Introduction Fabric pilling, which happens from wear and friction, is a common issue affecting fabric…
In order to avoid fire accidents caused by textiles and to reduce unnecessary losses, countries around the world have been paying more and more attention to flame retardant testing in recent years, Countries such as the United Kingdom, the United States and Japan also require by law that clothing for women, children, the elderly and the disabled, as well as pyjamas, must be labelled as having “passed flame resistance tests”.
There are many influencing factors, such as the moisture absorption rate of the fabric, weight, etc., but two main aspects are taken into account: one is ignition, i.e. the high or low ignition point, which indicates how easy it is for the fabric to catch fire; the other is combustion performance, i.e. the rate of burning along the sample under certain conditions. Throughout the world, flame retardant testing methods vary from country to country but are intrinsically linked. The oxygen index method is unique in terms of the environment in which the sample is tested, and in terms of the position in which the sample is tested, it can be broadly divided into three main categories: vertical, 45° direction and horizontal. There are, of course, a number of methods dedicated to certain materials such as paving fabric test methods. This article briefly introduces some of the knowledge of testing the flame retardant properties of textiles in conjunction with domestic and international flame testing methods and standards.
Table of Contents
- What are flame retardant fabrics?
- Flame retardant testing standards in different countries
- Test methods for flame resistance of textiles
- Combustion test method
- Oxygen Limiting Index (LOI) method
- Surface burning test method
- Smokiness test method
- Flashpoint and self-ignition point determination and ignition temperature determination
- Flame retardant finishing thermal analysis
- Conical calorimeter
- Simple test methods
What are flame retardant fabrics?
Flame-retardant fabrics are functional textile fabrics woven from materials that are inherently flame retardant or treated with a flame retardant finish. They are effective in preventing the spread of flame. Flame retardant fabrics are not flame retardant in the sense that they do not burn when they come into contact with an ignition source, but rather that they slow down the spread of flame when a fire occurs and do not form a large area of combustion; and when they leave the flame, they can quickly self-extinguish and no longer burn or ignite; they also have good durable washing properties.
Commonly used textile flame retardant materials: permanent flame retardant polyester, modified acrylic, aramid, aramid, polyimide, carbon fibre, glass fibre, pre-oxygenated fibre.
Flame retardant testing standards in different countries
The EU standards for flame retardant testing of protective clothing are mainly developed by the European Technical Committee (CEN/TC) and the current standards are EN ISO 11611:2007 (replacing EN470), EN ISO 11612:2008 (replacing EN531), EN ISO 14116:2008/AC:2009 (replacing EN533)
EN 11611:2007 Protective clothing for use in welding and allied processes
Testing is carried out in accordance with ISO 15025:2000, which includes both surface burning and vertical burning test methods. Depending on the type of material, either or both methods can be selected for testing. For the surface burning test, the material must meet the following requirements:
Any test specimen, when ignited, must not spread to the edge of the fabric or to the top end of the fabric.
No holes can be formed in any test specimen after ignition.
There must be no burning droplets or molten material falling from any test specimen after ignition.
The average time to re-ignition must be less than 2s.
The average negative ignition time must be less than or equal to 2s.
EN ISO 11611 classifies flame-retardant safety classes as Class 1 and Class 2. Both classes have the same technical specifications and the material must comply with the above-mentioned requirements for surface and bottom burning.
EN11612:2007 Protective clothing for workers operating in hot environments
This standard sets out requirements for the general properties of fabrics, construction design, dimensional stability, flame spread, heat and molten metal resistance, size marking and labelling, and flame retardant test methods in accordance with ISO 15025.
EN 14116 Protective clothing – Protection against flame – Limited flame spread materials, material assemblies and clothing
The purpose of protective clothing in accordance with this standard is to protect workers in working environments where there are occasional small, brief flames, no obvious thermal hazards and no other forms of thermal hazards present. The standard is divided into three classes, all of which require no molten droplets and no spread of insidious combustion. Class 2 and Class 3 require that there must be no holes and Class 3 requires that the renewal of ignition must not exceed 2 seconds.
The main flame retardant standards developed by the General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China and the National Standardisation Administration of China are: GB 8965.1-2009, GB8965-1:2009 Class B for firefighting and welding garments.
The flame retardant test is carried out in accordance with GB/T 5455-1997 vertical combustion method, and the Class B standard requires
Continued combustion time ≤ 2s
The time of negative combustion≤2s
No molten drops allowed
and GB 31701-2015 Safety Technical Specification for Infant and Children’s Textile Products, which requires the use of GB/T 14644-2014 Textiles Determination of burning rate in the 45° direction of burning performance.
The National Fire Protection Association (NFPA) has developed a series of standards for the technical performance of different flame-resistant protective clothing, and the main relevant ones for flame-resistant fabrics are the NFPA 2112 Standard for Industrial Personal Protective Flame-Resistant Clothing.
This standard uses the vertical burning method as defined by ASTM D6413 for flame retardant testing and the material must meet the following requirements after testing:
The average char length must not exceed 102 mm.
The average duration of ignition must not exceed 2s.
There must be no molten drips after ignition of the specimen.
For multi-layer materials, each layer needs to be tested separately and pass the above requirements.
The rest of the tests included are
Indirect HTP (Heat Transfer Performance) ≥ 25 J/cm2 (6.0 cal/cm2)
Direct HTP (Heat Transfer Performance) ≥ 12.6 J/cm2 (3.0 cal/cm2)
Thermal Shrinkage(Thermal Shrinkage)≤10%
Open Flame (Flash Fire) ≤ 50% (exposed areas, hands and feet)
Test methods for flame resistance of textiles
Combustion test method
The combustion test method is mainly used to determine the burning extensiveness (charring area and length of damage), renewal time and negative combustion time of a specimen. A specimen of a certain size is ignited in a prescribed combustion chamber with a prescribed fire source for 12 s. After removal of the fire source, the renewal time and negative combustion time of the specimen are measured. After the negative ignition has ceased, the length of damage is measured according to the prescribed method. Depending on the position of the specimen in relation to the flame, it can be divided into the vertical method, the 45° tilt method and the horizontal method.
This method provides for the specimen to be placed vertically (the length of the specimen is perpendicular to the horizontal line) and the burning source to ignite the specimen below the specimen. The specimen is tested for minimum ignition time, renewal time, flame retardation time, flame spread rate, char length (damage length), char area (damage area) and other indicators related to flame retardancy. The vertical burning method is mainly used for testing the flame resistance of textiles for clothing, curtains and other fabrics.
Common vertical method test standards
GB/T 5455 Textile burning performance test
GB/T 8745 Determination of burning time on the surface of textiles
CA TB117 California Fire Resistance Test
16 CFR 1615/1616 Standard for flammability of children’s pyjamas
Multi-purpose Textile Flammability Tester TF319 can determine the flammability resistance of various textiles, such as toy&toy materials, decorative fabrics, tent fabrics, safety protection nets, household materials, etc. It is Mainly used for burning testing in the vertical direction. It can be used by the printing and dyeing industry, textile inspection departments, and scientific research units. Equipped with different specimen clips, it is suitable for testing the flame retardant properties of different materials, i.e., the determination of the length of material damage, negative ignition, and continuous ignition time. Complies with ISO 6940 / 6941, ISO 15025, ANNEX8, EN71-2, ECE R118, etc.
Multi-purpose: at first, it meets most vertical-oriented tests.
Accurate: The test data are comparable to the test results obtained by well-known international third-party laboratories.
Smart: programmable PLC system, optical scanning devices for threads breaking detection, timing range 0-999.9s, and accuracy 0.1s.
Automatic: automatic flame ignition and flame, automatic gas open / off. Automatic change for butane gas and propane gas.
Easy-to-use： easy-set devices for burner position (surface & edge ignition, toys test).
Safety guarantee: the detachable controller ensures the safety of the operator.
Flexible: interchangeable, precision test frames for different standards.
User-friendly set: vertical and horizontal marker threads, a tray for the filter paper, and test debris.
45° burning method
This test method provides for the specimen to be placed at an angle of 45° (the length of the specimen is at an angle of 45° to the horizontal) and for the burning source to ignite the specimen on the upper or lower surface below the specimen and measure the time required for the specimen to burn upwards for a certain distance, or the time required for the specimen to burn upwards, the flame retardant time, the rate of flame spread, the length of charring, the charred area or the number of times the specimen needs to be exposed to the flame at a certain distance from the lower end of the specimen. The 45° tilt method is mainly used for testing the flame resistance of fabrics such as carpets.
Common tilt method test standards:
GB/T 14645 Determination of the area damaged and the number of flame contacts in the 45° direction of the burning properties of textile fabrics
ASTM D 1230 Test method for flammability of apparel textiles
NFPA 702 California Standard for Flame Retardancy of Hospital Garments and Bedding Fabrics
BIFMA Standard for the Testing of Upholstery Materials
45 Degree Flammability Tester, is to determine the fabric flammability (fabric burning test) under controlled conditions. This model 45 degree flammability test chamber is also suitable to evaluate the flammability of medical textiles such as medical face masks, surgical gowns, protective clothing, and drapes.
An automatic igniter is equipped to ensure the 45 degree fabric flammability tester safe and easy to operate. Besides, stainless steel test cabinet with a glass observation panel provides automatic timing of flame spread in 0.1-second increments from the ignition. What’s more, a brushing device is included.
Safety setting: equipped with heat-resistant observation window, so it is easy to observe the internal test status.
Long service life: the stainless steel case, highly resistant to corrosion.
Meeting various needs: different sample holders are available for replacement to meet the requirements of different standards.
Easy to use: automatic flame application according to the set time, automatic flame extinguishing when the flame application time is reached.
Intelligent and efficient operation: touch screen control, automatic recording of burning time and burning rate, with timer accuracy of
Horizontal burning method
This test method specifies that the specimen is placed horizontally, ignited at the head end of the specimen, the distance the flame spreads over the specimen and the time taken to spread this distance are measured, the burning rate is calculated and the burning rate is used to characterise the flame retardancy of the fabric. The horizontal method is mainly used for testing the flame resistance of automotive interior trim materials.
Common horizontal method test standards:
FZ/T 01028 Horizontal method for the determination of the burning properties of textile fabrics
GB 8410 Combustion characteristics of automotive interior materials
FMVSS302 (USA) Combustion properties of interior trim materials for federal transportation vehicles
IEC 60695-11-10 Fire hazard test Part 11-10: Test method for 50W horizontal and vertical flames
The Horizontal Flammability Tester TF311 is suitable for testing the flame-retardant properties of leather interior materials, polymer materials, textiles, etc. Such as used in all kinds of automobiles, including seat cushions, seat belts, roof linings, armrests, decorative panels, headrests, floor coverings, sun visors, curtains, and other interior parts. Thus, it provides the data basis for new material research and development, product quality acceptance, etc.
Safety settings: the flammability tester box shell is a steel structure and encloses the testing process. Through the transparent observation window, you can clearly observe the whole combustion process.
Accurate: the test data is consistent with internationally renowned third-party laboratories.
Very simple operation: gas and fire buttons, an LCD program, real-time display of ignition time and combustion time.
The high degree of automation: automatic recording of test time, automatic display of results and automatic timing once the test starts.
Reasonable design: Equipment with its own fan, test combustion fumes safely discharged.
The flammability testing machine is beautiful in appearance, easy to use, and reliable in performance.
Other relevant test standards and methods
GA10-2014: Fireman’s protective clothing for Firefighting
BS EN 14878: Textile materials. Combustion characteristics of children’s sleepwear. BS 5722: Specification for the flammability of fabrics for pyjamas and fabrics for dressing gowns 16 CFR 1610: Standard for the flammability of textile clothing
ASTM D1230: Standard test method for flammability of apparel textiles
ASTM D6545: Standard Test Method for Flammability of Textiles for Children’s Sleepwear
FTMS 191: Standard for Test Methods for Coated Textiles
SOR/87-443: Hazardous Products Regulations (Children’s Sleepwear)
JIS L1091: Test method for flammability of textiles
AS 2755.1/2/3:Textile Fibres – Flammability Properties
AS/NZS 1249:Standard for children’s pyjamas and general clothing to reduce the risk of fire
GB/T 17591:Flame retardant fabrics / Flame-retardant fabrics
More flammability testers with different functions and testing methods can be found on this page.
Oxygen Limiting Index (LOI) method
The oxygen limit index method is a widely used method for testing the burning properties of textiles, which refers to the minimum oxygen concentration required to maintain the burning state of the material in the oxygen and nitrogen gas mixture under the specified experimental conditions, expressed as LOI, LOI is the percentage of the volume of oxygen in the gas mixture. Clamp on the burning cylinder perpendicular to the upward flow of oxygen and nitrogen gas flow, ignite the upper end of the specimen, observe its combustion characteristics, and the prescribed limit value to compare its continued combustion time or length of damage. By testing a series of specimens in different oxygen concentrations, the minimum oxygen concentration value expressed as a percentage of oxygen to maintain combustion can be measured, with 40-60% of the specimens tested exceeding the specified renewal and negative ignition times or lengths of destruction.
Surface burning test method
This method is a method for determining the degree of combustion spread on the surface of a specimen and is suitable for thick textiles. For example, in the United States, the flammable fabrics ordinance requires the use of the horizontal cigarette butt method and the Ullotropin method of assessment; the UK uses the hot metal nut method. Urotropine method is in the centre of a certain size specimen put a piece of 6-6.5mm diameter urotropine tablets, ignite the tablets with a fire source, the specimen then burn, wait for the flame to extinguish, measure the maximum distance from the flame to the centre of the tablets, used to assess the burning properties of the specimen. The hot metal nut method involves heating a stainless steel nut in a furnace until it is scorching hot, placing it on the surface of the specimen in the sample chamber, and after the specimen has burned out, measuring the distance from the flame out to the centre of the nut and the time of ignition, which is used to assess the burning properties of the sample. As the combustion conditions of this horizontal method are not intense enough, many carpets can meet the requirements without flame retardant, so the combustion performance assessment is changed to the thermal radiation method which is close to the actual combustion conditions. For example, the United States requires residential use of carpets measured by the radiation plate method of critical radiation flux to ≥ 0.25W/cm2; carpets used in public facilities, critical radiation flux to ≥ 0.5W/cm2. Japan’s carpets are used on the flame method, the maximum charring distance required less than 7Omm, the average value of less than 5Omm.
The basic principle of the thermal radiation method is: in the specified temperature (180 ℃) and size of the box, the gas-fuelled thermal radiation plate and the horizontally placed specimen tilted into 30 ° and facing the specimen, the radiation plate generated by the specified radiation flux along the specimen distribution. Under the specified time with the igniter ignite the specimen, the flame extinguished to determine the length of damage to the specimen, and calculate the critical radiation flux. The distinctive features of this test method are: the experiment is carried out in a chamber and the chamber temperature is maintained at 180°C; the specimen is always subjected to the prescribed radiant heat; the specimen can be placed under the horizontally placed specimen on the specimen holder with the same lining material as the actual laying conditions. This test set-up simulates the intensity of heat radiation to the floor when the upper part of the building is heated by the flame, the hot air or both in the event of a large fire in the room or in an adjacent room. Obviously this device is closer to the actual burning conditions of the paving material and its experimental results better reflect the real burning performance of the paving material system. The critical radiant flux provides a basis for evaluating the combustion performance of the floor covering system when exposed to flame. The larger the measured critical radiant flux value, the more difficult the paving material is to burn.
Smokiness test method
According to the long-term accumulation of various types of fire information, analysis of the smoke and toxicity of combustion materials, the harm is often more serious than the flame and heat generated during combustion, is the main cause of human death. There are special instruments and equipment for this type of test, both at home and abroad, and the principle is mostly based on the light transmission method. The smoke density is measured by the transmittance and time curve can be derived from a variety of parameters, including optical density, maximum smoke density, average smoke rate and light transmission rate, from the maximum to 75% (than the optical density) of the time required, so that a more comprehensive evaluation of the smoke of flame retardant textile materials. These instruments and test methods are often used in the construction and transport sectors to study and select flame retardant materials.
Flashpoint and self-ignition point determination and ignition temperature determination
Flashpoint refers to the material decomposition by heat to release flammable gas and just can be ignited by a small external flame when the minimum initial temperature of the surrounding air. Self-ignition point refers to the material heated to a certain temperature without external ignition source ignition, and their own explosion or combustion when the lowest initial temperature of the surrounding air. The above various measurements are used for the combustion performance of various types of fabric under the action of heat or flame as a factor in the evaluation of fire risk. In addition, the analysis of fabric combustion gas toxicity research (in recent years also pay more attention to) available infrared instruments, gas chromatograph and mass spectrometer analysis.
Flame retardant finishing thermal analysis
When the fabric according to a certain temperature program in the heat or cooling often occur a series of physical or chemical changes. Thermal analysis technology is to study or determine when these changes occur, the quality or energy of the material as a function of temperature (or time) change. There are a number of thermal analysis techniques, and pyrolytic gravimetric analysis (TGA) and differential scanning calorimetry (DSC) are commonly used in flame retardant testing. Using pyrolytic weight analysis (TGA) the change in thermal weight loss of the fibres can be determined, it is relatively comparable to the flame retardant effect of the fabric and has a quantitative concept. Differential scanning calorimetric DSC allows the analysis of changes in the decomposition temperature of the fibres, indicating changes in the mode of cleavage before and after flame retardation. Chromatography-mass spectrometry can also be used in thermal analysis techniques to study the thermal cleavage products of fibres etc.
The conical calorimeter is a new type of combustion test device that has been developed since the early 1980s. It can simulate various parameters during real combustion. It is mainly used to measure the rate of heat release when the material burns. Research has shown that the Heat Release Rate (HRR), i.e. the amount of heat released per unit of time when a material burns, is the most important fire parameter for characterising the combustion risk of a material in a fire. As a result, various instruments and methods for measuring the heat release rate of materials have emerged in recent years. The conical calorimeter uses the principle of oxygen consumption to measure the rate of heat release during the combustion of materials. This method has now replaced the traditional method of testing the rate of heat release based on energy balance and is widely used in various heat release rate testing instruments and methods. In addition, it can measure the rate of heat release per unit area of material during combustion, sample ignition time, mass loss rate, smoke density, effective heat of combustion, harmful gas content and other parameters. These parameters are important in terms of evaluating the performance of a flame retardant or flame retardant system because in an actual fire situation, the victim is not only scorched by the heat emitted by the flame but also suffocated by the large amount of smoke generated by the combustion decomposition of materials such as polymers, among other hazards.
Simple test methods
In order to facilitate the operation, a variety of simple test methods are introduced. These methods do not require complex equipment or conditions, are low cost and are suitable for initial observation of flame retardant effects or for reference or comparison when selecting process conditions in general factories, but cannot be used as a standard test method, let alone as a basis for arbitration.
Match test method
The match test method can assess the flame retardant effect of the fabric or relatively comparative flame retardant performance. When the test is taken about 2.5cm x 3Ocm a fabric, with a lit match, placed under the strip specimen, burning until the match burned out (or the provisions of 5-12s), observe the burning situation or flame retardant effect. Sometimes it can be specified that the specimen burns for no more than 5s as qualified, more than the middle line or overcast for more than 15s as unqualified (other indicators can also be specified). Match specifications can be specified by yourself or by reference to the standard method. The method is close to the vertical test method.
Lighter test method
Specimen size can be based on the test needs, the heat source using a lighter, the time is generally 5s, the heat source can be placed in parts similar to the application conditions. After the fire is extinguished, observe the flame spread state, the spread is not serious that is qualified.
Ethanol burning test method
The heat source is 0.3mL anhydrous ethanol, placed in a small burning cup (bottle cap can also be), the test can be used in the vertical method (5cm × 3Ocm), horizontal method (20cm × 25cm) or 45. tilt method (5cm × l5cm), ethanol and fabric distance of 2.5cm, the measurement index can be determined according to the requirements, such as charcoal length, burning area, continued combustion time, yin combustion time and burning material dregs situation, etc. The indicators can be determined according to the requirements, such as charcoal length, burning area, renewal time, negative burning time and the condition of the residue of the burning material.