ARC protection is typically designed for electrical industry, specifically those workers who are involved in tasks that expose them to electrical hazards such as electricians, electrical engineers, linemen, and others who work with or around high-voltage electrical equipment.
ARC protection, also known as arc flash protection, is designed to protect workers from the thermal effects of an electric arc, which can generate extreme heat, intense light, and pressure waves that can cause serious injury or even death. The protection typically includes personal protective equipment (PPE) such as flame-resistant clothing, gloves, and face shields that can withstand the high temperatures and energy released during an arc flash incident. (Read more about what an ARC Flash is here)
Other industries where workers may also require ARC protection include the oil and gas industry, chemical plants, and other industrial settings where workers are exposed to electrical hazards.
Performance requirements for protective clothing against the thermal hazards of an electric arc is covered in the EN 61482 series . Divided into two methods:
EN 61482-1-1: Open ARC Method, popular in the American industries
EN 61482-1-2: Box Test Method, which is Mandatory for the European Market
What is an ARC Flash?
An arc flash is a sudden release of electrical energy that occurs when current jumps across a gap between two conductors or from a conductor to a ground. The arc flash generates an intense burst of heat and light that can cause serious injuries, damage to equipment, and fires.
Arc flashes can occur in a wide range of electrical systems and equipment, including switchgear, transformers, motors, and other high-voltage components. They can be caused by a variety of factors, including equipment failure, human error, or a short circuit.
The intense heat generated by an arc flash can cause severe burns, as well as ignite clothing and other materials in the surrounding area, leading to secondary fires. The bright light from the arc flash can also cause temporary or permanent vision damage.
To prevent arc flash incidents, it’s important to follow proper electrical safety procedures, including wearing appropriate personal protective equipment (PPE), de-energizing equipment before working on it, and maintaining a safe distance from energized equipment.
Understanding Arc Ratings and Calories
Now that you understand FR clothing is tested and given an arc rating, you know that the arc rating measures the amount of heat the flame resistant fabric blocks when exposed to electric arc. The arc rating is the number of calories that the garment is expected to “absorb” if exposed to an electric arc. Arc rating is, in essence, the level of protection provided to you, the wearer.
Calorie is the unit of measure of the heat energy of an arc flash and the protective level of FR clothing. The bigger the calorie number, the greater the heat energy level of arc flash and the greater the protective level of the clothing. You will be protected from an electric arc if your clothing has a higher calorie arc rating than the calories of heat generated by the arc.
While it does not matter if the fabric has an Ebt, ATPV and or ELIM value, it is important to pay attention to the calorie level the fabric can support* (as expressed in cal/cm2)
EN 61482-1-1: Open ARC Method & Cal Ratings explained
Arc Ratings for FR Clothing: What Is the Difference Between ATPV, Ebt and ELIM?
Arc Thermal Performance Value (ATPV) is “the incident energy on a fabric or material that results in sufficient heat transfer through the fabric or material to cause the onset of a second degree burn based on the Stoll curve. The level of protection provided by flame resistant clothing as measured in cal/cm2. An arc rating (ATPV) means that you have a 50% chance of being burned if exposed to an electric arc with the same number of calories of heat. The fabric will usually not break open unless exposed to energy levels higher than the arc rating.
Ebt is similar to ATPV but is determined when break-open occurs before the onset of a second degree burn. Energy breakopen threshold (Ebt) is “the average of the five highest incident energy exposure values below the Stoll curve where specimens do not exhibit breakopen. An arc rating (Ebt) means that the garment will break open if exposed to the same number of calories, but you will not be burned.
All FR fabrics will break-open if exposed to sufficient energy.
If an arc rated fabric is exposed to energies higher than its break-open value, the potential for direct skin exposure or non-FR inner layer ignition may result in additional injuries.
Important factors influencing a protective systems arc rating (ATPV, Ebt or ELIM) are the fabrics weight, construction, and fibre make-up.
Because PPE Regulation (EU) 2016/425 states that Personal Protective equipment shouldn’t bring any harm to the wearer which conflicts with APTV calculation of a 50% chance of harm to the wearer, therefor ELIM (Energy Limit Value) was created and is calculated by the highest level of energy with a 0% chance of break open or second degree burn.
ATPV, Ebt and ELIM are evaluated in the same test, EN61482-1-1 & ASTM F1959 in America , but the first one to be reached is the reported arc rating. While both values (ATPV and Ebt) can be reported, only one arc rating is given to fabric. Only the lowest value will be used on the clothing label according to ASTM F1506 specification. To be arc rated in the ASTM F1506 standard, the fabric must pass several tests including wash testing and the vertical flammability test using ASTM D6413.
If an Ebt value is determined and found to be equal or below a determined ATPV value, then the Ebt value is reported as the arc rating and will be noted as “Arc Rating (Ebt)” on the garment label. Ebt fabrics are typically more insulative than they are strong, and generally ATPV fabrics are stronger than they are insulative.
EN 61482-1-2: Box Test Method and “Ka” explained
The arc box test method is a standardized test used to evaluate the performance of electrical equipment and materials in the presence of an electrical arc. It is also known as the arc resistance test or the arc tracking test. It is the common test method for ARC flash protection in Europe
The test involves placing a sample of the material to be tested inside a box that is filled with a mixture of air and steam. An electrical arc is then generated inside the box, and the sample is observed for signs of damage or degradation caused by the arc.
During the test, the voltage and current are gradually increased until an arc is initiated. The arc is then maintained for a set period of time, typically several seconds, while the sample is monitored for any signs of damage or failure.
The arc box test is used to evaluate the ability of materials to resist arcing and prevent the spread of flames in the event of an electrical fault. It is commonly used to test the electrical insulation properties of materials such as plastics, rubber, and other polymers.
The results of the arc box test are reported in terms of the number of seconds the sample is able to withstand the electrical arc before failing, as well as any signs of damage or degradation observed during the test. This information can be used to select appropriate materials for use in electrical equipment and to help ensure the safety and reliability of electrical systems.
What does “Ka” mean?
Ka” is a unit used to express the magnitude of an electrical fault current, and is often used in the context of arc flash analysis and electrical safety.
In an electrical system, an arc flash can occur when a fault current flows through air between conductors or to ground, generating an intense burst of heat and light that can cause burns, injuries, and damage to equipment.
To calculate the potential hazard of an arc flash, it’s important to determine the available fault current at the point where the arc flash could occur. This is typically expressed in units of amperes (A), and can be used to calculate the incident energy of the arc flash.
The incident energy of an arc flash is the amount of thermal energy that is generated by the arc per unit area, measured in joules per square centimeter (J/cm²). Incident energy is dependent on a number of factors, including the available fault current, the duration of the fault, and the distance from the arc.
Ka is a unit used to express the available fault current in kiloamperes (kA), or thousands of amperes. For example, if the available fault current at a particular location is 20 kA, this means that a fault current of 20,000 amperes could flow through the system at that point.
Understanding the available fault current, expressed in units of kA or other appropriate units, is an important part of conducting an arc flash hazard analysis and implementing appropriate safety measures to protect workers and equipment from the hazards of arc flash incidents.
EN 61482-1-2 garments are certified to two levels, Arc Protection Class (APC) 1 and 2.
APC 1 protects against 4Ka
APC 2 protects against 7Ka