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In the study of building fire ratings, the concept of “metal sandwich panels” and their usage requirements often arise. However, for some, this building material may not be immediately recognizable, and its suitable application areas can be challenging to remember. This article provides a detailed explanation of metal sandwich panels and their specific uses.
1. Definition: Metal sandwich panels consist of two outer layers of thin metal sheets with an insulating core made of materials such as expanded polystyrene (EPS), polyurethane (PUR), or rock wool. Commonly referred to as “color steel panels,” metal sandwich panels are widely used in construction due to their lightweight, thermal insulation properties, and quick installation. They are commonly seen in temporary buildings on construction sites, such as steel-structured portable rooms.
2. Classification and Fire Resistance: Metal sandwich panels are categorized based on both the outer layer and core material, each with specific fire resistance properties.
By outer layer material:
- Galvanized steel sandwich panels
- Hot-dip galvanized color steel sandwich panels
- Electro-galvanized color steel sandwich panels
- Aluminum-zinc color steel sandwich panels
- Various alloy aluminum sandwich panels
By core material:
- Metal foam core panels: These include PUR (polyurethane) sandwich panels and EPS (expanded polystyrene) sandwich panels.
- Metal inorganic fiber core panels: These include rock wool sandwich panels, mineral wool sandwich panels, and glass wool sandwich panels.
Fire and Combustion Properties:
- For rock wool and slag wool (A-grade) sandwich panels, when the panel thickness is ≥ 80mm, the fire resistance rating is ≥ 60 minutes; for panels with a thickness < 80mm, the fire resistance rating is ≥ 30 minutes.
- Standards require rigid polyurethane sandwich panels to achieve a B1 combustion rating, with a core density ≥ 30kg/m³ and a combustion rating of B2.
- For expanded polystyrene (EPS) foam core sandwich panels, the oxygen index of the core material should be >30%, and the combustion rating should meet B2 standards.
3. Applications of Metal Sandwich Panels: There is a common misconception that metal sandwich panels wrapped in metal sheets are fireproof. In reality, when combustible core materials such as EPS or PUR are used, the metal sheets quickly soften during a fire, causing the core to ignite and spread the fire rapidly, producing toxic smoke. Conversely, sandwich panels with non-combustible cores like rock wool or mineral wool do not propagate fire during an emergency.
However, due to the inherent fire resistance limitations, structural capacity, and stability of metal sandwich panels, fire protection codes set forth specific usage guidelines:
- Non-usage areas: Metal sandwich panels are not permitted for use in firewalls, load-bearing walls, stairwell walls, walls in evacuation corridors, elevator shafts, or flooring components.
- Limited usage areas: Non-load-bearing exterior walls, interior partition walls, and roof panels not intended for human occupancy may use metal sandwich panels only if the core material is non-combustible, and the fire resistance limits comply with relevant standards.
4. Fire Regulations for Metal Sandwich Panels: Several fire safety regulations specify restrictions on the use of metal sandwich panels:
- “Fire Safety Management in Crowded Places” requires that temporary structures in such places, made from metal sandwich panels, must use A-grade non-combustible core materials.
- “Fire Safety Rules for Large Commercial Complexes” prohibit the use of metal sandwich panels with combustible or flammable core materials in the construction or partitioning of storage areas.
- “Fire Safety Technical Standards for Construction Sites” specify that temporary housing and office buildings made from metal sandwich panels must use A-grade core materials for fire safety.
Conclusion: Metal sandwich panels are a versatile and widely used building material due to their lightweight and thermal insulation properties. However, it is essential to select the appropriate core materials and adhere to fire safety regulations, especially when using these panels in buildings that house people or valuable assets. By ensuring compliance with national standards and fire safety codes, metal sandwich panels can be safely utilized in various construction applications.
This detailed guide on metal sandwich panels can help professionals in the construction industry understand their properties, classification, and fire safety regulations, ensuring informed decision-making and safer buildings.
