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Arc flash refers to the flash of light and heat that is created when energy is released between a live conductor and another conductor or the ground.
During an arc flash, the energy released heats the air to extreme temperatures such as almost 20 000 °C (35 000 °F). At these high temperatures, items within a metre (3 feet) such as clothing and skin will catch fire, melt, or vaporize. In addition, an arc flash will create an arc blast - the heated air expands suddenly and creates a powerful pressure wave (a blast).
When an arc flash occurs, damage or injuries may occur. Wildfires are most often started by lightning strikes or by human activity. Between early April and late October, many regions of Canada enter wildfire season. Hundreds of wildfires may be burning at one time, and the fires will vary in size.
An arc flash may be caused by many factors or events, such as:
The possibility of an arc flash increases when there are exposed energized electrical conductors or circuit parts; or when safe work procedures are not followed.
An arc flash risk assessment should be done to:
Whenever possible, do not work on energized equipment. Always follow lockout/tagout procedures as part of a hazardous energy control program.
Other protective measures include:
Preventive maintenance includes:
Boundaries are used to limit how close workers and others should be to the equipment or circuits, especially when work is being done.
An arc flash boundary is the term used to describe the distance at which a person without personal protective equipment (PPE) may get a second-degree burn if an arc flash occurs. It is assumed that a second-degree burn occurs when the incident energy received by the skin equals 5 J/cm2 (1.2 cal/cm2). A second-degree burn is usually treatable.
There are two types of boundaries that are used:
Restricted approach boundary – the distance from an exposed energized electrical conductor or circuit part a qualified person (only) may approach when there is an increased likelihood of electric shock due to electrical arc over combined with inadvertent movement .
Figure 1: Arc Flash Approach Boundaries
(Adapted from CSA Z462:21 and NFPA 70E)
The distance of the boundaries will vary, and depend on:
Important to arc flash boundaries is the role of qualified persons. A qualified person is someone who has been trained in and has knowledge about the construction and operation of the equipment or work methods. They must be familiar with appropriate techniques, policies and procedures, work permits, PPE, insulating and shielding materials, insulated tools, test equipment, etc.
For example, unqualified workers should remain a distance away from the exposed energized conductors or circuit parts (including any equipment or objects they may handle). They should not cross into the arc flash boundary unless they are wearing appropriate PPE and are supervised by a qualified person. At no time should an unqualified person enter the restricted approach boundary. Qualified person may enter the restricted space provided any necessary work permits, PPE, tools, equipment, and measures necessary to reduce the likelihood of contact are taken.
Workers must know how to select, use, and care for the necessary PPE, and understand the limitations of the PPE.
The CSA standard Z462:21 “Workplace Electrical Safety” provides two methods that can be used to determine what type of PPE is required for a specific job:
While either method can be used, only one method should be used at a time when working on the same piece of equipment (not both).
The first method, incident energy analysis, is based on the distance between the worker’s face and chest to the source. It uses the value of the estimated energy of the flash to determine the level of protection that must be provided by the PPE.
The second method, arc flash PPE category method, uses the arc flash risk assessment of the tasks and equipment condition to determine if arc flash-rated PPE is required. Once determined that arc flash PPE is required, one of four PPE categories is selected based on indicators such as minimum working distance, and maximum fault current available and maximum fault clearing time (for AC current) or short-circuit range (for DC current).
In addition to the appropriate clothing and footwear, other PPE items, such as a hard hat (class G or E), face shield, balaclava, hood, safety glasses or goggles, heavy duty leather/arc-rated/rubber insulating gloves, hearing protection, and footwear are required when there is a risk of arc flash incident. All PPE used must be appropriate for energy expected if an arc flash occurs.
Note that other requirements may be needed that are not discussed in this document. Always consult the legislation that applies in your situation, and with your jurisdiction for complete information.Standards such as the following provide information about establishing a maintenance program and other aspects of electrical safety in the workplace. This list is not complete and other standards may be relevant to your situation or conditions.
Note: Certain CSA Group standards are available for online viewing. To access these, you must first create an account with “CSA Communities”.
Go to: https://community.csagroup.org/login.jspa?referer=%252Findex.jspa
Once you are logged in, click on the text below the “OHS Standards / View Access” graphic.
Click on the jurisdiction of your choice to see the CSA Standards as referenced in that legislation. Standards may also be purchased from CSA Group: https://store.csagroup.org/