Steel Buildings in Europe

Part 7: Fire Engineering 7 - 13 5.1.2 Parametric fires Parametric fire models provide a rather simple design method to estimate gas temperature in fire compartment, taking into account in a simplified way the main parameters that influence the fire development, such as the fire compartment size, the fire load (corresponding to the mass of combustible materials in the fire compartment), ventilation conditions (openings) and thermal properties (such as thermal conductivity and specific heat) of the compartment walls and ceilings. Like nominal temperature-time curves, parametric temperature-time curves provide gas temperature-time relationships for design. They are based on the hypothesis that the temperature is uniform in the compartment, which limits their field of application to post-flashover fires (fires generalised to the whole compartment) in compartments of reasonable dimensions. The predicted fire curve comprises a heating phase represented by an exponential curve up to a maximum temperature, followed by a linearly decreasing cooling phase to a residual temperature that is usually the ambient temperature. The maximum temperature and the corresponding fire duration are the two main parameters affecting the fire behaviour of structural members. Consequently, they were adopted as the governing parameters in the design formulae for the parametric fires. Such a model is given in Annex A of EN 1991-1-2. It is valid for compartments up to 500 m² of floor area, without openings in the roof, and a maximum compartment height of 4 m, for compartment linings with thermal inertia between 100 and 2200 J/m 2 s 1/2 K, for an opening factor in the range 0,02 to 0.20 and for compartments with mainly cellulosic type fire loads. Due to these limitations, the model is mainly used for the office part of single- storey buildings.