- 203 - FINDINGS FROM FIRE TESTS IN TUNNEL CONSTRUCTIONS WITH VENTILATION SYSTEMS AND FIXED FIRE SUPPRESSION SYSTEMS Hofer R., IBS Institute for Technical Fire Protection and Safety Research, Linz / Austria OVERVIEW The IBS Institute for Technical Fire Protection and Safety Research was able to gather numerous findings during the last years which were obtained in the course of controlling fire tests in tunnel constructions. It is the aim of the lecture to take a look at the time flow from the start of fire, detection, system activation to the point of the stable state both by the example of ventilation systems and by the example of fixed fire suppression systems (in combination with ventilation systems) and to provide evidence with exemplary measured curves (flow speed, temperature profile, turbidity, etc.). On the basis of these kind of measured curves as well as visual observations (videos) an assessments can be made under consideration of the time course how far the ventilation system and/ or the fixed fire suppression systems are significant for reaching the intended protection goals in underground traffic constructions self-rescue phase, escape exit safety in the direct fire area and outside of the fire area, support of the fire fighting operations and sustainment of the carrying capacity of the tunnel construction. 1. INTRODUCTION Different guidelines for the operation of tunnel constructions, which have partly been declared binding in relevant laws in some countries, control the requirements concerning ventilation systems (for example RVS 09.02.31 in Austria) and partly already at fixed fire suppression systems, as far as they are considered as necessary based on an object-related risk assessment (expert observation of the potential risk depending on the traffic volume). In the Uptun - Engineering Guidance for Water Based Fire Fighting Systems for the Protection of Tunnels and Subsurface Facilities (Work Package 2 of the Research Project UPTUN of the European Commission (Revision 08) R251 - August 2007) there are for example very specific minimum requirements for the execution of fixed fire suppression systems. 2. FIRE TESTS For verification the IBS took charge of the testing for different fire tests and carried out all measurements accompanying. Finally the recorded test results got evaluated and an according test report including the evaluation of the results for the specific fire test series got issued. 2.1. Ventilation systems in case of fire The general requirements for ventilation systems in case of fire as required in Austria in the relevant RVS guidelines are as follows: Longitudinal ventilation with one-way traffic: - Set value longitudinal flow velocity : 1,5-2 m/s Longitudinal ventilation with two-way traffic: - Set value longitudinal flow velocity: 1,0-1,5 m/s - Jet fans: 250 C over 60 minutes
- 204 - Semi-transverse ventilation and transverse ventilation : - 120 m³/s suction capacity related to a section of 150 m - Max. distance between the suction ports: 110 m, - In case of full transverse ventilation: max. 55 m distance between the supply air insertion openings - Test for ventilators and flaps: 400 C over 120 minutes Regarding the smoke removal capability as well as the smoke control of emergency exits the transverse ventilation systems have an advantage compared to the longitudinal ventilation systems. But the smoke layer behaviour even though works very well in general in case of longitudinal ventilation as far as the specified longitudinal flow velocity is kept -. The aim is a low smoke zone of approx. 2m at ground level. A smoke-free layer, as often mentioned in specialized literature, is definitely not given in case of real fire in tunnels. The decisive protection goal in the direct fire area is to enable the Fire Brigade to move forward with the help of breathing apparatus to carry out the extinguishing process and if necessary and still possible rescue injured people.. Furthermore it should at least be possible to keep the smoke development in the area of the nearest emergency lay-bys at a minimum so that an escape for the purpose of the self-rescue concept under consideration of the allowed limit values (CO, CO2, O2, smoke gas temperature) - stays possible. 2.2. Test results (Extract) During the last two decades the IBS Institute for Technical Fire Protection and Safety Research was able to gather numerous findings in the field of functional verification of ventilation systems in case of fire. First of all it should be noted that the following mentioned measuring results are exemplary and have been chosen because they represent the typical process (trend) of the measuring results such as temperature, flow velocities in front of and behind the fire area as well as CO values in a very good way. The following example shows the test results of a standard fire test (RVS) in an approx. 3 kilometre long two-way traffic tunnel with semi-transverse ventilation. Figure 1: Overview
- 205 - Figure 2: Flow profile Figure 3: Temperature profile
- 206 - Summary: Because the worst case situation for starting the ventilation system into the fire smoke suction operation during low traffic is given the following adjustment for ignition of the pool fires has been chosen. This adjustment has the following parameters: Ventilators turned off Partition flap (vertical flap) closed Flap 24-29 approx. 50 % open The natural longitudinal flow direction in north direction was amounting to approx. 2 m/s. Approx. 1 minute and 30 seconds have been defined as pre-burning time because as known from according approval tests the alarm starts during this time in case of an open fire in all stationary linear heat detector systems in tunnel constructions. Directly after entry of the alarm signal which is normally transmitted to the tunnel control- and monitoring system redundant on the one hand by means of the serial interface of the heat detector controller, on the other hand by means potential-free contacts- the defined fire program starts (traffic light, emergency lighting activation, etc.) - and among other things the ventilation program sequence case of fire starts. In the specific case of semi-transverse ventilation the wind direction dependent ventilator north starts up 100% and the 3 suction flaps which are assigned to the fire area open up 100%. This start-up procedure (ventilators are normally started over frequency converters) takes about 2 minutes. Only at this point the ventilation system starts to activate regardless of the previously activated operating program -. Until then depending on the prevailing longitudinal flow velocity an uncontrolled smoke propagation is expected. Approx. 1 minute later the aimed start-up of the ventilation sections causes the stop of the longitudinal flow to => 0 m/s, whereby it is achieved that from this point the smoke which is produced by the source of fire can be controllably discharged over the ventilation section of approx. 130 m. Again 1 minute later the aimed smoke layer (at the top smoke layer, at the bottom low-smoke zone) is visually obvious. From this point it at least enables the Fire Brigade to move forward with appropriate protective equipment. The maximum smoke temperatures measured along the ceiling within the suction zone at that time already move < 60 C. 2.3. Fixed fire suppression systems The IBS Institute for Technical Fire Protection and Safety Research was already able to gather findings at the end of the 90 s which were obtained in the course of a fire test series with real burning tests in tunnel constructions in combination with fixed fire suppression systems. On the basis of the previously run research project EUREKA EU 499: FIRETUNE the following minimum requirements were made for these fixed fire suppression systems regarding the protection goal of these systems: - < 350 C in a distance of 5 meters within 120 seconds - < 250 C in a distance of 5 meters within 5 minutes - < 50 C in a distance of 20 meters within 120 seconds - Prevention of a flashover to neighbouring, combustible materials in a distance of 5 meters to the fire - Protection of the tunnel construction (< 100 C, 10 mm within the concrete layer)
- 207 - Many further test series during the last years confirmed the previously used system design which conceptually has stayed the same to date and which meanwhile has basically been recorded in the Uptun Engineering Guidance for all producers. Recent test series of the Dutch Ministry of Transport (RWS Rijkswaterstaat) in collaboration with the production and installer company Aquasys and the Norwegian test institute SINTEF showed once again the efficiency of these fixed fire suppression systems both for solid and liquid fires. The diagrams and definitions are partly taken from the report with the title Re- Scale of Aquasys Water Fire Suppression in Runehamer Test Tunnel, No.: NBL F08113, SINTEF NBL as dated 22 nd June 2008 and have been released for presentation both by the RWS Rijkswaterstaat and the Aquasys Technik GmbH. 2.3.1. Solid fires Enclosed an extract of the measuring results from a test series with an approx. 100 MW fire, which has been reached by ignition of a stack of 180 wooden pallets. Figure 4: Temperature Profile, 180 wooden pallets Data from +142 m not available Figure 5: HRR course, 180 wooden pallets
- 208 - At a pre-burning time of 8 minutes the fire develops to a total fire which causes a heat release rate of approx. 100 MW. From this point the fixed fire suppression system (high-pressure water mist) is activated. After approx. 5 minutes activity of the system the temperatures already start to move under 200 C at all measuring points in a distance of 5 meter to the fire. The heat release rate can now be reduced to 30-50 MW again. 2.3.1. Liquid fires The above mentioned protection goal definition, which has been defined in the late 90s, has been concretized especially for liquid fires in the course of this test series 2007 in the Runehamer test tunnel and is defined as follows: The requirements are: - The water mist system shall control the solid design fire scenario and achieve following conditions in maximum 1 minute after activation: in a distance of 30 m upstream of the fire (upstream end), the heat flux shall be not larger than 3 kw/m², at a maximum ambient temperature of 50 ºC; in a distance of 20 m upstream of the fire (upstream end), the heat flux shall be not larger than 5 kw/m², at a maximum ambient temperature of 50 ºC; in a distance of minimum 5 m downstream the fire (downstream end), the heat flux shall be not larger than 12.5 kw/m², at a maximum ambient temperature of 280 ºC. - The water mist system shall control the fire for at least 49 minutes after the fire reduction of the first minute. - The water mist system shall extinguish the liquid design fire scenario within 1 minute upon activation. Enclosed an extract of the measuring results from a test series with an approx. 250 MW fire, which has been reached by ignition of a 100 m² diesel pool fire. Figure 6: Temperature Profile, 100 m² diesel pool fire, +5 m downstream
- 209 - Figure 7: Temperature Profile, 100 m² diesel pool fire, +142 m downstream Figure 8: HRR course, 100 m² diesel pool fire The ignition of the 100 m² diesel pool fire already caused a ceiling temperature of approx. 1200 C and a heat release rate of approx. 250 MW after approx. 2 minutes. This worst case scenario can be controlled through the fixed fire suppression system within a very short time and the extinguishing success starts within 1 minute after activation of the system.
- 210-3. CONCLUSION The following table summarized what can be derived from the test findings and which protection goals with which system types resp. their combinations can be sustained. 1) The in the table mentioned 5 minutes are only orienting values. Thereby the incipient fire phase until the earliest possible effect of a technical devise under consideration of the fire detection and system run time of the single system components, until the complete system (for example the ventilation system) is 100% available, is supposed to be demonstrated. Object-specifically this can also take 7 or 10 minutes. The quoted absolute value is therefore not decisive for the assessment.