LEARN MORE about arc flash protective clothing
Learn the basics of protective clothing for electrical hazards
Information in this article is for general education about arc flash hazards and safety. Safety procedures for your workplace should be defined by qualified safety professionals that address specific hazards and appropriate standards.
In the United States alone, shock, electrocution, arc flash and arc blast cause an average of one fatality every workday. Each year, some 8,000 workers are treated in emergency rooms for electrical contact injuries. The proper use of personal protective equipment (PPE) could prevent many, if not all, of these injuries and fatalities.
About arc flash and arc fault
What is an arcing fault?
An arcing fault is a flow of current through the air between phase conductors or between a phase conductor and neutral or ground. In a fraction of a second, an arcing fault can release tremendous amounts of concentrated energy with extremely high temperatures, tremendous pressure blast, and high-velocity shrapnel.
What starts an arc?
Arcs can be started by a variety of causes. For example:
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Workers may incorrectly think energized equipment is de-energized and begin to work on it
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Workers may drop or improperly use tools or equipment components in energized equipment
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Dust, water or other contamination may accumulate and cause insulation breakdown
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Connections may loosen, overheat, reach thermal runaway and fail.
What determines chance of exposure to arc flash?
Chance of arc flash exposure depends on the following:
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How often workers perform a task involving exposed live equipment
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Task complexity, need for force, available space, safety margins, reach, etc.
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Training, skills, mental and physical agility, coordination with a helper
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Tools used
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Equipment condition
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Available short-circuit current; condition and rating of over-current protective equipment.
Consequences of arc flash
Exposure to arc flash can result in a variety of serious injuries and, in some cases, death. Workers have been injured even ten feet or more away from the arc center. Worker injuries can include damaged hearing, eyesight and severe burns.
Selecting PPE
Arcs vary in intensity and duration. Intensity is measured in calories per centimeter squared per second and depends on fault current magnitude. Arc duration depends on how quickly the protective device interrupts the fault. Intensity and duration must be known to calculate the incident energy to which a worker could be exposed. From this information, proper PPE can be specified.
In order to select proper PPE, incident energy must be known at every point where workers may be required to perform work on energized equipment. These calculations need to be performed by a qualified person such as an electrical engineer. All parts of the body that may be exposed to arc flash need to be covered by the appropriate type and quality of PPE. Proper PPE can include a hard hat, face shield, flame-resistant neck protection, ear protectors, flame-retardant suit, insulated rubber gloves with leather protectors and insulated leather footwear. All clothing must meet the requirements in the latest edition of NFPA 70E.
Arc flash protective clothing
Typical arc flash protective clothing includes coveralls, coats, overalls, hoods, Thermex® long underwear, Indura® shirts and pants, gloves, glove liners, glove protectors, face shields, plus gear bags for proper storage.
Definitions of arc flash protection terms
Arc Thermal Performance Value (ATPV) – This value is presented in calories per square centimeter and represents the maximum capability for arc-flash protection of a particular garment. This rating also applies to fabrics. However, a garment made from more than--one layer of arc-flash rated fabric will have a calories-per-square-centimeter rating greater than the sum of the ATPV ratings of the original fabrics. The calories-per-square-centimeter rating of most arc flash protective suits, coveralls, and coats is commonly sewn into the fabric in large letters on the outside of the garment.
Calories per centimeter squared – Expressed as cal/cm2, this is a number identifying the amount of energy that can be delivered to a point at a particular distance from an explosion. Once this value is known, the ATPV rating of the PPE required for work at that distance from the potential flash hazard is also known.
Energy break-open threshold (EBT) – Primarily, this addresses the physical strength of the fabric with respect to thermal energy and at what value the fabric will fail.
Flame resistant (FR) – Flame resistant can describe a fabric naturally resistant to burning but also can represent a material with special treatment applied to the fabric. Occasionally, the letters FR are used to represent flame retardant. This can lead to some confusion because a flame-retardant treated fabric is flame-resistant, but a flame-resistant fabric is not necessarily flame-retardant.
Flame retardant – This term could be used to describe a fabric made up of a flammable fabric treated in such a way that it will provide arc-flash protection.
Fabric weight – This is usually represented in one of two ways: ounces per square yard or grams per square meter. Both of these values essentially refer to the thickness of the fabric. The more ounces per square yard, the more material exists in the same square yard of fabric.
Hazard risk category (HRC) –This is a 2004 NFPA 70E rating of exposure levels for particular types of equipment. The values range from zero to four, with a zero HRC not requiring any ATPV rating. The minimum ATPV rating for Categories One through Four are as follows:
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Category One: five calories per square centimeter
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Category Two: eight calories per square centimeter
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Category Three: 25 calories per square centimeter
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Category Four: 40 calories per square centimeter
Heat attenuation factor (HAF) – This is the amount of heat blocked by the fabric. Even though a fabric may be 100 percent flame-resistant, that does not mean it will block all of the heat to which it is exposed. An HAF of 85 percent means that it will block 85 percent of the heat the fabric encounters. This applies to a short burst of heat – typically less than one second. In the event of prolonged heat exposure, the HAF would be much lower.
Personal protective equipment (PPE) – This term is primarily used to describe all safety equipment used by personnel to protect personnel. This includes fall protection, confined space, electrical hazards and so on.
Phase conductor – In alternating current circuitry, it is any conductor other than the neutral conductor.
Selected specifications and standards covering arc flash protective gear
ASTM F1506 Standard Performance Specification for Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards – This specification provides performance requirements for clothing worn by electric utility workers and other personnel working around energized parts. In addition to non-thermal requirements, the standard requires the fabric to be flame-resistant; that is, to not ignite and continue to burn after exposure to an ignition source.
ASTM F1891 Standard Specification for Arc and Flame-Resistant Rainwear – This standard applies to flame-resistant waterproof materials used in rainwear. Garments can be made from coated or laminated fabrics.
NFPA 1975 Standard for Station/Work Uniforms for Fire and Emergency Services – This standard applies to Fire Service station uniforms made from 100% cotton and flame-resistant fabrics.
NFPA 1977 Standard on Protective Clothing and Equipment for Wildland Fire Fighting – This standard is used by the Forest Service and Fire Departments involved in forest, field and other natural fires (in contrast to structural fires).
NFPA 2112 Standard for Flame-Resistant Garments for Protection of Industrial Personnel against Flash Fire – This is the first US standard that specifically addresses the need for industrial flame-resistant uniforms. This standard requires FR fabrics to pass a comprehensive battery of thermal tests.
NFPA 70E Standard for Electrical Safety Requirements for Employee Workplaces 2000 Edition – NFPA 70E addresses electrical hazard threats that are present in the workplace. NFPA 70E requires that the employer shall document the incident energy exposure of the worker when it has been determined that the worker will be performing tasks within the flash protection boundary.
NFPA bases incident energy exposure levels on the working distance of the employee's face and chest areas from a prospective arc source for the specific task to be performed. Flame-Resistant Clothing and Personal Protective Equipment shall be used by the employee, and an adequate level of protection based upon the incident energy exposure associated with the specific task shall be worn.
Jobs covered by 70E
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Installing conductors and other electrical equipment on industrial substations or buildings, residential or commercial
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Connecting the installations to a supply of electricity
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Installing other outside conductors
Jobs Not Covered by 70E
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Installations in ships, watercraft, railway rolling stock, aircraft, or automotive vehicles other than mobile homes and RVs
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Installations in underground mines
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Installations of railways for operation of rolling stock
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Installations of communication equipment under control of communication utilities
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Installations under the control of electric utilities
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NFPA 70E requirements for PPE
Movement and visibility
When flame-resistant, flame-retardant, or treated clothing is worn to protect an employee, it shall cover all ignitable clothing and shall allow for movement and visibility.
Body Protection
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Employees shall wear clothing resistant to flash flame wherever there is possible exposure to an electric arc flash.
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Such clothing can be provided as shirt and trousers, or as coveralls, or as a combination of jacket and trousers, or, for maximum protection, as coveralls and jacket.
Outer layers
Garments worn as outer layers over FR clothing, such as jackets or rainwear, shall also be made from flame-resistant material
Underlayers
Meltable synthetic fibers shall be avoided in fabric underlayers (underwear) next to the skin. Garments worn as underlayers that neither ignite nor melt and drip in the course of an exposure to the electric arc and related thermal hazard may provide additional thermal protection.
Coverage
Clothing shall cover potentially exposed areas as completely as possible
Care and maintenance
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All personal protective equipment shall be maintained in a sanitary and reliable condition.
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Individual protection items will normally be used in conjunction with one another as a system to provide appropriate layering.
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FR and natural fiber garments shall be permitted to be used for a layered system for added protection.
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A typical layering system may include an undershirt, a shirt and trouser and coverall.
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Specific tasks may call for specific protection systems.
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