- 157 - SOLIT PROJECT: WATER MIST FIRE SUPPRESSION SYSTEMS AS PART OF THE TUNNEL SAFETY SYSTEM Kratzmeir S. FOGTEC Fire Protection, Research & Development, Germany Keywords: Fire Protection, Fire suppression, water mist 1. INTRODUCTION Fire safety measures were increased during the last years. But recent serious fires in tunnels again showed that there are still similar problems with evacuation of people and access for fire fighters as well as serious damages on tunnel structures. Mainly this is affected by extremely high temperatures and smoke spread due to rapid fire development. Automatic fire suppression systems were considered for years to improve the situation in tunnels, especially shortly after fire detection. First tunnels with innovative suppression systems based on water mist technology are under installation. For these tunnels, applicability was proven in special fire tests. To create sufficient basics for a performance based layout of such systems more research work is carried out now. 2. CURRENT KNOWLEDGE ABOUT FIRE SUPPRESSION SYSTEMS IN TUNNELS Based on a report of PIARC active fire protection measures by means of sprinkler or water mist systems, most tunnel safety designers declined to propose such systems. However, due to lack of knowledge by real scale fire test, the arguments given in this report must be taken seriously into account in past. Anyway, in Australia and Japan, automatic fire suppression systems are to be installed in longer tunnels or tunnels with a high traffic density as a general rule. But the aim and therefore the Figure 1: UPTUN Fire Test Scenarios performance of these systems are mostly different to the aforementioned systems, as they are installed for protection of the tunnel structure against collapse. If a fire occurs, these systems will be activated after completion of the evacuation process, often after 30 60 Minutes. Recently it is under consideration if this strategy should also be changed to an activation of the system as early as possible. Beside some other experiments with suppression systems in tunnels or similar applications, the European research project UPTUN includes also scientific development of innovative and effective fire mitigation systems for use in tunnels. The main focus was given to a full scale fire test program to assess effectiveness of such systems independently. Fire scenarios for this test program were developed by Sintef (Norway) based amongst others on the results of the Runehamar fire tests. Two different scenarios were used: Partly covered pool fire with a maximum HRR of 20 25 MW Partly covered wooden crib fire with a potential HRR of approx. 50 MW
- 158 - These scenarios were designed not to simulate any specific fire load, e.g. trucks, cars, but repeatable fires with specific HRR. Obviously, 20 MW or even 50 MW, are not HRR of a full developed fire in a tunnel, but as the aim of such system is fire suppression on early stage, this figure is sufficient and should be taken into account in design process, e.g. for interface with the detection system. According to the internal UPTUN test report, test result of this test program can be summarized as follows: Generally, water mist systems are able to suppress Figure 2: UPTUN Fire Test fires in tunnels up to a certain limit efficiently even with ventilation. HRR can be stabilized or even reduced. Temperatures nearby the fire as well as in a distance of 20 m are reduced significantly. Evacuation conditions as well as conditions for fire fighters are improved during activation of the system. Due to reduction of the smoke production during activation of the system, visibility was improved particularly on the upstream side of the fire The layout of the system (nozzle position, flow rates, droplet size distribution) has a high effect on efficiency of the system. Scaling is only limited. The UPTUN fire tests have shown that especially designed and tested water mist systems can be a very effective fire safety tool for tunnels. Furthermore it turned out, that scaling, even with advanced simulation tools, is very limited. Real scale fire tests are necessary. Maximum effectiveness of such systems can be achieved by adequate interaction with other parts of the tunnel safety system, e.g. detection or ventilation. Although a lot of new knowledge was gathered during the UPTUN project, there are still some important questions to be answered; some even came during the test program and its assessment. Some general questions are as follows: Up to now, any suppression system was only tested with longitudinal ventilation. Are there any differences with other types such as semi transversal or transversal? It already turned out that interaction with other safety systems is of special importance. What influences do these safety systems have against each other? How to assess results of fire tests. Are strict acceptance criteria more useful or should results assessed case by case? 3. ASSESSMENT OF EFFECTIVENESS OF ACTIVE FIRE SUPPRESSION SYSTEMS 3.1. SOLIT Project The research project SOLIT (Safety of Life in Tunnels) further info at www.solit.info - addressed itself to the task to pick up current knowledge about suppression systems for tunnels to enhance these systems and test methods so they can be installed in tunnels efficiently and safe. SOLIT, funded by the German government, has two focal points: The technical aspects are mainly dealing with reliability and life cycle issues of such systems and are not described in this paper. The other main task is focusing on development of methods how such suppression systems for tunnels can be tested and assessed regarding their effectiveness for a wider range of
- 159 - applications than today. Furthermore, above mentioned questions should be analyzed more in detail. Experience has shown that full scale fire tests are still necessary. The SOLIT project is guided by a scientific advisory board containing organizations and institutions that are well experienced in the field of tunnel fire safety e.g. STUVA, Sintef, TNO, BaST or German ministry of transport and infrastructure and TÜV. 3.2. SOLIT Full Scale Fire Test Program Scenarios for real scale fire testing are always a compromise between reality and feasibility. Indeed, real trucks or cars as fire load would be more realistic but due to extreme differences in size and material composition any comparable and repeatable results would be achieved. Therefore, Figure 3: SOLIT Class A Fire Scenario similar to other fire test procedures, scenarios for tunnel fire testing should also consist of common agreed standard fire loads, e.g. EUR wood pallets, so repeatable results can be ensured. Based on a study of real tunnel fires and scenarios used in full scale fire tests, following scenarios will be used for to assess effectiveness of the tested system. The scenarios as well as the measurement concept were gathered together with the scientific advisory board of the SOLIT project, which consists of national and international well accepted experts in tunnel fire safety. Class A Scenario: Wood and plastics The mock up should simulate a common used loaded truck similar to the Runehamar tests presented by Ingason (2003). The load consists of wooden EUR pallets and plastic pallets with the ratio of 80:20. The whole load is covered with a tarpaulin. Total weight: approx. 8 to. Total energy content: 200 240 GJ Wood/plastic ratio: 80:20 To assess the control of fire spread between vehicles, target objects also consisting of wooden pallets will be used sideward and on downstream side of the mock up. Class B Scenario: Partly covered diesel pools According to the UPTUN fire tests for suppression systems, the scenario is slightly modified. By means of this scenario, specific HRR can be produced as well as fires of burnable liquids. Max estimated HRR: Total energy content: approx. 30 MW 20 30 MJ The cover ensures that the pool surface can not be hidden directly by any suppression system as this would be the situation with real vehicles in a tunnel. By using a similar scenario than within the UPTUN test program, available data can be compared.
- 160 - The measurement concept is not based on any fixed acceptance criteria. Moreover data should be collected in a way that assessment of efficiency can be done during design of performance based safety measures. Following data will be measured in general: - Temperatures in different positions - Radiant heat - Gas concentrations (CO, CO 2, O 2 ) Of course, toxicity of smoke is an important issue. Standard fire loads are not able to simulate different material compositions of real material. Therefore extended smoke measurement, e.g. HCl, HCN, NO x, is not indicated. - Humidity - Longitudinal air velocity - Visibility In past, no satisfactory results were achieved for visibility measurements during tunnel fires with suppression systems as measurements did not reflect subjective impressions. Therefore new methods of visibility measurements will be studied during these tests. The test program will be carried out between March and June 2006. More information about the test program and results will be available at www.solit.info 3.3. Assessment of Test Results Regarding performance of suppression systems for tunnels until know it was only spoken about effective in general. Assessment of effectiveness of such systems can be conducted in two different ways: performance based analysis or prescriptive based. Particularly in the field of fire protection, prescriptive based layouts of safety systems are often used. If a system fulfils specific requirements, e.g. water flow rate or spacing in case of sprinklers, the system is assumed to be effective. In case the layout of systems is based on real fire tests, e.g. for passive fire protection material but also for water mist systems, there are specific acceptance criteria which must be passed during the testing procedure. Acceptance criteria in a prescriptive way are fixed values based on measurements for defined aims of the system. For simple standard applications prescriptive guidelines are usually well accepted and can be seen as very safe. But especially for complex systems, such as tunnel safety systems, it is extremely complicated to adapt these guidelines and values on specific projects. Performance based layout of safety systems is usually based on an extended risk analysis. Thereupon individual safety measures and systems can be arranged for this specific application. Normally this method is used, when prescriptive guidelines are not available or applicable. Although even for performance based layout accepted guidelines and values should be used as far as possible. Performance based layout of safety systems gives much more flexibility to consultants to adopt systems especially for each project. But of course a much better knowledge and understanding of the whole safety system is necessary. In case of fire suppression systems for tunnels it can be assumed, that even after full scale fire testing no general acceptability for the system can be given. Moreover, for every tunnel project it should be verified individually, how such systems can be applied in combination with other safety measures. For such analysis profound knowledge and performance data, generated during real scale fire testing, is strictly necessary.
- 161 - The methodology to assess effectiveness of suppression systems for tunnels developed within the SOLIT project should not specify approval criteria which must be passed during fire testing but should give suitable fire scenarios and measurement concepts to determine sufficient data for a performance based layout. 4. CONCLUSIONS Based on new knowledge of scientific full scale fire testing open questions, e.g. given by PIARC can be answered basically. Water mist fire suppression systems as a part of the tunnel safety system are able to improve the atmosphere in tunnels during a fire significantly. As knowledge regarding scaling and analysis of test results as well as interaction with other parts of the tunnel safety system was limited in past the research project SOLIT is focusing on these questions. An extended full scale fire test program is carried out to develop a general accepted methodology to assess effectiveness of fire suppression systems in tunnels. REFERENCES Opstad, K, Brandt A, 2005. Test Report of UPTUN WP 2.4. for Real Scale Fire Test with Water Mist Fire Suppression Systems. Ingason, H, Lönnermark A, 2003. Large Scale Fire Tests in the Runehamar Tunnel. International Symposium on Catastrophic Tunnel Fires, pp. 93