An Introduction to Arc Flash

An arc flash is defined as a type of electrical explosion, a sustained short circuit conducted through ionized air. It is caused by a rapid release of energy due to an arcing fault between one phase busbar and another, a neutral, or a ground. An arcing fault is created manually, either by making a path for conduction or by a failure in the electrical system (such as a breakdown in insulation). A minimum of 120 volts (phase to ground) or 208 volts (phase to phase) is required to create an arc flash.

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The after effects of an arc flash incident

At the point of an arc flash, temperatures can reach up to 20,000 degrees Celsius. This massive discharge of energy has the ability to destroy phase busbars by vaporizing their thick strips of copper. The result is an explosive volumetric increase, the arc blast, estimated at an expansion of 40,000 to 1. A fiery arc flash explosion devastates everything in its path, produces sound levels up to 160 decibels and creates deadly shrapnel in its wake.

Causes of Arc Flash

An arc flash can be caused by a number of factors. These include accidents, equipment failures, and improper work procedures. Accidents may include: dropped tools, unintentional contact with electrical systems or the build-up of conductive dust, dirt, corrosion, and particles. Electrical system failures may include failures in either electrical equipment or in insulation. An arc flash can also be caused by the improper use or design of electrical equipment, including wiring errors, and improper work procedures.

Dangers of Arc Flash

An arc flash is capable of causing substantial damage. Eighty percent of electrical workplace accidents are associated with arc flash and involve burns or injuries caused by intense heat or showers of molten metal or debris. In addition to toxic smoke, shrapnel and thermoacoustic shockwaves, the creation of an arc flash produces an intense flash of blinding light. This flash is capable of causing immediate vision damage and can increase a worker's risk of future vision impairment.

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Depicting the importance of proper
Personal Protective Equipment (PPE)

Between 2004 and 2008, the province of Alberta experienced 178 injuries and 10 deaths related to electrical accidents. In the United States, 4000 non-disabling and 3600 disabling (defined as an injury preventing a worker from returning to work) electrical workplace injuries occur each year and 2000 workers are sent to burn centres with serious electrical burns. It has been estimated that, every day, one person dies from an electrical accident. Victims of electrical accidents often experience lifelong sensitivity to cold weather, impeded mobility, and other physical disabilities.

Regulations and Safety Standards

Occupational Safety and Health Administration (OSHA)

Occupational Safety and Health Administration (OSHA) has determined that electrical hazards in the workplace pose a significant risk of injury or death to employees. OSHA regulations mandate that employers provide a safe work environment for their employees. OSHA Standards 1910 Subpart S and 1926 Subpart K outline electrical safety regulations. OSHA 1910.132 states that employers are responsible for assessing hazards in the workplace and selecting, having and ensuring workers properly use the correct Personal Protective Equipment (PPE). OSHA Standards also require that employers document their hazard assessments. OSHA bases its electrical safety mandates on NFPA 70E (see section "NFPA 70E").

Occupational Health and Safety Act (OHSA) Regulation 851

The Occupational Health and Safety Act establishes procedures for dealing with workplace hazards to protect workers from health and safety dangers. If an employer fails to voluntarily comply with the Act, the Ontario Ministry of Labour provides for enforcement of the law. OHSA Regulation 851 addresses issues relevant to industrial establishments. Sections 40-44 provide procedures for machine guarding against electrical hazards. Section 40 (b) states that "electrical equipment, insulating materials and conductors shall be certified by (i) the Canadian Standards Association, or (ii) the Electrical Safety Authority, as defined in the Electricity Act, 1998." Section 42.1 addresses workplace situations in which it is not practical to disconnect from the power supply before commencing work on, or near, live exposed parts. The Act requires workers to properly follow work procedures and wear personal protective equipment, "to ensure protection from electrical shock and burns while performing the work."

National Electrical Code (NEC)

Published by the National Fire Protection Association (NFPA), the United States' National Electrical Code (NEC) provides standards for the safe installation of electrical equipment and wiring. The 2002 NEC outlines requirements for warning labels. NEC Article 110.16 necessitates "field marking" for potential arc flash hazards on panels expected to be serviced or examined in an energized state. All electrical equipment installed after 2002 must be labelled. For equipment installed prior to the publication of the 2002 NEC, labelling must be applied if any modifications or upgrades occur.

NFPA 70E

The United States NFPA 70E: Standard for Electrical Safety in the Workplace reports on the full range of electrical safety issues including proper work procedures, maintenance, special equipment requirements, and electrical installation.

IEEE Standard 1584

The Institute of Electrical and Electronics Engineers (IEEE) Standard 1584 was developed to help protect individuals from the dangers of arc flash. The incident energy level equations outlined in IEEE Standard 1584 allow for the proper "field marking" of electrical equipment and selection of appropriate overcurrent protective devices and PPE. The IEEE 1584 equations calculate an estimated arc current which is then used to predict the incident energy level.

CSA Z462

The Canadian Standards Association (CSA) recently published a new document focussed on Workplace Electrical Safety. The CSA Z462: Workplace Electrical Safety Standard is based on the United States NFPA 70E and was developed in tandem with the 2009 edition of NFPA 70E. CSA Z462 is the first comprehensive standard to protect Canadian electrical workers. It addresses safety requirements for the proper installation, operation and maintenance of electrical systems. CSA Z462 has been designed for use with the Canadian Electrial Code (CEC) Parts 1 and 2 and other workplace electricity standards such as CSA Z460.

Conclusions

Electrical hazards in the workplace pose significant risk to workers in the form of injury or death. An arc flash is a potentially deadly electrical explosion causing intense heat, thermoacoustic shockwaves, shrapnel, intense light and toxic smoke. An arc flash is caused by a rapid release of energy due to an arcing fault between two phase busbars. A variety of safety standards and regulations exist to protect workers from the dangers associated with an arc flash. Recently, the Canadian Standards Association published CSA Z462-08: Workplace Electrical Safety Standard, the first all-Canadian standard addressing electrical safety requirements in the workplace.