Heat- and flame-protective workwear is tested for limited flame spread almost everywhere in the world with the same document: ISO 15025:2016, Protective clothing — Protection against flame — Method of test for limited flame spread. ISO reviewed and confirmed the 2016 edition in 2021, so it remains current.
ISO 15025 is often treated as if it were a product standard. It is not. It tells you how to ignite a vertical specimen and what to observe. Whether the fabric passes is decided by the garment standard that calls it up — most often ISO 11612 for heat and flame protective clothing, or ISO 14116 for limited flame spread materials.
Two procedures, two different questions
ISO 15025 contains two ways of applying the flame to a vertically held specimen:
| Procedure A | Procedure B | |
|---|---|---|
| Ignition | Surface ignition | Bottom-edge ignition |
| Flame | Propane, applied to the face of the specimen | Propane, applied to the lower edge |
| Typical question | Does flame on the face spread? | Does a cut or hem edge carry the flame? |
| Code in ISO 11612 | A1 | A2 |
In Procedure A the flame is applied for 10 seconds. The burner position, distances and flame height are fixed in the standard; set them from the text and a positioning gauge, not from a photograph of someone else's set-up.
The two procedures are not interchangeable. A fabric with an inherently flame-resistant face can still carry a flame up a raw edge, and a laminate can behave well at the edge and poorly on the surface. If a specification lists A1 and A2, both are required.
What you observe
ISO 15025 asks the operator to record behaviour, not a single number. For each specimen:
- whether flaming reaches the upper edge or either side edge;
- afterflame time and afterglow time;
- whether flaming or molten debris falls;
- whether a hole forms, and in which layer of a multilayer assembly;
- whether afterglow spreads beyond the flamed area.
If the operator only writes "pass" or the afterflame time, the record is not enough to classify the fabric against any garment standard.
Where the criteria come from
ISO 11612 (code A1 / A2). The garment standard requires, in summary, that no specimen burns to the top or side edges, no flaming or molten debris falls, mean afterflame and mean afterglow do not exceed 2 seconds, and — for A1 — no hole of 5 mm or more forms. Check the current edition of ISO 11612 for the exact wording, including how seams are treated.
ISO 14116 (index 1, 2, 3). Materials are given a limited flame spread index. Index 1 is the lowest and allows behaviour that index 2 and 3 do not; index 1 garments may not be worn next to the skin and must be worn over an index 2 or index 3 garment. If a customer asks for "ISO 15025 compliance", ask which index or which code they mean.
Five errors that change the result
1. Testing without pre-treatment
Protective clothing standards require specimens to be tested after the cleaning pre-treatment they specify — washing or dry cleaning according to the care label. Flame-retardant finishes that pass as delivered may fail after laundering. A report on unwashed fabric is a development result, not a garment-standard result.
2. Testing only one direction
Specimens are taken in both machine and cross direction. Weaves with different yarns in warp and weft often behave differently. Testing a single direction to save fabric is the commonest shortcut and the hardest to defend in an audit.
3. Multilayer assemblies tested layer by layer
A garment with a shell, membrane and lining is tested as an assembly, flamed on the face that would be exposed in use. Testing the shell alone ignores a membrane that may melt and drip — and dripping is a failure criterion.
4. Measuring holes by eye
A 5 mm hole decides A1. Use a scale, measure in the largest dimension, and record which layer holed. In multilayer assemblies, a hole in the inner layer matters as much as one in the outer.
5. Ignoring the scope limits
ISO 15025 itself states that it is not appropriate for materials that show extensive melting or shrinkage, and it does not represent restricted air supply or large intense heat sources. Do not stretch the result to cover those hazards; other methods exist for them.
Equipment points that affect repeatability
- Draught-free enclosure. Air movement during the 10-second application changes the flame contact. Switch extraction off during the burn.
- Gas and flame confirmation. Use the gas the standard specifies and confirm flame height before each series.
- Specimen frame and pins. Hold the specimen flat at the defined distance from the burner; a specimen that bows towards the flame gets a hotter exposure.
- Timers. Afterflame and afterglow are separate times; you need to stop them independently.
Report checklist
- Procedure A, B or both — and the matching garment code or index.
- Pre-treatment applied, with number of cycles and method.
- Direction of each specimen and layer order of assemblies.
- Edge reach, afterflame, afterglow, debris and hole size per specimen.
- The garment standard and edition the criteria were taken from.
Our vertical flame spread tester covers ISO 15025 alongside other vertical textile methods and is built in our own workshop in Istanbul; see the ISO 15025 standard page.