Arc flash incidents occur every year in Australia - some resulting in severe injury and fatality. They also cause damage to electrical equipment, resulting in long outages and high equipment replacement costs. Due to the high-consequence nature of these incidents, many insurance companies will offer higher premiums to sites without arc-flash risk addressed.

Arc flash risk mitigation is an increasingly integral component of site management and safety assurance for sites with electrical equipment. So, what is arc flash, and how can arc flash risks be mitigated on site?

What is arc flash?

An arc fault, or arc flash, is a violent short circuit that produces an electrical arc and occurs when current flows through the air between phase conductors or between phase conductors and neutral or earth. When an arc flash occurs, the associated energy is typically high enough to cause serious burns, injury, and fatality to nearby persons, as well as significant damage to electrical equipment. The term ‘arc flash’ is derived from the primitive understanding that resulting burns were similar to that of a welding arc.

Figure 1 – Arc Flash Diagram [1]

So, how can you mitigate arc flash risks in the workplace?

Stage 1 – Identify the risk.

Generally, higher arc flash risks are associated with HV and LV electrical equipment where high-current switching can occur. This may include switching of HV/LV circuit breakers & onload switches, live racking, earth switching, or involuntary contact of live conductors.

To determine the risk and consequence of an arc fault, an Arc Flash Study is conducted to determine arc flash incident energy at all locations on the site where an arc flash risk is present. This is typically undertaken by a specialised and experienced engineering practice. Arc flash energy calculations are conducted for each location as per IEEE 1584:2018, and are determined as a function of short circuit fault levels and circuit breaker clearance time (among other physical factors).

Once incident arc flash energy levels have been quantified for all areas of the electrical infrastructure, an appropriate level of PPE may be determined for work on or near the specified piece of electrical equipment. Where higher arc flash energy risks occur, higher levels of PPE are required to mitigate this risk while working on or near the plant.

Figure 2 – Arc Flash PPE [1]

Labelling may additionally be implemented to allow for electrical personnel to understand the arc flash hazard and the PPE requirements for the work area.

Figure 3 – Typical Arc Flash Labelling [1]

While identification of arc flash risk (administrative control) and PPE are appropriate methods for arc flash risk mitigation, they are at the bottom of the hierarchy of controls and the arc flash hazard remains. Therefore, in practice, further measures are typically implemented to reduce the arc flash hazard.

Figure 4 – Hierarchy of Control

Stage 2 – Propose conceptual strategies to mitigate arc flash risk.

To mitigate the risk of arc flash, multiple aspects of the electrical system are considered, with conceptual strategies proposed to reduce the prospective arc flash energy in the event of a fault. This constitutes ‘Stage 2’ of the arc flash mitigation process.

Once arc flash hazards have been identified and quantified as part of ‘Stage 1’ of the arc flash mitigation process, areas that present high arc flash hazards are investigated to determine high-level risk mitigation methods.

Typical mitigation methods fundamentally involve the reduction of arcing current magnitudes and reduction of arcing time, which results in lower prospective arc flash energy in the event of a fault.

Reduction of arcing time is typically achieved through deliberate design of protective device settings. Settings are designed to trip the arc fault as quickly as possible, while maintaining appropriate coordination with upstream and downstream protective devices. 

Reduction of arcing current magnitudes may be achieved through the implementation of current-limiting devices, specified to integrate with the unique site characteristics.

Protection design and fault current limitation design is typically undertaken by a specialised engineering practice.

Once conceptual risk mitigation strategies have been designed for all areas of plant with high arc flash risk, arc flash levels are re-calculated as per IEEE 1584:2018.

Stage 3 – Detailed design of arc flash mitigation methods

Once conceptual risk mitigation strategies have been determined as part of ‘Stage 2’ of the arc flash mitigation process, detailed design may be undertaken.

Detailed design involves consideration of unique site scenarios and assesses the appropriateness of each of the recommended solutions. Where the protection settings of existing protective devices are not robust enough to reduce the arc flash risk at a piece of plant, detailed design is conducted for circuit breaker and/or relay replacement and installation. The detailed design stage may also involve a comprehensive protection system review and design where multiple protective devices are altered or replaced.

Where current-limiting equipment is required, site-specific installation requirements are determined during the detailed design process.

Detailed design for the electrical installation and protection systems may be undertaken by a specialised engineer.

Stage 4 – Implementation

Once detailed design has been conducted for risk mitigation strategies as part of ‘Stage 3’ of the arc flash mitigation process, implementation may be undertaken.

This stage involves the construction and installation of the proposed arc flash risk mitigation methods. Electrical engineering works are conducted in conjunction with an electrical contractor for the supply, installation, and commissioning of the specified electrical equipment.

 

Figure 5 – Arc Flash Mitigation, Four Stage Process

Addressing arc flash risks in the workplace can have a profound effect on improving safety for personnel working on, or even near, electrical equipment. 

Call (02) 4961 3344, or email info@pceng.com.au, to see how Power Control Engineers can support you through the Arc Flash Mitigation Process; toward achieving a safer workplace. 

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References

[1] Australian Energy Council, Electrical Arc Flash Hazard Management Guideline. Melbourne VIC 3000, 2019.

[2] Energy Safe Victoria, Arc flash hazard management. Glen Waverley VIC 3150, 2019.

[3] Government of Western Australia - Department of Mines, Industry Regulation and Safety, Safety management of electric arc flash hazards. 2018.

[4] Queensland Government, "Electrical arc flash", Worksafe.qld.gov.au, 2021. [Online]. Available: https://www.worksafe.qld.gov.au/safety-and-prevention/hazards/electricity/electrical-arc-flash#:~:text=If%20there%20are%20energised%20parts,choose%20not%20to%20work%20live. [Accessed: 13- Jul- 2022].

[5] Fluke, "What Causes Arc Flash? Electrical Arc Blast Explained", Fluke.com. [Online]. Available: https://www.fluke.com/en-au/learn/blog/safety/arc-flash-vs-arc-blast. [Accessed: 13- Jul- 2022].

[6] Creative Safety Supply, "Where do arc flashes occur?", Creativesafetysupply.com. [Online]. Available: https://www.creativesafetysupply.com/qa/arc-flash/where-do-arc-flashes-occur#:~:text=An%20arc%20flash%20occurs%20when,has%20a%20chance%20to%20escape. [Accessed: 13- Jul- 2022].

[7] SEAM Group, "Why You Need to Have an Arc Flash Hazard Assessment", SEAM Group. [Online]. Available: https://www.seamgroup.com/why-you-need-to-have-an-arc-flash-hazard-assessment/. [Accessed: 13- Jul- 2022].

[8] S. King, "The 7 Steps to Complete an Arc Flash Analysis", Hallam-ics.com, 2021. [Online]. Available: https://www.hallam-ics.com/blog/the-7-steps-to-complete-an-arc-flash-analysis. [Accessed: 13- Jul- 2022].

[9] Queensland Government Electrical Safety Office, Managing electrical risks in the workplace. 2021.