What Causes Arc Flash And How Can It Be Prevented?

In this article, we will investigate the nature of arc flash, what causes it, and the risk it poses to human life. We’ll also explain how to prevent arc flash and protect your workers against it. 

What Causes Arc Flash?

Arc flashes can arise from electric arcing, which occurs when an electric current continues to be live outside its normal path of conduction. This usually happens in the air and can be used to our advantage, such as in arc welding. While normal atmospheric air is usually non-conductive, it can become conductive if it somehow becomes ionised. In this case, the air creates a gas-like material called plasma, which allows electric current to flow through it.

If the current travels through the ionised air to another voltage phase or an earthed surface, this can result in an arc flash. An energised conductor might come unintentionally into contact with something like a bus bar or wire, or some other conductor. This can be caused by several factors, including moisture content, high levels of current and voltage, equipment failure and degraded or damaged insulation. It’s a common belief that high voltages offer a greater risk of arc flash, but some evidence shows that the risk is higher working at low voltage.

Other common causes of arc flash may include loose connections and exposed live parts, carrying out live work on damaged equipment, using incorrectly specified instruments and dropping uninsulated tools or metal parts. Lack of training and awareness of arc flash increase the dangers. You should be sure that everyone in your workplace is kept up to date on the risks.

What Damage Can An Arc Flash Cause?

An electric shock can occur if a live current touches your skin or passes through your body. Making this connection with electricity makes your body part of the electrical circuit. An arc flash can be far more dangerous. Though you won’t become part of the electrical circuit, you might find yourself at ground zero of an electrical arc where the electricity is conducted by the air, producing a violent and fiercely hot explosion. 

At the source of an arc flash, pressure, light and temperatures can all attain extremely high levels. Some arc flashes can exceed 35,000°F (19,400°C), or around three to four times as hot as the surface of the sun. Within milliseconds, an arc flash of this intensity will set your clothing alight and vaporise any materials in the area. It can even melt metal. 

Various factors influence the amount of harm that might result, including how much current can flow in an arc and how far you might be from the blast. It’s also dependent on how big a gap exists between the electrodes or conductive parts being bridged by the arc and for how long the arc is sustained. You also have to factor in the chemical composition of the conductors, how confined the arc may be, and what materials may surround it.

The kind of electrical discharge or explosion arc flash produces is also called a flashover. It can vary in severity. For instance, if the arc flash produces a rapid expansion of vaporised material and air, it could produce an arc blast with an explosive force of 100kPa (1 Bar) or more. Such a blast can propel objects outwards at great speed – up to 300 metres per second – including equipment parts, debris and molten metal.

The severity of an arc flash depends to a great extent on the amount of current it’s generating. From the human perspective, the nature of its impact depends on the route taken by the current through the body. Severe electric shock can burn your skin on the outside and your organs on the inside. It might cause ventricular fibrillation and even death from electrocution. Arc flash can do all this, plus many other devastating injuries. You might suffer damage to your hearing and eyesight, intoxication from inhaling vaporised metal or hot gases and be blinded by the ultraviolet light.

How To Prevent Arc Flash

The likelihood of an arc flash occurring is fairly slim, but if it does, the potential effects are serious. It’s hard to completely eliminate the risk of arc flash unless you isolate the power supply, but you can set up some control measures. These should reduce both the risk of arc flash occurring and the severity of its effects. 

For example, you can:

• Conduct a risk assessment

• Set up training programmes for on-site workers

• Keep at a safe distance, using barriers if necessary

• Wear suitable PPE

• Power down electrical equipment 

You could use this effective way to remember the essentials of arc flash hazard management: 

• Predict – identify and evaluate the potential risks

• Prevent – apply prevention principles to control risks

• Protect – always use appropriate protective clothing and barriers

• Publish – keep up to date with cataloguing changes in equipment state and prevailing conditions.

Arc Flash Training

Effective training is vital to reduce the risk of arc flash. Human error will increase the likelihood of it causing injury or death – especially to anyone working directly with electricity. Electrical engineers and electricians conducting tests or maintenance are at high risk, from both high- and low-voltage equipment. Arc flash training is vital in any profession based around electricity, including supervisors.

Qualified personnel should be trained to understand and prevent the risks of arc flash in the workplace. This includes recognising the risk of exposure, calculating safe arc flash boundaries and knowing how to use appropriate devices to limit fault currents and reduce arcing time. Also familiarise yourself with any applicable legislation, such as the Management of Health and Safety at Work Regulations 1999. This lays out an employer’s obligation to assess workplace risks and how effective your precautions are. Arc flash hazards should always be included when it comes to electrical work.