When a fire oc curs in a tun nel, it is of great im por tance to as sure the safety of the oc cu pants of the tun nel. This is achieved by cre at ing smoke-free spaces in the tun nel through con trol of the smoke gases. In this pa per, results are pre sented of a study con cern ing the fire safety in a real scale railway tun nel test case. Nu mer i cal sim u la tions are per formed in or der to exam ine the pos si bil ity of nat u ral ven ti la tion of smoke in in clined tun nels. Sev eral as

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... cts are taken into ac count: the length of the sim u lated tun nel sec tion, the slope of the tun nel and the pos si ble ef fects of ex ter nal wind at one por tal of the tun nel. The Fire Dy nam ics Sim u la tor of the Na tional In stitute of Stan dards and Tech nol ogy, USA, is ap plied to per form the sim u lations. The sim u la tions show that for the lo cal be hav iour of the smoke dur ing the early stages of the fire, the slope of the tun nel is of lit tle im por tance. Secondly, the re sults show that ex ter nal wind and/or pres sure con di tions have a large ef fect on the smoke gases in side the tun nel. Fi nally, some idea for the value of the crit i cal ven ti la tion ve loc ity is given. The study also shows that computational fluid dy nam ics calculations are a valuable tool for large scale, real life complex fire cases.