The self-extinguishing test, commonly known as the flame-removal or "away-from-fire" test, is a key flammability evaluation for extruded polystyrene (XPS) insulation boards, verifying that the material stops burning within a specified time after the ignition source is withdrawn. Performed in accordance with standards such as GB/T 10801.2, GB 8624, ISO 11925-2, and UL 94, this test determines whether flame-retardant XPS products meet fire-safety requirements for building construction. This guide explains the technical background, sample requirements, test items, procedures, evaluation criteria, and practical applications of the XPS board self-extinguishing test.
Technical Overview
Extruded polystyrene (XPS) board is a rigid, closed-cell foam insulation material produced by melting polystyrene resin together with a blowing agent and extruding it through a die into continuous boards. Because polystyrene is an organic polymer, it is inherently combustible in its raw state. To meet fire-safety requirements in building applications, flame-retardant additives are incorporated during production so that the finished board exhibits self-extinguishing behavior, meaning that once the ignition source is removed, flaming combustion ceases within a short, defined period and the extent of damage remains limited.
The self-extinguishing test (often referred to as the flame-removal test) is a small-scale flammability evaluation in which a controlled burner flame is applied to a conditioned XPS specimen for a specified duration. The burner is then withdrawn, and the specimen's burning behavior is observed and measured. The test provides direct evidence of whether the flame-retardant system in the board is effective and supports the classification of the product under fire-performance standards.
- GB/T 10801.2 — Product standard for rigid extruded polystyrene foam thermal insulation boards (XPS), which specifies burning behavior requirements.
- GB 8624 — Chinese classification standard for burning behavior of building materials and products, defining B1 (flame-retardant) and B2 (combustible) grades.
- GB/T 8626 and ISO 11925-2 — Single-flame-source ignitability tests widely used to support classifications.
- GB/T 2406.2 and ISO 4589-2 — Limiting oxygen index (LOI) test used as a complementary indicator of flame retardancy.
- UL 94 and ASTM D635 — Small-scale horizontal burning tests for plastic materials, frequently referenced for export products.
- GB/T 8627, ASTM E84, and EN 13501-1 — Smoke density and larger-scale fire tests often combined with self-extinguishing verification.
Testing is typically carried out either in manufacturers' in-house quality-control laboratories or in accredited third-party laboratories when certification, compliance reporting, or acceptance inspection is required.
Testing Samples
Sample Types and Sources
Samples should be taken from finished production boards that are representative of the batch being evaluated. Common sample categories include flame-retardant grade XPS boards intended for B1 classification, standard combustible grade boards, and boards of various thicknesses and densities (typically 25 to 45 kg/m³). Both the smooth skin surface and the cut core surface may be evaluated, since flame-retardant distribution can differ between the surface layer and the foam core.
Sample Preparation and Conditioning
Specimens are cut to the dimensions specified by the applicable test method, commonly rectangular strips such as 150 mm × 50 mm (or the dimensions required by GB/T 8626, ISO 11925-2, or UL 94 procedures), retaining the product's original thickness unless the standard requires reduction. The following preparation requirements apply:
- At least 5 specimens (or the number required by the method, sometimes up to 10) should be prepared for each test condition to allow statistical evaluation.
- Specimens must be free of visible defects, cracks, dust, and surface contamination.
- Conditioning is performed at 23 ± 2 °C and 50 ± 5% relative humidity for a minimum of 40 hours, or as specified by the relevant standard, to stabilize the material prior to testing.
- Gauge marks are applied to the specimen surface so that damaged length can be measured after the test.
- If different surfaces (skin versus core) are to be compared, separate specimen sets are prepared and clearly identified.
Testing Items
The core objective of the self-extinguishing test is to quantify the burning behavior of the XPS board after the ignition flame is removed. The principal measured items are:
- Afterflame time — the duration, in seconds, for which the specimen continues to burn with a visible flame after withdrawal of the burner.
- Afterglow time — the duration of glowing combustion without a visible flame after flaming ceases.
- Self-extinguishing capability — a pass or fail determination of whether combustion stops within the time limit defined by the standard.
- Damaged length — the maximum extent of char, burn, or melt damage measured along the specimen after the test.
- Flaming drips and debris — whether burning molten droplets fall and ignite indicator materials such as filter paper or surgical cotton placed beneath the specimen.
- Supporting flammability indicators — limiting oxygen index (LOI) per GB/T 2406.2 or ISO 4589-2, smoke density rating per GB/T 8627, and full classification data per GB 8624, EN 13501-1, or ASTM E84 when a formal fire rating is required.
Testing Methods
Apparatus and Test Environment
The test is conducted in a draft-free enclosure or fume chamber to prevent air movement from affecting flame behavior. The essential equipment includes a laboratory burner (Bunsen or wing-tip type) capable of producing a stable blue flame of the height specified by the method (typically around 20 to 30 mm), a precision timer, a specimen support that holds the sample at the required orientation, calibrated rulers or gauge marks for measuring damaged length, and indicator paper or cotton for detecting flaming drips.
Test Procedure
The general procedure, consistent with GB/T 10801.2, GB/T 8626, ISO 11925-2, and UL 94 horizontal burning practice, is as follows:
- Verify that specimens have completed conditioning and record specimen identification, thickness, density, and surface type.
- Adjust the burner to produce a stable blue flame of the specified height and allow it to stabilize.
- Mount the specimen horizontally or at the angle required by the method, with indicator material positioned beneath it where applicable.
- Apply the flame to the designated edge or surface of the specimen for the specified exposure time, commonly 10, 15, or 30 seconds depending on the standard.
- Withdraw the burner smoothly and immediately start the timer.
- Record the afterflame time, afterglow time, and any flaming drips or debris igniting the indicator material.
- After the specimen has fully extinguished and cooled, extinguish any residual smoldering if required by the method and measure the damaged length between gauge marks.
- Repeat the test on all specimens and evaluate results against the acceptance criteria.
Evaluation Criteria
Although exact limits depend on the governing standard and the declared product grade, typical acceptance requirements for a self-extinguishing, flame-retardant XPS board are:
- The specimen extinguishes within the specified time after flame removal, commonly within 30 seconds, demonstrating effective self-extinguishing behavior.
- Damaged length does not exceed the limit defined by the standard, for example a maximum of 150 mm in single-flame-source evaluations used for classification.
- No flaming droplets or debris fall that ignite the filter paper or cotton indicator, since dripping can propagate fire in real installations.
- For B1 classification under GB 8624, additional requirements such as smoke density rating and combustibility data from supplementary tests must also be satisfied.
- For export markets, equivalent criteria under UL 94 (for example HF or HB classifications) or EN 13501-1 Euroclass ratings may apply, and results should be documented in a formal test report issued by an accredited third-party laboratory.
Applications
The XPS self-extinguishing test serves multiple purposes across the material's life cycle:
- Factory quality control — XPS manufacturers use the test to verify the consistency of flame-retardant dosing during production and to release batches for shipment.
- Product certification — test data supports formal fire-performance classification of XPS boards under GB 8624, EN 13501-1, and related schemes required for market access.
- Construction acceptance — contractors, supervision engineers, and building owners use reported self-extinguishing results to confirm that insulation delivered to site matches the specified fire grade.
- Formulation development — R&D teams compare afterflame time, damaged length, and LOI results when optimizing halogenated or halogen-free flame-retardant systems.
- External wall and roof insulation — boards installed in ETICS systems, inverted roofs, and insulated facades must demonstrate reliable self-extinguishing performance.
- Cold storage and prefabricated panels — foam cores used in cold-chain facilities and sandwich panels are screened for flame-removal performance as part of fire-risk management.
- Underfloor heating and civil engineering — boards used below heating pipes or in road and railway subgrade frost protection are evaluated to confirm fire compliance where required.
FAQ
What does "self-extinguishing after flame removal" mean for XPS boards?
It means that when the external ignition source is withdrawn, the XPS specimen stops burning on its own within a short defined period, and the damaged area remains within the limits set by the standard. This behavior indicates that the flame-retardant system interrupts combustion rather than allowing the material to continue burning freely.
Which standards govern the XPS self-extinguishing test?
The primary references are GB/T 10801.2 for the XPS product itself, GB 8624 for burning behavior classification, and GB/T 8626 or ISO 11925-2 for the single-flame-source procedure. International equivalents and complementary methods include UL 94, ASTM D635, ASTM E84, EN 13501-1, and the limiting oxygen index tests GB/T 2406.2 and ISO 4589-2.
What results are considered a pass?
A typical pass requires that afterflame ceases within the time limit specified by the standard (commonly 30 seconds or less), damaged length stays within the permitted maximum, and no flaming drips ignite the indicator material. For a B1 or equivalent classification, additional requirements such as smoke density and heat release criteria must also be met.
How is B1 grade XPS different from B2 grade?
B1 grade denotes flame-retardant performance, requiring the board to self-extinguish promptly with limited damage and controlled smoke production, verified through a fuller set of fire tests. B2 grade denotes ordinary combustible performance, where the board still shows restricted burning behavior after flame removal but does not meet the stricter B1 limits. The self-extinguishing test is a practical screening method that clearly distinguishes the two grades in most cases.
Can the test be performed in-house, or is a third-party laboratory required?
Manufacturers routinely perform the test in-house for quality control. However, when results are needed for certification, regulatory compliance, or contractual acceptance, testing should be conducted by accredited third-party laboratories that can issue formal reports recognized by certification bodies and building authorities.
Do flame retardants affect other properties of XPS boards?
Correctly formulated flame-retardant systems achieve self-extinguishing performance without significantly compromising thermal conductivity, compressive strength, or long-term durability. The self-extinguishing test, combined with routine physical property checks, confirms that fire performance and mechanical performance are both maintained at the specified levels.
