Avoid Arc Flash Occurrences with Preventive Measures
Adhering to NFPA standards and safety best practices are the best deterrents.
By John Foged, Contributor
Today’s dependence on electrical energy has led to a lower tolerance for any outage. To meet these expectations, electrical workers are being pressed to perform maintenance work on energized electrical equipment. In addition to the electrical shock hazard that results from direct contact of live conductors with the body, workers are exposed to the risk of injury due to the accidental initiation of electric arcs. Arc flash injuries can occur without any direct contact with energized parts.
An electric arc, or an arcing fault, is the flow of electric current through the air from one
conductor to another or ground. When an arc fault occurs, there’s an immense electrical explosion. Both arc flash and arc blast are separate byproducts of that electrical explosion. The arc flash is the light and heat from the explosion, while the arc blast is a pressure wave that follows. Electrical hazards, specifically arc flash and arc blast, can potentially result in severe injury or even death of electrical workers. Exposure and risk to arc flash hazards have increased due to higher voltages and available fault currents in electrical systems.
Temperatures of an arc flash can reach as high as 2,800 to 19,000 °C (5,000 to 35,000 °F). For perspective, the temperature of the sun’s surface is estimated at 5,500 °C (9,932 °F). Temperatures that high can ignite the clothing and burn the skin of anyone within a few feet. Air expands dramatically when heated to these temperatures, and arcing can instantly vaporize metals like copper or steel. The ensuing shock waves result from the rapid expansion of air and metal vapors like those produced in an explosion and can pulverize concrete walls. Too often, employees who are not wearing personal protective equipment (PPE) are seriously injured or killed if an electrical arc occurs when they are working on it.
It’s estimated that between five and 10 arc fault incidents occur every day in the United States, based on the Bureau of Labor Statistics findings. The result is more than 30,000 injuries and 400 deaths annually, with approximately 80% of the fatalities due to burns, not shocks. Avoiding such instances takes diligence and results in a safer workplace.
Start With an Arc Flash Study
Every arc flash safety program should begin with an arc flash study to calculate how much energy an arc flash could release at various points along the power chain. Accuracy is essential with such measurements, so plant managers who lack direct and extensive experience with arc flash incident energy assessment should always seek assistance from a qualified power systems engineer. A detailed study should include the following steps:
- Identify all locations and equipment for arc flash hazard assessment.
- Collect data:
- Equipment data for short circuit study: voltage, size (MVA/kVA), impedance, X/R ratio, etc.
- Equipment data for protective device characteristics: type of device, existing settings for relays, breakers, and trip units, rating amps, time-current curves, and total clearing time.
- Equipment data for arc flash study: type of equipment, type of enclosure (open-air, box, etc.), the gap between conductors, grounding type, number of phases, and approximate working distance for the equipment.
- All power system equipment, their existing connections, and possible alternative connections.
- Prepare a one-line diagram of the system.
- Perform a short circuit study:
- Calculate bolted (available) 3-phase fault current for each piece of equipment.
- Calculate current for every contributing branch and load.
- Determine expected arc current:
- Calculate arc current.
- Calculate branch currents contributing to the arc current from every branch.
- Estimate arcing time from the protective device characteristics and the contributing arc current passing through this device for every branch that significantly contributes to the arc fault.
- Estimate the incident energy for the equipment at the given working distances.
- Determine the arc flash boundary for the equipment.
- Document the assessment in reports, one-line diagrams, and appropriate labels on the equipment.
An arc flash study is not a “one-and-done” type of study. The NFPA requires the analysis to be updated every time significant changes occur in the electrical system or at intervals not to exceed five years. In addition, there are mandatory audit procedures imposed by NFPA 70E: An electrical safety program should be updated at least once every three years. Fieldwork should have time intervals not to exceed one year. Your Lockout/Tagout (LOTO) program and procedure will require updating once a year.
Lack of compliance may expose workers to unknown hazards and severe financial penalties.
In addition to the arc flash study, make sure your electrical reliability services partner provides a complete solution, including the following tasks and activities:
- Site review/compliance assessment
- Protective scheme design review
- Electrical safety program review/development
- Training and performance evaluation
- PPE plan
- Preventive maintenance
- Annual recertification
Protection through electrical safety training
The NFPA 70E: Standard for Electrical Safety in the Workplace states that “Hazard elimination shall be the first priority in implementing safety-related work practices.” The proper use of safety equipment, knowledge of electrical hazards, and proper response in an electrical disaster are essential for all electrical personnel or those working on or around electrical equipment.
An electrical safety program should be designed to provide personnel involved with operating and maintaining a power distribution system with the knowledge, skills, and abilities to meet the NFPA 70E training requirements to be considered a “qualified” electrical worker by NFPA standards. The electrical safety program is a requirement imposed by the NFPA 70E standard and must be implemented as part of your overall occupational health and safety management system. An optimal training program should always be tailored to your specific needs and may include, but not be limited to, the following:
- Procedures to be used before employees exposed to electrical hazards start working
- Risk assessment procedures that need to address the potential for human error and its negative consequences
- Proper major electrical component operation/maintenance with manufacturer instructions
- Applicable testing and maintenance recommendations from ANSI/NETA, MTS, or NFPA 70B: Recommended Practices for Electrical Equipment Maintenance
- Site and equipment-specific safety hazards and mitigation techniques
- Lectures, presentations, and hands-on demonstrations to provide maximum possible exposure to power distribution system safety, operations, and maintenance requirements
- Emergency response and safe release methods
- A method for investigating electrical incidents (NFPA 70E requirement for incident investigations)
Preventive maintenance maintains compliance and safety
NFPA 70E requires maintenance on electrical equipment following manufacturers’ instructions or industry consensus standards. Your partner of choice for electrical reliability services should assist you in developing a preventive maintenance program to address arc flash hazards specifically. An optimal program needs to evaluate equipment conditions and determine the most cost-effective and manageable solution to ensure your protective devices operate correctly, safely, and reliably. Proper maintenance will ensure that you comply with the NFPA 70E requirements permitting regular operation of equipment, reducing hazards, thus often allowing tasks to be accomplished safely and without extensive PPE.
Optimal PPE plans need to fully protect employees while addressing all relevant OSHA standards to ensure compliance. Ideally, before work is performed on or around electrical equipment, it must be de-energized, if possible. Otherwise, recommendations for the minimum protective equipment workers must wear when they are near exposed energized equipment should be based on the arc flash risk assessment findings and calculated incident energy (IE) values. The plan also should cover how PPE should be worn, maintained, and disposed of at the end of the equipment’s life.
Do you meet compliance standards?
If you answer “No” to any of the following questions, then the chances are you may not be compliant.
- Is your arc flash hazard plan documented?
- Does your documentation include the results of the previous arc flash risk assessment and arc flash training?
- Have the single-line diagrams been updated following any changes in your electrical infrastructure?
- Do you have current signs and labels on equipment and at hazardous areas?
- Do all labels include the type, name/ID, incident energy at working distances, flash protection boundary, arc flash PPE category, shock protection information, date of analysis, and the certifying person per OSHA 29 CFR 1910.132 (d)(2)?
Planning for the future
Arc flash hazards are very serious, and it takes more than a label to ensure the safety and well-being of your employees while making sure that your critical assets are also protected.
Consider the financial and safety impact of ignoring these types of recurrent and mandatory studies. Then, wisely prioritize budgets to ensure funding is available for current study needs, future updates, and ongoing training requirements. ESW
John Foged, CSM, REM, is the Environmental, Safety & Health Manager at High Voltage Maintenance (hvmcorp.com) and has been a safety, environmental, health professional with over 30 years of experience working in the electrical safety and environmental field.