Fabric Flame Retardant Testing

Fabric flame retardant inspection mainly conducts scientific testing and analysis on limiting oxygen index, vertical burning performance, 45° inclined burning performance, thermal protective performance, smoke density and toxic gas analysis, and washing resistance, 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

Limiting oxygen index: LOI is the indicator for evaluating the minimum oxygen concentration required for the fabric to maintain combustion in the nitrogen-oxygen mixed gas, expressed as a percentage. The higher the LOI value, the more difficult the fabric is to burn. Usually, the LOI greater than 26% is considered to have the flame retardancy. This testing is the basic method for the laboratory screening of the flame retardant performance of the materials.

Vertical burning performance: This item simulates the burning behaviour of the fabric in the vertical state, and is the core testing for evaluating the safety of the flame retardant textiles. The main observation indicators include the afterflame time, afterglow time and damaged length. This testing can intuitively reflect the flame spread and self-extinguishing ability of the fabric after contacting the fire source.

45° inclined burning performance: Mainly used to evaluate the flame retardant performance of the textiles hanging in the inclined or near-horizontal states such as the garments and curtains. During the testing, the specimen is placed at a 45° angle, the flame spread rate is observed and whether it burns through is checked, particularly suitable for evaluating the flame spread risk of the light and thin fabrics.

Thermal protective performance: The TPP testing comprehensively evaluates the heat insulation and flame retardant performance of the fabric by measuring the time and heat required for the back surface temperature of the fabric to rise to the level causing the second-degree burns when it is exposed to the specific heat source. This indicator is crucial for evaluating the flame retardant effects of the protective products such as the firefighter clothing and welding clothing.

Smoke density and toxic gas analysis: Evaluates the smoke concentration and the toxic gas components (such as the carbon monoxide, hydrogen cyanide and hydrogen chloride) generated during the burning or pyrolysis of the fabric. The high smoke density and toxicity are the main causes of the casualties in the fires, and this item is an important part of the comprehensive evaluation of the environmental protection and safety of the flame retardants.

Washing resistance: Detects the attenuation of the flame retardant performance of the flame-retardant finished fabric after the specified number of standard washes (such as 5, 12 and 50 times). This is the key to evaluating the durability of the flame retardants and the stability of the finishing processes, directly affecting the service life and safety reliability of the product.

Physical and mechanical property changes: Evaluates the influence of the flame retardant finishing on the original performances of the fabric, including the breaking strength, tearing strength, abrasion resistance, hand feel, colour fastness and air permeability. The ideal flame retardants should minimize the negative influence on the original excellent performances of the fabric while imparting the flame retardant function.

Testing Scope

Fabrics for the protective clothing: Including the special protective clothing fabrics such as the firefighter clothing, welding clothing, military uniforms and petrochemical industry work clothes. This type of fabrics usually requires the extremely high flame retardant grades (such as the GB 8965.1 grade B), excellent heat resistance and heat insulation, and needs to pass the strict vertical burning and thermal protective performance testing.

Decorative textiles: Covering the curtains, drapes, sofa fabrics, stage curtains, carpets and wall coverings. According to the application places (such as the public places and vehicles), the specific flame retardant standards need to be met, such as the B1 grade requirement in the GB 8624 classification of the burning behaviour of the building materials, with the focus on the flame spread and heat release rate.

Children's sleepwear and home textiles: For the children's sleepwear, adult sleepwear and bedding, the various countries have the strict flame retardant regulations (such as the US CPSC 16 CFR Part 1615/1616). The testing focuses on the vertical burning and inclined burning performances, ensuring the rapid self-extinguishing when contacting the small fire sources, reducing the burn risks.

Industrial textiles: Including the interior fabrics of the vehicles (aircraft, high-speed rail and automobiles), tents, tarpaulins, conveyor belts and insulation materials. The testing needs to be combined with the specific application scenarios, evaluating the flame retardancy, smoke toxicity and weatherability, and needs to comply with the industry-specific standards such as FMVSS 302 and EN 45545-2.

Flame retardant fibres and raw materials: The testing is carried out on the intrinsically flame retardant fibres (such as the aramid, flame retardant polyester and flame retardant viscose), flame retardant masterbatches and flame retardant finishing agents themselves. Through the tests such as the thermogravimetric analysis, limiting oxygen index and vertical burning, their thermal decomposition behaviour, flame retardant efficiency and the compatibility with the substrates are evaluated.

Export trade compliance verification: The testing carried out to meet the regulatory requirements of the target markets, such as the CE certification of the EU (involving EN ISO 11612, etc.), the NFPA standards of the US and the BS 5852 of the UK. The testing contents need to fully cover all the mandatory testing items of the target regulations, ensuring the smooth trade.

New product development and quality control: The systematic testing is carried out during the development of the new flame retardants, the research of the new flame retardant processes and the monitoring of the production batch stability. By comparing the various performance data under the different formulas or process conditions, the product design is optimized, and the internal quality control standards of the enterprises are established.

Testing Methods

Limiting oxygen index method: In accordance with the standards such as GB/T 5454, ISO 4589-2 and ASTM D2863. The specimen is vertically fixed at the top of a transparent burning cylinder, and the cylinder is filled with the nitrogen-oxygen mixed gas of the controllable proportion. The specimen is ignited from the top, and the oxygen concentration is adjusted until the minimum concentration just maintaining the stable combustion is found, which is the LOI value.

Vertical burning test method: In accordance with GB/T 5455, ISO 6940/6941, ASTM D6413 and other standards. The specimen is vertically hung, and the standard flame of the specified size (such as 12 seconds) is used to ignite the centre of its lower edge for the specified time (such as 12 seconds). After the fire source is removed, the afterflame time and afterglow time are precisely recorded, and the damaged char length is measured.

45° burning test method: In accordance with GB/T 14644 (similar to ASTM D1230). The specimen is fixed on the test frame at a 45° angle, a small but specific flame contacts its surface, and the time required for the flame to spread to a certain marking line is measured, or whether it burns through is observed, to evaluate the resistance of the fabric to the small fire sources.

Thermal protective performance test method: In accordance with the relevant standards. A combined heat source (convection and radiation) vertically acts on the front of the specimen, a copper slug heat flux meter is placed on the back of the specimen, the temperature rise curve of the skin simulating sensor is recorded, and the time required to cause the second-degree burns (TPP value) is calculated.

Cone calorimeter method: In accordance with ISO 5660-1 and ASTM E1354. Under the standard heat radiation flux (such as 35 kW/m²), the specimen is forcibly ignited, and the key fire performance parameters such as the heat release rate, total heat release, effective heat of combustion, mass loss rate and smoke production rate are precisely measured. It is the research-level evaluation method.

Smoke density chamber method: In accordance with GB/T 8627 and ASTM E662. In a closed test chamber, the specimen burns or pyrolyzes under the specific conditions (flaming or non-flaming), the attenuation degree of the light by the smoke is measured through the light beam, the specific optical density is calculated, and the smoke generation characteristics of the material are evaluated.

Washing resistance test method: In accordance with GB/T 17596, ISO 10528, AATCC 61 and other standards. The flame-retardant finished specimen is placed in a standard washing machine, washed with the specified detergent, liquor ratio, temperature and time to simulate the domestic or commercial washing. After the washing and drying, the testing is carried out again according to the original flame retardant standards (such as the vertical burning), evaluating the performance durability.

Testing Standards

Domestic Standards:

1. GB 8624, Classification of burning behaviour for building materials and products

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

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

4. GB/T 14644-2014, Textiles — Burning behaviour — Determination of burning rate of 45° oriented specimens

5. GB/T 8627-2007, Test method for density of smoke from the burning or decomposition of building materials

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

International Standards:

1. ISO 4589-2, Plastics — Determination of burning behaviour by oxygen index — Part 2: Ambient-temperature test

2. ISO 6940, Textile fabrics — Burning behaviour — Determination of ease of ignition of vertically oriented specimens

3. ISO 5660-1, Reaction-to-fire tests — Heat release, smoke production and mass loss rate — Part 1: Heat release rate (cone calorimeter method)

4. ASTM D6413, Standard test method for flame resistance of textiles (vertical test)

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

6. 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

Limiting oxygen index tester: The core components include a heat-resistant glass burning cylinder, precision gas mixing and flow control system, specimen holder, igniter and timing device. The high-end models are equipped with the automatic oxygen concentration search and result calculation functions, ensuring the accuracy and repeatability of the LOI value determination.

Vertical burning test chamber: The equipment is a metal sealed chamber, internally equipped with a specimen holder, automatic igniter that can be precisely positioned and timed, and gas supply system. The back wall of the chamber is usually equipped with a scale and black background, convenient for observing the flame and measuring the damaged length. It is equipped with an exhaust system to discharge the burning waste gas.

Thermal protective performance tester: Composed of a radiant heat source (usually the quartz lamp array), convective flame burner, specimen holder, calorimeter module with the skin simulating sensor, and data acquisition and analysis system. It can precisely simulate the combined heat exposure environment, and is the key equipment for evaluating the heat insulation performance of the protective equipment.

Cone calorimeter: A large comprehensive analysis instrument, mainly including the cone heater, electronic igniter, specimen weighing platform, laser smoke density measurement system, oxygen analyser and complex gas pipelines. The heat release rate is calculated by measuring the oxygen consumption in the burning waste gas, with the comprehensive and accurate data.

Smoke density test chamber: A sealed cubic test chamber, internally equipped with a standard radiant heat source or flame application device, vertical light path system (light source, lens and photoelectric cell) for measuring the light transmittance change, and integrated with the temperature sensors and smoke purification device, used for the quantitative analysis of the smoke generation of the material.

Standard laboratory washing equipment: Including the standard horizontal drum washing machine, dryer or drying equipment. It needs to strictly comply with the requirements of the test standards for the drum dimensions, stirrer shape, rotating speed and temperature control precision, to ensure the repeatability of the washing conditions and the comparability of the results between the different laboratories.

Thermogravimetric-infrared combined system: TG-FTIR or TG-MS, used to study the thermal decomposition behaviour of the flame retardants and the finished fabrics. The thermogravimetric analyser measures the mass loss of the sample under the programmed temperature control, and the decomposition products are introduced into the Fourier transform infrared spectrometer or mass spectrometer in real time for the analysis, thereby revealing the flame retardant mechanism and the gas phase product composition.