The problem considered in this thesis concerns how the thermal expansion of steel beams in the ceiling of industrial halls affects the building and the fire protection. The subject has been up for discussion in Sweden for a while because of the difficulty in classifying the buildings correctly according to existing construction rules. In the thesis several dimensions of a fairly generic industrial hall with two compartments are analysed. One compartment exposed to fire consisting of three fourths of the building and the other sectioned off with a firewall class R30 and thus able to withstand fire for the full duration of the simulation. First the temperatures attained in the ceiling beams of the structures are simulated using Fluid Dynamic Simulator (FDS). After that these are used to calculate the strain caused by the thermal expansion on the firewall with the help of a worksheet developed during the course of the thesis.Using these beam calculations and computer programmes the problem has been reviewed and the following conclusion is drawn: Thermal expansion of the beams on its own is not enough to cause a collapse of the adjacent firewall in the cases studied in the thesis. Under simulated conditions the worst strain was nowhere near what was required to cause a collapse and temperatures would need to be a couple hundred degrees higher. The interactions between the bending and compression of the beams was not enough to cause a buckling either, further insuring the integrity of the firewalls protection.The thesis lends further support to the state of art regarding the construction of buildings sectioned with differing levels of fire protection.