GB8624 is the Chinese national standard for classifying the burning behavior of building materials and products, serving as a critical benchmark for fire safety compliance. Understanding the GB8624 testing process and classification levels is essential for manufacturers, architects, and regulatory bodies to ensure materials meet strict fire protection requirements.
Technical Overview
The GB8624 standard, formally known as "Classification for burning behavior of building materials and products," is the primary evaluation standard for fire performance in China. The current version, GB8624-2012, classifies materials based on their reaction to fire, aligning closely with the European standard EN 13501-1. The classification system divides building materials into several levels based on their ability to contribute to fire spread and smoke production.
The classification levels are defined as follows:
Level A: Non-combustible materials.
Level B1: Flame-retardant materials.
Level B2: Combustible materials.
Level B3: Flammable materials.
Each level, except for B3, is further subdivided to provide a more granular assessment of fire growth rate, smoke emission, and flaming droplets. This hierarchical structure ensures a precise understanding of how a material behaves under fire conditions.
Testing Samples
To achieve accurate and reproducible results, the preparation and selection of testing samples must strictly adhere to the specifications outlined in the standard. The samples must represent the final product as used in actual applications, including surface treatments and adhesives.
Sample Preparation
For standard testing, the product is typically supplied in flat sections such as boards or pipes. The conditioning of samples is critical; they must be stored in an environment with a specific temperature and relative humidity for a defined period prior to testing to reach a constant mass. This ensures that moisture content does not skew the combustion characteristics.
Sample Dimensions
The dimensions of the test specimens depend on the specific test method being employed. For example, the Single Burning Item (SBI) test requires a specimen composed of two wings forming a right angle, with specific lengths and widths. The Non-combustibility test requires small cylindrical specimens. Accurate cutting and assembly are mandatory to ensure the exposed surface area matches the standard requirements.
Testing Items
The GB8624 testing regime evaluates several key parameters to determine the classification of a material. The specific parameters tested depend on the anticipated classification level of the product.
The primary testing items include:
Gross Heat of Combustion (PCS): This measures the total heat energy released per unit mass during complete combustion. It is a critical criterion for Level A materials.
Fire Growth Rate (FIGRA): This index is derived from the ratio of heat release rate to time. It indicates how quickly a fire develops.
Total Heat Release (THR): The total amount of heat energy released by the specimen over a specified period.
Lateral Flame Spread (LFS): This measures the horizontal progression of the flame across the surface of the material.
Smoke Production: Parameters such as Smoke Growth Rate (SMOGRA) and Total Smoke Production (TSP) quantify the density and volume of smoke generated.
Flaming Droplets/Particles: This assesses whether the material sheds burning droplets that could spread fire to lower levels.
Testing Methods
Different classification levels require different combinations of test methods. The testing process is rigorous and conducted in specialized laboratories equipped with advanced calorimetry equipment.
Non-combustibility Test
For Level A materials, the non-combustibility furnace test is performed. A cylindrical specimen is placed in a furnace tube at a temperature of 750 degrees Celsius. The test measures the temperature rise inside the furnace, the duration of flaming, and the mass loss of the specimen. Materials suitable for Level A1 must show minimal temperature rise and mass loss.
Single Burning Item (SBI) Test
The SBI test is the core method for classifying materials from Level B to Level D. It simulates a fire scenario where a single item burns in the corner of a room. The apparatus measures heat release and smoke production through oxygen consumption calorimetry. The FIGRA and THR values derived from this test are pivotal in determining whether a material qualifies for B1 (B, C classes) or B2 (D, E classes) classifications.
Small Flame Ignition Test
For lower classifications or preliminary screening, the small flame test (similar to UL 94 or EN ISO 11925-2) is used. A small propane flame is applied to the edge or surface of a vertically oriented specimen. This test determines if the material ignites and if the flame spreads to a certain height, primarily used to verify performance against the E class criteria.
Applications
The results of GB8624 testing are legally required for the sale and use of construction materials in China. The specific applications vary by building type and fire safety codes.
Key application areas include:
Public Venues: High-occupancy buildings such as shopping malls, cinemas, hospitals, and schools require strict B1 or A level materials for interior finishes.
High-rise Buildings: Curtain walls, thermal insulation systems, and interior partitions must meet specific GB8624 ratings to prevent vertical fire spread.
Transportation: Materials used in subway stations, airports, and vehicle interiors often require certification to ensure passenger safety.
Fire Doors and Windows: Components used in passive fire protection systems must demonstrate high fire resistance and low smoke production.
FAQ
Below are answers to frequently asked questions regarding GB8624 testing.
What is the difference between GB8624-2006 and GB8624-2012?
The GB8624-2012 standard is the current version and more closely aligns with the European EN 13501-1 standard compared to the 2006 version. It introduced more specific definitions for smoke production and flaming droplets (s1, s2, d0, d1, etc.). While the basic hierarchy of A, B1, B2, and B3 remains similar, the test methods and threshold limits were adjusted to improve international harmonization.
Is GB8624 certification mandatory?
Yes, for most building materials sold in the Chinese market, GB8624 certification is mandatory. Regulatory authorities require this certification during the building inspection process to ensure the materials used comply with the national fire code.
How long does the testing process take?
The duration varies depending on the material type and the specific tests required. Typically, the laboratory testing phase takes 10 to 15 working days. However, the entire process, including sample conditioning, testing, and report issuance, may take three to four weeks.