Simply put, an arc flash is a phenomenon where a flashover of electric current leaves its intended path and travels through the air from one conductor to another, or to ground. The results are often violent and when a human is in close proximity to the arc flash, serious injury and even death can occur. Arc flash can be caused by many things including: · Dust · Dropping tools · Accidental touching · Condensation · Material failure · Corrosion · Faulty Installation Three factors determine the severity of an arc flash injury: · Proximity of the worker to the hazard · Temperature · Time for circuit to break Because of the violent nature of an arc flash exposure when an employee is injured, the injury is serious – even resulting in death. It’s not uncommon for an injured employee to never regain their past quality of life. Extended medical care is often required, sometimes costing in excess of $1,000,000. Typical Results from an Arc Flash · Burns (Non FR clothing can burn onto skin) · Fire (could spread rapidly through building) · Flying objects (often molten metal) · Blast pressure (upwards of 2,000 lbs. / sq.ft) · Sound Blast (noise can reach 140 dB – loud as a gun) · Heat (upwards of 35,000 degrees F)
Approach / Protection Boundaries
The National Fire Protection Association (NFPA) has developed specific approach boundaries designed to protect employees while working on or near energized equipment. These boundaries are:
· Flash Protection Boundary (outer boundary)
· Limited Approach
· Restricted Approach
· Prohibited Approach (inner boundary) Flash Protection Boundary (outer boundary):
The flash boundary is the farthest established boundary from the energy source. If an arc flash occurred, this boundary is where an employee would be exposed to a curable second degree burn (1.2 calories/cm2 ). The issue here is the heat generated from a flash that results in burns. Limited Approach: An approach limit at a distance from an exposed live part where a shock hazard exists. Restricted Approach: An approach limit at a distance from an exposed live part which there is an increased risk of shock. Prohibited Approach (inner boundary): A distance from an exposed part which is considered the same as making contact with the live part. This distance is not common between equipment. Some equipment will have a greater flash protection boundary while other equipment will have a lesser boundary. Ways to Protect the Workers There exists a number of ways to protect workers from the threat of electrical hazards. Some of the methods are for the protection of qualified employees doing work on electrical circuit and other methods are geared towards non-qualified employees who work nearby energized equipment.
Here are a few of the protective methods:
· De-energize the circuit
· Work Practices
· Ground Fault Circuit Interrupters (GFCI)
· Grounding (secondary protection)
If You Must Work on Energized Circuits If it has been determined that deenergizing a circuit is not feasible and the employee must work “hot”, the employer shall develop and enforce safety-related work practices to prevent electric shock or other injuries resulting from either direct or indirect electrical contacts. The specific safety-related work practices shall be consistent with the nature and extent of the associated electrical hazards. These safety related work practices could include: · Energized Electrical Work Permit · Personal Protective Equipment · Insulated Tools · Written Safety Program · Job Briefing Fast Fact: The most effective and fool-proof way to eliminate the risk of electrical shock or arc flash is to simply deenergize the equipment. Understanding the Arc Flash Warning Labels Each piece of equipment operating at 50 volts or more and not put into a deenergized state must be evaluated for arc flash and shock protection. This evaluation will determine the actual boundaries (i.e. prohibited, limited, restricted etc) and will inform the employee of what PPE must be worn. Once the evaluation is complete an Arc Flash Hazard warning label must be affixed to the equipment and readily accessible to employees who may work on the energized equipment.
The Employees Obligation
Employees must follow the requirements of the Arc Flash Hazard label by wearing the proper personal protective equipment (PPE), use of insulated tools and other safety related precautions. This includes not working on or near the circuit unless you are a “qualified” worker. Qualified person: One who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved. Additional requirements for qualified persons. Qualified persons (i.e. those permitted to work on or near exposed energized parts) shall, at a minimum, be trained in and familiar with the following: · The skills and techniques necessary to distinguish exposed live parts from other parts of electric equipment. · The skills and techniques necessary to determine the nominal voltage of exposed live parts, and · The clearance distances specified in 1910.333(c) and the corresponding voltages to which the qualified person will be exposed
Arc flash study analysis is one of the major components of electrical systems design that requires a meticulous level of detail and accuracy as it defines the available fault current, calculated incident energy which results in arc flash labels, boundary conditions and PPE requirements for the electrical safety programs. This webinar will address the information that needs to be gathered for system modeling to include, equipment details, duty cycles, single-line diagrams, overcurrent protection devices, transformer ratings with impedances etc. and how to analyze them. The topic will also touch on the importance and considerations for selective coordination to localize the faults to avoid nuisance tripping of the upstream breakers and how simple modifications to the breaker settings and the fuse ratings can be utilized to limit the arc flash potential.
If you are in need of an Arc Flash Study performed in Birmingham, Huntsville, Nashville, Mobile, or any of the surrounding areas, please fill out the form on the Contact Us page.
According to the U.S. Bureau of Labor Statistics (BLS), the rate of arc flash incidents has steadily declined over the last five years. Thankfully, progress in standards, increased educational awareness, and advanced technologies are helping to make work environments safer. But, arc flash incidents still can occur, placing anyone working near energized equipment at risk. In 2017, the United States saw 1,000 injuries and 134 fatalities due to arc flash accidents, with 80 percent of the incidents resulting from human error.
As electrical distribution environments become more digitized, arc flash reduction and mitigation techniques need to be reevaluated to ensure safety. The way medium voltage (MV) and low voltage (LV) electrical distribution equipment is designed can play an important role in minimizing arc flash hazards. Arc flash incidents can result in damaged equipment, injury, and, in some cases, even death.
Electrical Engineers can incorporate into their design a “Safety by Design” approach to minimize workplace arc flash risks. The “Safety by Design” concept considers all possible causes of arc flash incidents during the product design development phase. Our engineers are focused on the mindset of “how can we prevent an incident in the first place” when developing new MV and LV power distribution products.
There are many arc flash terms, standards and requirements that they overwhelm the senses but it is important to understand each one so that you can comply with these standards and most importantly – keep your employees safe.
1.) What exactly is an arc flash?
An arc flash is:
• Caused by an arcing fault - an electrical explosion due to a rapid release of energy
What happens when an Arc flash occurs:
• Pressures generated 100's - 1,000's lb./ft2
• Sounds due to pressure waves can exceed 160 dB
• Debris & molten metal can reach speeds that exceed 700 mph
• The flash can reach temperatures in excess of 30,000 degrees Fahrenheit
• Extreme temperatures can vaporize copper wires with an estimated expansion of 67,000:1
2.) Why Arc Flashes happen?
There are a variety of reasons why an Arc Flash can occur, but most of them are preventable. Most arc flashes occur when maintenance workers are manipulating live equipment for testing or repair and accidentally cause a fault. Improper tools, improper electrical equipment, corrosion of equipment, improper work techniques and lack of training are just some of the events that can lead to a devastating arc flash or arc blast.
3.) What standards or codes govern compliance?
There are 4 main regulations that govern electrical safety & arc flash:
1. OSHA Standards 29CFR, Part 1910. Occupational Safety and Health Standards. 1910 sub part S (electrical) Standard number 1910.333 specifically addresses Standards for Work Practices and references NFPA 70E. OSHA 29CFR 1910.335 (a) (1)(i) requires the use of protective equipment when working where a potential electrical hazard exists and 29CFR 1910.132(d)(1) which requires the employer assess the workplace for hazards and the need for personal protective equipment. OSHA compliance is required by any plant building or facility.
2. The National Fire Protection Association (NFPA) Standard 70 – 2002 “The National Electrical Code” (NEC) contains requirements for warning labels.
3. NFPA 70E provides guidance on implementing appropriate work practices that are required to safeguard workers from injury while working on or near exposed electrical conductors or circuit parts that could become energized. Part II 2-1.3.3 regarding Arc Flash Analysis states that a “Flash Hazard Analysis shall be done before a person approaches any exposed electrical conductor or circuit part that has not been placed in an electrical safe work condition”. This Arc Flash Hazard Analysis must be done to determine the level of Personal Protection Equipment PPE that a worker must use, and the Arc Flash Boundary in inches along with the incident energy found at each location. Each panel must be marked with an ANSI z535 approved Arc Flash Warning Label.
4. The Institute of Electronics and Electrical Engineers (IEEE) 1584 – 2002 Guide to Performing Arc-Flash Hazard Calculations.
Mobile Electrical Engineering Group, Inc. provides these services to ensure that your facility will be in compliance with the National Electric Code (NEC) electrical safety requirements for employee workplaces as set forth in NFPA 70E and OSHA 29 Code of Federal Regulations (CFR) Part 1910 Subpart S.
We have the expertise and know-how to assist you with any or all of the following:
• Single-Line Diagram Development
• Short Circuit Analysis
• Coordination Studies
• Arc Flash Analysis
• Shock Hazard Analysis
• Arc Flash Equipment Labeling
• Recommendations for PPE (Personnel Protection
JD has been an active Electrical Engineering for over 30 years.