ABSTRACT
It was once believed that only three things had to be present for fire to occur: fuel, oxygen and heat. While the fire triangle served as a working model for decades, recent research now indicates that a fourth element, a self-sustaining chemical reaction, must also be present. The new model is depicted as a tetrahedron with the phenomenon of fire resulting from the interaction of all four elements. Flammable atmospheres are excluded from equipment cabinets housing spark-producing devices by pressurizing the cabinet's interior with either compressed air or an inert gas such as nitrogen. This chapter examines some basic principles of fire dynamics and explains how they can be applied to control fire and explosion hazards in confined spaces. Substances with a wide flammable range are considered to be more hazardous since it is possible for them to be ignited over a wide range of circumstances.
