Implementing Arc Hazard Protection Part 1
This is the first in a three-part series that describes the planning and implementation for an effective, sustainable program. The first part in this series will focus on hazard awareness, safe work practices, and reducing potential for ignition of workers' clothing from arc incidents.
By Daniel R. Doan, H. Landis Floyd II, and Jennifer Slivka DuPont, Wilmington, D
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Over the past 15 years, the evolution in regulations, codes, standards, and the basic understanding of the arc hazard have elevated the importance and priority of managing and mitigating arc hazard in the workplace.
This series describes an approach that helps ensure compliance with NFPA 70E-2009, “Standard for Electrical Safety in the Workplace,” and incorporates guidance from ANSI Z10-2005, “Safety and Occupational Safety Management Standard,” to help provide an effective and sustainable program to reduce or eliminate risk of injury from electric arcs. It is intended to help plant engineers in managing this hazard through understanding and applying the appropriate regulations and standards, implementing hazard assessments, evaluating mitigation options, reducing risks, and designing and implementing control measures to help ensure an effective and sustainable program.
ARC FLASH IS DIFFERENT FROM ELECTRIC SHOCK
Although the electric arc flash hazard has only recently garnered the attention equal to the long-recognized hazard of electric shock, the arc hazard is not new. It has been present in industrial and commercial facilities since the beginning of electrification in the late 19th century. What is relatively new is that the science and technology necessary to understand and manage the hazard have evolved significantly over the past two decades.
Until the 1980s, occupational electrical hazards were generally described in terms of electric shock or electrocution—a fatal electric shock. Electric shock entails passage of electric current through the body. A shock victim generally must make contact with an energized conductor, or otherwise become part of the electrical circuit. Arc flash victims do not have to make physical contact with an energized conductor or be a part of the electrical circuit. The victim may be several feet away from energized conductors or equipment and be severely injured by the intense thermal energy transfer produced by an electric arc. Burn injuries can result from radiant burns to bare exposed skin, large area body burns from ignition or melting of clothing, or the from the heat transfer through clothing, including flame-resistant clothing.
Arc flash events are usually very short occurrences—typically less than 0.5 sec in duration. They can be initiated by a wide range of causal factors and complicated by other contributing factors. There can be human errors such as touching an energized conductor thought to be de-energized, or losing control of a tool resulting in it falling onto an energized conductor. There may be environmental causes such as roof leaks or dirt accumulation in electrical switchgear. There may be management system failures in critical aspects of training, maintenance programs, design specifications, or tool requirements such as allowing use of voltage testing devices not rated for industrial and commercial electrical systems.
Switchgear or other equipment failures during switching or operating interaction can expose workers to the hazards of electric arc flash. Most arc flash events occur faster than the unaided human eye can perceive. High-speed photography of laboratory simulations of arcing faults have provided images of how these events can engulf workers in a ball of fire.
Electric arcs are very hot—next to the laser, they are the most intense heat source on earth. Temperatures in the arc can reach 35,000 F. People within several feet of an arc can be severely burned. Arc flash events are actually multiple energy events, with intense blast, mechanical, and acoustic energy accompanying the intense thermal energy.
As the body of knowledge and understanding of the arc flash phenomena grew, leadership emerged to change federal regulations; building codes; design of electrical equipment; application of circuit protection; safe work practices; training of personnel in utility, industrial, and commercial work environments; and the development and application of PPE. Technologies to further reduce or mitigate arc flash hazards were brought to market, including current limitation, metal cladding, venting to redirect arc blast forces, and arc-resistant designs.
This work to expand our understanding continues. In 2004, the National Fire Protection Assn . (NFPA) and the Institute of Electrical and Electronics Engineers Inc. (IEEE) established a multi-million-dollar U.S. collaborative research project to further study the phenomena of electric arcs. This collaboration will help advance the protection of workers from heat, pressure, sound, toxicity, and other medical effects of exposure to electric arcs.
PROGRAM IMPLEMENTATION: REDUCING RISKS OF CLOTHING IGNITION AND ARC BURN INJURIES
In Stage 1, we are concerned about quickly implementing measures that can have an immediate impact on reducing risk of injury due to arc flash. In our facilities, quick implementation usually involves a plant that has not yet completed a thorough engineering analysis of arc flash hazards in its electrical systems. A common question when developing an arc flash hazard protection program is, “Can you provide a simple chart to show what PPE to wear in various work tasks?”
One of the options provided in NFPA 70E-2004 is based on tables that provide lists of common tasks, with appropriate arc flash protective equipment noted for each task. These tables can be useful, but they can also be misapplied. The explanatory footnotes accompanying the tables must be diligently considered with respect to available fault current and the characteristics of protective devices in the plant electric power distribution system. These notes explain that the electrical system must have certain specifications for the tables to be applicable. The user must be sure that their electrical system meets these requirements, and an electrical system study may be required to ensure these requirements in the notes are met.
A table-based approach can help the user set up a PPE plan that gives an improved measure of safety. But the table approach does not open up opportunities to identify, reduce, and possibly eliminate hazard exposure and risk. To reduce or eliminate the hazard, a more detailed study and assessment of the electrical system and worker tasks is required.
ABOUT THIS SERIES Part 2 of this series will focus on engineering analysis, reduction or elimination of arc hazard exposures through engineering solutions, and optimization of personal protective equipment requirements. Part 3 will focus on applying proven safety management systems that are important for the program's long-term effectiveness and sustainability.
All of the authors are principal consultants, Electrical Safety & Technology, for DuPont in Wilmington, Del.
Floyd holds a B.S. in Electrical Engineering from Virginia Polytechnic Institute & State University. He is a Professional Member of ASSE, a member of the NFPA, a member of the board of directors of Electrical Safety Foundation International, and an IEEE fellow.
Doan holds B.S. and M.S. degrees in Electrical Engineering from the Massachusetts Institute of Technology. He is a senior member of IEEE, a member of the IEEE 1584 standards committee, and member of the IEEE/NFPA Arc Flash Hazards Research and Testing Planning Committee.
Slivka received a B.S. in Electrical Engineering from Ohio State University. She was certified as a Six Sigma Black Belt in 2003. She is a member of IEEE and ISA, and a registered Professional Engineer in Delaware.
ACHIEVING AN ELECTRICALLY SAFE WORKING CONDITION
NFPA 70E emphasizes the safety advantages of avoiding work on energized systems. The steps to achieve an electrically safe working condition are described in article 120.1. Once these steps are completed, the hazards of shock and arc flash are eliminated. However, it is important to recognize that the steps to achieve an electrically safe working condition and the steps to return the system back to an energized condition are themselves considered work on or near energized equipment. Attention to safe work practices, including the use of appropriate shock and arc flash personal protective equipment (PPE), is important during the tasks of de-energizing and re-energizing electrical systems.
RELEVANT REGULATIONS, CODES, AND STANDARDS
U.S. regulations, codes, and standards that apply to developing and implementing an arc flash hazard mitigation program are included in the following lists:
• OSHA General Duty Clause
• OSHA 1910.132, “Personal Protective Equipment for General Industry”
• OSHA 1910.269, “Electric Power Generation, Transmission, and Distribution”
• OSHA 1910.335, “Safeguards for Personnel Protection.”
Safe work practices consensus standards
• NFPA70E, “Standard for Electrical Safety in the Workplace”
• IEEE/ANSI C2, “National Electrical Safety Code.”
Hazard analysis standard
• IEEE 1584, “Guide for Performing Arc-Flash Hazard Calculations.”
Personal protective clothing and equipment materials performance standards
• 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 F-1891, “Standard Specification for Arc and Flame Resistant Rainwear”
• ASTM F-1958, “Standard Test Method for Determining the Ignitability of Non-flame resistance Materials for Clothing by Electric Arc Exposure Method Using Mannequins”
• ASTM F-1959, “Standard Test Method for Determining the Arc Thermal Performance Value of Materials for Clothing”
• ASTM F-2178, “Determining the Arc Rating of Face Protective Products.”
Occupational Health and Safety Administration (OSHA) regulations are not descriptive in arc hazard assessment and mitigation/control methods. The requirements are clear that employers must assess the workplace for hazards, enable employees to recognize and avoid these hazards, and implement mitigation and control measures to protect employees from these hazards.
NFPA 70E-2009, “Standard for Electrical Safety in the Workplace,” provides the most comprehensive guidance for general industry to accomplish OSHA objectives relative to electrical hazards. For electric utility workers, the applicable standard is IEEE/ANSI C2 “National Electrical Safety Code.” The 2007 revision of this standard was expanded to require assessment and implementation of a protective clothing system. IEEE Standard 1584, “Guide for Performing Arc-Flash Hazard Calculations,” provides the technical basis for several commercial arc hazard analysis software programs available today.
To support the technology evolution in personal protective clothing and equipment, the American Society for Testing and Materials (ASTM) has published test standards to quantify how well clothing materials perform when exposed to arc flash and flame. These ASTM standards have enabled flame-resistant clothing manufacturers to rate their products for arc flash applications.
GLOSSARY OF TERMS
Arc blast : Force of plasma and fire from an electric arc.
Arc flash hazard : Danger associated with the arc flash (e.g., the possibility of radiation burns, inhalation of vapors, temporary blindness, hearing damage, lung damage, barotrauma, and injury from projectiles).
Arcing fault current : The current that flows during a short circuit in which an arc is present. The impedance of the arc reduces the fault current to a level below the bolted fault current.
Barotrauma : Injury from pressure caused by acoustic or vibratory forces during an arc blast.
Bolted fault current : The current that flows during a short circuit in which the phases are directly connected together with no appreciable impedance. During a bolted fault, there is no arc present.
Burn, first degree : A burn involving only the outer layer of skin. The skin is usually red, and some swelling and pain may occur.
Burn, second degree : A burn involving both the first and second layers of skin. In these burns, the skin reddens intensely and blisters develop. Severe pain and swelling occur, and the chance for infection is present.
Burn, third degree : A burn involving all the layers of skin. This is the most serious type of burn. Fat, nerves, muscles, and even bones may be affected. Areas may be charred black or be dry and white in appearance, and infection may occur. If nerve damage is substantial, there may be no pain at all.
Electric arc : The flow of current between two electrodes through ionized gases and vapors. It is started by flashover or the introduction of some conducting material between energized parts.
Electrically safe work condition : A state in which the conductor or circuit part to be worked on or near has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.
Flash hazard analysis : A study investigating a worker's potential exposure to arc-flash energy, conducted for the purpose of injury prevention and the determination of safe work practices and the appropriate levels of PPE.
Flash hazard boundary : The boundary within which arc flash PPE is required.
Incident energy : Total arc energy, both radiant and convective, that is actually received per unit area, in calories per square centimeter.
Personal protective equipment (PPE) : Clothing and equipment designed to mitigate the effects of hazards to which workers might be exposed.
Plasma : A collection of charged particles that exhibits some properties of a gas but differs from a gas in being a good conductor of electricity and in being affected by a magnetic field.
Qualified person : One who has skills and knowledge related to the construction and operation of the electrical equipment and installations, and has received safety training on the hazards involved.
Working near : Any activity inside the limited approach boundary of exposed, energized electrical conductors or circuit parts that are not put into an electrically safe working condition.
Working on : Coming in contact with exposed, energized electrical conductors or circuit parts with the hands, feet, or other body parts, or with tools, probes, or test equipment, regardless of the PPE an individual is wearing.
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