A freight train derailed close to Kungsbacka, Sweden in February 2005. The train carried 12 tank wagons, each of them containing 65 tons of chlorine. Fortunately, none of the tanks were disrupted. However, the event gave rise to questions regarding consequences of the accident in case of a leakage. An evaluation of the emergency services preparedness - when it comes to responding to chemical accidents - was performed by using this event as a model. Mathematical model simulations of how a release of chlorine is dispersed during the actual weather conditions were performed. The impact on the population around the disaster area was calculated using population data provided by the local authorities in Kungsbacka. We recommend the health societies to - at an early stage - prioritize medical countermeasures rather than decontamination ones, at least in incidents involving industrial chemicals. The access to medications must be investigated. Our modelling showed that release of chlorine after the actual incident would have caused severe consequences to people in the dissemination area. None of the emergency services involved had the preparedness to handle the scenario. It must be strongly noted that the scene of the accident is not the same geographic area as that of the dissemination area where victims are found. The casualties are scattered within a wide area, inside as well as outside buildings.