Understanding the Concept of Arc Flash Boundary: A Review of the 2018 NFPA 70E Standard

Introduction

Arc flashes are a significant hazard in the electrical industry, posing a risk to workers' safety and health. The concept of arc flash boundary is crucial in determining the distance from which an employee can safely approach an electrical source without being exposed to potentially harmful thermal energy. In this article, we will review the 2018 NFPA 70E standard and explore the misconceptions surrounding the arc flash boundary.

Thermal Injury and Dosage

A common misconception about arc flashes is that a large amount of energy delivered over an extended period does not cause injury, whereas a smaller dose delivered instantaneously can be devastating. This idea is based on the assumption that thermal injury follows the law of reciprocity, where equal doses produce equal injury. Mathematically, this concept is represented by the product of flux and exposure time for a shaped pulse.

Critical Thermal Load

The critical thermal load is another important concept in understanding arc flashes. It refers to the total energy required to produce a given endpoint, such as a blister, during a single exposure. However, the use of rule-of-thumb terminology has led to serious misconceptions in this field.

NFPA 70E and Arc Flash Boundary

The National Fire Protection Association (NFPA) has published several editions of NFPA 70E, which provides guidelines for electrical safety in the workplace. The revised definition of arc flash boundary in NFPA 70E 2018 is particularly noteworthy. The standard defines the arc flash boundary as the distance at which the incident energy equals 1.2 cal/cm^2.

However, there are some glaring contradictions and inconsistencies within the standard. For example, the same standard prohibits using incident energy and PPE category together, yet it also references a sample label with fields for available incident energy and level of PPE.

History of Arc Flash Boundary

NFPA 70E has undergone several changes since its inception in 2004. The 2012 edition stated that a second-degree burn is possible by exposure to an electric arc flash above the incident energy level of 1.2 cal/cm^2 (5.0 J/cm^2) for systems with 50 Volts or greater. This threshold was later removed in the 2012 edition.

In conclusion, understanding the concept of arc flash boundary is crucial for ensuring electrical safety in the workplace. The 2018 NFPA 70E standard provides guidelines for determining the distance from which an employee can safely approach an electrical source without being exposed to potentially harmful thermal energy. However, there are some serious misconceptions and contradictions within the standard that need to be addressed.

As the industry continues to evolve, it is essential to stay up-to-date with the latest developments in NFPA 70E standards. The upcoming changes to the definition of arc flash boundary will likely provide further clarity on this critical topic.

Arc flash boundary 2018