Understanding Arc Flash
What is arc flash? Electrical work presents a variety of specialized safety considerations, and arc flash events are some of the most dangerous. As many as 80% of all electrical […]
What is arc flash?
Electrical work presents a variety of specialized safety considerations, and arc flash events are some of the most dangerous. As many as 80% of all electrical injuries are burns that resulted from an arc-flash and ignition of flammable clothing. Consequently, it is imperative that workers understand the risks of arc flash events and the safety procedures that can prevent serious injury or death in the event of an arc flash.
Arc flash events can cause serious injuries or death from burns, electrical shock, and flying shrapnel. In the past decades, workers in the electrical industry made up 21% of all electrical-related fatalities. The most common type of work among these incidents was repair and maintenance. The majority of electrical fatalities (the other 79%) involved workers in other occupations, including millwrights, apprentices, labourers, equipment operators, drivers, and ventilation and air conditioning technicians.
An arc flash occurs when a large-scale short circuit causes electricity to travel through the air. The electric current leaves its intended path and travels from one conductor to another or to the ground. The movement of massive electric currents rapidly vaporizes the conductive material and causes an explosion
An arc flash is hotter and brighter than the surface of the sun and louder than a jet, propelling metal shrapnel at more than 1000 km per hour.
Causes of arc flash
Arc flash events most frequently occur when circumstances provide the electric current with a way to complete the circuit that differs from the intended path. This could involve a dropped tool contacting conductors, accidentally touching an energized component, or residue providing a starting route for the short circuit.
Some of the more common causes of arc flash events include:
- Falling parts.
- Material failure.
- Dropped tools.
- Accidental touching.
- Faulty installation.
Arc flash events involve several dangerous conditions occurring simultaneously. These can include a bright flash, an explosive expansion of molten metal, a loud concussive blast, thermal radiation, and an intense flow of electric current.
In this section, we will explore individually the types of conditions created in an arc flash and the injuries these conditions can cause.
Remember that arc flashes and electrical incidents generally result from three common root causes:
- Working on unsafe equipment and installations.
- Working in an unsafe manner.
- Working in unsafe environments.
Direct contact with exposed energized conductors or circuit parts. When electrical current travels through our bodies, it can interfere with the normal electrical signals between the brain and our muscles (e.g., the heart may stop beating properly, breathing may stop, or muscles may spasm).
CSA outlines a number of controls for establishing electrically safe work conditions. These include:
- Determining all sources of electrical supply and checking applicable up-to-date drawings, diagrams, and identification tags.
- Opening the disconnecting devices for each source after properly interrupting the load current.
- Visually verifying that all blades of the disconnecting devices are fully open or that draw-out-type circuit breakers are withdrawn to the fully disconnected position.
- Applying lockout devices in accordance with a documented and established policy.
- Using an adequately rated test instrument to test each phase conductor or circuit part to verify that it is de-energized.
Before workers are required to perform tasks with electrical equipment, control measures can be applied to reduce the risk of arc flash events. Design elements that ensure thorough insulation of the equipment and reduce the amount of time that an arc flash can continue are effective in lessening the potential injuries these events possess.
Arc flash code
The following codes in the electrical discipline are currently in force:
- CSA C22.1-18 Canadian Electrical Code (24th Edition): Declared in force on February 1, 2019
- Alberta Electrical Utility Code, 5th Edition, 2016: Declared in force on May 1, 2017
Personal Protective Equipment for Arc Flash Hazards
Personal protective equipment (PPE) is essential for the protection of workers operating in areas at risk for an arc flash. Given the nature of the forces present in one of these events, the correct PPE can directly determine whether workers caught in an arc flash survive. The type of PPE required for workers depends on the nature of the work to be performed and their proximity to energized electrical equipment.
The CSA requires employers to ensure that workers are provided with clothing and equipment that protects them from shock and arc flash hazards.
PPE includes shirts, pants, coveralls, jackets, and parkas worn by workers who are exposed to momentary electric arc and related thermal hazards. Arc-rated rainwear for use during inclement weather is also included in this category of clothing.
Arc-rated clothing must cover the intended parts of the body as well as any flammable apparel while also allowing for movement and visibility. Clothing and equipment required for the degree of exposure can be worn alone or in conjunction with flammable, non-melting apparel.
Garments that are not arc-rated are not permitted to be used to raise the arc rating of a clothing system.
Though it is vital for the protection of the worker, PPE acts as the last line of defense against arc flash hazards. All measures available at the engineering, administrative, and procedural levels should be taken prior to a worker approaching the equipment.
The CSA has set a number of standards regulating the materials that personal protective clothing can be made from.
Arc-rated materials, including flame-retardant-treated cotton and poly-benzimidazole fibres, provide thermal protection and are effective when used as PPE. They can ignite, but they will not continue to burn once the ignition source has been eliminated.
Non-arc-rated cotton and other materials, such as silk and rayon, can ignite and will continue to burn, causing serious burn injuries. Clothing consisting of fabrics, zipper tapes, or made from flammable synthetic materials that melt at temperatures below 315°C may not be used alone or in blends.
Other prohibited materials include: wool, acetate, acrylic, nylon and nylon-cotton blends, polyester, polyethylene, spandex etc.
However, fibre blends that contain these materials may be used if the fabrics meet the requirements of the American Society for Testing and Materials International (ASTM) F1506 and do not present a melting or sticking hazard during arc testing in accordance with ASTM F1959/F1959M.
Workers are required to wear non-conductive PPE for the face, neck, and chin whenever there is a risk of injury from exposure to electric arcs or flashes, or from projectiles. Head protection should include an arc-rated balaclava (cloth headgear intended to cover most of the head, neck, and face) used in conjunction with an arc-rated face shield whenever the back of the head is within the arc flash boundary.
Heavy-duty leather gloves or arc-rated gloves should be worn whenever there is a risk of arc flash. Heavy-duty leather gloves must be made completely of leather with a minimum thickness of 0.7 millimetres. They should be unlined or lined with non-flammable, non-melting fabrics. When insulating rubber gloves are worn for shock protection, leather protectors must be worn over the rubber gloves to provide additional arc flash protection.
Arc-rated clothing, such as an arc flash suit, is required wherever exposure to an electric arc flash above the threshold incident-energy level for a second-degree burn is possible. Arc flash suits must be designed to permit the wearer to move easily and quickly. The entire suit, including the hood’s face shield, should have an arc rating that is suitable for the arc flash exposure risk.
The types and level of PPE required for a task depend on the hazard posed by the involved equipment. Using the same units to rate the PPE and arc flash hazards allows for direct assessment of the ability of the PPE to withstand the conditions that might occur.
Who needs arch flash safety training?
All employees who work on or near electrical assemblies can benefit from Arc Flash Safety training. Workers in the following industries are more likely to require Arc Flash Safety training:
- Energy & Electricity,
- Oil & Gas,
- Automotive & Manufacturing,
- Waste Management.
eSafetyFirst ArcFlash Safety training program has been developed in accordance with provincial legislation as safety training for workplaces across Canada. This course consists of 3 modules and tests. Once you pass all the tests, you may print your certificate of completion (wallet & wall-sized). Training may be paused or resumed at any time, is fully narrated, and includes interactive exercises to ensure understanding of course content.