Arc-flash Protective Clothing Testing

Arc-rated clothing testing mainly conducts scientific testing and analysis on the arc thermal performance value, energy break-open threshold, vertical burning performance test, fabric and seam breaking strength test, thermal shrinkage test and colour fastness test, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Arc thermal performance value (ATPV) determination: This is the core indicator for evaluating the thermal protection performance of arc-rated clothing, referring to the incident energy value at which the arc energy causes a 50% probability of a second-degree burn to the material, in cal/cm². This test simulates the enormous thermal energy generated by an arc flash. By determining this key threshold, the level of protection that the clothing material can provide to the wearer in the event of an arc accident can be scientifically determined.

Energy break-open threshold (EBT) determination: When the material breaks open under the action of the arc energy, the EBT value is used to replace the ATPV value for evaluation. It represents the energy value transmitted through the broken opening to the sensor at the moment of material rupture. The EBT test is crucial for evaluating the integrity of the fabric under extreme energy impact, and is an important supplementary basis for determining the protection level.

Vertical burning performance test: This item mainly evaluates the afterflame time, afterglow time and damaged length of the arc-rated clothing fabric after contacting an electric arc or flame. It checks whether the fabric has flame-retardant characteristics, i.e., whether it can rapidly self-extinguish after leaving the fire source, avoiding secondary injury. This is the basic safety requirement of arc-rated clothing and is directly related to escape safety after an accident.

Fabric and seam breaking strength test: This test is used to evaluate the strength of the arc-rated clothing fabric itself and the sewn seams when subjected to external tensile forces. It is determined with a professional fabric strength tester, ensuring that when the clothing is pulled during daily wear and accidents, the protection will not fail due to fabric tearing or seam opening, maintaining the overall protection integrity of the clothing.

Thermal shrinkage test: After the arc-rated clothing is subjected to high-temperature electric arc action, the fabric may shrink. This test aims to determine the dimensional change rate of the fabric after treatment at a specified temperature and duration. Excessive thermal shrinkage may cause the clothing to be tight on the body after an accident, affecting the movement and subsequent removal of the personnel, and even causing additional heat injury.

Colour fastness test (perspiration fastness, rubbing fastness and light fastness): Mainly evaluates the firmness of the clothing colour under the action of perspiration, rubbing and ultraviolet irradiation. Good colour fastness is not only an aesthetic requirement, but also related to the durability and functionality of the clothing. Fading may mean that there are defects in the fabric fibres or the finishing process, which may affect the stability of its protective performance in the long term.

Testing Scope

Arc protection coveralls and separate suits: Testing covers the complete protective clothing system, including coveralls and separate suits composed of an upper garment (jacket) and trousers. During testing, the complete clothing set needs to be evaluated as a whole. Especially for separate suits, the protection effectiveness of the overlapping part of the upper and lower garments needs to be considered, ensuring that there is no weak protection area in the actual wearing state.

Arc-rated fabrics: As the basic material for making clothing, the testing of the fabric is the primary link. The testing scope includes commonly used flame-retardant fibre fabrics, such as aramid (Nomex® and Kermel®), flame-retardant cotton and aramid/flame-retardant viscose blended fabrics, evaluating their basic thermal protection, flame retardancy and physical and mechanical properties. This is the fundamental factor determining the protection grade of the final finished product.

Clothing accessories and components: The testing scope extends to all non-fabric components, including sewing threads, zippers, Velcro, buttons and reflective strips. These accessories must have the same flame-retardant performance and thermal stability as the fabric, ensuring that they will not melt, drip or burn in an arc accident, thus becoming a new source of danger.

Multi-layer clothing combination system: Considering that in actual applications, workers may wear other clothing (such as underwear and thermal layers) inside the arc-rated clothing. Testing needs to evaluate the overall thermal protection performance of the multi-layer clothing combination from the inside to the outside (such as calculating the total ATPV value), ensuring that when the inner layer clothing is made of combustible materials, the whole dressing system can still reach the claimed protection grade.

New, used and washed clothing: The testing scope is not limited to new clothing, but also includes clothing that has been washed a certain number of times according to standard procedures (such as the provisions of GB/T 17599-1998). This is to evaluate the performance decay of the clothing in its life cycle, ensuring that it can still maintain the necessary protection capability after use and maintenance.

Special designs and accessories: For clothing with special designs, such as detachable liners, vents, tool pockets and three-dimensional knee and elbow reinforcement layers, these areas all need to be included in the testing scope. It needs to be evaluated whether the special structures affect the heat flow distribution under arc exposure, and whether the accessories are firm to avoid falling off at high temperatures.

Testing Methods

Open arc test method (in accordance with ASTM F1959/F1959M): This is the internationally recognized standard method for determining the ATPV and EBT. The test is carried out in a simulated open arc environment, using electrodes and a power source of a specified configuration to generate controllable arc energy. The sample worn on a test mannequin is exposed to different grades of arc energy, and the heat transmitted through the sample is measured by copper calorimeters placed behind it, thereby calculating the injury probability curve.

Vertical burning test method (in accordance with GB/T 5455 or ASTM D6413): Used to evaluate the flame retardancy of the fabric. A fabric specimen of a specific size is vertically hung in a dedicated combustion test chamber, ignited at its lower edge with a specified standard flame for a certain time (such as 12 seconds). After removing the fire source, the afterflame time and afterglow time of the specimen are precisely recorded, and the damaged length is measured, thereby determining whether its flame-retardant performance is qualified.

Fabric tensile strength test method (in accordance with GB/T 3923.1 or ISO 13934-1): A constant rate of extension (CRE) strength testing machine is adopted. The fabric or seam sample is clamped in the grips and stretched at a constant speed until breakage, recording the maximum breaking strength and elongation at break. For the seam strength, the "grab method" is usually adopted to test the tensile resistance at the seam.

Thermal shrinkage test method: Usually, the fabric sample is placed in an oven at a specified temperature (such as 260 ℃ or 285 ℃) and treated for a specific period of time (such as 5 minutes). The distances between the marked points before and after the treatment are precisely measured in the warp and weft directions, and the percentage of the dimensional change is calculated. This test simulates the instantaneous influence of the high temperature of the arc on the dimensional stability of the clothing.

Perspiration and rubbing fastness test methods (in accordance with GB/T 3922 and GB/T 3920): For the perspiration fastness, the specimen is placed in contact with a standard adjacent fabric, immersed in a simulated perspiration solution containing histidine, pressed in a specific device for a certain time under pressure, and after drying, the change in colour and staining grades are rated. For the rubbing fastness, the specimen is rubbed with standard white cotton cloth in dry and wet states, and the staining grade of the cotton cloth is rated.

Overall clothing system thermal protection performance evaluation method: When evaluating the multi-layer clothing combination, the "additive calculation" or the direct test method is usually adopted. The additive calculation is a theoretical summation based on the data of each layer tested separately (such as the ATPV value). The more accurate method is to directly wear the multi-layer combination on the test mannequin for the arc test, to obtain real and reliable overall protection data.

Testing Standards

Domestic Standards:

1. GB/T 5455-2014, Textiles — Burning behaviour — Determination of damaged length, afterglow time and afterflame time

2. GB/T 3923.1-2013, Textiles — Tensile properties of fabrics — Part 1: Determination of breaking force and elongation at breaking force using the strip method

3. GB/T 3922-2013, Textiles — Tests for colour fastness — Colour fastness to perspiration

4. GB/T 3920-2024, Textiles — Tests for colour fastness — Colour fastness to rubbing

5. GB 18401-2010, National general safety technical code for textile products

International Standards:

1. ISO 13934-1, Textiles — Tensile properties of fabrics — Part 1: Determination of maximum force and elongation at maximum force using the strip method

2. ISO 105, Textiles — Tests for colour fastness

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Arc test system: The core parts of this system include a high-current power source, electrode array, test chamber and data acquisition system. The power source can simulate a real fault arc and generate a short-circuit current of up to tens of thousands of amperes. The electrodes are arranged in a standard geometry to form a stable arc plasma. The test chamber is used to safely contain the arc and the test sample, and the data acquisition system precisely records the current, voltage and sensor temperature data.

Copper calorimeter (also called the "copper slug calorimeter"): This is the key sensor for measuring the incident energy of the arc. It is made of pure copper with a thermocouple attached to the back, and its thermophysical properties are known. During the test, the sensor is placed behind the sample, and by measuring its temperature rise curve during the arc exposure, the thermal energy received per unit area (cal/cm²) is calculated using the heat formula, thereby determining the ATPV or EBT value.

Vertical burning tester: This equipment is a front-opening chamber with a glass observation window, internally equipped with a specimen holder, automatic igniter and flame height scale. There is a smoke outlet at the top and ventilation holes at the bottom. The instrument can precisely control the ignition time and provide a draft-free, stable test environment, ensuring the repeatability and comparability of the combustion test results.

Electronic fabric strength tester: A computer-controlled constant rate of extension testing machine, equipped with a high-precision force sensor and elongation measuring device. It is used to test the breaking strength of the fabric and the seam strength. The equipment software can display the force-elongation curve in real time and automatically calculate results such as the maximum strength and elongation at break, and the test process complies with the relevant international and national standards.

High-temperature oven: Used for the thermal shrinkage test. It is required that the temperature uniformity in the oven is high, the temperature control is precise (usually up to above 300 ℃), and it has a timing function. The sample needs to be heated uniformly in the oven, to accurately simulate the reaction of the fabric at the high temperature of the arc. The interior of the oven should have sufficient space to prevent the sample from contacting the inner wall and affecting the test results.

Standard light source color assessment cabinet and grey scales: Used for rating after the colour fastness test. The standard light source cabinet provides a stable and consistent light source environment such as D65 daylight, avoiding rating errors caused by changes in the ambient light. During rating, the tested specimen and the untested original sample are placed side by side, and under the standard light source, the grade is determined by comparison with the "grey scale for assessing change in colour" and the "grey scale for assessing staining".