The ISO 15025 standard provides a uniform testing procedure for determining limited flame spread in protective clothing. This standard covers two testing methods: surface ignition (A) and edge ignition (B). In this standard, a 560 mm × 170 mm fabric specimen is exposed to a 20 mm flame for 10 seconds.
What is ISO 15025
Background and Development of the Standard
ISO/TC 94/SC 13 and CEN/TC 162, these two technical committees developed the ISO 15025 standard to establish a uniform testing procedure for determining limited flame spread in protective clothing.
ISO 15025 is derived from ISO 6940 and ISO 6941, which address vertical flammability tests. In 2005, the second edition of this standard added more terms, such as after-flame time, afterglow time, and char formation.
The purpose is to measure flame spread more precisely. The specimen size for testing was reduced from 160 mm to 80 mm to get uniform ignition and better control of flame spread. These changes were made to increase the precision rate.
Purpose and Application Scope
ISO 15025 testing standards operate on two different testing methods
- Surface Ignition (A)
- Edge Ignition (B)
Both methods are performed under vertical orientation in the flammability tester. The fabric specimen measuring 560 mm × 170 mm is exposed to a flame 20 ± 2 mm high. The fabric specimen remains in contact with the flame for 10 seconds.
The test standard specifies that the fuel for the flame must be propane to avoid variation in flame temperature, and that the flammability test must be performed under atmospheric conditions, according to ISO 139, at 20 ± 2 °C and 65 ± 5 % RH.
This fabric flammability test measures the afterflame, afterglow, and char length. This data helps to classify the textile material as either supporting limited flame spread or not.
The ISO 15025 test standard applies to single-layer fabric, multi-layer, coated, laminated, or composite materials, but not to materials that shrink or melt on heating.
Test Parameters
Terminology and Measurable Variables
We use the ISO 15025 standard test mainly to monitor the fabric’s burning behaviour. This testing standard has these important parameters: afterflame, afterglow, and char length.
These parameters indicate that the fabric specimen continues to burn or glow for a long time after the flame is removed.
Char length represents the damage to the fabric caused by heat and is measured in millimetres. Flame debris and hole formation are two other parameters which define the secondary risks that can occur due to ignition.
Following the vertical flame test procedure in ISO 15025, we can obtain consistent flame-spread test results for performance textiles.
The Physics of Flame Spread in Textile Materials
The fabric-burning process occurs in several stages. The flame or residual heat catches fire and heats; eventually, it starts to break down and continues to burn.
As the fabric heats to 250-350 °C, the gases help it ignite, and it begins to fall apart and release more gases. Synthetic materials, like polyester, affect the rate at which fire spreads upward, and before they catch fire, some clothes melt.
In front of a propane flame (10 seconds, 20 ± 2 mm high), the flame tester shows the sample and produces a heat flux of 4 kW/m² at the spot.
ISO 15025 Vertical Flame Test Configuration and Execution
Apparatus and Environmental Requirements
The ISO 15025 specifies a robust vertical tester with a frame measuring 560 x 170 mm to contain samples.
A flame of 20 ± 2 mm is produced by the burner, which is positioned almost directly above the sample holder, and is measured using a metal measuring instrument. Each sample is kept in a flame for 10 ± 0.2 s.
Filter paper is placed under to catch drips of burning. These laboratories are under the same conditions as stipulated in ISO 139, such as a relative humidity of 65 ± 5 per cent and a temperature of 20 ± 2 °C.
Step-by-Step Vertical Flame Test Procedure
Procedure B (edge) or Procedure A (surface) ignition is specified in ISO 15025. Samples should be placed in an upright position. Fix cotton markers 250 and 300mm below.
Time afterglow, char length, apply flame of 30 degrees for 10 seconds. Indicate whether the sample is debris or holed. For layered samples, one must apply seams or coatings to the flame.
Five samples should be evaluated, and the average calculated to give reliable results on the speed of spread and solid heat resistance.
Data Interpretation, Classification, and Compliance
Evaluating Flame Spread Results
Under ISO 15025, we need a minimum of five valid specimens to perform a flame-retardant test on fabric. The test data is recorded as mean afterflame time, mean afterglow time, and mean char length and all these values are measured precisely with an accuracy of 0.1 second or 1 millimetre.
There are two classifications of materials based on their performance, i.e. A1 or A2 (Limited Flame Spread) and B1 or B2. The former is used for surface ignition and the latter for edge ignition.
For a material to be classified as A1 or A2, its afterflame should not be more than 2s, and its afterglow should stop before char touches the upper edge. The flaming debris must not ignite the filter paper. These attributes correspond to PPE Compliance standards, such as ISO 11612.
Quality Assurance and Laboratory Validation
The rigorous calibration and verification of the flame tester apparatus indicate the reliability of a Flame Spread Test. The propane gas flowing under a constant flow pressure of 1.5-2 kPa should provide a stable 20 ± 2mm flame through the burner orifice.
Conclusion
ISO/TC 94/SC 13 and CEN/TC 162, these two technical committees developed the ISO 15025 standard to establish a uniform testing procedure for determining limited flame spread in protective clothing.
The ISO 15025 test standard applies to single-layer fabric, multi-layer, coated, laminated, or composite materials, but it does not apply to materials that shrink or melt on heating.
Under ISO 15025, we need a minimum of five valid specimens to perform a flame-retardant test on fabric. The test data is recorded as mean afterflame time, mean afterglow time, and mean char length and all these values are measured precisely with an accuracy of 0.1 second or 1 millimetre.
FAQs
What is the purpose of ISO 15025?
The ISO 15025 standard provides a uniform testing procedure to determine the limited flame spread of protective clothing.
How to test the fabric specimen through the flame spread test?
The fabric specimen measuring 560 mm × 170 mm is exposed to a flame 20 ± 2 mm high. The fabric specimen remains in contact with the flame for 10 seconds.