What is an Arc Flash?
An arc flash is the result of a rapid release of energy due to a short circuit through the air. Superheated air turns into highly conductive plasma, helping to sustain the arc, and leading to:
- Heat, up to 20,000°C (35,000°F)
- Sound, can exceed 160dB
- Shrapnel, can exceed 1,100km/h (700mph)
- Concussive shockwave, can exceed 50,000+N/m2
It can burn and vaporize bus bars and devastate everything in its path.
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Arc Flash & Electrical Safety Training »
Arc Flash Study
An arc flash study is an engineering study that identifies the specific arc flash hazard for an electrical equipment within a facility. It provides actual calculated short circuit currents, tripping times and incident energy (arc flash energy). It also reviews coordination to mitigate arc flash energy levels while focusing on eliminating nuisance tripping, both during a ground fault and/or phase fault condition.
Performing the Study
To perform an arc flash study, a short circuit and coordination study (see Engineering Studies) must first be performed or the results of these studies must be made available to the qualified engineer performing the arc flash study.
The minimum requirements to perform an Arc Flash Study, as per IEEE 1584 is: any 3-phase system that is 480V or higher and any 208V system, provided it is fed from a 125kVA or larger transformer.
The deliverables of the analysis include a report detailing all input parameters of the study, along with all the calculated results. The results of study will reveal what the incident arc flash energy values are at all analyzed locations of the electrical distribution system.
- Tables of findings / results
- Time-Current Curves (TCCs) along with a review of coordination of protection devices
- Short Circuit Currents
- Arc Flash Incident Energy Values
- Software Produced Single Line Diagrams
- CSA Z462 Approved Arc Flash Hazard Labels
- Any recommendations or mitigation methods that can be implemented to reduce arc flash hazards and improve safety
- PPE requirements as per CSA Z462
In Canada, the importance of having an Arc Flash Hazard Analysis completed is highlighted within Provincial Occupational Health and Safety Regulations (OH&S):
- Section 232 (1): If a worker may be exposed to a flash fire or electrical equipment flashover, an employer must ensure that the worker wears flame resistant outerwear and uses other protective equipment appropriate to the hazard.
- Section 232 (2) The worker must ensure that clothing worn beneath the flame resistant outerwear and against the skin is made of flame resistant fabrics or natural fibers that will not melt when exposed to heat.
- Section 232 Flame Resistant Clothing - OH&S Code Explanation Guide
- The employer is not required to pay for and provide flame resistant outerwear. However, the employer is required to ensure that a worker wears this equipment if there is a danger of a flash fire or flashover.
- The employer can chose to use CSA Z462 for guidance, or any other standard or information source that the employer considers appropriate.
Engineering study may be required to determine how to comply with Standards like CSA-Z462 2015 Edition (Workplace Electrical Safety)
CSA-Z462 does provide tables for use as safety guidelines when performing electrical work, those tables also list a number of conditions and parameters that must be met. For example, in Table 4B, to achieve a Category 2 level of PPE while working on a 600V MCC requires a maximum of 65kA short circuit current available and a maximum of 0.03s (less than 2 cycle) tripping time. To determine the level of short circuit current at any given MCC or Panel requires a short circuit study to be completed. Furthermore, to achieve a 2-cycle tripping time, given a certain calculated amount of short circuit current, would require reviewing time-current tripping curves. This 2-cycle tripping time is unachievable with a typical molded case breaker, as they require 3-5 cycles to trip. In the same Table 4B, to achieve a Category 4 level of PPE while working on a 600V MCC requires a maximum of 42kA short circuit current available.