Fire Rating Testing for Thermal Insulation Materials: Standards, Methods and Classification

Fire rating testing for thermal insulation materials evaluates how boards, foams, and pipe coverings ignite, spread flame, release heat, and produce smoke, forming the technical basis for building code compliance and product certification. This guide explains the classification systems under GB 8624, EN 13501-1, and ASTM E84, the specimen requirements, the core laboratory test methods, and how accredited third-party laboratories help manufacturers demonstrate fire performance. Whether you produce mineral wool, PIR panels, EPS/XPS boards, or elastomeric foam, understanding these procedures is essential for market access and fire safety.

Technical Overview

Thermal insulation materials are installed in continuous layers across facades, roofs, and mechanical systems, which means their fire behavior directly influences building fire safety. Fire rating testing subjects representative specimens to standardized ignition sources, controlled heat flux, and exhaust-gas analysis in order to classify the material according to internationally recognized frameworks. The results determine whether a product may be used in a given building type, wall assembly, or occupancy classification.

The principal classification frameworks for insulation materials include:

• GB 8624-2012 (China): classifies building materials as A (subdivided into A1 and A2), B1 (subdivided into B and C), B2 (subdivided into D and E), and B3 (F, no performance determined). The standard is technically aligned with EN 13501-1 and adopts the same test methods.
• EN 13501-1 (Europe): defines classes A1, A2, B, C, D, E, and F, supplemented by additional classifications for smoke production (s1, s2, s3) and flaming droplets or particles (d0, d1, d2).
• ASTM E84 / UL 723 (North America): the Steiner tunnel test measuring Flame Spread Index (FSI) and Smoke Developed Index (SDI), yielding interior finish classes A (FSI 0–25), B (26–75), and C (76–200), each with SDI typically limited to 450.
• UL 94: small-scale burning tests for polymeric and foam components, with grades such as V-0, V-1, V-2, and 5VA.
• JIS A 1321 (Japan): categorizes interior finish materials as non-combustible, quasi-non-combustible, or flame-retardant.

In addition to the primary class, most schemes report smoke and dripping subclasses because smoke obscuration and burning droplets are major hazards in real facade fires. Accredited third-party laboratories perform these tests under controlled instrumentation, calibration, and quality management so that results are accepted by regulators, certifiers, and project specifiers.

Testing Samples

The validity of a fire classification depends heavily on specimen preparation. Samples must represent the product as placed on the market, including any facings, coatings, or composite layers, and must be conditioned before testing.

Rigid Boards and Panels

Mineral wool boards, glass wool boards, PIR/PUR panels, phenolic foam boards, and XPS/EPS boards are cut to the dimensions required by each method. For the Single Burning Item test, two wings are prepared: a long wing of approximately 1000 mm × 1500 mm and a short wing of approximately 495 mm × 1500 mm, each mounted on a non-combustible substrate to simulate end-use conditions.

Foam Plastics for Facade Systems

EPS, XPS, PUR, and PIR foams are tested in their final configuration, including adhesive, base coat, reinforcement mesh, and render where these form part of the certified system. Because thin facings can dramatically alter flame spread and dripping behavior, testing a bare foam board does not automatically support classification of the finished assembly.

Fibrous, Loose-Fill, and Flexible Insulation

Granular wool, cellulose fiber, calcium silicate, and elastomeric foam require dedicated fixtures or standard substrates so that the material cannot collapse or shift during exposure. Test houses document the mounting arrangement in the report, since classification is only valid for the tested configuration and orientation.

Specimen Conditioning and Quantity

Specimens are conditioned to equilibrium at 23 ± 2 °C and 50 ± 5% relative humidity in accordance with standards such as EN 13238 or GB/T 2918 before testing. Typical quantities include five cylindrical specimens for the non-combustibility furnace test, three determinations for the bomb calorimeter, three complete runs for the Single Burning Item test, and six specimens for small-flame ignitability covering both surface and edge exposure.

Testing Items

A full classification program measures the following parameters, and the combination of results determines the final class:

• Non-combustibility: furnace temperature rise, mass loss, and duration of sustained flaming.
• Gross heat of combustion (PCS): total energy released per unit mass under complete combustion.
• Fire growth rate (FIGRA): the maximum rate of heat release relative to total energy released, a key indicator of flashover potential.
• Total heat release (THR600s): cumulative heat released during the first 600 seconds of the SBI test.
• Lateral flame spread (LFS): whether flame reaches the edge of the specimen wing.
• Smoke production: smoke growth rate index (SMOGRA), total smoke production (TSP600s), or smoke density rating depending on the method.
• Flaming droplets and particles: timing and ignition capability of molten debris.
• Ignitability: flame spread distance and filter paper ignition under a small pilot flame.
• Limiting oxygen index (LOI): the minimum oxygen concentration required to sustain candle-like burning.
• Flame Spread Index and Smoke Developed Index: tunnel test outputs used for North American classification.

Testing Methods

Non-Combustibility Furnace Test (ISO 1182 / GB/T 5464)

A cylindrical specimen, typically 45 mm in diameter and 50 mm high, is inserted into a tubular furnace stabilized at 750 °C for 20 minutes while thermocouples record furnace and surface temperatures. Class A1 requires a temperature rise no greater than 30 °C, mass loss no greater than 50%, and no sustained flaming; A2 permits a 50 °C rise and up to 20 seconds of flaming. This method is central to qualifying stone wool and other mineral-based insulation.

Bomb Calorimeter Test (ISO 1716 / GB/T 14402)

A small, powdered specimen is burned in a high-pressure oxygen bomb, and the gross heat of combustion is calculated from the temperature rise. PCS values of 2.0 MJ/kg or less support A1, while values up to 3.0 MJ/kg can support A2 when combined with SBI results. This test catches organic binders and facings that elevate the fuel load of otherwise inorganic products.

Single Burning Item Test (EN 13823 / GB/T 20284)

Two specimen wings form a vertical corner exposed to a 30 kW propane burner for approximately 21 minutes. Oxygen-consumption calorimetry and laser smoke photometry quantify FIGRA, THR600s, SMOGRA, lateral flame spread, and droplet behavior. Typical class thresholds include FIGRA ≤ 120 W/s and THR600s ≤ 7.5 MJ for class B, and FIGRA ≤ 250 W/s and THR600s ≤ 15 MJ for class C, with SMOGRA ≤ 30 m²/s² required for smoke class s1.

Small Flame Ignitability (EN ISO 11925-2 / GB/T 8626)

A 250 mm × 90 mm specimen is exposed to a small burner flame for 15 or 30 seconds on its surface or bottom edge. To pass, the flame tip must not reach the 150 mm gauge mark within 60 seconds, and burning droplets must not ignite filter paper placed beneath the specimen. This test underpins classes B through E and the droplet subclasses.

Steiner Tunnel Test (ASTM E84 / UL 723)

A specimen approximately 508 mm wide and 7.3 m long forms the ceiling of a horizontal tunnel and is exposed to a gas-fired ignition source for 10 minutes. Flame travel over the specimen length is compared against calibrated references to calculate the Flame Spread Index and Smoke Developed Index. Because melting foams may run on the tunnel ceiling, supplementary room-corner evaluations such as ISO 9705 or ASTM E2257 are often required for thermoplastic insulation.

Supplementary and Screening Methods

The cone calorimeter (ISO 5660-1, ASTM E1354, GB/T 16172) measures heat release rate, ignition time, and smoke yield of 100 mm × 100 mm specimens under irradiance of 25 to 50 kW/m², and is widely used for research and formulation screening. Limiting oxygen index testing (ISO 4589-2, ASTM D2863, GB/T 2406.2) provides quick comparative data, with B1-grade foams typically exceeding LOI values of 30%. Smoke chambers (ASTM E662, GB/T 8627) quantify specific optical density or smoke density rating, and UL 94 procedures grade small polymer specimens for component-level acceptance.

Applications

Fire classification data for insulation materials supports decisions across the entire construction and industrial value chain:

• Building envelopes: exterior wall insulation, ETICS/EIFS systems, and sandwich panels must meet the class mandated by fire codes such as GB 50016 in China or the national regulations of European Union member states, with class A or B1 frequently required for high-rise facades and fire barriers at floor lines.
• Interior finishes: wall, ceiling, and roof cavity insulation relies on tunnel test classes or Euroclasses for code acceptance in schools, hospitals, and assembly occupancies where smoke and flame spread limits are strictest.
• Mechanical systems: HVAC duct wrap, chilled water pipe insulation, and equipment lagging are qualified using the relevant fire, smoke, and flame-spread indices specified in mechanical codes.
• Transport and specialized sectors: rolling stock insulation is tested against EN 45545-2, while marine and industrial installations apply their own flame, smoke, and toxicity protocols.
• Certification and market access:
• Quality management: manufacturers use LOI, cone calorimeter, and small-scale screening during R&D, incoming material verification, and production audits to keep formulations within the classified envelope.