Arc Flash Risk Assessments: An Overview
Arc Flash

ABSTRACT
Recently, arc flash risk assessments have become more challenging as a result of additional researching and modelling implications required to comply with the 2015 version of the NFPA 70E.

Prior to 2015, the applicable codes defaulted to the IEEE, which states “equipment below 240v need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply”. The current updates now require a hazard analysis for all equipment rated higher than 50V.

Electrical arc flash protection is becoming a larger concern throughout the industry as a result of numerous injuries, especially with work on live equipment becoming more commonplace in many industries. Arc fault can result from many things, including failed/damaged equipment or wiring, loose connections, transients, and system faults. Arc flash is a rapid release of energy due to an arcing fault, in which the air serves as the conductor. Typically, the bus voltage is greater than 120V since lower levels generally will not sustain an arc. After the initial flash, the fault is sustained through highly conductive plasma which typically vaporizes the bus bars, causing an explosive blast creative, releasing radiation and creating shrapnel as it dissipates.

These events raise concerns for nearby safety personnel and property. Some key considerations for individuals responsible for facility safety relating to these events include:

• Protecting personnel from potential harm (severe burns, hearing damage, and eye injuries) and preventing loss of life.
• Complying with Occupational Safety and Health Administration (OSHA) codes and with National Fire Protection Association (NFPA) standards on employee safety, NFPA-70E.
• Preventing loss to companies through loss of skilled laborers, litigation fees, higher insurance costs, and loss of morale.
• Reducing accidents resulting in increased process uptime.
• Meeting requirements of insurance carrier.
This report identifies the codes that help to establish safer practices relative to arc flash. The basis for the arc flash protection of personnel as defined by the industry is to establish guidelines to limit injuries to onset of second degree burns (≤ 1.2 calories/cm2). The basic means to do this fall into the following categories:
• Ensure that only qualified personnel are completing work on the electrical system.
• Energized work is only permitted where it can be demonstrated that de-energizing the equipment will introduce additional hazards/increased risk, or that the task to be performed is infeasible in a de-energized state due to equipment design or operational limitations. In any of these cases an energized work permit shall be completed to justify those limitations. Otherwise, all equipment should be placed in an electrically safe condition.
• Proper PPE shall be worn at all times while completing electrical work, but should be considered as a last line of defense, and not as a replacement for safe work practices or engineering controls that can help limit exposure to arc-flash hazards.
• A hazard risk assessment/analysis shall be completed for all systems. The key variables for determining arc flash hazards are distance, magnitude, time, and PPE.

This white paper contains a compilation of current relevant codes, methods, and information in addition to providing the results of the risk assessment completed for the featured water plant and sewer plant. The report documents the calculated available incident energy and the required level of PPE at each bus throughout each system to meet requirements defined in the applicable codes/regulations.

Click here for the full white paper: An Overview of Arc Flash Risk Assessments

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