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An arc flash is an electrical explosion due to a fault condition or short circuit, when either a phase-to-ground or phase-to-phase conductor is connected and current flows through the air.
Arc flashes cause electrical equipment to explode, resulting in injury or death to workers and destruction of electrical equipment. Temperatures may exceed 35,000°F (the surface of the sun is 9000°F). These high temperatures cause rapid heating of surrounding air and extreme pressures, resulting in an arc blast. The arc flash/blast will likely vaporise all solid copper conductors which will expand up to 67,000 times their original volume when vaporised. The arc flash/blast produces fire, intense light, pressure waves and flying shrapnel. When an arc flash happens, it does so without warning and is lightning quick. The result of this violent event is usually destruction of the equipment involved, fire, and severe injury or death to any nearby people. Proper safety and protection measures must be taken to limit the damage from an arc flash, which include conducting an arc flash study, short circuit study, and electrical safety training. There are a variety of reasons why an arc flash can occur, but most of them are human error and preventable. Many arc flashes occur when maintenance workers are manipulating live equipment for testing or repair and accidentally cause a fault or short circuit. Improper tools, improper electrical equipment, corrosion of equipment, improper work techniques and lack of electrical safety training are just some of the events that can lead to a devastating arc flash or arc blast.
Causes of arc flash incidents
One of the primary reasons for electrical injuries is electric arcing, commonly referred to as arc flash. Arc flash incidents are often related to human error when work is being performed on or around energised electrical equipment. Even when the work involves control equipment and the handling of small, low-voltage electrical components, the risk of arc flash still exists. An arc flash may cause severe burns, hearing loss, eye injuries, lung damage, and blast injuries. Arc flashes are rare but when they do happen, the impact on personnel and the business can be significant. Maintaining a heightened sense of awareness can help to protect equipment and save lives.
“an arc flash may cause severe burns, hearing loss, eye injuries, lung damage, and blast injuries”
Accidental contact
Working around exposed, live parts presents a hazard, and the fact is –accidents do happen. When it comes to accidents around electrical equipment, a mere drop of a tool or physical contact with the live part can set off an arc flash and instantly generate an energy explosion releasing temperatures in excess of 35,000˚F.
Testing and troubleshooting live equipment
The importance of uptime for critical processes often results in the need to perform troubleshooting on live equipment. If a test probe accidentally establishes a phase-to-phase or phase-to-ground connection during a routine check, it could result in personal injury and downtime. Ensuring the right tools are used for the job will help to reduce the risk and probability of an arc flash occurring.
Installing and operating live equipment
Adding or removing circuit breakers, contactors or components in energised control circuits or motor control centre (MCC) buckets, or installing or removing MCC buckets from a live bus, can all incite an arc flash. Routine operation of breakers and disconnect switches, especially racking breakers in or out of both low and medium-voltage switchgear, all present a risk of arc flash in equipment that has not been properly installed, tested and maintained.
Poor condition of equipment
Damaged insulation, or loose or incorrectly wired control connections, can all lead to failures and ultimately arc flash incidents. Insulation breakdown can cause arcing or heat, potentially triggering an arc flash. It is important to verify the integrity of cable installation prior to working on any electrical equipment. Missing or damaged insulation, barriers and guards may increase worker exposure to hazardous locations and components. Damaged equipment enclosures, operating mechanisms, and cable/bus supports, are important factors in assessing the likelihood of exposure to hazards and the probability of an accident occurring.
Improperly maintained equipment and tools
The primary purpose of a circuit protective device is to interrupt current flow after a downstream short circuit or fault is detected. If the protective device has not been properly maintained and it fails to interrupt the fault, the result could be an explosive arc flash and the ensuing damage to equipment and personnel. Regular testing and preventative maintenance can help ensure the equipment will operate within manufacturer’s limitations. Poor environmental conditions, such as moisture, or a build-up of conductive dust or contaminants, can result in corrosion or compromised insulation systems. Damaged or improperly rated tools and test equipment, including worn insulating material for screwdrivers and wrenches, can lead to accidental arcing from conductors to ground.
Arc flash risk assessment
An arc flash risk assessment is required to determine the risk level of all areas in which employees perform work. This is essential to ensuring worker safety, and helps save lives and money by minimising the risk of injuries and lost time due to accidents.
In general, arc flash risk assessment includes the following:
Data Collection – Collect necessary data about the facility’s power distribution system, including details of all three phase electrical components, nameplate specifications, and lengths and cross-section of all cables.
Engineering Analysis of the Data – Perform a short circuit analysis followed by a coordination study and determine the minimum PPE requirement.
Protective Device Coordination – Coordinate PPE to ensure selection and arrangement are sufficient for mitigating arc flash hazards.
Arc Flash Calculations – Determine incident energy levels and flash protection boundaries, and complete calculations of all relevant equipment busses.
Arc Flash Study and Analysis Report – Once the calculations are done, deduce the results of the report carefully.
Label Installation – Create and install warning labels pinpointing incident energy and working distance, arc flash boundary, and nominal system voltage. Include limited and restricted approach boundaries, date, upstream protective device, and recommended personal protection equipment (PPE) as well.
Arc flash incident risk controls
1. Perform a Hazard Analysis
Every arc flash mitigation program should begin with a hazard analysis aimed at calculating how much energy an arc flash could release at various points along the power chain. Accuracy is essential with such measurements, and 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. To ensure employees are always aware of potential arc flash hazards, companies must place warning labels on any piece of electrical equipment that poses an arc flash risk. They must also mark arc flash hazard zones on the floor, so workers not wearing appropriate personal protective equipment (PPE) can clearly see how far away from electrical equipment they must stand to avoid serious injury.
2. Reduce Available Fault Current
Though not applicable to environments protected by fuses and current-limiting breakers, facilities using non-current limiting breakers (NCLBs) can reduce the amount of incident energy released during arc flashes by reducing the amount of available fault current. The following three strategies can help plants with NCLBs significantly reduce available fault current:
Operate with an open tie during maintenance – When maintaining dual electrical sources, current limiting devices above current values can increase available fault current and reduce incident energy. Sometimes, however, opening the tie between dual power feeds during maintenance procedures reduces arc flash dangers by cutting available fault current in half. Of course, opening ties during maintenance also temporarily renders your power scheme redundant, exposing equipment to a heightened risk of failure.
Employ high-resistance grounding – During ground faults, high-resistance grounding (HRG) systems provide a path for ground current via a resistance that limits current magnitude, dramatically reducing the size of line-to-ground faults and associated arc flashes. HRG can be used on systems that service only three-phase loads.
Use current-limiting reactors – Current-limiting reactors act as a bottleneck on electrical flows, restricting current during faults. For example, low-voltage motor control centres can be supplied with three single-phase reactors that limit available short circuit current, resulting in smaller energy releases when faults occur.
3. Shorten Clearing Time
To shorten arc flash events by decreasing fault clearance times, you should:
Utilise zone selective interlocking – Zone selective interlocking (ZSI) is a protection scheme that uses an “inhibit” signal transmitted from downstream breakers that detect a fault to the next breaker upstream. The upstream breaker detects both the fault current and the inhibit signal, and therefore delays tripping, allowing the downstream breaker to clear the fault. Should a fault occur between the downstream and upstream breaker, however, the downstream feeder does not detect the fault or send an inhibit signal to the upstream breaker. That causes the upstream breaker to bypass any intentional time delay settings, significantly reducing arc flash incident energy.
Implement a bus differential scheme – These are coordinated zones of protection within an electrical system. When a fault occurs within a given zone of protection (e.g., between the main and feeder breakers), protective devices trip instantaneously, limiting arc flash durations while also confining arc flash damage to specific portions of your infrastructure. Bus differential systems are typically faster and more sensitive than ZSI, but require additional current transformers and relaying equipment, making bus harder to implement and more expensive than ZSI.
Deploy an Arc flash Reduction Maintenance System – An ARMS shortens faults by bypassing all time delays in the trip circuit any time a current exceeds an ARMS preset maximum. This enables faults to clear even faster than a circuit breaker’s “instantaneous” function. Technicians must manually enable ARMS circuits before doing maintenance work and then disable them when that work is complete, employing familiar lockout/tag out procedures.
4. Adopt Remote Operation
Executing potentially dangerous procedures remotely can help protect personnel from injuries. Here are two ways to limit maintenance operations performed in range of arc flash events:
Install remote monitoring, control and diagnostics software – Modern power management systems equip administrators with the ability to perform many administrative tasks remotely. They also equip companies with the ability to remotely de-energise electrical equipment before staff members come into contact with it.
Employ remote racking devices – Traditionally, technicians have had to stand close to equipment with live, electrical connections when racking and unracking breakers. Remote racking devices enable operators to perform these extremely dangerous tasks from
a safe distance.
5. Predict and Prevent Faults
One of the most effective ways to prevent arc flashes is to anticipate and eliminate the conditions that cause them. The following three solutions help spot potential arc flash dangers before they have a chance to do harm and keep personnel safely away from live connections:
Monitor insulation integrity – Deteriorating insulation is the leading cause of arc-producing electrical failures. Identifying and repairing compromised insulation before it fails can help avert arc flash explosions. Predictive maintenance systems provide early warning of insulation failure in medium-voltage switchgear, substations, generators, transformers and motors.
Monitor pressure junctions – Most electrical equipment contains pressure junctions, such as shipping splits, load lugs, and compression fittings. Over time, vibration and thermal cycling can loosen these connections. When current flows through a loose connection, it can cause overheating and eventually produce an arc flash.
However, non-contact thermal sensors called pyrometers can monitor pressure junctions continuously and provide advance notification of loose connections before they create an arc flash explosion.
Use infrared (IR) windows – Using contactless IR thermography technology, IR windows enable technicians to perform IR scans without removing switchgear side panels, lessening the likelihood of arc flash events caused by accidental contact with live bus.
6. Redirect blast energy
Equipment that directs arc flash energy away from personnel is called “arc resistant”. Arc resistant switchgear, for example, utilises sealed joints, top-mounted pressure relief vents and reinforced hinges, to contain the energy and heat released by arc flashes and channel them via ducts to an unoccupied area inside or outside the building. When all else fails, arc resistant switchgear offers vulnerable employees a critical last line of defence from the explosive power of arc flash incidents. However, its protective qualities are effective only when equipment doors are closed, so companies should train their technicians to fasten doors securely during normal operation.
Arc flash events can cause serious harm, ranging from disabling or fatal injuries to heavy fines and expensive lawsuits. Though no combination of countermeasures can completely eliminate the risks, utilising the solutions and strategies discussed in this article can help organizations make arc flash incidents less likely to happen, and less harmful when they do.
Human factors and risk controls
The risk of arc flash incidents or incidents involving electrical hazards (such as working on energized equipment when permitted by law) are affected by any range of human factors in people who perform tasks as electrical workers. On occasion, electrical work is performed by people who are young (such as apprentices who are largely less than 25 years of age) or who are deemed ‘vulnerable’ – perhaps as a result of their age, experience or length of service, their level of skill and competence, or as a result of relevant and potentially multiplied ‘human factors’ that are present across the Energy Industry. As these human factors may contribute to electrical incident, and accidents, the management of (and training in) human factors is an important issue for all electrical workers in the energy industry. By definition, human factors are the wide range of issues that affect how people perform tasks in their work (and non-work environments); how they interact with each other across teams, equipment and workplaces; and how they interact with management systems and technology. Human factors are the social and personal skills which can complement (but also distract from) technical skills, and they are important for safe and effective electrical work. Electrical workers in the energy industry are deemed ‘vulnerable’ workers as they have a greater exposure and are at increased risk of fatality or injury/incident than most – due to both the types of electrical work that they perform and in recognition of the many ‘human factors’ that interact with their safe and effective performance of technical work in the energy industry.
The types of human factors that can interfere with safe and effective electrical arc flash risk controls being implemented by electrical workers can include (but are not limited to):
1. Training and competency – where electrical workers are not educated and competent in the arc flash hazard. They are unaware of the potential for an arc flash incident to cause harm.
2. Errors, mistakes and lapses – where people make errors in a process (for a wide range of reasons) that result in compromising the effectiveness of arc flash risk controls.
3. Complacency – both with the risks and the process of arc flash risk controls.
4. Time pressure – where the ability to properly implement an administration control (such as a permit to work) is compromised.
5. Violations – where people deliberately and willingly work ‘outside’ known risk controls, and expected skills and competencies.
6. Information overload – where the information is unclear, overwhelming, or duplicated, leading to confusion and errors (this often affects a contracted workforce who are commonly assigned higher-risk work).
7. Distractions – that are both work and non-work related, and all lead to the ‘breaking’ of a person’s concentration, resulting in error (such as non-work-related distractions from mobile phones).
8. Mental health issues and concerns.
9. People whose actions are affected by the interaction of (actual or perceived) workplace culture, being bullied or facing peer pressure from team-members and/or their Supervisors/Team Leaders, and a lack of accountability across all aspects of electrical works.
The above-mentioned human factor risks can be controlled by:
Training and competency –
- Commit to an implementation of the minimum competency requirements when working on/around electrical arc flash hazards
- Instruction, supervision, information or training in human factors
- Appropriate worker selection and monitoring to the ongoing suitability of workers selected to perform relevant works
Errors, Mistakes and lapses –
- Verification activities
- Isolation, plant ID and activity required
- Appropriate worker selection and monitoring to the ongoing suitability of workers selected to perform relevant works
- Stop and think processes
- Ongoing safety observation process (behavioural based)
- Management, Team Leader, Supervisor and Peer walk downs
- Effective QA documentation
- Switching or job instruction
- Interlock and control
- Error tolerant equipment
Complacency –
- Ensure levels and type of supervision match the actual (or potential) for arc flash hazards and risk
- Commit to arc flash awareness activities by way of alerts, training, refreshers, toolbox talks, and lessons learned (post industry incidents and accidents)
Time pressure –
- Executive and Senior Management oversight
- Proper planning and resourcing for activities
- Higher risk activities emphasised in risk assessment
- Management, Team Leader, Supervisor and Peer walk down
Distractions –
- Ensure levels and type of supervision match the actual (or potential) for arc flash hazards and risk
- Stop and think processes
- Ongoing safety observation process (behavioural based)
- Management, Team Leader, Supervisor and Peer walk down
Mental Health issues and concerns –
- Ensure levels and type of supervision match the actual (or potential) for arc flash hazards and risk
- Stop and think processes
- Ongoing safety observation process (behavioural based)
- Management, Team Leader and Supervisor and Peer walk downs
- Employee Assistance Programs (EAP) and other Mental Health
- First Aid assistance in the event of worker disclosure of mental health issues and concerns
Conclusion An electric arc flash is a very serious incident which causes severe property damage and human fatality. There are various factors contributing towards arc flash incidents. Proactive risk assessments and risk mitigation controls are mandatory to prevent such hazardous incidents. An effective safe work procedure, appropriate supervision, and competent workers are required to overcome arc flash incidents. Human factors and behavioural aspects are contributing factors of the arc flash incidents, and so it is evident behavioural based safety needs to be incorporated in arc flash prevention. Arc prevention PPEs, properly rated and tested PPEs, and insulated tools and equipment are all important controls required for arc flash prevention.
