The Single Burning Item (SBI) test is an intermediate-scale reaction-to-fire test that evaluates the fire performance of building products, excluding floorings, when exposed to the thermal attack of a simulated burning object in a room corner. Specified in EN 13823 and its technically aligned Chinese counterpart GB/T 20284, the test produces core classification parameters such as FIGRA, THR600s, SMOGRA, and TSP600s, which determine Euroclass B, C, and D ratings under EN 13501-1. This article explains the test principle, specimen requirements, instrumentation, calculation methodology, classification criteria, and typical applications of the SBI test.
Technical Overview
The Single Burning Item (SBI) test is a room-corner fire simulation designed to reproduce the early stages of a fire in which a single burning item, such as a waste paper basket placed in the corner of a room, attacks the interior linings of walls and ceilings. It is one of the most important intermediate-scale reaction-to-fire tests in the European fire classification system and forms the technical backbone for classifying the majority of construction products other than floorings.
The test method is specified in EN 13823, "Reaction to fire tests for building products — Building products excluding floorings exposed to the thermal attack by a single burning item." In China, the equivalent national standard is GB/T 20284, which is technically aligned with EN 13823, and the resulting parameters feed into the classification framework of GB 8624, the Chinese counterpart of EN 13501-1.
- Intermediate-scale test on two vertical specimen wings arranged in a right-angle corner configuration
- Thermal attack from a sandbox-type propane burner with a nominal heat output of approximately 31 kW
- Total test duration of about 26 minutes, including a 1260-second burner exposure period
- Heat release measured by oxygen consumption calorimetry; smoke measured by an optical system in the exhaust duct
- Results used to assign Euroclass A2, B, C, and D ratings (in combination with other test methods) as well as smoke and droplet sub-classes
Testing Samples
Standard Specimens for Flat Products
A standard SBI specimen consists of two wings mounted vertically on a movable trolley to form a right angle. The long wing measures 1000 mm in width and 1500 mm in height, while the short wing measures 495 mm in width and 1500 mm in height. Products are tested in their end-use configuration wherever possible, including any substrate, backing board, air gap, joint, or mechanical fixing that reflects the intended application, following the mounting and fixing rules of EN 15715 and applicable extended-application standards.
Linear and Shaped Products
Pipes, ducts, profiled sheets, and joint coverings can also be assessed using dedicated mounting arrangements described in the standard and in product-specific application documents. For such products, the wings are constructed from representative sections of the product arranged to preserve the geometric exposure of a flat corner assembly.
Conditioning and Number of Specimens
Prior to testing, specimens are conditioned to constant mass at a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5 % in accordance with EN 13238. A complete test series typically comprises three replicate specimens for each product configuration, and classification parameters such as FIGRA and SMOGRA are derived from the averaged results.
Testing Items
The SBI test quantifies both heat release and smoke production behavior, as well as the physical phenomena of lateral flame spread and flaming debris. The principal measurands and derived parameters are listed below.
- FIGRA (Fire Growth Rate Index), reported as FIGRA0.2MJ and FIGRA0.4MJ, expressed in W/s
- THR600s, the total heat release over the first 600 seconds of burner exposure, expressed in MJ
- SMOGRA (Smoke Growth Rate Index), expressed in m²/s²
- TSP600s, the total smoke production over the first 600 seconds, expressed in m²
- LFS, the occurrence of lateral flame spread along the long wing up to or beyond its far edge
- Flaming droplets and particles observed within the first 600 seconds of exposure
Fire Growth Rate Index (FIGRA)
FIGRA is defined as the maximum value of the quotient of heat release rate and elapsed time, computed from 30-second rolling average heat release data. It combines the intensity and the speed of fire development into a single index, making it the primary discriminator among the main Euroclasses. FIGRA0.2MJ applies a total heat release threshold of 0.2 MJ, while FIGRA0.4MJ applies a 0.4 MJ threshold.
Total Heat Release (THR600s)
THR600s represents the cumulative heat energy released during the first 600 seconds of exposure. It reflects the overall contribution of the product to fire load in the critical early phase of a developing room fire.
Smoke Growth Rate Index (SMOGRA) and Total Smoke Production (TSP600s)
SMOGRA is the maximum of the ratio between the rolling-average smoke production rate and time, analogous to FIGRA but based on optical smoke measurements. TSP600s is the integrated smoke production over the first 600 seconds. Together these parameters determine the smoke sub-classes s1, s2, and s3.
Lateral Flame Spread and Flaming Droplets
Lateral flame spread is assessed by visual observation and video recording of whether the flame front reaches the edge of the long wing. Flaming droplets and particles are recorded by observation of the specimen area outside the burner zone, and their persistence determines the droplet sub-classes d0, d1, and d2.
Testing Methods
Apparatus and Instrumentation
The test rig comprises a movable trolley carrying the specimen wings, a fixed frame with an exhaust hood, and a measurement section in a 315 mm diameter exhaust duct. Instrumentation includes gas analyzers for oxygen, carbon monoxide, and carbon dioxide; a mass flow measurement system based on differential pressure and duct temperature; and a white-light optical smoke measurement system. A data acquisition system records all channels continuously, and video cameras document flame spread and flaming droplets throughout the test.
Test Procedure
- The conditioned specimen is mounted on the trolley and positioned beneath the exhaust hood, with the burner placed in the corner formed by the two wings.
- A baseline recording of at least 300 seconds is collected to establish background levels.
- The propane burner is ignited at 300 seconds and operated at a nominal heat output of about 31 kW for 1260 seconds, giving a total test duration of 1560 seconds.
- Throughout exposure, heat release rate, smoke production rate, gas concentrations, and visual phenomena are recorded.
- After the burner is switched off, recording continues until the end of the test sequence, and the specimen is inspected and documented.
Data Reduction and Calculation
Heat release rate is calculated using oxygen consumption calorimetry based on the well-established principle that approximately 13.1 MJ of heat is released per kilogram of oxygen consumed. Gas concentrations and smoke obscuration signals are corrected for transport delay and drift using the baseline period. From the time histories of heat release rate and smoke production rate, the software computes FIGRA0.2MJ, FIGRA0.4MJ, THR600s, SMOGRA, and TSP600s, together with intermediate results such as peak heat release rate and effective heat of combustion.
Classification Criteria
Under EN 13501-1 and GB 8624, the SBI parameters are combined with the small-flame ignition test of EN ISO 11925-2 (and, for the higher classes, with non-combustibility or gross heat of combustion tests) to assign reaction-to-fire classes. The key SBI thresholds are summarized below.
- Class B: FIGRA0.2MJ ≤ 120 W/s and THR600s ≤ 7.5 MJ, with no lateral flame spread to the specimen edge
- Class C: FIGRA0.4MJ ≤ 250 W/s and THR600s ≤ 15 MJ
- Class D: FIGRA0.4MJ ≤ 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
- Droplet class d0: no flaming droplets or particles within 600 seconds; d1: flaming droplets or particles persisting no longer than 10 seconds; d2: all other cases
Applications
SBI test data underpin the mandatory fire classification of construction products in the European Union under the Construction Products Regulation, supporting CE marking and the declaration of performance of reaction-to-fire classes. In China, the same test conducted to GB/T 20284 supports classification under GB 8624, which is widely referenced in national fire safety codes for interior decoration materials, public buildings, high-rise buildings, and railway and metro projects.
- Wall and ceiling linings, including gypsum boards, calcium silicate boards, and decorative panels
- Thermal insulation products such as mineral wool, EPS, XPS, PUR, and phenolic foam boards
- Sandwich panels and facade cladding components for interior applications
- Wood-based panels, including plywood, MDF, and particleboard, and fire-retardant-treated timber
- Plastic wall panels, decorative films, coatings, and wallcoverings
- Pipes, ducts, and linear building components assessed under product-specific application rules
Manufacturers, architects, and regulators rely on SBI results to compare products, demonstrate compliance with fire safety requirements, and support design approval. Testing should be carried out by accredited third-party laboratories with calibrated SBI rigs and recognized expertise in reaction-to-fire assessment.
FAQ
What does "single burning item" mean in this test?
The term describes the reference fire scenario: a single object burning in the corner of a room, similar to a waste paper basket, attacks the wall and ceiling linings. The propane burner in the test reproduces the heat output of such an item, allowing the contribution of the lining products to fire growth to be measured under realistic conditions.
Which products require the SBI test?
The SBI test applies to construction products excluding floorings that are intended for classes A2, B, C, or D under EN 13501-1 or GB 8624. Floorings are instead assessed by the burning radiant panel test of EN ISO 9239-1, while electric cables follow their own test suite under the EN 50399 series.
How large are the specimens?
The specimen assembly consists of a 1000 mm × 1500 mm long wing and a 495 mm × 1500 mm short wing arranged at a right angle. Including backing boards and supporting frame elements, roughly two square meters of representative product construction are required per specimen, and three replicate specimens are normally tested.
Are EN 13823 and GB/T 20284 results equivalent?
GB/T 20284 is technically aligned with EN 13823, so the test procedures, specimen geometry, and calculated parameters are the same. However, the classification decision is made under the respective classification standard, EN 13501-1 for Europe or GB 8624 for China, and specific project requirements may dictate which scheme must be used.
Why is FIGRA so important?
FIGRA captures both how intensely and how quickly a product releases heat, which are the two dominant factors in the early growth of a room fire. Because flashover risk is closely linked to rapid fire growth, regulators use FIGRA as the main parameter for distinguishing between classes B, C, and D.
How long does a full SBI test take?
A single test run lasts approximately 26 minutes plus setup, trolley positioning, and post-test documentation. Considering conditioning, calibration checks, and replicate runs, a complete test series for one product configuration typically requires one to several days of laboratory work.