Fireproof Fabric Testing

Fire-resistant fabric inspection mainly conducts scientific testing and analysis on burning performance, vertical burning testing, horizontal burning testing, thermal protective performance, damaged length and charred area, and smoke density testing, 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

Burning performance: This is the core item of the fire-resistant fabric inspection, mainly evaluating the flame retardant characteristics of the material in accordance with the relevant standards. Specifically, it includes the determination of its limiting oxygen index (LOI), i.e., the minimum oxygen concentration required for the material to maintain flaming combustion in a nitrogen-oxygen mixed gas. The higher the LOI value, the better the flame retardancy. At the same time, it is necessary to evaluate whether it has the phenomena of afterflame, afterglow and molten dripping.

Vertical burning testing: Simulates the burning behaviour of the material in a vertical state. The specimen of the specified size is vertically hung, ignited at its bottom edge with a standard flame for a specified time (such as 12 seconds), and after the fire source is removed, its afterflame time and afterglow time are precisely measured, and the damaged length and whether the molten drippings ignite the absorbent cotton below are observed and recorded.

Horizontal burning testing: Evaluates the burning rate and flame retardant performance of the material in a horizontal state. The specimen is horizontally clamped, one end is ignited with a standard flame, and the time required for the flame to spread over a certain distance (usually 100 mm) is measured, or the maximum distance of the flame spread within the specified ignition time is recorded, thereby calculating the burning rate.

Thermal protective performance (TPP) testing: Quantitatively evaluates the protective ability of the fire-resistant fabric to the skin when contacting the heat source (convective heat and radiant heat). In the testing, the specimen is placed under a specified heat flux (usually 84 kW/m²), and the time required for its back surface temperature to rise to the second-degree burn threshold (skin temperature rise of 24 ℃) is measured. The longer the time, the better the thermal protective performance.

Damaged length and charred area: After the burning testing, the physical measurement is carried out on the specimen. The damaged length refers to the maximum length of the specimen burned or charred in the burning direction; the charred area is the area of the region where the material loses its original performance after burning. These two indicators intuitively reflect the damage degree of the material after contacting the fire.

Smoke density testing: Evaluates the concentration of the smoke generated by the material during burning or thermal decomposition. Under the specific burning conditions, the attenuation degree of the light by the smoke in the two states of flaming combustion and afterglow (flameless combustion) is measured, expressed by the parameters such as the maximum smoke density and the smoke density grade, which is crucial for evaluating the escape visibility in a fire.

Flame retardancy after washing testing: Examines the durability of the flame retardant performance of the fire-resistant fabric after multiple washes. In accordance with the standard procedures, after the specimen is washed and dried for the specified number of times (such as 5, 12 and 50 times), the vertical burning and other tests are carried out again, to verify the durability grade of its flame retardant finishing effect.

Testing Scope

Aramid fire-resistant fabrics: Woven with meta-aramid (Nomex) or para-aramid (Kevlar) fibres, with the characteristics of intrinsic flame retardancy, high-temperature resistance and high strength. The testing needs to cover their LOI value (usually >28%), heat shrinkage, mechanical property retention rate at high temperatures and acid and alkali corrosion resistance, applicable to the fields of firefighting clothing and welding clothing.

Modacrylic fire-resistant fabrics: Made of the modified acrylic fibres, with the flame retardancy given by the chemical modification. The testing focus is on their charring shrinkage performance after burning, afterflame and afterglow times, and the colour fastness and flame retardant durability after dyeing, commonly used as the decorative fabrics and protective clothing fabrics.

Glass fibre fire-resistant fabrics: Woven with the alkali-free glass fibre yarns, belonging to the non-combustible materials (Class A). The testing items mainly focus on their breaking strength, abrasion resistance, coating adhesion (such as after coating with silicone and rubber), and the strength loss rate under long-term high temperature, widely used for the wrapping of high-temperature pipelines and welding spark guards.

Carbon fibre fire-resistant fabrics: Composed of the carbon fibre fabrics, with excellent high-temperature resistance and oxidation resistance. The testing needs to pay attention to their thermal stability in the inert atmosphere and air, dimensional stability at high temperatures, conductivity and the interfacial bonding performance when used as the base fabric of the composite materials.

Post-finished flame retardant fabrics: The flame retardant finishing is carried out on the ordinary fabrics such as cotton, polyester and polyester-cotton blends through the processes such as padding and coating. The testing core is the uniformity of the finishing effect, flame retardant grade (such as the B1 grade), wash resistance (washing/dry cleaning), and whether the finishing agent has a negative influence on the handle, colour tone and strength of the fabric.

Silicone-coated fire-resistant fabrics: Silicone rubber is coated on the base fabrics such as glass fibre fabrics to form a flexible composite material. In the testing, in addition to the base fabric properties, the peeling strength of the coating, the resistance to high and low temperature alternation, the ozone aging resistance, and the overall air tightness and waterproofness also need to be key-tested.

Basalt fibre fire-resistant fabrics: Woven with the fibres made by melting and drawing the basalt ore, with a temperature resistance better than that of the glass fibre. The testing items include their long-term use temperature, thermal conductivity change at high temperatures, corrosion resistance in acid and alkali environments, and the monofilament strength dispersion coefficient related to the quality of the original yarn.

Testing Methods

Oxygen index method (such as GB/T 5454 and ISO 4589-2): The specimen is vertically fixed in a combustion tube, and the tube is filled with the oxygen and nitrogen mixed in proportion. The specimen is ignited from the top, and by adjusting the oxygen concentration, the minimum oxygen volume percentage concentration required for the specimen to maintain combustion over the specified length for at least 3 minutes or with a combustion length of 50 mm is found, i.e., the LOI value. It is the basic method for evaluating the flame retardancy of the material.

Vertical method (such as GB/T 5455 and ISO 6941): The specimen size is usually 300 mm×80 mm, clamped vertically. A specific methane flame (with a flame height of 40 mm) is used to ignite the centre of the bottom of the specimen for 12 seconds. The afterflame time and afterglow time after the fire source is removed are recorded, and the damaged length is measured. This method can effectively simulate the fire scenarios of the garment hem or the vertical curtains.

45° inclined method (such as GB/T 14644 and ASTM D1230): The specimen is placed at an angle of 45° and ignited from below. It is mainly used to evaluate the flammability of the apparel and decorative fabrics, measuring the flame spread rate or evaluating whether it ignites to the marking line, applicable to the materials other than the light and thin fabrics and the floor coverings.

Thermal protective performance TPP test method (such as GB/T 38302 and ISO 17492): A TPP tester is used, and the specimen is horizontally placed above a copper slug calorimeter containing a heat flux sensor. A combined heat source of two Meker burners (simulating the convective heat) and a group of quartz lamps (simulating the radiant heat) is used for irradiation, and the heat accumulation curve is recorded through the sensor, calculating the time required to cause the second-degree burn.

Smoke density test method (such as GB/T 8627 and ASTM E662): In a sealed smoke density chamber, the specimen of the specified size is horizontally placed. An electric heating or propane radiant furnace is used as the heat source, and the flaming combustion (open flame) and flameless combustion (radiant heat) tests are respectively carried out. The light transmittance change over time is measured and recorded through the vertical light path system, calculating the parameters such as the specific optical density.

Washing resistance test method: In accordance with the standards such as GB/T 17596, the specimen is washed with a standard washing machine, detergent and the specified water temperature, water level and time, and then dried according to the specified procedure. The number of washes is determined according to the requirements of the final use, for example, the protective clothing usually requires that the flame retardant performance still meets the standard after 50 washes. After washing, the specimen needs to be left to equilibrate before the burning test.

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC): Belonging to the thermal property analysis means of the material. The TGA measures the change of the specimen mass with the temperature under the programmed temperature control, and can analyse the thermal decomposition temperature and residual char rate of the fire-resistant fabric. The DSC measures the energy difference between the specimen and the reference material under the programmed temperature control, used to analyse the temperatures of the thermal effects such as the glass transition, melting and decomposition.

Testing Standards

Domestic Standards:

1. GB/T 5454-1997, Textiles — Burning behaviour — Oxygen index method

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

3. GB/T 14644, Textiles — Burning behaviour — 45° test determination of flame spread rate

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

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

International Standards:

1. ISO 17492, Clothing for protection against heat and flame — Determination of heat transmission on exposure to both flame and radiant heat

2. ASTM E662, Standard Test Method for Specific Optical Density of Smoke Generated by Solid Materials

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

4. 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

Oxygen index tester: The core components include a transparent heat-resistant combustion tube, specimen holder, gas mixing and flow control system, igniter and timing device. The high-precision model is equipped with the automatic oxygen concentration rise/fall and end-point judgement system, and can quickly and accurately determine the LOI value. It is the basic flame retardant testing equipment of the laboratory.

Vertical burning tester: Composed of a stainless steel test chamber, adjustable specimen holder, standard methane gas supply and ignition system and an automatic timer. The equipment needs to ensure the precise control of the flame height and ignition time, and is equipped with an exhaust system to discharge the combustion waste gas, ensuring the consistency and safety of the test conditions.

Thermal protective performance (TPP) tester: A highly integrated equipment, including the radiant heat source (quartz lamp array), convective heat source (Meker burners), specimen holder, moving mechanism, calorimeter sensor (copper slug heat flux meter) and data acquisition and analysis system. It can precisely simulate the mixed heat flow, automatically record the temperature curve and calculate the TPP value.

Smoke density test chamber: A sealed chamber with the inner wall painted black, equipped with a standard heat source (radiant furnace or burner), specimen holder, vertical light path system (light source, lens, light trap and photomultiplier tube), and a computer system for recording the light transmittance change. The chamber needs to have good sealing and corrosion resistance.

Standard washing and drying equipment: Including the rotary drum washing machine meeting the standard requirements (such as the Wascator), tumble dryer and the possibly used flat press machine. The equipment needs to precisely control the water temperature, water level, rotating speed, drying temperature and time, to ensure the repeatability and comparability of the washing procedures.

Thermogravimetric analyser (TGA): Composed of a precision balance, programmed temperature control furnace, atmosphere control system (which can introduce nitrogen, air, etc.) and data recording system. The specimen is heated in a crucible, the balance monitors the mass change in real time, and the software plots the thermogravimetric (TG) curve and its first derivative (DTG) curve, used to analyse the thermal decomposition process.

Universal material testing machine: Used to test the mechanical properties of the fire-resistant fabric under the normal state or after the high-temperature and burning treatments, such as the breaking strength, tearing strength and peeling strength. After being equipped with a high and low temperature environmental chamber, the performance testing within a temperature range can be carried out, evaluating the reliability of the material in extreme environments.