Fire Resistance Duration and Combustion Classification

Often asked: What is the fire resistance rating in hours of this calcium silicate board?

This simple question actually contains two questions that cannot be answered in one sentence. Why do I say that? Is it that when someone casually asks, you have to stammer and rack your brains for half an hour to explain the answer clearly? Believe it or not, that's exactly the case.

Let's first talk about the fire resistance hours. This generally refers to the fire resistance limit, meaning how long it can withstand burning. More precisely, it refers to a building component, which is a structurally complete system. Taking calcium silicate board as an example, related components include lightweight partition walls, ventilation ducts, fireproof ceilings, steel beam column covers, etc. These include the framework, facing panels, and internal rock wool filling. In short, it is a finished product, not just a single board.

Currently, lightweight fireproof partition walls are relatively widely used as partitions inside steel structure factories or ordinary buildings. Lightweight fireproof partition walls are commonly seen in factory projects in industries such as electronics, electrical appliances, warehousing, automotive, and new energy. Depending on the wall thickness and structure, the fire resistance limit ranges from 1 to 4 hours to meet the fire protection requirements of different fire zones. As facing panels, inorganic boards such as calcium silicate board and magnesium oxide board are widely used in these applications. Comparatively, magnesium oxide board is cheaper but has average moisture resistance, while calcium silicate board has a more balanced overall performance.

Additionally, with the implementation of mandatory fire resistance requirements for ventilation ducts, duct components that meet fire resistance requirements by wrapping galvanized ducts with calcium silicate board or other inorganic boards and filling them internally with rock wool are gradually being promoted in various commercial complexes and public buildings. Next, let's talk about the non-combustibility of the boards. For single materials, we generally use combustion performance grades to indicate this. Inorganic boards like calcium silicate board and magnesium oxide board mentioned earlier are of the highest grade: non-combustible materials. Here, it is necessary to explain that the national standard "GB 8624-2012 Classification of Combustion Performance of Building Materials and Products" divides materials into four grades: Class A non-combustible, Class B1 flame-retardant, Class B2 combustible, and Class B3 easily combustible. However, in daily use, we also find some materials labeled as non-combustible A1 or A2. What does this mean?

Have you noticed that materials labeled as Class A1 non-combustible are generally homogeneous materials, while those labeled as Class A2 non-combustible are mostly composite materials? This is because the testing standard for Class A1 non-combustible is extremely strict: no combustion phenomena are allowed, and under open flame and high temperature, it will not ignite, produce smoke, or molten droplets. In contrast, Class A2 non-combustible materials may produce a small amount of smoke or combustion under extreme conditions but will not spread. Common decorative wall panels with inorganic board substrates and surface finishes mostly use organic materials for the finish layer, so their combustion performance grade is Class A2.

From the above explanation, I believe everyone now has a general understanding of fire resistance limits and combustion performance. Therefore, for the frequently asked question, we provide the following answer: In terms of combustion performance, calcium silicate board belongs to non-combustible Class A (A1) materials; however, the fire resistance duration depends on its application scenario—whether it is used for firewalls, fireproof duct boards, or fireproof ceilings. In different application scenarios, the fire resistance duration of calcium silicate board of the same thickness varies depending on the structure.