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Arc Flash Hazards and Take Proper Precautions
An arc flash is a short circuit through the air. In an arc flash incident, an enormous amount of concentrated radiant energy explodes outward from electrical equipment, creating:
- Pressure waves that can damage hearing, fracture ribs, collapse lungs, and knock a worker off a ladder or blow him or her across a room
- Pressure waves that can send loose material like pieces of damaged equipment, tools, and other objects flying through the air at speeds in excess of 700 miles per hour
- A high-intensity flash that can damage eyesight and leave a person blind
- A superheated ball of gas with temperatures in excess of 5,000 degrees that can ignite clothing and cause serious burns over much of the body
Workers have been injured even though they were 10 feet away from the arc center. Furthermore, electrical arc flash hazards do not occur only in the presence of high voltage sources. In fact, locations consisting of many low voltage equipment sources account for the most arc flash incidents.
Causes
Arc flash occurs when electrical current flows between two or more separated energized conducting surfaces. Common causes of arc flash include:
- Insulation failure
- Buildup of dust, impurities, and corrosion on insulating surfaces, which can provide a path for current
- Equipment failure due to use of substandard parts, improper installation, or even normal wear and tear
- Birds, bees, and rodents snapping leads at connections
- Human error, including dropped tools, accidental contact with electrical systems, and improper work procedures
Difference between ARC flash and ARC blast
Arc Flash
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. This discharge of energy results in an intense flash of light and heat, which can cause severe burns, blindness, and even fatal injuries. Key characteristics of an arc flash include:
- Extreme Heat: The temperature can reach up to 35,000 degrees Fahrenheit, which is hotter than the surface of the sun.
- Intense Light: The bright flash can cause temporary or permanent blindness.
- Electrical Burns: The high-temperature plasma can cause severe burns.
- Pressure Wave: The rapid heating of air and vaporized material can create a pressure wave that can damage hearing and throw objects.
Arc Blast
An arc blast often accompanies an arc flash and refers to the explosive force created by the rapid expansion of air and vaporized materials. When an arc flash occurs, the intense heat causes materials to vaporize and expand rapidly, creating a powerful blast. Key characteristics of an arc blast include:
- Explosive Force: The rapid expansion of vaporized materials can create a pressure wave with a force strong enough to throw objects and personnel.
- Shrapnel: The blast can cause nearby equipment and materials to break apart, sending dangerous shrapnel flying.
- Sound Waves: The explosion generates a loud noise that can cause hearing damage.
- Pressure Wave Injuries: The blast pressure can cause injuries similar to those experienced in other types of explosions, such as ruptured eardrums and lung damage.
Applicable Rules
Because of the serious risks associated with arc flash, safety standards have been established to protect workers.
- OSH regulations require the use of safety signs, symbols, or accident prevention tags to warn employees about electrical hazards that may place them in danger.
- Fire Protection standard recommend that employers perform an arc flash hazard analysis before allowing employees to work on energized equipment. Although OSH does not enforce this standard, the agency considers it a recognized industry practice, and OSH field inspectors may use it as a reference.
- The standard also recommends PPE and clothing to protect workers as well as addresses the issue of safe flash protection boundaries designed to restrict entry into areas where are flash hazards exist.
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