Application of the Standard Fire Curve for Expressing Natural Fires for Design Purposes

Abstract

A method suitable for design purposes is presented which allows postflashover compartment fires to be expressed in one single curve; time is then modified or scaled to take into consideration ventilation conditions and wall properties. Ventilation-controlled combustion, uniform temperature, and wall losses proportional to the thermal inertia of the wall material are assumed. Although the proposed method allows the designer to consider important parameters, it is still very approximative and must be used with care. Several assumptions are made, and many parameters are difficult to assign values in the general case. The method therefore should be looked upon as an improvement of the current technique of carrying out fire engineering design by simply employing a standard curve like ISO 834. An analysis of the postflashover compartment fire, basically the same as has been presented elsewhere, is summarized. The parameters of ventilation and wall properties are grouped together in such a way that their influence on the temperature development may be expressed as a time factor. It is further shown that for certain parameter values the fire temperature response in the heating phase nearly coincides with the ISO 834 standard curve. Therefore, as this curve is well-established in fire engineering, it is suggested that it be employed with the here suggested method; the time scale, however, is modified with a compartment time factor depending on the properties of the fire compartment. The assumed fire temperatures may be used to estimate the temperature in fire-exposed structures. It is demonstrated how very compact diagrams may be used for concrete structures, which allows the designer to take into account various fires and thermal material properties of the structure. The diagrams were obtained from finite-element computer calculations in which various fires and material properties were simulated. By then plotting the temperature response versus suitable parameter groups, it was possible to present the results in a very compact way. Corresponding diagrams have earlier been presented for insulated steel structures [1].