Understanding Fireproof Material Ratings: An Overview of the Three Major Standards
Fireproof material ratings are not self-claimed by manufacturers—they are determined through specific test standards. Currently, there are three major systems used globally, originating from Europe, North America, and China. Understanding how they work is the key to truly reading the codes on a test report.
The defining feature of this system is its multi-dimensional assessment. It doesn’t just assign a combustion class; it also evaluates how much smoke a material produces when burning and whether it sheds flaming droplets or particles—two factors that are often more lethal than the flames themselves in a real fire.
Main Classes (A-F): From “Non-combustible” to “Unrated”
Classes A1 & A2: Non-combustible materials. Cement, gypsum boards, stone wool, glass, and similar products fall into this category. A1 is the highest tier—it does not participate in combustion under any fire scenario. A2 also barely contributes to combustion under rigorous testing; in practical terms, both are considered “non-combustible.”
Class B: Difficult to ignite. Typically includes flame-retardant treated wood and certain specialized fire-resistant boards. These materials resist ignition from small fire sources and, even if they catch fire, burn at a very slow rate.
Class C: Combustible. These materials will burn when exposed to flames, but combustion slows down or stops when the fire source is removed. Some flame-retardant plastics fall into this range.
Class D: Easily ignitable. They catch fire readily, and combustion continues after the fire source is removed.
Class E: Highly flammable, posing a significant fire risk.
Class F: Not tested or does not meet any rating requirement. Not recommended for use in any application with fire safety considerations.
Supplementary Information: Smoke and Droplets
Beyond the main class, EN 13501-1 provides two additional indicators:
Smoke production (s1/s2/s3): s1 indicates little to no smoke; s3 indicates heavy smoke production.
Flaming droplets/particles (d0/d1/d2): d0 means no flaming droplets; d2 indicates flaming droplets are present.
A full designation like “B-s1, d0” reads as “difficult to ignite, produces little to no smoke, and produces no flaming droplets”—representing a material with excellent overall performance.
The United States and Canada primarily use ASTM E84 (or UL 723, which is technically equivalent). This system takes a simpler approach, centered on two key indices:
Flame Spread Index (FSI): Measures how quickly flames spread across the material’s surface. The lower the index, the better the fire performance. Based on FSI values, materials fall into three classes—
Class A: FSI 0-25, representing excellent fire resistance. Typical materials include masonry and gypsum boards.
Class B: FSI 26-75, representing good fire resistance. Flame-retardant treated wood usually falls here.
Class C: FSI 76-200, representing moderate fire resistance.
Smoke Developed Index (SDI): Measures the density of smoke produced when the material burns. The lower the value, the better—because in a real fire, smoke often poses an earlier and more immediate threat than high temperatures.
This system’s strength lies in its straightforward test method and intuitive results. However, compared to the European standard, it does not evaluate factors like flaming droplets.
III. Chinese Standard GB 8624: A Localized Framework Based on the European Model
China’s GB 8624 (current version: GB 8624:2012) follows a classification logic similar to EN 13501-1, though the class names and some details have been adjusted to better suit domestic engineering practices.
Class Comparison:
Class A (Non-combustible): Corresponds to European A1 & A2. Materials in this class barely produce combustion phenomena in a fire. The distinction between A1 and A2 lies in the stringency of test conditions—A2 allows for trace amounts of smoke.
Class B1 (Difficult to ignite): Corresponds to European B & C. Materials are resistant to ignition, smoldering, and charring under flame or high heat; combustion stops immediately once the fire source is removed.
Class B2 (Combustible): Corresponds to European D & E. These materials ignite readily under open flame and continue to burn after the fire source is removed.
Class B3 (Easily ignitable): Corresponds to European F. These materials pose a high fire risk and should be strictly restricted in building interior finishes.
GB 8624 also includes sub-classifications for specific applications—for example, flooring materials are designated as A1fl, A2fl, Bfl, Cfl, etc., and thermal insulation for pipes has its own classification system. Supplementary information on smoke production and flaming droplets is also provided.
Class A (Non-combustible): Concrete, masonry, gypsum boards, stone wool, glass wool, ceramic tiles. These are used in structural elements, firewalls, evacuation routes, and other critical areas.
Class B1 (Difficult to ignite): Flame-retardant treated wood, fire-retardant coatings, flame-retardant plastics, fire-rated doors and windows. Commonly found in commercial spaces and interior finishes of high-rise buildings.
Class B2 (Combustible): Ordinary wood, PVC, some carpets and textiles. These may be used in limited quantities and specific locations in ordinary residential buildings and low-risk areas, but their usage and placement must be strictly controlled.
Class B3 (Easily ignitable): Foam plastics, untreated paper and textiles. These should be prohibited or strictly restricted in building interior finishes.
Fire ratings are not just cold codes on a page. Behind them lies a simple reality: in the minutes following a fire outbreak, they determine how much time a building can buy for the people inside. Understanding them, taking them seriously, and using the right materials is a responsibility that every decision-maker in construction should carry.