As steel gradually loses its strength during heating up, at a certain temperature the remaining strength of a steel element will be insufficient to carry the mechanical loads, and the element will collapse. This depends on the utilisation degree: the ratio of mechanical loads under fire conditions that act on an element vs. its strength at room temperature. The higher the utilisation degree of an element, the lower the temperature at which it would fail.
In order to avoid failure of a steel element, the steel temperature must remain lower than the theoretical temperature at which failure would occur. The maximum allowable temperature that is low enough to avoid failure is called the critical steel temperature. The lower the critical steel temperature, the more fire protection is needed.
The critical steel temperature for each element can be calculated by a structural engineer, or safe values (typically 450-620°C) can be used based on local regulations. For more information, please contact your local Promat office.