Influence of ventilation on ro-ro space fire development : A study using two-zone fire models in order to explore tendencies of how different ventilation parameters affects the fire development in a ro-ro space
Sammanfattning: A ship to which vehicles and other loads can be rolled on and off is usually named ro-ro ship. A ro-ro ship consists of large corridor shaped space, normally extending to a considerable length or the entire length of the ship, which is usually loaded with various vehicles or stowage units. A ro-ro space can either be designed as an open space, closed space or a weather deck. There have been several fire incidents in ro-ro ship spaces and these fires occur with a relatively high frequency. A fire on a ro-ro ship is a very complex phenomenon. The fire development is hard to predict, and the fire tend to grow very quickly. One crucial parameter for the development of these fires is the ventilation, and the ventilation conditions may be totally different depending on the design of the ro-ro space. This study was conducted in co-operation with RISE, the department of Fire Research, and the research project RO5. RO5 aims to clarify how the ventilation in ro-ro spaces affects the development of a fire and to possibly establish conceptual solutions for fire protection measures for ro-ro spaces with different ventilation conditions. The aim of this study is to explore tendencies of how both natural and mechanical ventilation affects the fire development within a ro-ro space. The intention is to provide basic knowledge regarding this subject, so that further simulations and tests could be optimized. The long-term goal of this study is to reduce the consequences, the severity and the number of fires within ro-ro spaces. The first step in the project is to explore the usefulness of two-zone models and compare the applicability of such method to experimental data. This is crucial in order to assess the applicability of two-zone models, especially as the aim is to make a parametric study of the influence of ventilation of fire development inside ro-ro space. A literature study of previous incident investigations of fires in ro-ro spaces was performed to gain knowledge concerning possible fire scenarios, ship constructions, fire development, consequences etc. and to provide an insight into how the ventilation was used in the case of a fire. In 2002, the research project “Model Scale Fire Tests on a Vehicle Deck Aboard a Ship” was issued by SP Swedish National Testing and Research Institute (now RISE). The aim was to simulate possible fire scenarios on a vehicle deck and examine what parameters can affect the fire development. To study this, tests were performed in model scale 1:8. The model had the dimensions 11.425 m x 2.786 m x 0.625 m (length x width x height). It was concluded that the ventilation and air supply being crucial for the fire development in ro-ro space. Although fires in a closed ro-ro space can quickly become ventilation-controlled, the fire may initially grow to be very large. One part of this study was to simulate some of the tests in “Model Scale Fire Tests on a Vehicle Deck Aboard a Ship” in the same sized model (scale 1:8). This was done since no tests on a full-scale model could be found. The simulation programs used were CFAST and B-RISK. The results were used for comparison to see how the two-zone simulations cohere with the tests. This was considered necessary due to limitations of the simulation programs and to the simplifications of two-zone fire model. By the comparison it was possible to choose the most suitable simulation program of the two, to use for further simulations in the study. The most suitable program was CFAST. Another part of the study was to conduct a parameter study. Since the model used in the tests in 2002 corresponded to an eight times larger model, the model was upscaled using Froude scaling to the dimensions 91.4 m x 22.3 m x 5 m (length x width x height). This model (scale 1:1) was then used in the parameter study. In the model, steel was used as material of the walls, ceiling and floor in order to imitate a real ro-ro space. By the results of the parameter study using two-zone fire simulations in CFAST, it is concluded that increased natural ventilation results in larger fire development, as well as increased mechanical ventilation results in larger fire development. Due to the results, open ro-ro spaces are recommended to be avoided. The regulations and definitions addressing closed ro-ro spaces are suggested to be reviewed since a closed ro-ro space can have relatively large natural ventilation. If natural ventilation is nevertheless required, the simulations indicate that openings constructed as wide as possible and with as low sill- and soffit height as possible are preferable. Because of the large size of a ro-ro space, there is enough oxygen to sustain a large fire during a given period. The fire will produce inert gases in the burning process such as CO2. As the gases reaches down to the fire source, the fire will start to fade. The oxygen within the ro-ro space will get pushed away by the process. The phenomenon is called inerting/vitiation and may occur when there is a fire within a ro-ro space. Previous investigations show that, the mechanical ventilation has been used to extract smoke in order to improve visibility and locate the fire. This measure may however be risky since mechanical ventilation may increase the fire development. Also, the mechanical ventilation may not be designed to be used for this purpose. In order to locate the fire efficiently for final extinguishment new improved and safer tactical methods is suggested to be evaluated.
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