A natural fire concept, instead of the usual procedure based on the ISO curve, taking into account the Active Fire Safety Measures is a global approach which will greatly increase the competitivity of steel buildings because it enables the cost of insulating materials to be reduced or avoided. The objectives of this research are: - to perform some tests to complete experimental data and to validate fully the Natural Fire Safety Concept; - to include this Natural Fire Safety Concept in the Eurocodes; - to produce a user-friendly design tool to disseminate use of the method.