What is an Arc Flash?

An arc flash is a type of electrical explosion that occurs when an electric current passes through the air between two ungrounded conductors. According to the Electrical Safety Foundation International, an “arc flash is a sudden release of electrical energy through the air when a high-voltage gap exists and there is a breakdown between conductors.”

An arc flash results in intense heat and light. The energy discharged from one can reach 35,000°F. Serious or fatal burns can occur at distances of more than 10 feet from the source of the arc flash. In addition to burns from the flash itself, flammable clothing can ignite; synthetic fibers such as polyester will melt to the body, increasing the severity of the burn. The high-intensity light can also damage eyesight.

An arc blast is the pressure wave component that occurs from the fault current during the arc flash. The pressure wave is caused by rapid expansion of air and vaporization of conducting material from intense heat.

What causes an arc flash?

Unfortunately, the main cause of an arc flash is human error or equipment failure due to poor design or lack of maintenance and cleaning. Accidents caused by touching a test probe to the wrong surface or slipped tool are the most common cause of an arcing fault. Other causes of an arc flash include:

• Sparks due to breaks or gaps in the insulation
• Equipment failure due to improper installation, substandard parts, or normal wear and tear
• Dust, corrosion, or other impurities on the surface of the conductor

How is arc flash measured?

An arc flash is measured in terms of incident energy. Incident energy is the amount of thermal energy impressed on a surface, a certain distance from the source, generated during an electrical arc event. It is measured as calories/cm² (cal/cm²).

A calorie is the energy required to raise one gram of water one degree Celsius at one atmosphere. 1 cal/cm² is equal to holding your finger directly over a lighter’s flame for one second. 1.2 cal/cm² of heat can lead to second-degree burns.

Prevention is key

The best way to protect yourself against arc flash is to prevent it from occurring. The first step is to make sure that you are working on de-energized equipment. If there is no current flowing through a device then there is no need to worry about an arc flash happening.

From the inspection and maintenance side, you need to make sure there is no dust or debris laying around the equipment and that every part is in good working order — contacts aren’t corroded, insulation isn’t worn through or thinning, equipment has been properly installed.