Safety Analysis of Commonly Used Exterior Wall Insulation Materials:
Currently, in China, the most commonly used organic thermal insulation materials for building exteriors are polystyrene and polyurethane rigid foam. While these materials offer excellent thermal insulation and are lightweight, they have significant fire safety risks that cannot be ignored.
1. Polystyrene Board
Polystyrene foam is mainly divided into Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS). Among them, EPS is widely used due to its low cost. However, even though it is required to be flame retardant, it still falls under B2 flammable materials. This means it can easily catch fire, melt, drip, and spread flames, posing serious fire hazards. The key dangers include:
(1) When exposed to heat, polystyrene boards can melt and drip, forming a melting zone along the wall base. If this area comes into contact with an open flame, the fire can spread rapidly along the melted path, leading to rapid fire escalation;
(2) In the event of a fire, the burning of organic insulation materials releases large amounts of toxic gases and dense smoke. These substances are often referred to as "the number one killer of fires" by the fire industry. In many past fires in China, over 80% of casualties were caused by toxic gases and smoke from burning building materials;
(3) Heat from the polystyrene board can cause shrinkage and deformation, as well as overheating of the mesh cloth, which may lead to tiles falling off. This not only creates hazards but also makes internal rescue operations difficult and dangerous for firefighters;
(4) If the surface of the insulation material cracks or falls off, it can quickly ignite the underlying material, causing the fire to spread rapidly across a wide area;
(5) Once a high-rise building’s exterior wall catches fire, the indoor fire-fighting systems are often unable to reach the affected area, making it extremely challenging to control the fire.
2. Polyurethane Rigid Foam Material (PU)
Polyurethane is considered one of the best thermal insulation materials globally, with a thermal conductivity of only 0.018–0.023 W/m·K. However, it is an organic polymer and therefore highly flammable. Despite the risks, some manufacturers ignore fire safety regulations and use substandard polyurethane foam in certain applications. The dangers associated with this material include:
(1) Rigid polyurethane foam is porous and has very low thermal conductivity, making it prone to heat accumulation. Once ignited, it burns extremely quickly;
(2) When burned, polyurethane foam often does not fully combust, producing thick, black smoke filled with harmful gases like carbon monoxide (CO), hydrogen cyanide, and benzene cyanide. These gases are not only toxic but also highly dangerous;
(3) The massive smoke generated during a fire significantly hinders firefighters’ visibility, making it hard to locate the fire source and conduct effective search and rescue operations.
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