Three stages for implementing arc hazard protection: Part 3
Editor’s note: The first and second installments in this series covered the introduction of the requirements and regulations for arc hazard protection, Stage 1: Reducing Risks of Clothing Ignition and Arc Burn Injuries, and Stage 2: Applying Engineered Solutions. In summary, Stage 1, NFPA 70E, should be used immediately to set up a minimal arc hazard protection program. Then a more detailed hazard assessment can be made. Stage 2, formal engineering analysis and arc flash hazard assessment, will show the way to reduce arc flash energy, reduce risk, and provide proper PPE levels for workers. The analysis also provides benefits in improving maintenance, operability, and worker training.
Stage 3 is about implementing robust management systems to help assure sustainability as well as ongoing improvement. NFPA 70E provides specific requirements unique to the hazards of electrical energy; however, this standard by itself does not constitute a comprehensive and effective electrical safety program. An organization desiring to design and implement an electrical safety program, including the mitigation of electric arc hazards, must look beyond the requirements in NFPA 70E for guidance on applying a comprehensive set of control measures.
A subtle, yet very important revision to the 2009 edition of NFPA 70E is the addition of a fine-print note in section 110.7 that references ANSI Z10-2005, Occupational Health and Safety Management Systems. This safety management standard provides a hierarchy of hazard control measures applicable to any hazard in the workplace, and uses the Plan–Do–Check–Act management model for effectiveness and sustainability. The hazard control measures are shown in Table 1. ANSI Z10 is harmonized with other internationally recognized occupational safety and health management standards, including CSA Z1000, ISO 14001, and OSHAS 18001. Some companies and organizations may have proprietary safety and health management systems that are aligned with the key elements of ANSI Z10.
The first five hazard control measures in Table 1 serve to help prevent an electrical incident. The last control measure, the application of personal protective equipment, serves to minimize injury to the worker if the other control measures have failed to prevent an incident. NFPA 70E addresses in great detail hazard control measures 4, 5, and 6. Plant engineers must look beyond NFPA 70E in applying the first three control measures.
|Table 1: Hierarchy of hazard control measures in ANSI Z10|
|1. Elimination of the hazard|
|2. Substitution of less hazardous equipment or materials|
|3. Engineering controls to reduce exposure or severity|
|4. Warnings, signs, and other communications|
|5. Administrative controls, including safe work practices|
|6. Personal protective equipment|
The hierarchy provides a way to identify the most effective measures to reduce risks associated with hazards in the workplace. By engaging experts in electrical technology, electrical work practices, and safety management systems, the plant engineer can facilitate discussion and identification of mitigation solutions aligned with all control measures.
Hazard control measures: Application examples
Below are a few examples of applying the control measures in Table 1 to the unique hazard of electric arc flash. The examples are not all-inclusive and serve only to illustrate concepts useful in helping assure long-term effectiveness and sustainability. The most effective design and application of an arc flash mitigation program incorporating these control measures can usually best be achieved through a collaboration involving electrical subject matter experts, safety professionals knowledgeable in safety management systems, and management resources that can help assure financial and other resources are allocated to the program. Electrical experts may be knowledgeable in all things electrical, but not in the subtleties of safety management systems. Safety professionals, on the other hand, may be expert in safety management but have only a general or limited knowledge of electrical equipment and work practices. Bringing experts from different competencies together can produce high-quality results in fleshing out details of an effective and sustainable electrical safety program.
Elimination of the hazard. With a high degree of certainty, the best way to protect people from an arc flash exposure is to completely eliminate the arc hazard. This is easier when looking at designs of new facilities than those of existing electrical installations. However, an organization that asks the question, “Do we have any exposures that are unnecessary and could be eliminated?” may indeed find some opportunities. An example is the discovery that a long-established employee break area, located in an electrical control room, was within the calculated arc flash boundary. While the individuals in the break area may not have interacted directly with the electrical equipment, the routine congregation of people within the arc flash boundary created an unnecessary risk. It was eliminated by relocating the break area to a different location.
Substitution of less hazardous equipment or materials. With increased understanding of the need to reduce worker exposures to arc hazards, equipment manufacturers and system designers are bringing innovative solutions to market to help employers reduce arc flash exposures to their workers. The design of new installations and modifications to existing electrical systems should be analyzed for arc flash hazards and potential exposures, their severity identified, and options to reduce severity or frequency of exposures considered. Design choices that tend to reduce the severity and/or frequency of exposure to arc hazards include high resistance grounding for industrial power systems, arc resistant switchgear that directs thermal energy from an arc away from personnel interacting with the gear, current-limiting protective devices that reduce the exposure by shortening the arc duration, and “smart” switchgear and motor control centers that can reduce exposures by changing how people interact with the equipment during troubleshooting and other maintenance tasks.
Engineering controls to reduce exposure or severity. Engineering controls impacting arc flash exposure span a wide range of consideration. Engineering analysis to identify and quantify potential arc hazard exposures is one very important engineering control measure in arc hazard mitigation. Remote switching and remote racking of power circuit breakers are examples of equipment options that allow personnel to work outside of the arc flash zone. Other engineering functions critical to arc flash mitigation include maintenance and reliability improvement programs. It is important that workers responsible for operating and maintaining the electrical system are familiar with the effects of their work on the arc flash incident energy. For example, if there is a process upset and they change out a fuse to a larger size (because no fuse of the existing size was available quickly), then they need to understand that the arc flash energy of the equipment has been changed and may be higher. Protective devices, including protective relays, circuit breakers, and switchgear, must be maintained, inspected, and tested to help assure designed functionality when operating during an arc fault. Given that some of the highest frequency and severity of exposures to arc hazards involve interaction with 600 V class motor control centers, programs to increase the mean time between failure of motors serve to reduce maintenance and operations personnel’s interaction with motor control centers. Consider these tasks that occur every time a motor fails mechanically or electrically: the motor starter disconnect switch is operated at least twice—to disconnect and eventually to re-energize, voltage testing is performed to verify electrical isolation, motor leads are disconnected and then reconnected, and fuses may be removed and reinstalled. Each one of these interactions has some risk for an arc flash incident. Electrical equipment and systems reliability improvement is an important component of an arc flash hazards mitigation program.
Warnings, signs, and other communications. Labels and signage help to assure personnel understand their proximity to potential hazards. Signs and labels may be temporary or permanent in nature, depending on the work activity or duration of the potential hazard. The warning could be a sign on switchgear, or a boundary marked on the floor. It could be a temporary barricade during certain work activity. Because signage and labeling practices may not be consistent industry wide, contractors working in multiple facilities need to be aware of each facility’s standards. One important consideration is consistency and uniformity, at least within the site operations, to help assure common understanding by the people potentially at risk.
Administrative controls, including safe work practices. Administrative controls include training and qualification requirements, job procedures, planning tools, lockout practices, and auditing systems. These administrative controls are well addressed in NFPA 70E; however, some circumstances may call for additional procedures not described specifically in the standard.
Personal protective equipment. The use of personal protective equipment (PPE), including flame-resistant clothing, face shields, and other accessories, is a critical control measure of any arc flash hazards mitigation program. It should not be the only control measure, however. Arc flash PPE works in conjunction with the other control measures described above. Arc flash PPE serves to minimize the injury severity in the event of an arc flash incident. For the PPE to perform effectively, its arc thermal performance rating (ATPV) must meet or exceed the thermal energy transfer during the arc flash incident. The best way to predict the thermal energy transfer, or incident energy, is to have performed an arc flash hazard analysis. PPE clothing and accessories can then be selected on performance rating (i.e., Hazard Risk Category 1-4 from NFPA70E) and matched to the predicted energy exposure. There are many flame-resistant clothing products designed for arc flash application on the market today, but all are based on two technologies: fabric made from 1) inherently or 2) chemically treated flame-resistant fibers. “Inherent,” as it relates to flame-resistant garments, means that the flame-resistant properties have always been a part of the fibers used in the fabric, from the first moment the fibers were created. In other words, the protection is intrinsic, permanent, and cannot be washed out or worn away no matter how the garment is used or laundered. The terms “treated” or “topically treated” refer to a manufacturing process whereby a mixture of chemicals is added to a naturally flammable fabric, such as cotton or cotton/nylon blends. Unlike inherent flame-resistant fibers, treated fibers’ flame-resistant properties may be diminished or removed completely depending on how the garment is laundered or which chemicals it is be exposed to in the work environment.
In selecting protective garments, the most important criteria is that they are from a reputable manufacturer and are labeled with the Hazard Risk Category that meets or exceeds the potential incident energy exposure. The selection of fabric technology may depend on frequency of use, environmental conditions, worker feedback from wear trials, garment durability, and evaluation of total costs that considers initial purchase, garment life expectancy, and laundry and maintenance.
Personnel at risk need to be educated on when, where, and how to properly use PPE garments and accessories. PPE garments and accessories need to cleaned, inspected, and maintained in accordance with manufacture’s recommendations to preserve the designed protection performance.
Ten years ago, it was uncommon to see articles and resources in the industry media on the topic of arc flash hazards and mitigation. Today it is rare not to see articles on this topic in electrical and safety trade and professional journals. Manufacturers and suppliers of electric power equipment and PPE often hold seminars on the topic. Resources without commercial interest include the National Fire Protection Association (NFPA), Institute of Electrical and Electronics Engineers (IEEE), National Institute of Occupational Safety and Health (NIOSH), and Electrical Safety Foundation International (ESFI). The NFPA regularly conducts seminars to aid implementation of safe work practices described in NFPA70E, and information is at www.nfpa.org. The IEEE IAS Electrical Safety Workshop, sponsored by the IEEE Industry Applications Society holds an annual conference with a mission to change and advance the electrical safety culture to enable sustainable improvement in eliminating electrical incidents, injuries, and fatalities. It targets two areas: (1) advancing the application of state-of-the-art knowledge and practices, and (2) stimulating innovation in creating the next generation of safe work practices, technology, and managing systems. Information is available at www.ewh.ieee.org/cmte/ias-esw. NIOSH has a 25-minute video and leaders guide, “Arc Flash Awareness,” intended to stimulate awareness and discussion of practical steps in improving electrical safety. The DVD package is available in English and Spanish from the Electrical Safety Foundation International at www.esfi.org
An effective arc flash hazards mitigation and protection program is more than buying flame-resistant garments and making them available for potentially exposed personnel to wear. An effective program involves management commitment to design and implement a comprehensive set of proven control measures, consistent with occupational safety and health management systems standards, such as ANSI Z10. An effective program should include, but is not limited to:
- Project engineering practices that include analysis for opportunities to eliminate or reduce arc flash exposure through wise evaluation of engineering operations in equipment and systems design
- Maintenance programs that help assure electrical equipment is kept in proper condition to help assure the safety features and functionality critical to prevention and/or mitigation of arc flash hazards maintains or exceeds design intent
- Warnings, labels, signs, and other means to help assure personnel are informed of identified hazards
- Administrative/management controls to help assure personnel are trained and qualified for their roles and responsibilities, proper tools and resources are available to perform work safely, and all elements of the program are audited periodically to monitor and control drift from designed expectations
- Flame-resistant personal protective garments and accessories that are (1) engineered and manufactured to recognized industry standards, (2) selected based on engineering analysis to determine predicted thermal incident energy to help assure PPE rated performance meets or exceeds the exposure potential, and (3) are worn by personnel at risk who know when, where, what, and how to wear PPE appropriate for the task and exposure.
All of the authors are principal consultants, Electrical Safety and Technology, for DuPont in Wilmington, Del.
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. Floyd holds a B.S. in Electrical Engineering from Virginia Polytechnic Institute and State University. He is a Professional Memeber of ASSE, a member of the NFPA, a member of the board of directors of Electrical Safety Foundation International, and an IEEE fellow. Slivka received a B.S. in Electrical Engineering from The 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.
Arc blast: force of plasma and fire from an electric arc.
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.
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).
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.