In Swedish law, fire protection in buildings facing antagonistic threats is not regulated. Buildings facing antagonistic threats with fire as a consequence can include services important for the community, for example embassies and military facilities. The Swedish police and military intelligence service states that the level of terrorism threats is elevated in Sweden. The Swedish Civil Contingencies Agency has assigned the Swedish Fortifications Agency to compile a handbook on how buildings should be designed to be safe based on the threat level. The aim of this thesis is to develop a basis for how buildings can be protected against deliberately lit fires and antagonistic fire threats. Ten respondents have been interviewed and the interviews were in the form of openly directed interview. The respondents represent for example emergency service, the consulting industry and fire researchers. The questions asked concerned how to think when designing fire protection, which parts of a building that are more exposed, what line of action and which starting area that is most likely when deliberately lighting a fire. Furthermore, questions about differences between a deliberately lit fire and an accidental fire as well as the probability for an attack were posed. A thematic analysis was performed on the interview data.The results show that the most common starting area for a deliberately lit fire was the façade, since it is accessible. Plausible lines of action for a deliberately lit fire for the studied type of building were to use flammable liquids, explosives or materials found at the scene as the ignition source. The difference between the two fire developments seemed to lie in the initial growth stage of the fire. A fire that is lit with flammable liquids has a much faster growth rate. Another difference was that for the deliberately lit fire an optimum starting area can be chosen to obtain great damage. The working process when designing the fire protection should be initialized with a risk and sensitivity analysis. The solutions that are chosen should be seen as an investment for the future. The outside has been shown to be the most common starting area, but Boverket’s building regulations are generally developed for a fire that starts inside the building. Due to this, the façade might need more protection for example by availability restrictions and that the façade is made out of nonflammable material. To secure the safety of the people the requirement for two independent means of egress should always be fulfilled. Surveillance, dividing the building into zones and classifying the building plans are some actions that can prevent an attack. An easy action to prevent a fire is to keep the areas clean from garbage. The consequences of a fire can be limited by fire alarm systems. The deliberately lit fire attributes can mean that the fire protection systems in the building are under designed, redundancy in the systems can solve this problem.