What Causes Arc Flash? Electrical Arc Blast Explained

When an arc fault occurs, there’s a massive electrical explosion. Both arc flash and arc blast are separate byproducts of that electrical explosion. The arc flash is the light and heat from the explosion, while the arc blast is a pressure wave that follows.

It’s estimated that between five and ten arc fault incidents occur every day in the United States, based on findings from the Bureau of Labor Statistics. The goal of anyone working with electricity is to go home safely at the end of the job. Step one is to understand the dangers you’re working with.

What is arc flash?

Arc flash is the light and heat created from an arc fault explosion. Temperatures of an arc flash can reach as much as 2,800 to 19,000 °C (5,000 to 35,000 °F). To give you some perspective; the temperature of the surface of the sun is estimated at 5,500 °C (9,932 °F). Temperatures that high can ignite the clothing and burn the skin of anyone within a few feet. The arc flash can also melt metal, cause lung and eyesight damage and even lead to hospitalization or death.

What is arc blast?

The arc blast is the pressure wave created after an arc fault. These can be strong enough to throw a fully grown technician to the ground or cause additional equipment damage. Arc blasts can cause damage to your hearing or brain functions. The blast can also cause loose equipment, tools, machinery and debris to go flying which can cause further damage or injury.

What causes arc faults?

One of the major causes of arc flash is voltage transients (spikes), resulting from switching reactive loads or lightning strikes. The transient might last only microseconds, but it can carry thousands of amps of energy. If this happens while measurements are being taken, a plasma arc can form; either inside the measurement tool or outside.

Other causes of arc faults include situations as simple as:

• Touching a test probe to the wrong surface
• Worn or loose connections
• Gaps in insulation
• Improperly installed parts
• Dust
• Corrosion

Preventing injuries

Both arc flash and arc blast can cause injuries and be potentially fatal. Taking the proper precautions to prevent an arc fault and stay safe if one does occur is important. Read Arc fault boundary and safety to learn what steps to take in order to stay safe.

Video transcript:

This video is not intended to provide safety training.

You must comply with your employer’s safety standards and obtain necessary training before making electrical measurements.

In addition to shock hazards, one of the most dangerous anyone working with electricity faces is an arc flash.

An arc flash is an explosive release of energy from an electrical arc when the electrical current passes through ionized air.

In less than a second, an arc flash is initiated from a phase to ground or a phase to phase fault.

It can result from accidental contact with the electrical systems, the buildup of conductive dusts, corrosion, dropped tools, or improper work procedures.

The plasma arc has a virtually unlimited current carrying capacity once it’s established.

The energy of an arc flash converts primarily to heat and light.

Although there are other hazards created such as the arc blast or pressure wave, the acoustic wave, and toxic gasses.

Within a millisecond, temperatures at the epicenter of an arc flash can reach 35 thousand degrees Fahrenheit. That’s 4 times hotter that the surface of the sun.

These extreme temperatures are capable of explosively vaporizing metals such as copper, aluminum, and steel.

The presence of these vaporized metals can help sustain the arc causing a single-phase arc to propagate into a three-phase arc.

The arc blast that closely follows is a dynamic pressure wave created the instantaneous expansion of gas, air and the arc plasma ball.

The pressure wave can cause panels to rupture, create flying debris, acoustic injuries, and physical trauma.

An arc flash lasts until the overcurrent protectant devices open the circuit.

A fast-acting fuse may open the circuit in several milliseconds, or a circuit breaker may operate within six cycles or less but, by that time, the damage has already been done.

You might think that these are isolated or infrequent events, but that’s not the case.

Industry sources estimate that in the U.S., 5 to 10 arc flash accidents occur each day.

The U.S. Bureau of Labor reported that in one recent year, 1 thousand electrical workers suffered shocks and burns, some fatal.

Even though there are far more fatalities from shock than from arc flash, the injuries received from an arc flash can be devastating.

While you can’t totally eliminate the dangers of working with electricity, with careful planning and applying what you’ve learned here today, you can reduce them.

On behalf of everyone at Fluke Corporation, thank you for watching.

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