The Single Burning Item (SBI) test is an intermediate-scale reaction-to-fire evaluation that measures heat release, smoke production, lateral flame spread, and flaming droplet behavior of building products exposed to the thermal attack of a single burning item. Performed to EN 13823 in Europe and GB/T 20284 in China, it generates the key classification parameters (FIGRA, THR600s, SMOGRA, TSP600s) used for EN 13501-1 Euroclass ratings and GB 8624 fire performance grades. This article explains the test principle, specimen requirements, measured parameters, methodology, applications, and frequently asked questions to help manufacturers prepare for SBI evaluation at accredited third-party laboratories.
Technical Overview
The Single Burning Item (SBI) test is a cornerstone of modern reaction-to-fire classification for construction products other than floorings. It is specified in Europe by EN 13823 and in China by GB/T 20284-2006, which is technically aligned with the European method. The test scenario is derived from room-corner fire research and simulates the thermal attack that a burning item, such as a waste-paper basket placed in the corner of a room, imposes on adjacent wall and ceiling linings.
The specimen consists of two vertical wings mounted at a right angle on a movable trolley beneath a standardized exhaust hood. A propane-fired gas burner with a triangular, perforated top is placed in the corner at the base of the specimen. The burner operates at approximately 30 kW when ignited and is adjusted to 30.7 kW during the exposure, which lasts around 21 minutes. Heat release is determined by oxygen consumption calorimetry in the exhaust duct, while smoke production is quantified photometrically. The test results feed directly into classification schemes such as EN 13501-1 (Euroclass A2, B, C, D) and GB 8624-2012 (grades A2, B, C, D), supplemented by small-flame ignition tests such as EN ISO 11925-2.
- Standards: EN 13823, GB/T 20284-2006, classification per EN 13501-1 and GB 8624-2012
- Specimen geometry: two wings at a right angle, long wing approximately 1000 mm wide and 1500 mm high, short wing approximately 495 mm wide and 1500 mm high
- Exposure: propane gas burner, nominally 30 kW to 30.7 kW, ignition at 120 s, exposure until 1380 s, data recorded over 1560 s
- Primary outputs: FIGRA, THR600s, SMOGRA, TSP600s, lateral flame spread, flaming droplets and particles
Testing Samples
Flat Wall and Ceiling Products
Typical samples include gypsum boards, wood-based panels, decorative laminates, aluminum composite panels, coatings, and wall coverings intended for vertical or ceiling applications. Products must be tested at their end-use thickness and mounted on the substrate or support frame used in practice, because the backing material significantly influences heat release behavior. Where the product standard allows, a standard non-combustible substrate may be used, and this choice must be documented because it is part of the classified application field.
Composite Panels and Assembled Systems
Sandwich panels, ventilated façade cassettes, cladding kits, and insulated lining systems are tested as complete assemblies incorporating representative joints, air gaps, fixings, and edge details. The standard specimen arrangement reproduces a vertical corner with the exposed surface facing the burner, and manufacturers must ensure that the tested configuration represents the most unfavorable mounting conditions permitted by the installation instructions.
Linear Products and Pipe Insulation
Linear products such as pipe insulation sections can also be evaluated using special mounting arrangements in which the specimens are attached to vertical supporting tubes. This allows thermal insulation products that cannot be presented as flat boards to be classified under the same FIGRA and THR600s criteria as other building products.
Specimen Preparation and Conditioning
A minimum of three complete specimen sets is normally required, and additional sets may be needed if results fall close to classification limits. Prior to testing, specimens are conditioned in a controlled environment, typically at 23 ± 2 °C and 50 ± 5 % relative humidity, until constant mass is reached, in line with the conditioning requirements referenced by the test standard. Specimens must be cut accurately, mounted without pre-compression or gaps other than those specified, and clearly marked with orientation and test sequence information.
Testing Items
The SBI test yields a set of quantitative and observational parameters that together characterize the contribution of a product to fire growth and smoke hazard.
Fire Growth Rate (FIGRA)
FIGRA is the running maximum of the ratio between the averaged heat release rate and elapsed time, expressed in W/s. Two variants are reported: FIGRA0.2MJ, computed only after the total heat release exceeds 0.2 MJ, and FIGRA0.4MJ, computed after 0.4 MJ. FIGRA expresses how quickly a developing fire accelerates and is the single most decisive parameter for distinguishing Euroclass B, C, and D performance.
Total Heat Release (THR600s)
THR600s is the cumulative heat energy released over the first 600 seconds of burner exposure, expressed in MJ. It represents the overall fuel contribution of the product during the early, critical stage of a fire.
Smoke Growth Rate (SMOGRA)
SMOGRA, expressed in m²/s², is derived from the averaged smoke production rate divided by elapsed time after the total smoke production exceeds a defined threshold. It characterizes the speed at which smoke develops, which is central to visibility and tenability in escape routes.
Total Smoke Production (TSP600s)
TSP600s is the cumulative smoke production over the first 600 seconds, expressed in m². Together with SMOGRA, it determines the smoke classification indices s1, s2, or s3 under EN 13501-1.
Lateral Flame Spread and Flaming Droplets
Observations include whether flame spreads laterally along the specimen wings to reach the specimen edge (LFS), and whether flaming droplets or particles are released within the first 600 seconds. These observations support the additional classifications for flame spread and droplets (d0, d1, d2) attached to the fire class.
Testing Methods
Test Apparatus
The apparatus comprises a wheeled trolley carrying the two-wing specimen, an exhaust hood and duct system, and a measurement section instrumented with gas sampling probes, oxygen, carbon dioxide, and carbon monoxide analyzers, bi-directional flow probes, and a photometric smoke obscuration system. Propane is supplied to the burner through calibrated mass-flow control, and the entire system is verified against reference burner output checks before testing.
Test Procedure
After instrument verification and baseline recording, the specimen trolley is pushed into position and data acquisition begins. The burner is ignited at 120 s at 30 kW, the output is adjusted to 30.7 kW at 300 s, and exposure continues until 1380 s, with overall data recording extending to 1560 s. During the run, the operator continuously records lateral flame spread, after-flaming, and the occurrence and duration of flaming droplets or particles falling from the specimen. After the test, the remains of the specimen are documented photographically and the wings are inspected for burn-through and damage extent.
Data Reduction and Calculation
Heat release rate is calculated by oxygen consumption calorimetry using the well-established relationship of approximately 13.1 MJ of energy per kilogram of consumed oxygen, corrected for the burner contribution. The heat release rate and smoke production rate curves are processed with 30-second averaging windows to compute FIGRA, THR600s, SMOGRA, and TSP600s. Final reported values are determined from the replicate tests according to the averaging and reporting rules of the classification standard.
Repeatability and Number of Tests
At least three valid replicate tests are performed on identical specimens. If the results straddle a classification boundary, further tests may be required so that the classification decision is statistically defensible. Full test documentation, including mounting details, substrate identification, and calibration records, is essential for the classification report and subsequent conformity assessment.
Applications
SBI test data support a wide range of regulatory, commercial, and engineering purposes across the building industry.
- European regulatory compliance: generation of Euroclass B, C, or D fire classification under EN 13501-1 for CE marking and declarations of performance under the EU Construction Products Regulation
- Chinese regulatory compliance: determination of GB 8624-2012 grades for interior decoration materials governed by fire codes for public buildings, high-rise buildings, and transportation hubs
- Product development: comparison of formulations, core materials, coatings, and joint designs for wall panels, ceiling systems, sandwich panels, and insulation composites
- Specification and procurement: evidence of the fire performance class required by architects, façade consultants, and approving authorities
- Quality control: ongoing verification that production output remains consistent with the classified reference specimen
FAQ
What FIGRA and THR600s limits apply to Euroclass B, C, and D?
Under EN 13501-1, Euroclass B requires FIGRA0.2MJ not exceeding 120 W/s and THR600s not exceeding 7.5 MJ; Euroclass C requires FIGRA0.2MJ not exceeding 250 W/s and THR600s not exceeding 15 MJ; and Euroclass D requires FIGRA0.4MJ not exceeding 750 W/s and THR600s not exceeding 15 MJ. For the smoke indices, s1 requires SMOGRA not exceeding 30 m²/s² and TSP600s not exceeding 50 m², while s2 allows up to 180 m²/s² and 200 m² respectively. All products classified B to D must also pass the EN ISO 11925-2 single-flame source test.
How does the SBI test differ from the cone calorimeter test?
The cone calorimeter (ISO 5660-1) is a bench-scale method using small horizontally or vertically oriented specimens exposed to a radiant heater, whereas the SBI test is an intermediate-scale method that reproduces a realistic corner-fire geometry with direct flame impingement. SBI results are therefore closer to end-use behavior for construction assemblies and are the mandatory basis for European and Chinese fire classification of non-flooring building products.
Can floorings be tested with the SBI method?
No. Floorings are excluded from the scope of EN 13823 and GB/T 20284 and are instead evaluated using the burning spread test of EN ISO 9239-1 together with EN ISO 11925-2, depending on the target class.
How many specimens are needed and how long does testing take?
A typical program requires a minimum of three complete specimen sets, each set consisting of one long wing and one short wing. The exposure itself lasts about 26 minutes per run including baseline and post-exposure recording, while the overall project time is dominated by conditioning, mounting preparation, and reporting, and is commonly measured in a few weeks.
Are GB/T 20284 and EN 13823 results interchangeable?
The two standards are closely harmonized, so technical results such as FIGRA and THR600s are directly comparable. However, official classification and certification depend on the jurisdiction, so products intended for both the Chinese and European markets should be classified under the respective applicable scheme using test reports from appropriately accredited laboratories.
Why is mounting configuration so important in SBI testing?
Because the test evaluates a complete corner assembly, the substrate, air gap, joint type, and fixing method all affect heat feedback and flame spread. Testing must reflect the exact end-use configuration for which classification is sought, and any deviation may invalidate the classification for other mounting arrangements.