The Formation and Hazards of Arc Flash

 The cause of Arc Flash can be attributed to accidental contact, protective devices with insufficient short-circuit current ratings, contaminated insulating surfaces, deteriorated or corroded equipment or parts, and other reasons.

Arc Flash is a phenomenon that occurs when a large amount of lethal energy is discharged due to a short-circuit of an exposed conductor, causing the air to ionize. During the period of air ionization, a large amount of arc fault current generates tremendous heat, with temperatures that can reach up to 35,000 degrees Fahrenheit, higher than the temperature on the surface of the sun. This can cause serious burns on human skin and even ignite clothing. It can also liquefy or vaporize nearby metal objects, such as copper, aluminum wires or iron components. At this time, the volume of metal rapidly expands due to its change in state from solid to vapor, causing explosive pressure and sound waves. The strong sound wave impact may cause deafness, and the accompanying bright light can cause temporary or permanent blindness. Solid metal fragments and other loose items such as tools may become lethal flying projectiles, causing serious harm to human beings. The phenomena that may occur during Arc Flash are shown in Figure 1.

Figure 1 The phenomena during Arc Flash

Arc Flash Introduction

 Introduction

To the general public, an electric arc may seem like just a visual flash of light with little relevance to themselves. However, the high temperature and energy released by an electric arc pose a much greater threat to the safety of personnel working in the vicinity than flame burns. During routine system operation, there is always a risk of electric arc hazards when circuit breakers or switches are used to switch power or equipment is inspected. The threat to personnel and equipment safety in the work area is significant, and news reports of accidents caused by electric arcs are common, often with disturbing images.

Although fatalities caused by electric arcs do not occur more frequently than those caused by electrical shocks, they still have a significant impact, with a high mortality rate. According to statistics, there are nearly 30,000 electric arc accidents of varying degrees in the United States each year, with around 1,000 fatalities. In advanced societies that value human life, prevention is an essential issue.

For many years, the US government has invested significant resources and manpower into researching and discussing the potential harm that electric arcs can cause to personnel and equipment. The results of the research and experiments have been translated into practical, quantifiable values and classifications, and the electrical regulations have been updated and strictly enforced to improve the working environment for electrical workers. If the requirements are violated, heavy penalties are imposed, and there is no leniency. As a result, positive results have been achieved.

Compared to the United States, where various agencies have actively improved the working environment for electrical personnel by revising relevant regulations, such as NESC, NEC, NFPA-70E, and IEEE 1584, domestic regulations in this area are far behind. Apart from the second chapter of the Occupational Safety and Health Act of the Executive Yuan's Ministry of Labor, which states that "employers must have necessary safety and health equipment and measures in place to prevent hazards caused by electricity, heat, or other sources," there is a lack of concrete and specific guidelines to follow.

As a result of the vigorous enforcement of US regulatory agencies, electric arc flash evaluation and analysis have become a hotly debated topic. Around 2002, major power system analysis software companies began publishing electric arc flash calculation modules, and with the combination of existing short circuit calculation and protection coordination modules, they quickly gained market share. After years of updates and revisions, electric arc flash calculations are now relatively mature and widely used.