In the frame of the European RFCS (Research Fund for Coal and Steel) TRAFIR (Characterization of TRAvelling FIRes in large compartments) project, three natural fire tests in a large compartment were conducted at Ulster University. The aim of this investigation was to understand the conditions in which the travelling fires develop and to study the impact of such fires on the surrounding steel structure. This paper provides details of the second fire test where the size of the openings was reduced to induce different ventilation conditions in comparison to the first fire test. During the test, behaviour of the travelling fire was observed and the gas temperatures at different levels and locations were recorded. The influence of travelling fires on the surrounding structure is studied in terms of the temperatures recorded in the selected steel columns and beams. The influence of change in the ventilation conditions is presented and highlighted through the comparison of results of the second fire test with those recorded earlier during the first fire test. It was found that the travelling fires produce non-uniform temperatures in the compartment irrespective of the ventilation conditions although the magnitude of this non-uniformity is related with the opening sizes. This non-uniformity exists along the length as well as along the height of the test compartment. It was found that for reduced opening sizes, more heat is retained within the compartment which induces higher temperatures in the surrounding steel structure. The transient heating of the surrounding structure caused by travelling fires should be considered while performing the structural fire design of large compartments. The results obtained during the test are state-of-the-art and will help in understating the behaviour of travelling fires and their influence on the surrounding structure which will help to devise fire design methods for future use.