The Single Burning Item (SBI) test is the intermediate-scale reaction-to-fire method specified in EN 13823 and GB/T 20284, used to evaluate how building products excluding floorings contribute to a developing fire when exposed to the thermal attack of a single burning item. By measuring parameters such as FIGRA, THR600s, SMOGRA, TSP600s, and LFS, the test supplies the core classification data for EN 13501-1 (Euroclass) and GB 8624-2012 fire performance grading. This technical guide explains the test principle, apparatus, specimens, procedure, reported parameters, and typical applications of the single burning item combustion performance test.
Technical Overview
The Single Burning Item (SBI) test, known in Chinese standards as the single burning item combustion performance test, is an intermediate-scale reaction-to-fire test performed on building products and assemblies other than floorings. It simulates a fire scenario in which a product mounted in a room corner configuration is exposed to the thermal attack of a single burning item, typically representing a wastepaper basket or similar moderate ignition source. The test quantifies how much the product contributes to fire growth in terms of heat release and smoke production.
The governing test methods are EN 13823, "Reaction to fire tests for building products — Building products excluding floorings exposed to the thermal attack by a single burning item," in Europe, and GB/T 20284, "Single burning item test for building materials or products," in China, which is technically aligned with the European method. The results feed directly into the classification systems of EN 13501-1 in Europe and GB 8624-2012 in China, determining whether a product achieves classes A2, B, C, or D, together with smoke classes s1, s2, or s3 and burning droplets/particles classes d0, d1, or d2.
Heat release is determined by oxygen consumption calorimetry, based on the principle that approximately 13.1 MJ of heat is released per kilogram of oxygen consumed, while smoke production is determined from optical attenuation of a light beam across the exhaust duct. Because the test reproduces realistic corner-fire geometry, specimen mounting, backing, joints, and fixings, it is widely regarded as the decisive fire performance assessment for wall and ceiling products in regulated construction markets.
Testing Samples
Applicable Product Types
The SBI test applies to building products that are not floorings and that can be mounted in the standard corner geometry. Typical product categories submitted to accredited third-party laboratories include:
- Internal wall and ceiling linings, decorative boards, laminates, and panels
- External wall claddings, facade panels, and aluminum composite or metal-faced panels
- Thermal insulation products for walls, roofs, and building services
- Sandwich panels and sandwich panel systems with metallic or other facings
- Gypsum boards, cement boards, wood-based panels, and engineered wood products
- Coatings, renderings, and finishes applied to standard or defined substrates
- Linear pipe insulation and ductwork products
Specimen Construction and Dimensions
The test specimen consists of two vertical wings arranged at a right angle on the trolley of the test apparatus: a long wing nominally 1000 mm wide and a short wing nominally 500 mm wide, each 1500 mm high and made from the product at its actual end-use thickness. The total exposed surface area is approximately 2.25 square meters. Products are tested in their end-use configuration, which means the specimen incorporates the backing board, substrate, air gaps, mechanical fixings, and joints that will exist in the final application, in accordance with the relevant mounting and fixing rules such as EN 13238, EN 15715, or the product-specific harmonized specification.
Specimen Conditioning and Quantity
Specimens are conditioned to constant mass at a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5 % before testing. A minimum of three replicate specimens is normally required, with additional specimens tested when results fall near classification boundaries or when the standard requires confirmation of borderline data. Any surface treatment, membrane, or facing applied in practice must be present on the test specimen, since omitting end-use layers is one of the most common causes of non-representative results.
Testing Items
The SBI test produces a set of quantitative fire performance parameters that are used either directly for classification or for engineering assessment of fire growth contribution:
- FIGRA (Fire Growth Rate, W/s): the maximum value of the heat release rate divided by elapsed time, evaluated with a total heat release threshold of 0.2 MJ (FIGRA0.2MJ) and 0.4 MJ (FIGRA0.4MJ); FIGRA0.2MJ is the value used for classification
- THR600s (MJ): the total heat released by the specimen during the first 600 seconds of exposure to the primary burner
- LFS (Lateral Flame Spread): a visual observation of whether flames spread over the surface of the long wing to reach its far vertical edge, with the time of any sustained edge contact recorded
- SMOGRA (Smoke Growth Rate, m²/s²): the maximum rate of smoke production growth, derived from the smoke production rate divided by elapsed time, subject to defined minimum thresholds
- TSP600s (m²): the total smoke produced during the first 600 seconds of primary burner exposure
- Flaming droplets and particles: qualitative observations of whether flaming droplets or debris fall during the test, supporting the d-classification
- Supporting records: heat release rate curve, smoke production rate curve, oxygen and carbon dioxide/carbon monoxide concentrations, duct flow, and mass observations as required by the standard
Classification Thresholds under EN 13501-1 and GB 8624-2012
For construction products excluding floorings, the main class criteria based on SBI results are:
- Class A2 and Class B: FIGRA0.2MJ ≤ 120 W/s, THR600s ≤ 7.5 MJ, and no lateral flame spread to the edge of the long wing (Class A2 additionally requires compliance with EN ISO 1182 or EN ISO 1716 criteria)
- Class C: FIGRA0.2MJ ≤ 250 W/s, THR600s ≤ 15 MJ, and no lateral flame spread to the edge
- Class D: FIGRA0.2MJ ≤ 750 W/s
- Smoke class s1: SMOGRA ≤ 30 m²/s² and TSP600s ≤ 50 m²
- Smoke class s2: SMOGRA ≤ 180 m²/s² and TSP600s ≤ 200 m²
- Smoke class s3: no requirement beyond the classes above
Classes B, C, and D additionally require satisfactory performance in the small-flame ignition test of EN ISO 11925-2, which also governs the d0, d1, and d2 droplets and particles classification.
Testing Methods
Apparatus and Instrumentation
The SBI apparatus comprises a trolley carrying the specimen wings, a trolley frame, and a combustion hood connected to an exhaust system with a duct of approximately 315 mm internal diameter. A primary burner of the sandbox type, fueled by propane at a nominal heat output of about 30 kW, is positioned in the corner between the two wings, while an auxiliary burner of identical output is mounted to the side of the corner. The measurement section of the duct is instrumented with a gas sampling probe feeding oxygen, carbon dioxide, and carbon monoxide analyzers, an optical smoke measurement system based on light extinction, a bidirectional flow probe with differential pressure measurement, and a duct thermocouple. Laboratory environmental conditions, air inlet to the test room, and duct velocity are controlled and recorded throughout the test.
Test Procedure
The test is conducted under the exhaust hood with the burner switched between the auxiliary and primary positions so that the heat and smoke generated by the burners themselves remain constant and the net contribution of the specimen can be isolated. The standard sequence is as follows:
- Baseline recording of all measurement channels for the first 120 seconds
- Ignition of the auxiliary burner at 120 seconds, directed away from the specimen, to stabilize the exhaust and measurement conditions
- Ignition of the primary burner at 300 seconds, exposing the specimen corner to the thermal attack of approximately 30 kW
- Continued exposure for 1260 seconds, ending the test at a total elapsed time of 1560 seconds
- Continuous visual observation of flame spread, sustained flaming, and flaming droplets or particles throughout the exposure
Data Reduction and Calculations
Heat release rate is calculated from the measured oxygen depletion, corrected for carbon monoxide and carbon dioxide formation and for the dilution of the exhaust flow, applying the oxygen consumption factor of approximately 13.1 MJ per kilogram of oxygen. Smoke production rate is derived from the measured optical transmission across the duct using light extinction theory, normalized by the volumetric exhaust flow. From the resulting heat release rate and smoke production rate curves, the software prescribed by the standard computes FIGRA, THR600s, SMOGRA, and TSP600s, while LFS is assessed from visual observation. Reported values are typically the mean of the replicate tests, with individual run values also stated so that classification can be verified run by run.
Calibration and Quality Control
Reliable SBI results depend on rigorous calibration and verification performed before and between test series. This includes verification of burner heat output against the nominal value, calibration of gas analyzers with certified calibration gases, verification of duct velocity and flow measurement, checking of the optical smoke system, and periodic confirmation of apparatus response using reference materials such as non-combustible calcium silicate board and combustible reference specimens as specified in the standard. Testing is normally carried out by accredited third-party laboratories operating under an ISO/IEC 17025 quality management framework, which is essential when results are used for regulatory classification, declaration of performance, or market surveillance.
Applications
The single burning item test is a cornerstone of fire safety compliance for construction products in Europe, China, and numerous other jurisdictions that have adopted the Euroclass or GB classification frameworks. Its results are used for:
- Fire performance classification of building products under EN 13501-1 for CE marking and declarations of performance under the EU Construction Products Regulation framework
- Combustion performance grading of building materials and products under GB 8624-2012 for the Chinese market, including grades A, B1, B2, and B3 with their sub-classes
- Product development and optimization of formulations, thicknesses, substrates, and mounting systems for wall linings, claddings, and insulation products
- Compliance demonstration for facades, interior finish codes, and passive fire protection requirements in building design approvals
- Technical documentation supporting tenders, green building submissions, and fire risk engineering studies
- Benchmarking and comparative assessment of competing materials, coatings, and assemblies during material selection
Because the test evaluates the product in an end-use corner configuration with realistic joints and backing, its results are directly relevant to how a product will behave in the early stages of a compartment fire, making it one of the most influential inputs in reaction-to-fire regulation worldwide.
FAQ
What is the difference between EN 13823 and GB/T 20284?
EN 13823 is the European test method and GB/T 20284 is the corresponding Chinese national standard, which is technically aligned with the European method. Both use the same apparatus, specimen geometry, burner exposure, and calculated parameters, so results are broadly comparable, but classification is made under the applicable classification standard: EN 13501-1 in Europe or GB 8624-2012 in China.
How does the SBI test differ from the cone calorimeter and the room corner test?
The cone calorimeter of ISO 5660 is a small-scale test on 100 mm by 100 mm specimens under controlled radiant flux, suitable for material screening. The SBI test is intermediate scale, using a 2.25 square meter corner specimen exposed to a 30 kW burner, and it is the basis for regulatory classification. The full-scale room corner test of ISO 9705 reproduces an entire room fire and is used mainly for reference and system validation rather than routine product classification.
What specimen size and quantity are needed?
Each specimen set consists of two wings, 1000 mm and 500 mm wide, each 1500 mm high at end-use thickness, mounted on the appropriate backing. A minimum of three complete specimen sets is required, and laboratories generally request additional sets in case retesting is needed for borderline or discrepant results.
Which fire performance classes require the SBI test?
Under EN 13501-1 and GB 8624-2012, the SBI test is required for classes A2, B, C, and D for products excluding floorings. Class A1 and the A2 path rely on EN ISO 1182 and EN ISO 1716, while classes B through E also require passing the EN ISO 11925-2 small-flame ignition test.
Is the SBI test applicable to floor coverings?
No. Floorings are excluded from the scope and are instead evaluated using the radiant panel flaming spread test of EN ISO 9239-1 together with EN ISO 11925-2, since fire spread over a horizontal floor surface follows a different mechanism.
What do FIGRA and SMOGRA actually indicate?
FIGRA expresses how quickly a product releases heat and is the dominant indicator of its contribution to fire growth, expressed in W/s. SMOGRA expresses how rapidly smoke is produced, in m²/s², and together with TSP600s determines the s1 to s3 smoke classification. Lower values in both parameters indicate better fire performance.
How long does an SBI test program take?
A single test run lasts 1560 seconds, or 26 minutes. Including conditioning to constant mass, apparatus calibration, mounting of specimens, and replicate testing, a complete program for one product typically takes one to two weeks in an accredited third-party laboratory, plus reporting time.
Do test results depend on how the product is mounted?
Yes, strongly. Backing boards, air gaps, joints, and fixings can materially change FIGRA, THR600s, and smoke results. Specimens must therefore replicate the declared end-use application in accordance with the applicable mounting rules, and the classification is only valid for the mounting configuration that was tested.