According to the diversification in European fire standards, building materials are classified into seven different categories:
* A1 and A2 are inorganic non-combustible materials.
* B, C, D, E are combustible materials.
* F includes materials that cannot be classified.
Rigid polyurethane foam is a material classified from B to E, depending on its chemical structure and other factors.
Another method that indicates the combustion properties of insulation materials is the classification of smoke gases produced during combustion into S1 and S2 criteria. A material in the S3 class is considered to have no smoke gas during combustion. Polyurethane can be classified into S1 to S3 classes based on the type of chemicals and additives in its formula.
Another fire classification is the classification of burning droplets and particles, known as d0, d1, and d2. Rigid polyurethane foam is classified as d0 because it is a material that does not melt under intense heat and does not produce burning droplets and particles.
Rigid foam does not continue to burn internally when it is not supported by a flame source. Unlike structure materials with porous structures like fiber panels, which may continue to burn even after the flame source is removed due to reactions in their internal structures when exposed to flame. This can lead to a chain reaction as the temperature in the environment increases. Since insulation materials are commonly used in large interior spaces in buildings, internal combustion reactions are considered highly risky. Polyurethane insulation materials have the advantage of not being a material that continues combustion reactions, making them superior in fire safety.