Offshore and onshore structures continuously experience hydrocarbon fire accidents almost every year. To secured structure against extreme fire conditions, passive fire protection (PFP) is applied. However, PFP is a costly material which is applied only on critical structural members. Any unprotected surface can cause major structural damages during fire incidence if the behaviour of an unprotected surface is unknown. Usually, PFP applied easily around the column, but for beams, the application varies with the beam locations. In this paper the behaviours of steel beam compared with three different common scenarios such as fully protected, unprotected and partially protected under hydrocarbon fire. Fully protected beam has tremendous fire resisting capability compared to partially protected beams or unprotected beams. The study revealed that temperature of the top flange in partially protected beam exceeds more 600°C in less than 10 minutes which caused rapid failure in less than 30 minutes. Under extreme fire conditions the strength and stiffness of a beam affected which cause instability of structure during fire accident. © The Authors, published by EDP Sciences, 2018.