Structural Properties of Composites in Fire

Abstract

A large quantity of information is available on the fire reaction properties of polymer composites (as described in chapters 2 to 5), and the level of fire hazard associated with their use is known for a large number of materials. We also have a good understanding of the chemical, thermal and physical mechanisms that control reaction properties such as time-to-ignition, heat release rate, flame spread rate, smoke production and toxicity. In short, we have quite a good quantitative understanding of the fire reaction behaviour of composites. Unfortunately, less is known about the fire resisting properties, such as burn-through resistance, dimensional stability and structural integrity, especially when the structure is under load. Moreover it is not usually possible to estimate the fire resistive behaviour based solely on the known fire reaction properties. A composite that has good fire reaction properties, such as low heat release rate and smoke yield, may not necessarily have good fire resistive properties. Composites with a polymer matrix having high thermal stability, decomposition temperature and char yield may not necessarily have better fire resistive properties than more flammable materials. For example, phenolic laminates generally show better fire reaction properties than unsaturated polyester laminates, including longer ignition time, lower heat release rate, slower flame spread and less smoke, but their mechanical properties can often degrade more rapidly in fire. Until recently, little was known about the structural properties of composites in fire. Understanding the structural performance in fire is a critical safety issue because the loss in stiffness, strength and creep resistance can cause composite structures to distort and collapse; possibly resulting in injury and death. Structural properties of composites in fire are therefore arguably as important to safety as the fire reaction properties that have generally been more widely studied.