Single Burning Item (SBI) Testing for Building Products: Technical Principles, Procedures, and Appli

Single Burning Item (SBI) testing is an intermediate-scale reaction-to-fire method that evaluates the heat release, smoke production, and lateral flame spread of building products exposed to a 30 kW ignition source. Specified in EN 13823 and GB/T 20284, the test forms the technical basis for fire performance classification under EN 13501-1 (Euroclass) and GB 8624, and is routinely performed by accredited third-party laboratories for regulatory compliance and CE marking. This article explains the principle, apparatus, specimen requirements, measured parameters, test procedure, and typical applications of SBI testing.

Technical Overview

The Single Burning Item (SBI) test simulates the thermal attack of a single burning item, such as a waste paper basket, placed in the corner of a room that has been lined with the product under evaluation. Two vertical specimens arranged in a right-angle corner configuration are exposed to a propane-fired sandbox burner with a nominal heat output of 30 kW. Heat release rate is determined by the principle of oxygen consumption calorimetry, while smoke production is derived from optical extinction measurements in the exhaust duct.

The SBI test occupies an intermediate position in the hierarchy of reaction-to-fire testing: it is larger and more realistic than small-flame ignition tests, yet far more economical than full-scale room corner tests. Because of this balance, it serves as the primary classification test for the middle fire performance classes of both the European and Chinese classification systems.

• EN 13823 – Reaction to fire tests for building products excluding floorings, exposed to the thermal attack by a single burning item
• GB/T 20284 – Chinese national standard for the single burning item test of building materials and products, technically aligned with EN 13823
• EN 13501-1 – Fire classification of construction products and building elements, using SBI results to assign Euroclasses B, C, and D
• GB 8624-2012 – Chinese classification of burning behavior of building materials and products, using SBI results for grades A2, B, C, and D
• EN ISO 11925-2 – Complementary small-flame ignitability test normally required alongside SBI for full classification

Testing Samples

Specimen Configuration and Dimensions

Each SBI test requires a complete specimen set consisting of two rectangular wings mounted vertically on a trolley to form an inner right-angle corner. The long wing measures 1000 mm × 1500 mm, and the short wing measures 495 mm × 1500 mm. The specimen thickness corresponds to the end-use product thickness, and the substrate, backing board, and any air gaps behind the specimen must represent the intended installation conditions defined in the relevant product standard or end-use application.

Typical Product Types

• Wall and ceiling lining panels, including gypsum boards, calcium silicate boards, and fiber cement boards
• Decorative laminates, veneered panels, and wood-based boards
• Aluminum composite panels and other metal-faced sandwich constructions
• Thermal insulation products tested as part of lined wall or roof systems
• Coatings, sprayed finishes, and intumescent systems applied to standard substrates
• Door surfaces, pipe boxes, and other interior fit-out components

Conditioning and Mounting

Prior to testing, specimens are conditioned to constant mass at a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5 %. Mounting must faithfully reproduce the end-use construction, including joint geometry, mechanical fixing, and any protective facing, because the classification obtained applies only to the tested configuration.

Testing Items

The SBI test yields a set of quantitative fire performance indices, each of which feeds directly into the classification rules:

• FIGRA (Fire Growth Rate Analysis): the maximum value of the ratio of total heat release to elapsed time, expressed in W/s, calculated over defined windows of the exposure. FIGRA0.2MJ and FIGRA0.4MJ variants are used for different classes.
• THR600s: the total heat release integrated over the first 600 seconds of burner exposure, expressed in MJ, indicating the overall contribution of the product to fire growth.
• SMOGRA (Smoke Growth Rate): the maximum rate of smoke production development, expressed in m²/s², analogous to FIGRA but based on smoke production rate.
• TSP600s: the total smoke production over the first 600 seconds of exposure, expressed in m².
• LFS (Lateral Flame Spread): a visual determination of whether flaming reaches the edges of the long wing above the lower region of the specimen.
• Flaming droplets and particles: observation of whether burning droplets or particles fall, and whether flaming persists, which determines the sub-classification for droplets (d0, d1, or d2).

Testing Methods

Test Apparatus

The SBI apparatus comprises a combustion chamber with internal dimensions of approximately 3.0 m × 3.0 m × 2.4 m high, a movable trolley carrying the specimen frame, and a propane-fired sandbox burner positioned at the base of the corner. Combustion gases are collected by an exhaust hood and extracted through a measurement duct equipped with instrumentation: a bidirectional probe and differential pressure sensor for mass flow, thermocouples for gas temperature, a gas sampling ring feeding oxygen, carbon dioxide, and carbon monoxide analyzers, and a laser optical system for measuring smoke obscuration. The complete system is calibrated against reference heat release sources and smoke generators to ensure traceability of all measured quantities.

Test Procedure

• Mount the conditioned specimen set on the trolley in the corner configuration and introduce it into the combustion chamber.
• Record baseline readings of gas concentrations, temperature, pressure difference, and light transmission for the first two minutes of the run.
• Ignite the burner and bring it to the nominal 30 kW output, applying the flame to the bottom edge of the specimen corner.
• Continue the exposure for approximately 20 minutes, logging heat release rate and smoke production rate continuously while visually observing flame spread and flaming droplets.
• Terminate the run after the standard observation period, allow the system to stabilize, and verify post-test baseline data.

Data Processing

Heat release rate is calculated from oxygen depletion using the oxygen consumption principle, corrected for measured CO2 and CO concentrations and for the transport delay of the gas sampling system. Total heat release and smoke production are obtained by integration, from which FIGRA, THR600s, SMOGRA, and TSP600s are derived in accordance with the calculation rules of EN 13823 and GB/T 20284. A minimum of three valid specimen sets is normally tested, and the reported values are combined as specified by the classification standard.

Applications

SBI test results are the decisive evidence for the middle tier of fire performance classification in Europe and China. Under EN 13501-1, typical classification thresholds are FIGRA0.2MJ ≤ 120 W/s and THR600s ≤ 7.5 MJ for Euroclass B, FIGRA0.4MJ ≤ 250 W/s and THR600s ≤ 15 MJ for Euroclass C, and FIGRA0.4MJ ≤ 750 W/s for Euroclass D. GB 8624-2012 applies analogous criteria for domestic grades A2, B, C, and D, with additional smoke classes (s1, s2, s3) and droplet classes (d0, d1, d2).

• Demonstrating compliance with building regulations that mandate B1 (flame retardant) or higher grades for interior finish materials in public buildings, high-rise structures, and evacuation routes
• CE marking of construction products under the European Construction Products Regulation, where SBI data support the declared reaction-to-fire class
• Product development and formulation screening for fire-retardant treatments, core compounds, and coating systems
• Factory production control audits, batch verification, and tender documentation for facade, partition, and ceiling systems
• Technical due diligence for material substitution, renovation projects, and export market access

FAQ

Why is SBI testing called "single burning item" testing?

The test reproduces the scenario of a single item, roughly equivalent in heat output to a burning wastebasket at 30 kW, attacking the corner of a room lined with the product. This scenario is considered representative of the early growth stage of a real interior fire.

Which products cannot be tested by the SBI method?

Floorings are explicitly excluded from the scope of EN 13823 and GB/T 20284; flooring products are instead evaluated by radiant panel and small-flame methods. Linear pipe and cable products follow their own dedicated reference scenarios.

How many specimens are required, and how long does testing take?

At least three complete specimen sets are required for a standard determination, with additional sets needed when testing jointed or variant constructions. Including conditioning to constant mass, a typical SBI project requires one to two weeks in an accredited third-party laboratory.

How is SBI different from the full-scale room corner test?

The SBI test is an intermediate-scale method that has been statistically correlated with the ISO 9705 room corner test. It provides comparable heat release and smoke information at significantly lower specimen cost and shorter turnaround, which is why it was adopted as the reference test for Euroclasses B, C, and D.

Does an SBI result apply to any installation condition?

No. The classification is valid only for the tested construction, including substrate, air gap, fixing method, and joint design. Changes to the end-use configuration generally require retesting or extended application assessment.