Determination of combustion performance of flammable materials is an essential fire safety evaluation that measures how building products, plastics, textiles, foams, and other combustible materials ignite, propagate flame, release heat, and generate smoke under controlled laboratory conditions. This technical guide summarizes the internationally recognized standards (GB, EN, ISO, IEC, ASTM, UL, JIS), typical sample types, key test parameters, and laboratory methods used by accredited third-party laboratories to classify materials into grades such as A, B1, B2, and B3. Understanding these test protocols helps manufacturers achieve regulatory compliance, optimize flame-retardant formulations, and reduce fire hazard across the construction, transportation, electronics, and consumer product industries.
Technical Overview
Combustion performance determination refers to the systematic laboratory evaluation of how a flammable material behaves when exposed to an ignition source, radiant heat, or a developing fire. The evaluation characterizes ignitability, flame spread, heat release rate, smoke production, flaming droplets and particles, and the toxicity of fire effluent gases, and it provides the technical basis for assigning materials to standardized fire performance grades.
In China, the mandatory classification standard GB 8624 divides building materials and products into grade A (non-combustible, subdivided into A1 and A2), B1 (flame-retardant, subdivided into B and C), B2 (combustible, subdivided into D and E), and B3 (highly combustible, grade F). The European system EN 13501-1 adopts a parallel structure with classes A1, A2, B, C, D, E, and F. Comparable frameworks exist in North America, where ASTM E84 assigns tunnel furnace classes, and in Japan under JIS A 1321. Testing is normally performed by accredited third-party laboratories according to the destination market of the product.
The selection of test methods depends on the intended application, the substrate, and the target classification level. Most classification schemes combine several tests: for example, non-combustibility, gross heat of combustion, single burning item, and small flame ignition tests are jointly required to assign grades A1 through D under GB 8624 and EN 13501-1.
Testing Samples
Typical materials submitted for combustion performance determination include the following categories:
Building and Construction Materials
Wall and ceiling panels, decorative laminates, gypsum boards, wooden panels, flooring coverings, thermal insulation boards (EPS, XPS, polyurethane, phenolic foam, mineral wool), pipes and ducts, door and window assemblies, sealants, coatings, and fireproofing materials. These products are most commonly tested against GB 8624 or EN 13501-1 for construction product certification.
Plastic and Polymeric Materials
Engineering thermoplastics, thermosetting resins, polymer composites, films, sheets, and molded parts used in appliances, enclosures, and functional components. These are typically evaluated with the UL 94 or IEC 60695-11-10 horizontal and vertical burning tests and the limiting oxygen index method.
Textiles and Furnishing Fabrics
Curtains, draperies, upholstery fabrics, bedding articles, awnings, tents, carpets, and vehicle interior textiles, evaluated using vertical flame tests such as GB/T 5455, textile burning methods under JIS L 1091, and ASTM D6413 for flame resistance.
Foam and Soft Furnishing Materials
Flexible polyurethane foams, rigid foams, seat cushions, and mattresses, which are frequently assessed for ignition resistance, after-flame time, and melting or dripping behavior using small ignition source methods such as EN 1021 and EN ISO 11925-2.
Electrical, Electronic, and Cable Products
Insulation materials, connectors, switch and enclosure housings, printed circuit boards, and wire and cable sheathing materials, which must satisfy flammability requirements of the IEC 60695 fire hazard testing series and UL 94.
Testing Items
Depending on the applicable classification standard, one or more of the following combustion performance parameters are determined:
- Ignitability: time to ignition, occurrence of ignition, and flame spread beyond a defined limit under small flame attack (GB/T 8626, EN ISO 11925-2)
- Non-combustibility: mass loss, sustained flaming time, and furnace temperature rise at 750 °C (GB/T 5464, ISO 1182)
- Gross heat of combustion (PCS) determined by oxygen bomb calorimetry (GB/T 14402, ISO 1716)
- Heat release rate (HRR), peak heat release rate, and total heat release (THR) using the oxygen consumption technique (GB/T 16172, ISO 5660-1)
- Fire growth rate index (FIGRA) and total heat release over the first 600 seconds (THR600s), the primary grading parameters in the single burning item test (GB/T 20284, EN 13823)
- Lateral flame spread (LFS) and the occurrence of flaming droplets and particles
- Smoke production rate (SPR), total smoke production (TSP600s), smoke growth rate index (SMOGRA), and smoke density or light transmittance (GB/T 8627, ASTM E662)
- Limiting oxygen index (LOI), the minimum oxygen concentration that supports candle-like burning (GB/T 2406.2, ISO 4589-2, ASTM D2863)
- After-flame time, after-glow time, damaged length, and burning rate in horizontal and vertical burning tests (GB/T 2408, IEC 60695-11-10, UL 94)
- Flame spread index (FSI) and smoke developed index (SDI) in the 25-foot tunnel furnace (ASTM E84)
- Critical heat flux at extinguishment and smoke density for flooring by radiant panel (GB/T 11785, EN ISO 9239-1)
- Toxicity and irritancy classification of fire effluent gases (GB/T 20285)
Testing Methods
Single Burning Item (SBI) Test
The SBI test, specified in GB/T 20284 and EN 13823, exposes a corner-shaped specimen assembly consisting of a 1500 mm × 500 mm long wing joined to an 800 mm × 500 mm short wing to a 30 kW propane burner. Oxygen consumption calorimetry and laser photometry yield FIGRA, THR600s, SMOGRA, TSP600s, lateral flame spread, and observations of flaming droplets. The SBI test is the decisive method for classes B, C, and D and is performed on multiple specimen sets conditioned at 23 ± 2 °C and 50 ± 5 % relative humidity.
Small Flame Ignition Test
GB/T 8626 and EN ISO 11925-2 apply a small diffusion flame, typically for 15 or 30 seconds, to the surface or edge of a specimen mounted at 45 degrees. The material passes if ignition does not occur, or if the flame front does not reach the 150 mm gauge line within the prescribed time and no flaming drips ignite the filter paper placed beneath the specimen. This test underpins classes B through E.
Non-combustibility and Heat of Combustion Tests
For the highest grades, ISO 1182 and GB/T 5464 place cylindrical specimens in a stabilized 750 °C furnace and record mass loss, duration of sustained flaming, and furnace temperature rise, while ISO 1716 and GB/T 14402 determine the gross heat of combustion in an oxygen bomb calorimeter. Combinations of these results with SBI data establish grades A1 and A2.
Cone Calorimeter Test
The cone calorimeter (ISO 5660-1, GB/T 16172) irradiates 100 mm × 100 mm specimens at heat fluxes of 25 to 100 kW/m² and measures time to ignition, heat release rate by oxygen consumption, effective heat of combustion, mass loss rate, and smoke yield. It is widely used for comparing materials in research and development and for generating input data for fire safety engineering.
Limiting Oxygen Index (LOI) Test
In the LOI method (GB/T 2406.2, ISO 4589-2, ASTM D2863), a vertically mounted specimen is ignited in a controlled nitrogen-oxygen mixture, and the minimum oxygen volume fraction that just supports burning is determined. LOI values above approximately 27 percent generally indicate self-extinguishing behavior, making the method popular for quality control of flame-retarded plastics and textiles.
Horizontal and Vertical Burning Tests
These small-scale methods apply a 20 mm (50 W) premixed flame to 125 mm × 13 mm bar specimens. Depending on after-flame time, after-glow time, ignition of a cotton indicator by flaming droplets, and burn-up distance, materials receive 94HB, V-0, V-1, V-2, 5VA, or 5VB ratings under UL 94, with equivalent HB and V classifications defined in GB/T 2408 and IEC 60695-11-10.
Smoke Density and Toxicity Tests
GB/T 8627 and ASTM E662 measure the specific optical density of smoke accumulated in a closed chamber under flaming or smoldering exposure, while GB/T 20285 evaluates the smoke toxicity hazard of materials by determining the effluent gas concentrations associated with incapacitating effects. These results supplement heat release data and are increasingly required for occupied spaces.
Tunnel and Radiant Panel Tests
The ASTM E84 Steiner tunnel measures the flame spread index and smoke developed index of 25-foot specimens for interior finish classification, while EN ISO 9239-1 and GB/T 11785 evaluate flooring products by radiant panel, reporting the critical heat flux at flame extinguishment and integrated smoke density.
Applications
Combustion performance determination supports regulatory compliance, product certification, and fire safety engineering across many industries:
- Construction product certification: demonstrating compliance with GB 8624 for the Chinese market, EN 13501-1 for CE marking of construction products in Europe, and ASTM E84 classification in North America
- Public assembly occupancies: verification of flame-retardant finishes and components used in hotels, theaters, stations, and airport terminals under GB 20286
- Transportation: fire performance approval of interior and structural materials for rail vehicles under EN 45545-2, and for road vehicle and aircraft cabin interiors
- Electrical and electronics: qualification of enclosures, insulating parts, and components under UL 94 and the IEC 60695 fire hazard testing series
- Furniture and furnishings: ignition resistance assessment of upholstered seating and mattresses under EN 1021
- Textile procurement and labeling: flame resistance verification of curtains, drapery, bedding, and protective clothing fabrics
- Research and development: screening and benchmarking of flame-retardant formulations using LOI, UL 94 ratings, and cone calorimeter parameters
- Quality control: incoming material inspection and batch conformity testing during series production
FAQ
What is combustion performance determination?
It is a set of standardized laboratory procedures that quantify how a flammable material ignites, burns, spreads flame, releases heat, and produces smoke and toxic gases, allowing the material to be assigned an objective fire performance classification.
Which standards apply to my product?
Building and decoration materials for the Chinese market are classified under GB 8624 using GB/T 20284, GB/T 8626, GB/T 5464, and GB/T 14402; products sold in Europe follow EN 13501-1 with EN 13823, EN ISO 11925-2, ISO 1182, and ISO 1716; plastic components for electrical products are generally rated under UL 94 or IEC 60695-11-10; and textiles are commonly tested to GB/T 5455, JIS L 1091, or ASTM D6413.
What specimen sizes and quantities are needed?
Requirements vary by method: the SBI test needs at least three sets of corner assemblies with 1500 mm × 500 mm and 800 mm × 500 mm wings, cone calorimeter specimens are 100 mm × 100 mm, LOI bars are typically 80 to 150 mm long by 10 mm wide, and UL 94 uses bars of 125 mm × 13 mm together with plaques for the 5V ratings. Laboratories confirm exact quantities and orientation requirements before testing begins.
What do grades A, B1, B2, and B3 mean?
Under GB 8624, grade A materials are essentially non-combustible (A1) or of very limited combustibility (A2); B1 materials spread flame slowly and contribute little heat to a developing fire (sub-grades B and C); B2 materials burn readily but with moderate contribution to fire growth (sub-grades D and E); and B3 (F) materials ignite and propagate flame easily and are generally prohibited in regulated applications.
How should materials be conditioned before testing?
Most standards require conditioning to constant mass at 23 ± 2 °C and 50 ± 5 % relative humidity, typically for a minimum of 48 hours, because moisture content strongly influences ignitability, flame spread, and heat release measurements.
How long does testing take and what does a report include?
Depending on the number of methods required for the target grade, testing at accredited third-party laboratories generally takes one to three weeks after sample conditioning. The report documents the standards applied, specimen description, measured parameters such as FIGRA, THR600s, SMOGRA, LFS, and LOI, observations of flaming droplets, and the resulting classification, together with measurement uncertainty where applicable.