The combustion performance of thermal insulation materials is a critical safety parameter that determines their suitability for building facades, roofs, industrial equipment, and piping systems. This article provides a comprehensive technical overview of combustion performance testing for insulation materials, covering internationally recognized standards such as GB 8624, EN 13501-1, ISO, and ASTM methods, along with sample requirements, classification criteria, and typical applications.
Technical Overview
Thermal insulation materials are installed in large quantities on building envelopes, facades, roofs, and industrial installations. Because many organic insulation products—such as expanded polystyrene (EPS), extruded polystyrene (XPS), and polyurethane (PU) foam—are inherently combustible, their fire behavior must be evaluated systematically before use. Combustion performance determination measures ignitability, flame spread, heat release, smoke production, and the formation of flaming droplets under standardized fire conditions.
The most widely applied classification frameworks include GB 8624-2012 (Classification for burning behavior of building materials and products) in China, EN 13501-1 (fire classification of construction products) in Europe, and ASTM E84 (surface burning characteristics) in North America. These classifications are supported by fundamental test methods published by ISO and regional standards organizations. Under GB 8624-2012, materials are graded as Level A (A1, A2 – non-combustible), B1 (B, C – flame-retardant), B2 (D, E – combustible), and B3 (F – highly flammable). Accredited third-party laboratories perform these tests to demonstrate regulatory compliance and support product certification.
Testing Samples
Organic Foam Insulation Materials
This category includes EPS boards, XPS boards, rigid polyurethane (PU/PIR) foam, and phenolic foam. These materials are typically evaluated as finished products, including any facings, coatings, or composite layers, since surface treatments significantly influence fire performance. Specimens must retain their commercial thickness and density as representative of the marketed product.
Inorganic Fiber Insulation Materials
Rock (mineral) wool and glass wool products are principal candidates for Level A (non-combustible) classification due to their inorganic composition. Testing verifies furnace temperature rise, mass loss, and the absence of sustained flaming, with or without organic binders and facings as actually supplied.
Sample Preparation and Conditioning
Prior to testing, specimens are conditioned in a standard atmosphere of 23 ± 2 °C and 50 ± 5 % relative humidity until constant mass is reached, typically for a minimum of 48 hours (and up to several weeks for SBI specimens). Required dimensions vary by method:
- Non-combustibility test: cylindrical specimens 45 mm in diameter and 50 mm in height, five replicates.
- Single flame source test: rectangular specimens 250 mm × 90 mm with exposed face prepared as installed.
- Single Burning Item (SBI) test: two vertical wings of 1500 mm × 500 mm and 1500 mm × 1000 mm assembled in a corner configuration.
- ASTM E84 tunnel test: specimen 7.32 m (24 ft) in length by approximately 508 mm in width.
- Cone calorimeter: specimens 100 mm × 100 mm, thickness not exceeding 50 mm.
Testing Items
Combustion performance determination typically encompasses the following parameters, selected according to the target classification level:
- Non-combustibility: furnace temperature rise, mass loss, and duration of sustained flaming (ISO 1182 / GB/T 5464).
- Gross heat of combustion (PCS): potential total heat release per unit mass (ISO 1716 / GB/T 14402).
- Ignitability under small flame impingement, including flame spread distance and flaming droplets (ISO 11925-2 / GB/T 8626).
- Fire growth rate index (FIGRA), total heat release (THR600s), and lateral flame spread (LFS) from the SBI test (EN 13823 / GB/T 20284).
- Smoke growth rate (SMOGRA) and smoke production rate.
- Flame spread index (FSI) and smoke developed index (SDI) from the tunnel furnace method (ASTM E84 / UL 723).
- Limiting oxygen index (LOI) for material screening (ISO 4589-2).
- Heat release rate, peak heat release rate, and total heat release via cone calorimetry (ISO 5660-1).
- Smoke density and light transmittance in a closed chamber (ISO 5659-2).
Testing Methods
Non-Combustibility Test (ISO 1182 / GB/T 5464)
A cylindrical specimen is placed in a furnace stabilized at 750 °C for 30 minutes while thermocouples record the furnace and specimen surface temperatures. For Level A1 classification, temperature rise must not exceed 30 °C, mass loss must not exceed 50 %, and no sustained flaming (exceeding 10 seconds) is permitted. Level A2 permits flaming of up to 20 seconds.
Gross Heat of Combustion (ISO 1716 / GB/T 14402)
A specimen is completely combusted in an oxygen bomb calorimeter under 3 MPa oxygen pressure. The measured gross heat of combustion (PCS) must not exceed 2.0 MJ/kg for A1 classification or 3.0 MJ/kg for A2 classification of homogeneous products.
Single Flame Source Test (ISO 11925-2 / GB/T 8626)
A small propane flame (20 mm high) is applied to the bottom edge or surface of a vertically mounted specimen for 15 or 30 seconds. The specimen must not ignite the filter paper below via flaming droplets, and the flame tip must not reach the 150 mm gauge mark within a prescribed time, commonly 60 seconds after ignition begins.
Single Burning Item Test (EN 13823 / GB/T 20284)
Two specimens arranged in a corner are exposed to a 30 kW propane burner for 20 minutes while exhaust gas analysis quantifies heat release and smoke production. Classification is based on FIGRA0.2MJ and FIGRA0.4MJ thresholds, THR600s, lateral flame spread not reaching the wing edge, and SMOGRA limits for smoke classes s1, s2, and s3. Flaming droplets determine the additional d0, d1, or d2 suffix.
Surface Burning Characteristics (ASTM E84 / UL 723)
The Steiner tunnel test exposes a horizontally mounted ceiling specimen to a controlled flame at one end for 10 minutes. The flame spread index and smoke developed index support classifications of Class A (FSI ≤ 25), Class B (FSI 26–75), and Class C (FSI 76–200), each with SDI not exceeding 450.
Limiting Oxygen Index (ISO 4589-2)
The LOI determines the minimum oxygen concentration in a nitrogen–oxygen mixture that just supports candle-like combustion of a vertically mounted specimen. Values of 32 % and above generally indicate self-extinguishing behavior and are frequently used for material development and incoming quality control.
Cone Calorimetry and Smoke Density (ISO 5660-1, ISO 5659-2)
Cone calorimetry exposes a 100 mm × 100 mm specimen to radiant fluxes of 25, 50, or 75 kW/m², yielding heat release rate curves, total heat release, and effective heat of combustion. Smoke density testing in a closed chamber with radiant heating measures specific optical density, supporting the assessment of smoke hazard in escape routes.
Applications
Combustion performance determination is essential for demonstrating compliance with fire safety design codes and product certification schemes:
- Building envelope systems: external wall insulation, ETICS/EIFS, and curtain wall backing, where Chinese fire design codes require Level A or B1 materials for high-rise and public buildings.
- Roof and floor insulation, below-grade boards, and cavity fill products requiring verified flame-retardant grades.
- Industrial thermal insulation for piping, ductwork, vessels, and equipment operating at elevated temperatures, where non-combustible mineral wool products are often mandated.
- Cold storage and refrigeration facilities utilizing PU and PIR foam systems with fire-retardant modifications.
- Product certification, CE marking under the Construction Products Regulation, and conformity declarations to GB 8624-2012 for the Chinese market.
- Fire hazard research and the development of flame-retardant formulations, screening additives, and composite facings.
FAQ
What grade of insulation material is required for building facades in China?
Under the national fire protection design code for buildings, insulation materials used on external walls of high-rise residential and public buildings generally must achieve Level A, while other applications may permit B1 grade, subject to additional protective measures such as fire barriers and non-combustible covering layers.
How are A1 and A2 classifications determined under GB 8624-2012 and EN 13501-1?
Level A1 requires passing both the ISO 1182 non-combustibility test and the ISO 1716 calorific value test. Level A2 requires the SBI test combined with either ISO 1182 (allowing brief flaming) or ISO 1716, depending on the product type.
What is the difference between B1 and B2 grade materials?
B1 (flame-retardant, corresponding to classes B and C) materials must satisfy the SBI test and the single flame source test, demonstrating limited heat release and limited flame spread. B2 (combustible, classes D and E) materials only need to pass the small-flame ignitability test.
Are GB 8624 and EN 13501-1 results interchangeable?
The two systems are technically aligned because GB 8624-2012 adopts the EN 13501-1 classification logic and the same underlying ISO/EN test methods. However, formal classification reports must be issued against the specific standard cited in the applicable regulation, and results should be confirmed by accredited third-party laboratories.
How long does combustion performance testing take?
Depending on the classification level, the testing program—including conditioning, specimen preparation, furnace testing, SBI testing, and report issuance—typically requires two to six weeks, with non-combustibility certification of mineral wools being comparatively faster due to the simpler test matrix.