Safety Analysis of Commonly Used Exterior Wall Insulation Materials:
In China, the most commonly used organic thermal insulation materials in buildings are polystyrene and polyurethane rigid foam. These materials are favored for their lightweight nature and excellent thermal insulation properties. However, a major concern is their poor fire resistance, which poses significant safety risks.
1. Polystyrene Board
Polystyrene foam is typically divided into Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS). EPS is the most widely used due to its lower cost. Despite being classified as flame-retardant, these materials are still considered B2 grade flammable. This means they can catch fire, melt, drip, and spread flames, leading to serious fire hazards. The dangers include:
(1) When heated, polystyrene boards can melt and drip, forming a melting zone along the wall base. If exposed to an open flame, the fire can quickly spread along this area, intensifying the blaze.
(2) During a fire, the combustion of organic insulation materials produces large amounts of toxic gases and thick smoke, which are among the leading causes of fire-related deaths. In many Chinese fires, over 80% of casualties were due to smoke and toxic fumes released from burning building materials.
(3) Heat from the polystyrene board can cause shrinkage and deformation, leading to the detachment of tiles or mesh cloth. This not only creates hazards for people but also makes internal rescue operations difficult for firefighters.
(4) If the surface of the insulation material cracks or falls off, it can ignite quickly, allowing the fire to spread rapidly across a large area.
(5) Once a high-rise building’s exterior wall catches fire, standard firefighting equipment may not be able to reach the affected area, making it extremely challenging to control the fire.
2. Polyurethane Rigid Foam (PU)
PU is recognized globally as one of the best thermal insulation materials, with a thermal conductivity of only 0.018–0.023 W/m·K. However, it is an organic polymer that is inherently combustible. Despite this, some manufacturers ignore fire safety concerns, especially in regions where regulations are not strictly enforced. This has led to the continued use of substandard polyurethane foam in certain applications, posing serious risks. The dangers include:
(1) Rigid polyurethane foam is porous and highly insulating, which can lead to heat accumulation. If it catches fire, it burns very quickly.
(2) When burned, polyurethane foam often does not fully combust, producing thick black smoke and releasing large amounts of toxic gases, including carbon monoxide, hydrogen cyanide, and benzene cyanide. These substances are extremely dangerous to human health.
(3) The massive smoke generated during a fire severely hinders visibility for firefighters, making it difficult to locate the fire source and conduct effective search and rescue operations.
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