Test for Burning Growth Rate of Building Materials

The test for burning growth rate of building materials is a critical evaluation method used to assess the fire performance of construction products. By measuring parameters such as Heat Release Rate (HRR) and Fire Growth Rate (FIGRA), this test determines how quickly a material contributes to the development of a fire. It is an essential requirement for fire safety classification and regulatory compliance in the construction industry.

Technical Overview

The burning growth rate test, commonly referred to as the Single Burning Item (SBI) test in many international standards, is a cornerstone of fire safety engineering. This method evaluates the reaction to fire of building materials when exposed to a thermal attack from a single burning item, typically simulating a waste paper basket fire in a room corner. The primary objective is to quantify the contribution of a material to fire growth, which is vital for designing safe egress routes and preventing structural collapse.

The test operates on the principle of oxygen consumption calorimetry. By measuring the oxygen concentration in the exhaust gases, the apparatus calculates the heat release rate. This data provides a comprehensive profile of the fire development characteristics of the tested product, including ignition time, heat release, and smoke production.

Testing Samples

The preparation and selection of samples are strictly regulated to ensure reproducibility and accuracy. The samples must represent the final application of the product as closely as possible.

Sample Dimensions and Configuration

For a standard SBI test according to standards like GB/T 20284 or EN 13823, the specimen consists of two wings forming a right-angled corner. The long wing typically measures 1000mm by 1500mm, while the short wing measures 500mm by 1500mm. This specific geometry is designed to simulate the interaction of fire with surfaces in a corner setting, which is often the worst-case scenario for fire spread.

Substrate and Mounting

The building material is often tested on a representative substrate. The way the material is mounted, including any air gaps or insulation, must reflect the intended end-use installation. This ensures that the test results are applicable to real-world construction scenarios. Incorrect mounting can significantly alter the thermal exposure and lead to inaccurate fire growth rate data.

Testing Items

During the burning growth rate test, several key parameters are recorded to classify the material's fire performance. These metrics are essential for engineers and regulators.

• Fire Growth Rate (FIGRA): This is the most critical index derived from the test. It is calculated by dividing the Heat Release Rate (HRR) by the elapsed time. FIGRA indicates how rapidly the fire grows once the material is involved.

• Heat Release Rate (HRR): Measured in kilowatts (kW), this parameter quantifies the amount of thermal energy released by the burning specimen. The peak HRR (THR600s) is particularly important for assessing the potential for flashover.

• Smoke Growth Rate (SMOGRA): This index measures the rate at which smoke is produced during the combustion process. It is calculated similarly to FIGRA but uses the Rate of Smoke Production (RSP) values.

• Total Smoke Production (TSP): This measures the cumulative volume of smoke generated over the test duration, which is vital for assessing visibility and toxicity risks during evacuation.

• Lateral Flame Spread (LFS): This visual observation determines if the flames reach the edge of the specimen, indicating a high propensity for fire spread across the surface.

Testing Methods

The standard testing procedure follows a rigorous protocol established by organizations such as ISO and GB. The GB/T 20284 standard is widely utilized in the construction sector, harmonizing closely with the EN 13823 standard used in Europe.

Apparatus Setup

The test apparatus comprises a trolley holding the specimen, a main burner, a smoke hood, and an exhaust system equipped with gas analyzers. The specimen is placed on the trolley, which is then pushed into the test enclosure beneath the hood. Sensors measure temperature, pressure, and gas concentrations (O2, CO, CO2) in the exhaust duct.

Exposure Protocol

The test begins by igniting the main burner, which applies a propane gas flame to the bottom corner of the specimen. The burner provides a specific heat output, typically ramping up to simulate a growing fire. The test duration is usually around 20 minutes. Throughout this period, the heat release and smoke production are continuously monitored. The data collected is processed through software to calculate the FIGRA, SMOGRA, and other critical values required for classification.

Applications

The results from the burning growth rate test are fundamental to fire safety compliance and product development across various sectors.

• Building Material Classification: The test data is used to classify materials into grades (such as A, B, C, D, E, and F) according to national standards like GB 8624. These classifications dictate where materials can be used within a building, such as in high-rise structures or public assembly areas.

• Product Development: Manufacturers use this test to optimize the formulation of fire-retardant materials. By analyzing FIGRA values, researchers can adjust chemical compositions to lower the fire growth potential.

• Fire Risk Assessment: Fire engineers use the HRR curves generated from these tests as input data for computer modeling of fire scenarios, helping to design safer buildings and effective suppression systems.

• Quality Control: Accredited third-party laboratories conduct these tests as part of routine quality assurance to ensure that production batches maintain the certified fire performance level.

FAQ

What is the difference between FIGRA and THR?

FIGRA (Fire Growth Rate) measures the speed at which the fire intensity increases, while THR (Total Heat Release) measures the total energy released over a specific period. FIGRA is a dynamic parameter used to evaluate the potential for rapid fire spread, whereas THR indicates the total fuel contribution of the material.

Why is the corner configuration used in the test?

The corner configuration represents a geometrically challenged scenario where heat flux is maximized due to the radiation feedback from the walls. This setup is considered a worst-case scenario that often leads to higher burning growth rates compared to open surface burning.

How do dripping particles affect the test result?

Flaming droplets or particles can ignite secondary fires on the floor or other surfaces. Standards often record the occurrence of flaming droplets as a separate criterion. If a material produces flaming droplets that burn for a certain duration, it may receive a lower fire safety classification.

Can the test be performed on irregular shapes?

The standard test is designed for planar products. However, irregular shapes or complex building components can be tested by creating a representative assembly or by using specific mounting fixtures that simulate the end-use conditions, ensuring the thermal exposure mimics the actual installation.