Preventing and Minimizing Arc Flash Risk

December 9, 2019

Following OSHA regulations and using good design can reduce the risk of damage to workers and equipment from arc flashes.

Arc flashes present a serious hazard involving electrical equipment that is more common than many would believe. Due to OSHA’s reporting requirements for arc flashes, they are under-reported or not reported at all. No one is certain how frequently they occur, but some sources estimate there are five to 10 electrical equipment explosions (aka arc flashes) each day in the U.S.

Most reports on electrical-related injuries focus on shock and electrocution, rather than arc flashes in which explosive forces, heat, and gasses cause the injuries and deaths, according to the National Fire Prevention Assoc. But research conducted across burn centers show arc flashes cause 34% to 55% of all the electrical burns received on the job.

It has been estimated that more than 2,000 workers are admitted to burn centers annually to be treated for severe arc-flash burns, and arc flash incidents kill one to two people every day. In addition to injuries and fatalities, arc flash also carries significant financial costs. Medical treatment for arc-flash injuries costs an average of $1.5 million per incident, which is borne by the factory owner. This makes arc-flash prevention and risk reduction a high priority when designing electrified equipment.

Labels indicate boundaries around electric enclosures and levels of personal protective equipment  for working inside it.

Arc Flashes vs. Arc Faults

An arc flash is the explosion caused by a phase-to-phase or phase-to-ground short circuit. Arc flashes emit extreme heat, intense light, and violent pressure blasts. In comparison, an arc fault is the high-power discharge that causes the short and triggers an arc flash. Arc faults can be caused by several different conditions, including a faulty wire, a loose fuse, a tool dropped into a live cabinet, or even personal contact with live components.

Arc flashes pose a significant risk for bodily harm from the force of the explosion, heat of the blast, and the corrosiveness of the gasses. Physically, the pressure of the explosion can be as much as 10,000 psi, which compares to the force of a high-speed collision.

In addition to its explosive force, arc flashes carry high temperatures and can reach up to 35,000°F, which is hotter than the surface of the sun. Arc events also create noxious and corrosive gasses that, if inhaled, increase the chances of catastrophic injury or death.

Arc-Flash Regulations and Standards

The Occupation Safety & Health Administration (OSHA) is the governing body that regulates workplace safety, including arc flash prevention, equipment labeling, and use of personal protection equipment (PPE). Specific standards related to arc flash include OSHA 1910.137 for electrical protective equipment and OSHA 1910.269 App E on protection from flames and electric arcs.

 The National Fire Prevention Association’s standard NFPA 70E covers safety-related work practices, maintenance requirements, and special equipment requirements. Companies that comply with NFPA 70E must conduct an Arc Flash Risk Asessment, sometimes called an Arc Flash Study or Arc Flash HazardAnalysis. The review determines safe work practices, arc-flash boundaries, and appropriate levels of PPE to be used.

Underwriters Laboratory also has a standard specifically for industrial control panels and switchgear (manufactured and modified). It covers control panels intended for general industrial use and operating at 600 V or less. Equipment meeting this standard is installed in “ordinary” locations in accordance with the National Electrical Code, ANSI/NFPA 70.

As the governing body for workplace safety, OSHA regs are the driving force for compliance in the U.S. Manufacturers that do not meet the regs can be fined by OSHA and lose their insurance. With OSHA issuing fines and penalties when workers are put at risk for arc flash injuries, a common misconception arose that the agency enforces NFPA 70E. Although companies are not specifically required to comply with NFPA 70E, it acts as an outline on how to ensure compliance with OSHA’s arc flash safety regulations.

A Closer Look at NFPA 70E

NFPA 70E sets arc flash boundaries for organizations, including keeping 3 ft away from cabinets with electrical circuits running at less than 750 V and keeping 19 feet away from cabinets holding circuits running at 15,000 to 36,000 V. Boundaries are delineated by tape or a chain and show the safe distance from cabinets for workers without PPE.

Arc flash boundaries vary with the risk level and the voltage of the equipment. For instance, a “limited” range is for minimal shock hazards from electrical overarcs; a “restricted” range is for increased shock risks; and a “prohibited” range entails significant risks of direct contact with electrified components. Ranges for these boundaries are outlined in NFPA 70E table 2-1.3.4. and OSHA 29 CFR,1910.269 table R6.

Energized panels or boards must be marked with a danger or warning label that indicates the potential hazard and the level of PPE required (from 0 to 4). Category 0 PPE requires cotton, untreated fiber shirts and pants, safety glasses, and hearing protection. It warns against wearing polyester or synthetic fabrics near the equipment that could melt This category is for areas with the lowest potential for an arc flash event, but the standard warns against wearing polyester or synthetic fabrics that could melt near the equipment. At the other end of the spectrum, Category 4 protection includes an arc-rated suit, along with protection for face and head, hands, eyes, and hearing, as well as a hard hat and appropriate footwear.

Reducing the Risks

To minimize the possibility risk of an arc flash, follow OSHA’s lockout/tagout procedures. When followed closely, they can protect workers from hazardous energy release and from the unexpected energization or startup of machinery and equipment.

Lockout/tagout requires that machinery be turned off and disconnected from its energy source before anyone performs maintenance on it. It mandates that authorized individuals either lock or tag the energy isolating device(s) to prevent the release of hazardous energy. An authorized person must also take the required steps to verify energy has been isolated effectively. Lockout devices hold energy-isolation equipment in a safe or off position. They prevent equipment from being energized and can only be unlocked with a key. Tagout devices feature prominent warnings that are fastened to energy-isolating equipment to warn workers not to reenergize the equipment while it is being serviced. Details for using tagout devices are listed in the OSHA standard, The Control of Hazardous Energy (Lockout/Tagout), Title 29 Code of Federal Regulations Part 1910.147.

 The safest way to work on any panel is when the panel is turned off. If lockout/tagout is done correctly, maintenance staff can safely work on electric panels without risking exposure to arc flash.

An arc flash assessment, another required safety measure, determines both the potential and intensity of an arc flash. Calculations done in these assessments (found in IEEE 1584, Guide for Performing Arc-Flash Hazard Calculations) helps in creating appropriate training and procedures for anyone working with energized electrical parts, switches, breakers, or other equipment.

To minimize arc flash risks, it is critical to understand that NFPA 70E standards make it easier to comply with OSHA regulations. NFPA 70E outlines proper training and  procedures and PPE standards for manufacturers and their maintenance staff. In addition, engineers can design arc-flash prevention into enclosures so that they serve as the first line of defense. Using the isolated box approach, customized with appropriate accessories, manufacturers can prevent unsafe access inside enclosures. As manufacturers look to improve efficiency and safety of their operations, developing and executing proper arc flash prevention standards will ensure the health of their staff and their bottom line.

 

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