltable undergarments (such as those made with 100% cotton or a flame resistant fabric) is permitted.

    C. Criteria To Consider

    There are many criteria an employer may use in deciding exactly what type of PPE to use for electric arc flash protection. For flame resistant clothing, these criteria usually include: level of protection including compliance to relevant standards, garment durability, ease of care, and wearer comfort. Cost effectiveness is another important factor. In addition to the initial cost of the garments, employers must consider life cycle costs, such as how long the garment will last and how often it will need to be removed from service for repair.

    When selecting flame resistant clothing for arc flash protection, the employer should consider the following steps for implementing a clothing program:

    1) Organize Determine what job task workers may conduct which

    could expose them to an electric arc flash Determine the possible arc hazard level of each of

    these tasks Select appropriate PPE and protective clothing options

    for all of the tasks. 2) Implement Develop a plan for implementing PPE, especially

    protective clothing solutions, for each hazard identified Make sure that all involved parties (e.g. workers and

    supervisors) understand the plan Distribute the PPE and protective clothing along with

    instructions for its use and care to all those involved Educate workers to the need for the new PPE and

    protective clothing to ensure a seamless integration of the plan.

    3) Monitor Schedule regular meetings to discuss how well the

    plan has been implemented at the work sites Be prepared to address questions about protection

    level, comfort, durability, and use and care.

    VI. CASE STUDY

    A. Site information

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  • A manufacturing facility near Taipei, Taiwan was built in 1990. The plant electrical system includes a 69 kV substation with a set of gas-insulated switches, two 69/13.8 kV main transformers and a 13.8 kV main switchgear. The main switchgear supplies power to five switch centers. Each switch center powers three to four motor control centers (MCCs). Total electricity demand for the system is 16,700 kW. The site electrical operations workers wear two-layer aramid suit and hood to protect them from thermal arc flash.

    B. Arc flash study

    In 2001, the operating management received information regarding the requirement to meet NFPA 70E changes which have impact on arc flash PPE. The business unit electrical safety network invited a corporate electrical safety resource to study the impact of the changes and received management support to complete a study on arc flash incident energy hazards.

    As this manufacturing plant is the newer plant in the business, and had a recently completed short circuit study on file, the site was selected to be the first plant to complete an arc flash study. The study was completed in March 2001. The results of the study are summarized in Figure 4. Over 70% of the exposures were estimated to be below 4 cal/sqcm, and approximately 1% of the exposures were above 20 cal/sqcm. No design changes to further reduce these exposures were recommended.

    Percent of Annual Exposures

    0%10%20%30%40%50%60%70%

    40

    Incident Energy in cal/sqcm

    Figure 4. Case Study results, percent of annual exposures.

    C. Clothing Testing and Program Implementation At the same time, to fully meet compliance on garment

    selection, the regional engineer communicated with a local aramid garment manufacturer in Taiwan to conduct a test of available clothing. This test included selected compositions of two-layer 4.5 oz/sqyd aramid cloth, two-layer 6 oz/sqyd aramid cloth, and two-layer 7.5 oz/sqyd aramid cloth. The test helped the engineer develop an understanding of the capability of locally-made aramid clothing manufacturers.

    After the arc flash incident energy study was completed, the company started a local team consisting of representatives from seven company sites in Taiwan to discuss the garment selection program, and to share the requirements of arc flash incident energy studies. The intent is to purchase the locally made aramid garments to reduce

    replacement cost and work with other local sites to set up PPE programs consistently. An example of the PPE used is shown in Figure 5.

    Figure 5. Typical PPE used.

    VII. CONCLUSIONS

    Engineers, managers, and workers are beginning to realize

    that electrical arc flash contains serious hazards. Research is continuing, and there is a lot more to learn about these hazards. A comprehensive arc hazard safety program includes understanding the hazards, analyzing the electrical system to estimate the energy released, reducing the hazards through design and work practices, and protecting with arc protective clothing as a last defense.

    A case study for a facility in Asia was described, and shows the importance of detailed review of hazards and work practices. Local manufacturers of clothing may be available to help set up and maintain a personal protective clothing plan.

    VIII. REFERENCES

    [1] IEEE P902, IEEE Guide for Maintenance, Operation,

    and Safety of Industrial and Commercial Power Systems.

    [2] D.R. Doan, H.L. Floyd, and T.E. Neal, Comparison of methods for selecting personal protective equipment for arc flash hazards, IEEE Transactions on Industry Applications, Vol 40, Issue 4, July/Aug 2004, pp 963 969.

    [3] R.H. Lee, The Other Electrical Hazard: Electric Arc Blast Burns, IEEE Transactions on Industrial Applications, Vol. 1A-18, No. 3, May/June 1982, p246.

    [4] T.E. Neal, A.H. Bingham and R.L. Doughty, Protective Clothing Guidelines for Electric Arc Exposure, IEEE Transactions on Industry Applications, Vol 33, Issue 4, Jul/Aug 1997, pp 1041-1054.

    [5] R.L. Doughty, T.E. Neal, T.A. Dear, and A.H. Bingham, Testing Update on Protective Clothing and Equipment for Electric Arc Exposure, IEEE Industry Applications Magazine, Vol 5 Issue 1, Jan/Feb 1999, pp. 37-49.

    [6] R.L. Doughty, T.E. Neal and H.L. Floyd II, Predicting Incident Energy to Better Manage the Electric Arc Hazard on 600-V Power Distribution Systems, IEEE Transactions on Industry Applications, Vol 36, Issue 1, Jan/Feb 2000, pp 257-269.

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  • [7] IEEE 1584, Guide for Arc Flash Hazard Calculations. [8] D.R. Doan, et. al., Development of the Guide for

    Performing Arc-Flash Hazard Calculations, IEEE Industry Applications Magazine, Volume 11, Issue 3, May-June 2005, Page(s):30 - 39

    [9] NFPA 70E, Standard for Electrical Safety in the Workplace, National Fire Protection Association, Boston, MA 02210.

    [10] G.E. Heberlein, Jr., J.A. Higgins, R.A. Epperly, Report on enclosure internal arcing tests, IEEE Industry Applications Magazine, Volume 2, Issue 3, May-June 1996, Page(s):35 42.

    [11] M. Wactor, G.H. Miller, J. Bowen and M. Capelli-Schellpfeffer, Modeling of the Pressure Wave Associated with Arc Fault, IEEE Industry Applications Magazine, Volume 10, Issue 4, July-Aug. 2004, Page(s):59 67.

    [12] T.E. Neal and R.F. Parry, Specialized PPE testing for electric arc hazards beyond heat exposure - shrapnel, pressure, and noise, IEEE Industry Applications Magazine, Volume 11, Issue 3, May-June 2005, Page(s):49-53.

    [13] EPRI (R.E.Wyzga and W. Lindroos), Health Implications of Global Electrification, Occupational Electrical Injury: An International Symposium, Annals of the New York Academy of Sciences, Vol 888, October 30, 1999, pp 1-7.

    [14] A.D. Stokes and D.K. Sweeting, Electric arcing burn hazards, IEEE/IAS/Petroleum and Chemical Industry Technical Conference, Sept 2004, Page(s):351 - 359.

    [15] D.R. Doan and R.A. Sweigart, "A Summary of Arc Flash Hazard Calculations, IEEE Transactions on Industry Applications, Volume 39, Issue 4, July-Aug. 2003, Page(s):1200 1204.

    [16] ASTM F-1959, Standard Test Method for Determining the Arc Thermal Performance Value of Materials for Clothing, ASTM International.

    [17] ASTM F-1506, Standard Performance Specification for Flame Resistant Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards, ASTM International.

    [18] ASTM F-1891, Standard Specification for Arc and Flame Resistant Rainwear, ASTM International.

    [19] ASTM F-2178, Standard Test Method for Determining The Arc Rating Of Face Protective Products, ASTM International.

    IX. VITA

    C T Wu is an Electrical Safety and Technology Consultant for DuPont, supporting operations in the Asia/Pacific region. C T majored in Electronic Engineering at the Taipei Institute of Technology. C T is chair of the DuPont Taiwan electrical safety team, promoting arc flash hazard analysis at facilities in the region. He is also developing electrical safety practices in local language for DuPont China sites.

    Daniel R. Doan (S80, M81, SM00) is a Consultant for

    DuPont in Wilmington, Delaware. Dan received the BSEE and MSEE degrees from the Massachusetts Institute of

    Technology. He has co-authored IEEE papers at IAS/PCIC and Pulp&Paper on subjects ranging from electrical safety to electrical system reliability and operations. He has co-authored PCIC Tutorials on Electrical System Reliability and Arc Flash Hazard Analysis, and has participated in many IAS Electrical Safety Workshops as author and presenter. Dan is a senior member of the IEEE, a member of the IEEE 1584 Guide for Arc Flash Calculations Working Group, a member of the IEEE/NFPA Research and Testing Planning Committee, and is a registered Professional Engineer in Pennsylvania.

    H. Landis Floyd, II (M73, SM91, F00) received his BSEE

    degree from Virginia Polytechnic Institute & State University in 1973. He has been employed with the DuPont Company since then, with assignments in manufacturing facilities design, operation and maintenance. He currently serves as a Senior Consultant in electrical technology and specializes in power system reliability and electrical safety in plant construction, operation, and maintenance. He chairs the DuPont Corporate Electrical Safety Team. Lanny currently is Vice-Chair of the PCIC. He is Past Chair of the PCIC Safety Subcommittee and the Awards Nominating Subcommittee. In the IAS Industrial and Commercial Power Systems Department, he is Past Chair of the Power Systems Engineering Committee, the Power Systems Engineering Maintenance, Operation & Safety Subcommittee, and the IEEE Standard, Guide to Maintenance, Operation and Safety of Industrial and Commercial Power Systems. Lanny is a member of the board of directors for the Electrical Safety Foundation International and chairs the ESFI Workplace Safety Committee. He is a Professional Member of the American Society of Safety Engineers (ASSE), a member of Panel 1 of the National Electrical Code, and a registered professional engineer in Delaware. He was the 1999 recipient of the PCIC Electrical Safety Excellence Award, the 2002 recipient of the IEEEs Richard Harold Kaufmann Award, and a 2004 co-recipient with Thomas E. Neal and Richard L. Doughty of the IEEE Medal for Engineering Excellence.

    Susan L Lovasic is a Research Associate with DuPont

    Personal Protection in Richmond, Virginia. A graduate of Penn State with a bachelors degree in Chemical Engineering, she has worked for DuPont since 1984. Susans work experience has included both research and marketing responsibilities in several DuPont fiber businesses, including Kevlar aramid, Stainmaster and Antron nylon, and Nomex aramid. Her current research efforts focus on materials for use in garments to protect workers from the thermal hazards of flash fire and electric arc exposures. Susan has participated on various ASTM and NFPA technical committees related to thermal protection and flame resistant clothing and is a member of AIChE, ASSE, and AATCC. She has conducted extensive research to assess critical properties of flame resistant apparel including instrumented thermal mannequin flash fire and electric arc flash testing as well as broad assessments of the comfort and durability properties of garments.

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