According to a report conducted by Industrial Safety and Hygiene News it is estimated 30,000 arc flash incidents on average occur each year, resulting in an average of 7,000 burn injuries, 2,000 hospitalisations and 400 fatalities.
NFPA 70E defines an arc flash hazard as;
“a dangerous condition associated with the possible release of energy caused by an electric arc.”
An arc flash occurs when a surge of electrical current caused by short circuit conditions flows from one energised conductor to another, which results in an explosion of heat and pressure into the external environment. Despite the transient nature of arc flash incidents, they have the potential to reach temperatures of up to 35,000°F
The risk of arc flash is ever increasing, as organisations strive to increase power capacity while simultaneously reducing their physical footprint - calling for higher power density within switchgear and data centres in general. As a result, operating personnel are required to work in closer proximity to high voltage systems. It is standard practice for modern switchgear systems to come fitted with arc reduction technologies, however these technologies are not enough to mitigate arc flash risk as standalone solutions. Due to its potentially fatal consequences, it is crucial that organisations adopt a more proactive approach to assessing and preventing arc flash incidents through careful and ongoing analysis and training.
What is an Arc Flash Risk Assessment?
An Arc Flash Risk Assessment is a study conducted in line with NFPA 70E section 130.5. - A Standard for Electrical Safety in the Workplace enforced by National Fire Protection Association. An Arc Flash Risk Assessment provides organisations with a quantifiable indication of the arc flash hazard level. The intended outcome this study is a to determine the appropriate level of PPE required by personnel and to limit exposure to dangerous incident energy levels when working in proximity to energised systems
Firstly, the organisation must assess where a significant risk exists. The risk will then be evaluated to determine what safety precautions are required to mitigate the risk. In order to comply with NFPA 70E assessments must be conducted at least every 5 years – This forces organisations to continually assess and evolve their safety protocols and designs to ensure employee safety in high risk areas.
Arc Flash Risk Assessment Steps
- Assess The risk
The first step of arc flash risk assessment is predicting the likelihood and severity of the hazard by performing Arc flash calculations. NFPA 70E and IEEE 1584 “Guide for Performing Arc-Flash Hazard Calculations,” each outline their own methods for calculating the available arc flash energy of equipment, however there is no preference given to a specific method.
- Incident Energy
When calculating the incident energy of an arc flash the two most important measurements are the ‘Arcing current’ which determines the current required to cause an arc fault, and the ‘arcing time’ which is the duration of the arc flash, together these variables will identify the levels of arc energy a worker could potentially be exposed to during an arc flash incident.
- Arc Flash Boundaries
The arc flash boundary is the specified safe working distance from energised conductors that have a potential to arc, these boundaries are used to advise safety protocols and limit injury when working at specified locations. The boundaries can be calculated using boundary tables outlined in NFPA 70E, which use a combination of the arcing current and arc duration to determine safe working distance. Alternatively, both NFPA 70 E and IEEE Standard 1584 provide formulas to can be used to calculate arc flash boundaries with more accuracy.
2. Eliminate the Risk
Now that the severity of the hazard has been identified, efforts must be made to either design out or eliminate the hazard at source. Firstly, the switchgear system should be assessed for general wear and tear, which may have resulted in loose connections, worn insulation, water damage etc – All of which could increase arc flash risk. In cases such as these the hazard can easily be reduced by performing maintenance or replacing the source component. However, even after replacing potentially faulty components, every MV switchgear system will carry a low risk of arc flash. For this reason, it is important that systems are designed with the latest arc limiting technologies installed to mitigate unanticipated incidents.
3. Protect Personnel
As previously discussed, despite the availability of new arc limiting technologies, arc flash risk in MV switchgear can never truly be eliminated due to the high levels of voltage present. Therefore, precautions must be implemented to ensure the safety of for personnel working in proximity to energised systems. This will include the selection of appropriate PPE for the working within the arc flash boundary, clear warning labels and other protections such as remote access.
When an arc flash occurs personnel not wearing adequate PPE are at risk of being fatally injured However, this tragedy can often be avoided by conducting a detailed arc flash risk assessment to determine the level of PPE required for adequate protection.
4. Inform and Enforce
NFPA 70E requires organisations to display appropriate warning labels on MV switchgear by law, however employers also have a responsibility to ensure that operating personnel fully understand the risks associated with their role and how to comply with the operational guidelines put in place – This can be achieved through adequate staff training and documented policies and resources. Additionally, once the arc flash risk assessment has been completed and new safety measures have been identified It is important that the employer does not neglect the findings and continues to enforce and develop safe working conditions for employees.
To conclude, arc flash risk assessment is the most effective tool for mitigating arc flash risk within MV switchgear as it provides a complete overview of the risk level, the source and sets out clear guidelines for ensuring personnel are fully protected whilst carrying out operations. Although, arc limiting technologies are critical in mitigating unanticipated incidents, they are merely one part of the larger arc flash mitigation solution and must be implemented alongside regular risk assessments to pre-empt impending serious incidents.