ABSTRACT
Fires can occur anywhere and have different severity. This chapter will only describe fires which take place in an enclosure. Fire development in an enclosure undergoes a number of stages. In the early stages, combustion is restricted to local areas near the ignition source and temperatures of the combustion gases are low, but there is a large quantity of smoke and toxic chemicals. It is the reduced visibility due to smoke and the toxicity of chemical products that pose the biggest threat to life. Therefore, the main focus of the fire research community has concentrated on understanding ignition, production of smoke and toxic gases, their movement and their effects on human behaviour. Since fire temperatures at this stage are usually low, the safety of a structure exposed to fire attack is very rarely threatened. Hence this aspect of fire behaviour has not attracted the attention of many structural fire engineers. Their interest is usually focused on the later stage of fire development when the fire involves all combustible materials and the combustion gases attain very high temperatures. The stability of the structure may be threatened, the consequence of which can lead to rapid fire spread and loss of life and property. This is the so-called post-flashover fire and it is this stage of the fire development that will be addressed in this chapter.
