The complex hazard of electric arc

Paul Boughton
Mike Frain and Elaina Harvey outline how to assess and manage this risk of electric arc flash.

Unfortunately, electrical flashover or arc flash is one of the most deadly and least understood hazards of electricity and is prevalent in most industries, particularly the utility sector.

Each year around 1,000 electrical accidents at work are reported and as many as 251 people die from their injuries. It is widely recognised the higher the voltage of an electrical power system, the greater the risk for people working on or near energised conductors and equipment. However, arc flash can actually be worse and more common at lower voltages and can cause devastating, severe burn injury and even death.[Page Break]

The law

The introduction of the Corporate Manslaughter Law in April 2008 in the UK meant that, for the first time, companies and organisations can be found guilty of corporate manslaughter through serious management failures resulting in a gross breach of a duty of care.

The Act clarifies the criminal liabilities of companies including large organisations where serious failures in the management of health and safety result in a fatality.

Ultimately this law has been implemented to persuade businesses and those responsible to conduct best practice at all times to ensure the safety of their employees and reduce accidents and deaths at work.[Page Break]

What is an electric arc flash?

An arc flash is usually caused by inadvertent contact between an energised conductor such as a bus bar or wire with another conductor or an earthed surface. When this occurs, the resulting short circuit current will melt the conductors, ionise the air and create a conducting plasma fireball with temperatures in the core of the arc that can reach upwards of 20,000°C. Severe injury and even death can not only occur to persons working on the electrical equipment but also to people located nearby.

Arc flash injury can include external burns to the skin, internal burns from inhaling hot gasses and vaporised metal, hearing damage, eye damage such as blindness from the ultraviolet light of the flash as well as many other devastating injuries. Depending on the severity of the arc flash, an explosive force known as an arc blast may also occur which can result in pressures of over 100 kiloPascal (kPa), launching debris as shrapnel at speeds up to 300metres per second (m/s).

Survivors of such injuries may require extensive treatment and rehabilitation and the cost of these injuries can be extreme, physically, emotionally and financially. While legislation requires businesses to perform risk assessments for all work activities, electric arc risk is often overlooked because most people are unsure how to assess and manage this hazard effectively.[Page Break]

How to manage the hazard

The management of tasks, where the arc flash hazard is present, needs to be determined by risk assessment. The risk assessment approach with the four steps of Predict, Prevent, Protect and Publish as defined in the DuPont Arc-Guide is a recommended method to develop safe work practices for the protection of people, where this hazard exists:

1. Predict - the severity of the thermal effect of an arc flash by the amount of 'incident energy' that a victim, standing at a given distance away from the arc, could receive.

2. Prevent - design out, eliminate or remove the hazard at its source.

3. Protect - where the risk cannot be controlled by prevention or where there is a residual risk of injury then it may be necessary to consider personal protective equipment (PPE) to prevent injury to the worker.

4. Publish - communicate and document results of site arc flash to those who are at risk.[Page Break]

In Summary

The DuPont Arc-Guide, the European approach to electric arc risk assessment, has been developed by DuPont in conjunction with independent experts, to help companies better assess the arc flash hazards (with the use of simple calculators) and provide them with the knowledge on how to both reduce the severity and consequences of an arc flash. The arc flash hazard is a serious electrical risk that needs to be managed in many industrial environments and risk assessment for workers who operate in proximity to, or on, energised electrical equipment and cables is essential to ensure safety and compliance with the law.

1. In the UK, HSE Electrical Safety at Work

Enter √ at

Mike Frain, Electrical Consultant, Electrical Safety UK Ltd, and Elaina Harvey, DuPont Nomex Account Manager, are with DuPont UK. and

Recent Issues