The Columbus fire suppression procedure is based on a centralized CO2 distribution system which injects the CO2 stored in a tank into the volume where the fire has to be extinguished. The fire is detected in each volume by means of the so-called REP (Rack Essential Package), which contains a fan and the smoke sensor. In order to assess the Fire Detection and Suppression design concept and to identify possible critical areas, Alenia Spazio - with the support of Flowsolve UK, and on behalf of EUROCOLUMBUS - has performed an analysis using a Computational Fluido-Dynamic (CFD) tool. The rack containing the water pump assembly and other electronic equipment has been chosen for the study.As far as the Fire Detection is concerned, the simulation intends to predict the flow field established in the rack by the ventilation system and the transport of smoke by this velocity field from a supposed point source. The smoke from any fire within the rack must be transported to the sensor so the fire can be detected within a “reasonable” time.The Fire Suppression System has more stringent targets to meet: the CO2 must reach a 50% concentration by volume everywhere in the rack within 60 seconds. The aim of the CFD simulation was to study various combinations of CO2 nozzle and pressure relief vent positions and numbers so that the configurations which fulfill the 50% requirement can be determined. The simulation has been performed using the 1.6.5 version of the PHOENICS general-purpose CFD code.