What is the Fire Rating of PU Sandwich Panels?

Polyurethane (PU) sandwich panels are widely adopted in construction for their excellent insulation, lightweight nature, and ease of installation. However, their fire rating is a pivotal consideration, particularly in environments requiring high safety standards.

Fire Rating Standards

Fire ratings for building materials are defined by standards like China’s GB 8624-97, categorizing them as:

• Class A: Non-combustible materials that resist all burning.
• Class B1: Flame-retardant materials, difficult to ignite, stopping combustion without a fire source.
• Class B2: Combustible materials with some flame-retardant ability, self-extinguishing post-ignition.
• Class B3: Highly flammable materials with no fire resistance.

The fire performance of PU sandwich panels hinges on their core material, ranging from PUR and PIR to hybrid PU-edged rock wool designs.

Fire Rating of PUR Sandwich Panels

Standard polyurethane (PUR) sandwich panels, made with polyether polyols and a lower isocyanate index, excel in insulation but falter in fire resistance:

• Without Flame Retardants: Rated Class B3, they burn easily with an oxygen index (OI) below 26.
• With Flame Retardants: Additives elevate them to Class B2, reducing ignition ease and enabling self-extinguishing, with an OI of 26–32.
• Enhanced Formulations: Rarely, they reach Class B1, though this is less common due to cost.

A quick test with a lighter on a PUR core sample shows continuous burning and dripping for B3, or self-extinguishing for B2.

Fire Rating of PIR Sandwich Panels

Polyisocyanurate (PIR) panels, crafted with polyester polyols and a higher isocyanate index (>250), offer better thermal stability (up to 150°C) and fire resistance:

• Standard PIR Panels: Typically Class B1, resisting ignition with an OI ≥32.
• Optimized PIR Panels: With advanced formulations and non-combustible facings (e.g., steel), they near Class A, though full non-combustibility requires additional materials.

PIR panels suit applications needing elevated fire safety, such as industrial or public structures.

PU-Edged Rock Wool Sandwich Panels

PU-edged rock wool sandwich panels combine polyurethane as an edge sealant with a rock wool core, a naturally non-combustible material:

• Fire Rating: These panels consistently achieve Class A, the top tier, thanks to rock wool’s ability to withstand over 1000°C without burning or significant smoke production. The PU edges enhance insulation and structural integrity.
• Applications: Ideal for cold storage, high-rise buildings, and industrial facilities, they balance fire safety, insulation, and durability.

Comparison: Advantages and Disadvantages of PU-Edged Rock Wool Panels

When compared to PUR and PIR sandwich panels, PU-edged rock wool panels have distinct pros and cons:

Advantages

1. Superior Fire Resistance: Achieving Class A, they far exceed PUR (B2–B3) and PIR (B1), making them ideal for high-risk areas.
2. Minimal Smoke Production: Rock wool generates little smoke when exposed to fire, unlike PUR and PIR, which can emit toxic fumes.
3. Thermal Stability: The rock wool core endures extreme heat, while PU edges maintain insulation, outperforming PUR’s lower heat tolerance.
4. Regulatory Compliance: Easily meets strict fire codes, unlike PUR, which often requires costly upgrades.

Disadvantages

1. Higher Cost: The combination of rock wool and PU edging increases production costs compared to standalone PUR or PIR panels.
2. Weight: Rock wool is denser and heavier than PU foam, potentially complicating installation and increasing structural demands.
3. Limited Insulation: While PU edges aid insulation, the rock wool core is less efficient than PUR or PIR foams, requiring thicker panels for equivalent thermal performance.
4. Complex Manufacturing: Integrating PU edging with rock wool demands precise processes, raising complexity over uniform PUR or PIR production.

Factors Affecting Fire Performance

Fire ratings depend on:

1. Core Material: Rock wool (Class A) outshines PUR (B2–B3) and PIR (B1).
2. Flame Retardants: Boost PUR and PIR but are unnecessary for rock wool.
3. Facing Material: Steel or aluminum limits flame spread across all types.
4. Design: PU-edged rock wool benefits from its non-combustible core dominance.

Conclusion

PU sandwich panels range from B1 to B2 for PIR and PUR, with untreated PUR at B3. In contrast, PU-edged rock wool sandwich panels achieve Class A, blending rock wool’s non-combustibility with PU’s insulation benefits. While they excel in fire safety and compliance, their higher cost and weight may limit use in budget-sensitive projects. Selection should align with local regulations and specific needs, verified by manufacturer data.