Single Burning Item (SBI) Test: Heat Release Rate Testing for Building Products

The Single Burning Item (SBI) test, standardized in EN 13823 and its Chinese counterpart GB/T 20284, is the key intermediate-scale method for measuring the heat release rate of building products under a simulated corner fire. By quantifying performance parameters such as FIGRA, THR600s, lateral flame spread and smoke production, the test underpins fire classification systems including EN 13501-1 (Euroclass) and GB 8624. This article explains the test principle, specimen requirements, measured parameters, methodology, applications and frequently asked questions.

Technical Overview

The Single Burning Item (SBI) test is an intermediate-scale reaction-to-fire test for building products other than floorings, specified in EN 13823 and adopted in China as GB/T 20284. It simulates a single burning item, such as a waste basket fire, positioned in the corner formed by two vertically mounted product panels. The central measurand is the heat release rate (HRR) of the specimen, which directly reflects how much energy the product contributes to fire growth and, therefore, its potential hazard in a real compartment fire.

HRR is not measured directly. The method applies oxygen consumption calorimetry, based on Thornton's rule, which states that for most combustible materials the heat released per unit mass of oxygen consumed is essentially constant at approximately 13.1 MJ/kg of oxygen. Combustion products are collected by an exhaust hood and duct system, where gas analyzers continuously measure O2, CO2 and CO concentrations, while a thermocouple grid and a differential pressure probe establish the duct mass flow. From these signals, the instantaneous heat release rate is calculated and recorded throughout the test.

Beyond heat release, the SBI test also yields smoke production data and visual observations of lateral flame spread and flaming droplets. The results form the technical basis for fire classification under EN 13501-1 (Euroclasses A2, B, C and D) and GB 8624 in China, typically in combination with EN ISO 11925-2 small-flame ignition tests and, where required, EN ISO 1182 non-combustibility furnace tests.

Testing Samples

The SBI test is applicable to a wide range of construction products intended for wall and ceiling applications. Typical sample categories include:

Flat Panels and Boards

Gypsum boards, wood-based panels such as plywood, MDF and particleboard, fiber cement boards, calcium silicate boards, PVC panels and decorative wall coverings.

Thermal Insulation Products

Mineral wool boards, expanded and extruded polystyrene (EPS/XPS), polyurethane (PUR/PIR) boards, phenolic foam and faced insulation composites.

Sandwich and Composite Panels

Metal-faced sandwich panels with insulated cores, aluminum composite panels and multilayer cladding assemblies, tested in their end-use build-up including adhesives, coatings and substructure.

Coatings, Paints, Laminates and Textile Coverings

Thin surface treatments that cannot stand alone are applied to a defined standard substrate and tested as a complete system so that the reaction-to-fire performance of the finished product is evaluated.

Specimen Configuration and Conditioning

• Long wing: 1000 mm wide by 1500 mm high.
• Short wing: 495 mm wide by 1500 mm high.
• The two wings are mounted vertically in a right-angle corner configuration on the test trolley, facing the primary ignition source.
• Specimens are conditioned to constant mass at (23 ± 2) °C and (50 ± 5) % relative humidity prior to testing.
• Products are tested in their end-use orientation, thickness, joint arrangement and fixing method, or on a standard backing with a defined air gap when no product-specific mounting standard exists.

Testing Items

The SBI test generates a set of classification parameters, each characterizing a different aspect of fire behavior:

• Fire Growth Rate Index (FIGRA), expressed in W/s, reported as FIGRA0.2MJ and FIGRA0.4MJ. FIGRA is the maximum of the ratio of the 30-second averaged heat release rate to the elapsed exposure time, determined after total heat release exceeds 0.2 MJ or 0.4 MJ respectively. It captures how rapidly a fire develops.
• Total Heat Release (THR600s), expressed in MJ, representing the cumulative heat energy released during the first 600 seconds of exposure.
• Lateral Flame Spread (LFS), a qualitative assessment of whether flame spreads along the long wing beyond defined zones or reaches the specimen edge.
• Smoke Growth Rate Index (SMOGRA), expressed in m²/s², characterizing the rate of smoke development.
• Total Smoke Production (TSP600s), expressed in m², the cumulative smoke area generated during the first 600 seconds.
• Transient heat release rate curve, peak HRR, occurrence of flaming droplets and particles, and post-test observations of specimen damage and char patterns.

FIGRA and THR600s determine the main Euroclass (B, C or D) under EN 13501-1, while SMOGRA and TSP600s support the additional smoke classes s1 to s3, and droplet observations support classes d0 to d2.

Testing Methods

Apparatus and Instrumentation

The test rig comprises a wheeled trolley carrying the corner-mounted specimen, a fixed frame with an exhaust collection hood above, and a 315 mm diameter exhaust duct operated at approximately 0.6 m³/s. The duct measurement section contains a gas sampling probe, a thermocouple, a differential pressure probe and an optical smoke measurement system (white light or laser) for extinction-based smoke determination. The ignition source is a triangular sand-bed propane gas burner positioned in the specimen corner.

Calibration

Prior to testing, the system is verified through burner heat output calibration, duct flow verification with a calibrated gas burner, gas analyzer span and zero checks, and optical system calibration using neutral density filters. These steps ensure traceability of heat release and smoke measurements.

Test Procedure

• Mount the conditioned specimen wings in the corner configuration and move the trolley into the frame.
• Record baseline duct data to establish reference gas concentrations, temperature and flow.
• At the start of exposure, place the burner in the corner with a nominal heat output of 30.7 ± 2.0 kW supplied by propane.
• Maintain the flame exposure for 1200 seconds, with data recorded continuously through 1260 seconds.
• Observe and record lateral flame spread along the long wing, flaming droplets and particle fall, and whether any burning debris ignites filter paper placed beneath the specimen.
• Extinguish the burner, document post-test specimen condition, and repeat the test on further specimens; at least three valid replicates are normally required per product configuration.

Data Reduction

The instantaneous heat release rate is computed from oxygen depletion, corrected for CO2 and CO concentrations and duct mass flow. HRR values are averaged over 30-second intervals (HRRav30s), from which FIGRA indices and THR600s are derived. Smoke production rate is calculated from light transmission measurements using the Beer-Lambert law, giving SMOGRA and TSP600s. Results are rounded and reported in accordance with EN 13823 or GB/T 20284, as applicable.

Applications

SBI heat release rate data serve multiple regulatory, commercial and engineering purposes:

• Fire classification of construction products under EN 13501-1 for CE marking in the European market, supporting declared performance under the EU Construction Products Regulation.
• Classification of building materials under GB 8624 in China, including grades B1 (with sub-grades B and C) and B2 (with sub-grade D) for interior finishing and insulation materials.
• Compliance demonstration for wall and ceiling linings, facade systems, insulated panels and decorative products specified in building codes and project specifications.
• Product research and development, including optimization of flame retardant formulations, core materials, coatings and joint designs to achieve target FIGRA and THR thresholds.
• Quality control and batch conformity verification in manufacturing, and comparative benchmarking of competing products or design variants.
• Input data for fire safety engineering assessments and risk analyses where heat release characteristics of linings influence compartment fire development.

For regulatory use, testing should be performed by accredited third-party laboratories operating EN 13823 or GB/T 20284 within a recognized conformity assessment framework.

FAQ

What is the difference between the SBI test and the cone calorimeter test?

The cone calorimeter (ISO 5660) is a small-scale test using specimens of roughly 100 by 100 mm exposed to a radiant heater, whereas the SBI test is an intermediate-scale corner test using panels of approximately 1.5 m in height exposed to a 30 kW gas burner. SBI results link directly to Euroclass and GB 8624 classifications for building products, while cone calorimeter data are mainly used for research, material screening and fire modeling.

How long does a single SBI test take?

The flame exposure itself lasts 20 minutes, with data recorded for a further 30 seconds. Including mounting, baseline recording, calibration checks and post-test documentation, a complete laboratory test typically requires several hours, and a full evaluation normally involves three replicate tests plus conditioning time.

What FIGRA values correspond to Euroclass B, C and D?

Under EN 13501-1, Euroclass B requires FIGRA not exceeding 120 W/s with THR600s not exceeding 7.5 MJ; Euroclass C requires FIGRA not exceeding 250 W/s with THR600s not exceeding 15 MJ; and Euroclass D requires FIGRA not exceeding 750 W/s. Comparable limits apply under GB 8624 for grades B1(B), B1(C) and B2(D). Lateral flame spread, droplet behavior and small-flame test results must also be satisfied.

Can SBI test results be used directly for CE marking or GB 8624 certification?

Yes. EN 13823 is the harmonized test method behind Euroclasses A2 through D under EN 13501-1, and GB/T 20284 provides the corresponding data for GB 8624 grading. In both cases the tests must be conducted by accredited third-party laboratories or notified bodies, with specimens mounted according to the relevant product or mounting standard.

Does the mounting configuration influence the heat release results?

Yes, significantly. Substrate type, air gaps, mechanical fixings, joints, coatings and adhesive layers all affect heat transfer and burning behavior. Products must therefore be tested in the exact end-use configuration defined by the applicable product standard or extended application rules, otherwise classification results may not be valid for the intended installation.