What Causes an Arc Flash?
Arc Flash incidents (AFIs) occur from electrical sources and electric potential devices producing electric currents that travel through the air or other mediums as opposed to traveling through its intended path. As electric arcs or flash-overs happen, they produce large amounts of energy with extreme heat. These fire-like flashes happen very quickly in under a second or can sometimes continue for longer periods of time, even reaching minutes in duration. Arc flash events (AFEs) are extremely dangerous. Wikipedia defines arc flash (AF) as “a type of electrical explosion or discharge that results from low-impedance connection through air to ground or another voltage phase in an electrical system. It’s also “the light and heat produced from an electric arc supplied with sufficient electrical energy to substantially damage, harm, cause fire, injure,” including death.
An arc can occur during electrical shorts, faults, and voltage spikes, capable of producing flash-overs between two or more electrodes through an air gap or other medium.
Electrical arcs can be caused by malfunctions of protective equipment, deteriorated or defective insulation, human contact, or contact with other
conducting materials. Breaks, cracks, or corrosion in insulation and electrical connections can cause AFIs. AFs can also be caused by breaching the minimum safe zone of an electric energy source or an electric potential device (PD).
AFEs can create deadly and harmful consequences to humans and their surroundings with excessive temperatures reaching over 35,000 degrees
Fahrenheit at the arc terminals, which is surprisingly hotter than the surface temperature of the sun. This extreme heat can ignite equipment and combustible materials that are nearby, including melting steel and other metals within a second or less. Even worse, it can severely burn human skin and tissue while igniting all types of combustible clothing. AFs produce large amounts of energy that discharge flashes of bright light, like lightning, causing momentary or permanent blindness.
Arc blasts can create high pressure forces and electrical explosions sending debris and equipment thru the air like dangerous missiles. Arc blasts can also produce enough pressure to burst human eardrums.
AFs can occur from both alternating current (AC) and direct current (DC) electrical circuits.
Shown below are examples of various AFEs and arc blasts.
Protection against AFEs is extremely important since, on average, there are close to 30,000 AFIs each year with approximately 400 related deaths per year.
The Importance of Performing an Arc Flash Analysis
AF studies are very important for minimizing hazards and providing increased safety for craft, electrical workers, contractors, vendors, and a company's overall safety culture. The arc flash analysis (AFA) is needed to help identify the electrical risk levels and to assist in applying appropriate safety practices in place in order to minimize the risk of burns and injuries to employees, contractors, and vendors. An AFA is very important for the electrical industry and its workers. The AFA is required for all utilities, manufacturing, industrial, commercial, and any other facility with major electrical components containing electrical disconnects, motor control centers (MCCs), electrical transformers, panel-boards, switchboards, industrial control panels, meter socket enclosures, etc. An AFA is also required by OSHA, NFPA, IEEE 1584, and NESC.
The OSHA standards that apply to AF are:
- OSHA 29 CFR 1910.132(d)(1)
- OSHA 29 CFR 1910.332(b)(1)
- OSHA 29 CFR 1910.333(b)(2)(iv)(B)
- OSHA 29 CFR 1910.335(a)(1)(i)
- OSHA 29 CFR 1910.335(a)(1)(iv)
The NFPA 70E codes that apply to AF are:
- Article 130.5
- Article 130.7
The NEC that apply for AF is:
- Article 110.16(A)
- Article 110.16(B)
Since the formation of IEEE 1584 (The Guide for Performing Arc Flash Hazard Calculations) in 2002, IEEE 1584-2018 has been revised with different calculation methods that require previous AF calculations to be updated to the latest standards. The IEEE 1584-2018 revisions involve identifying various electrode configurations, enclosure sizes, variation adjustments for arc current, including updated voltage ranges, changes to IELs (cal/cm2), etc.
OSHA requires AFA to be performed since AFEs are considered one of the workplace safety hazards.
Failure to comply with OSHA concerning an AFA for the protection of affected employees (including proper training for employees) can result in loss of life, serious injuries, large medical claims, litigation, OSHA violation & fines, damage to critical equipment and systems, lost production, and company downtime.
Listed below are the main benefits of performing an AFA.
- Improved safety for employees, contractors, and vendors
- Reduced medical costs and legal fees
- Regulatory compliance with OSHA, NFPA, and NESC
- Reduced OSHA violations and fines
Performing the Arc Flash Analysis
In order to adequately label and warn electrical workers of the AF hazards for specific equipment, cabinets, and panels; an AFA must be created.
The AFA should be performed by professional electrical engineers or other qualified electrical personnel.
Various software packages are available in aiding AF calculations, like: ArcPro, ASPEN, CYME, EasyPower, EDSA, ETAP, Matlab, SKM, etc.
Before the AFA can be performed, data collection and field documentation must be verified. Below is a simple outline showing the data required and steps performed for completing the AFA process.
- Data Collection
- Obtain an existing, accurate, and up-to-date electrical single line or one-line diagram of the electrical supply system.
- Obtain copies of previous analysis or studies of short circuits, faults, PD coordination, or load flow calculations (including any equipment maintenance records or abnormal issues).
- Perform Field Verification
- Verify all loads are accurately documented.
- Update any and all documentation as required.
- System Modeling
- Using desired AFA software, enter in all required data.
- Perform the short circuit calculations.
- Perform the coordination analysis with all PDs.
- AFA Report
- Print and install all AF hazardous warning labels.
Shown below are two examples of AF warning labels.
The Importance of Arc Flash Labels
AF labels are used as warnings in order to protect all electrical workers and craft personnel, by displaying the recommended safe working distances from the hazard and the amount of protective clothing, arc rated (AR) clothing to wear that is quantified in energy of calories per square centimeter (cal/cm2). AF energy levels depend on several factors, such as: maximum fault current, types of protection devices (PDs), duration and trip settings of PDs, conductor sizes and lengths, etc. IEL is the amount of energy that can be created during an AFE, while the arc flash protection boundary (AFPB) is the closest distance allowed before requiring proper personal protective equipment (PPE).
The NFPA 70E, 130.5 & 130.7, and the NEC 110.16, requires dangerous and high hazard electrical equipment to be clearly labeled with warnings of AF.
These labels list the amount of energy that can be produced from a possible AFI.
AFA software can provide various warning label templates for applying to electrical cabinets, panels, motor control centers (MCCs), and equipment. Warning labels should include the following items:
- Arc Flash Hazard Boundary (AFHB)
- Incident Energy Level (IEL)
- Hazard Risk Classification
- PPE Required
- Potential Shock Hazard
- Equipment Name, Bus, or Node Identification
- Date when label was printed
Some labels may also include upstream and/or downstream equipment or PDs.
Proper PPE is used for personal safety and protection against the hazards of AF, such as AR clothing that can help protect against severe burns if an AFI occurs. PPE for AF hazards can consist of AR shirts, AR pants, AR coveralls, AR full body suits, AR boots, AR gloves, AR helmets, AR face shields, etc.
Shown below are the hazard risk categories along with the required PPE for each category, including the IEL for each category. If the IEL is less than 1.2 cal/cm2, it's considered a category zero “0”, which requires PPE of hard hat, untreated cotton long sleeve shirt, pants, safety glasses and hearing protection. This is to protect against possible 2nd degree burns, while the 8.0 cal/cm2, being part of category 2 (shown below) is for protecting against possible 3rd degree burns.
3 Phase Associates has professional electrical engineering consultants with several years of AFA experience who are ready to serve you. We would be glad to help you with all of your electrical engineering needs.
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