05.10.2015 : Tim Ritson

Arc flash – The other electrical hazard

Arc flash is a phenomenon that can cause serious injury or death without direct contact. It is a significant risk to safety in the workplace, particularly for electrical workers, but is often overlooked.

As all of us know, an electric shock is a serious hazard associated with electrical assets. A person coming into contact with a live conductor can be injured or killed. But there is another kind of electrical hazard that is less appreciated. Arc flash is a phenomenon that can cause serious injury or death without direct contact. It is a significant risk to safety in the workplace, particularly for electrical workers, but is often overlooked.

While serious arc flash incidents are infrequent, they are one of the most common causes of injury to electrical workers. In February 2015, an explosion occurred at a Perth shopping mall, in which two workers died while changing fuses on a power transformer. In April 2013, some electrical switchgear failed at an electrical substation in Hamilton. While there were no injuries, it caused major outages to the area, impacting the asset owner and customers.

As an employer, do you know your obligations for mitigating such hazards and providing a safe working environment for your employees?

What is arc flash?

An arc flash is an explosive release of energy caused by an electrical arcing fault, usually associated with electrical switchgear or industrial equipment. An arc flash can cause burns, retina damage, respiratory damage and hearing loss. In extreme cases, arc flash can result in serious injury or even loss of life.

There are various causes of arc flash, including human error and equipment failure. Many cases are caused by poor maintenance and operating practices. Errors, such as dropping tools or components across conductors or incorrectly applying earths, can initiate a fault that progresses into an arc flash. Equipment failure is also a common cause. While equipment can fail spontaneously, it is more likely to happen during switching or maintenance. But even something as simple as a build-up of dust inside switchgear can be enough to cause a flashover between conductors.

The far-reaching consequences

Arc flash has the potential to be both harmful and destructive. Serious injuries can drastically impact the lives of those involved, as well as their families, friends and colleagues. In addition to the human effect, arc flash can be disruptive and costly for business. The worst incidents often have legal implications that can result in large fines to companies and affect those in positions of responsibility. Even if less severe, a damaged switchboard can cause significant outages, sometimes for long periods while repairs are undertaken. Companies must consider these consequences if they do not take responsibility for making their equipment safe.

Who is accountable?

In New Zealand, the Health & Safety in Employment Act 1992 requires employers to take all practicable steps to ensure the safety of their employees, contractor’s employees and the public. Employers are required to have a method for identifying and regularly assessing hazards, and take all practicable steps to eliminate or minimise significant hazards.

Specific industry standards have also been developed for the management of arc flash hazards. Policy documents such as that produced by the Electricity Engineers’ Association (EEA) state that it is the asset owner’s responsibility to carry out an assessment to determine potential exposure to an electric arc. If an arc flash incident were to be investigated, these documents would likely be used to determine if employers and asset owners had taken all practical steps to prevent it.

How can we approach this issue?

The energy released by an arc flash can be quantified from factors such as the ’strength’ of the connection to the high-voltage electrical network, the extent to which the electrical network will limit fault current, and how quickly fuses or circuit breakers can clear a fault. Often, the hazard is found to be low enough that no specific mitigations are required. However, it is important to assess the significance of the hazard so that the most cost-effective mitigations can be put in place.

Depending on the installation, the most practical mitigation may be the use of the appropriate arc-rated personal protective equipment (PPE), assessed against the actual hazard level. Warning labels should be placed on all equipment that state the PPE requirements and the boundary distance inside which the PPE must be worn. Alternatively, fault clearance times can sometimes be improved to clear a fault faster, thus reducing the release of energy. Sometimes the hazard can be removed by remotely operating or isolating the equipment being worked on.

It’s important to take a wider view

It is a common misconception that features of a switchboard alone, such as arc containment or arc venting, are enough to safeguard employees. However, the protection afforded by arc containment or arc venting is negated as soon as a panel on the switchgear is open. In fact, no single switchboard feature can ensure the equipment is safe. A system-wide study must be undertaken, taking into account other parts of the network and operational scenarios.

Conclusion

As the electrical industry gains a better understanding of the risks that equipment poses, we have the opportunity to make our environment safer. Operators need to take responsibility for managing these risks to keep employees safe. This not only demonstrates the employer’s commitment to workers’ wellbeing, but more importantly, could save lives.

As an owner or operator of electrical switchgear, are you doing everything reasonable to prevent arc flash and ensure the safety of your employees, contractors and the wider public?

About the Author

Tim Ritson

Associate - Power Systems Engineering

Tim is a senior power systems engineer and is involved in leading Beca’s approach to arc flash assessments. He's an expert on industry guidelines and best practices for arc flash hazard assessments, and has been involved in arc flash projects in New Zealand and throughout Asia.

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