COMPENSATORY EFFECTY OF FIXED FIRE FIGHTING SYSTEMS IN TUNNELS

Transcription

1 COMPENSATORY EFFECTY OF FIXED FIRE FIGHTING SYSTEMS IN TUNNELS Kratzmeir S. 1, Rothe R. 1 Peters B. 2, 1 IFAB Institute for applied fire safety research, Rostock 2 Fogtec Fire Protection, Cologne ABSTRACT During the last years, more and more tunnels are equipped with fixed fire suppression systems (FFFS). Obviously the purpose of the systems somehow differs for each tunnel, but in up to now they are used to increase the level of safety. The research project SOLIT², a consortium of FOGTEC, STUVA, BUNG, Ruhr University and TÜV Süd, followed a different approach. Major aim of the project was to identify compensatory measures by FFFS in tunnels aiming for technical easier and more costeffective solutions, but ensuring the same or even a better level of safety. In 2011 a large scale fire test program was carried out by the German Institute of Fire Brigades and IFAB on behalf of the SOLIT² consortium. The paper will focus on the interaction of water mist systems with longitudinal and semi-transversal ventilation systems. Based on tests with a severe truck fire load as well as pool fires up to 100 MW it was possible to show that with a combination of both systems it was possible to reduce the ventilation power by up to 70% achieving the same effects. The paper gives an overview of possible compensatory effects of fixed fire suppression systems and will give some advice regarding minimum requirements for the design of tunnel safety systems by using compensatory effects. Keywords: ventilation, FFFS, fire protection, fire tests, compensation, SOLIT² 1. INTRODUCTION The beneficial effects of fire suppression systems in tunnels are well known and were studied extensively during the last years. However, the evaluation of test data from full scale fire tests and further data already showed that more benefits can be achieved by FFFS as simply increasing the level of safety. The research project SOLIT², funded by the German government studied during the last 2 years the possibilities of compensating accepted and well established safety measures by using FFFS in tunnels. Furthermore tools were developed to check the level of safety of various combinations of safety measures as well as to evaluate and compare the life-cycle-costs of these systems. Further information about the SOLIT² project can be found at 2. FIXED FIRE FIGHTING SYSTEMS IN TUNNELS STATE OF THE ART During the last years several tunnels throughout Europe where equipped with fixed fire fighting systems (FFFS), mainly based on water mist technology. Just recently, the new tube of the New Tyne Crossing was opened after an extensive testing and training program with

2 the water mist system that is installed in the tunnel. Within Europe more than 35 km of tunnel are equipped with FFFS but these systems can be seen in most cases as ad-on safety measure. They were installed to increase the level of safety but were not required according to rules or standards. Referring to the opinion of many experts the benefits of these systems are obvious. According to the work of several research projects, e.g. UPTUN or SOLIT, the main aims of these systems are [1]: Protect the tunnel structure and minimize the damages on the tunnel Hampering fire spread to adjacent objects, e.g. other trucks Facilitate the work of the rescue services Improvement of the self-rescue conditions for people inside the tunnel Figure 1: Spray test with a water mist system in the New Tyne Crossing The layout basis for all systems are full scale fire tests with severe truck fire loads as it were used during the SOLIT research project or e.g. for the New Tyne Crossing General recommendations for the system layout and minimum technical requirements can be found in the UPTUN guidance R251 [2] as well as in the latest version of the NFPA 502. Also PIARC recently published some recommendations for FFFS in tunnels [3]. 3. COMPENSATION OF SAFETY MEASURES 3.1. GENERAL In general, compensation describes the possibility to achieve the same effect by using different methods. Looking at safety concepts for road tunnels and other underground facilities the way how safety systems are designed is changing more and more from a prescriptive based methodology by simply applying standards and fixed rules to a more performance based approach. This development leads to a much higher flexibility in design but gives also higher responsibility and requirements for the design process. Furthermore, with a performance based approach it is possible to also customize safety systems to the special risks that can be found in the specific tunnel or building.

3 More complex underground structures and complex tunnel systems but also higher requirements on safety increased the costs for safety systems and in particular fire fighting systems during the last years. When it comes to refurbishment of existing tunnels, an upgrade of safety systems is often technical extensive or even impossible, but in most cases extremely expensive. In buildings the compensation of structural fire protection measures where the implementation is difficult technical, expensive or against design aspects is common practise. The idea of compensatory effects can be summarized as increasing the level of safety with same costs or keep the equal level of safety with same costs.. Safety level Increasing Safety Level same costs Todays accepted safety measures (prescriptive) Same Safety Level less costs Costs of the safety system Figure 2: Correlation between the safety level and the costs of a safety system [4] In the following chapters, possible compensation methods are described. The effects are based on the SOLIT² full scale fire test program which was carried out in summer STRUCTURAL FIRE PROTECTION Real fire accidents in tunnels showed that within a short period of time, high temperatures up to 1200 C might occur. This also reflects in the standard time-temperature curves for testing material such as the RWS-curve or the ZTV-Ing-curve. Applying these temperatures over a long period of time on structural elements, this will lead to extreme damages which might also risk the stability of such structural elements. In any case the repair works that are necessary after fires, even smaller ones, are extensive, time consuming and expensive. One of the major effects of FFFS in tunnels is the cooling of the environment. Compared to standard deluge or foam systems, water mist systems are having a much higher cooling potential. Even if the fire size is not reduced by the FFFS, as most fires are inside the compartments or covered, the temperature level inside the tunnel is reduced significantly. The effects of water mist systems regarding temperature management can be summarized as follows:

4 The zone of higher temperatures (> 200 C) is limited only to the fire source itself. Usually the spread of the fire is also hampered so that the fire zone can be limited to the initial vehicle. - Directly above the fire load inside the flame zone (e.g. for truck fires if the load is burning), in some small areas temperatures of C may occur. These temperatures were only observed locally and for a short period of time. Using the results of specific FFFS from real full scale fire tests with representative fire loads, the time-temperature curves which defines the requirements for structural elements can be modifies. The absolute height of the temperature is reduced, the radiant heat impacting structural elements is significantly less and the exposure time is much shorter than in standard time-temperature curves. Basically, this means that the requirements on passive fire protection linings or boards are reduced significantly or they can be even avoided. Moreover, the repair works on the concrete structure of tunnels in case of incidents is also much less VENTILATION Already during the fire tests within the UPTUN and SOLIT projects the positive effect of FFFS on the ventilation where observed. During the SOLIT² fire tests program the effects of Abbildung Figure 1: Smoke 3: Smoke Lyer layer shortly after ignition and after activation of the FFFS various FFFS on the ventilation program were evaluated. For this purpose, pool fires with sizes of 30, 60 and 100 MW were used as the smoke production is extremely high and smoke

5 management effects can be studied. For the ventilation a longitudinal ventilation system as well as a semi-transversal ventilation system was used. The systems were calculated dimensioned to be effective for fires of 30 MW which means that the longitudinal ventilation systems avoids back-layering and the semi-transversal system should keep a smoke free layer of at least 2 m. During free burning tests it turned out that the semi-transversal ventilation system, although designed correctly and working in normal mode, was hardly able to keep the smoke free layer. It should be taken into account that the conditions in the test tunnel were almost ideal as there were no obstacles or any other situations that my effect the smoke layer negatively. During the fire tests with FFFS it turned out that in combination with activating the FFFS the same effectiveness of the ventilation and smoke extraction system can be achieved with a 100 MW fire. That means that the longitudinal air velocity designed for a free burning 30 MW fire was able to prevent back-layering for a 100 MW fire in combination with a FFFS. For the semi-transversal ventilation system an analogue effect was observed. Although the SOLIT² consortium is still evaluating the test data, these positive effects are most likely based on the enormous cooling effect of the water mist and therefore a volume reduction of the smoke. Of course, there is an interaction of the smoke layer and the activated FFFS. In the area where the FFFS is activated, there is a mixture of smoke and the water mist and therefore the smoke layering is partly disturbed. But, as described before, it is a question of future research and studies if a smoke free area as intended can be created in case of real bigger fires. The reduction of visibility in the area of the activated FFFS was not considered as a problem as it is still enough to orientate and to find illuminated exits signs. 4. FURTHER EFFECTS The chapters before are describing the main effects regarding compensation of elements of the tunnel safety system by using FFFS. Applying FFFS in a tunnel of course give further beneficial effects. Due to the significantly reduced temperatures and because fire spread is reduced, damages in the tunnel are also reduced. This further leads to a significantly reduced down time in case of an incident as well as reduced costs for the repair works. A major beneficial effect can be seen for the fire brigades. An active FFFS allows fire brigades to enter the fire zone quickly and with a very limited risk compared to a free burning fire. In no case during more than 100 large scale fire test steam production that might cause a risk were reported, although the fire men were in a distance to the fire of less than 5 m. As soon as the fire brigade is close to the fire zone, the fire can be extinguished quickly. This also leads to an enormous reduction in damages to the tunnel. 5. REQUIREMENTS AND PROCEDURES The performance based approach of designing and effective safety systems for tunnels and underground stations is always based on a profound risk analysis. After that it is up to the designer to combine the various safety measures to create a holistic safety system for each specific tunnel or underground facility. Depending on the special requirements and conditions it might be beneficial to compensate well accepted safety measures as described above.

6 However, it is always essential to proof the effectiveness of the new combination of measures to show, that at least a same level of safety can be achieved with the new safety system. Of course this procedure must be well documented and approved by independent bodies. In particular if technical systems are used as safety systems, it should be ensured that these systems have an acceptable reliability. This not only should apply for FFFS but also for all other technical systems acting as safety systems in a tunnel, such as ventilation, communication and data transfer. For such systems RAMS analysis as well as SIL levels should be applied. 6. OUTLOOK The SOLIT² research program ends in spring As part of the work of the consortium a technical engineering guidance will be produced to explain the procedures during compensation of elements of tunnel safety systems. The SOLIT² engineering guidance will also include minimum requirements on the performance of FFFS as well as on the reliability, maintainability and safety of technical elements. Furthermore it will give advice how life cycle costs are correctly evaluated for various combinations of elements of the tunnel safety system. This is essential to not only evaluate various technical solutions based on their efficiency but also on costs. This document will be public available in summer REFERENCES [1] Kratzmeir S, Starke H. (2007); SOLIT Safety of Life in Tunnels Forschungsbericht. [2] UPTUN (2005); UPTUN R251 Guidance for water based fire fighting systems for sub-surface facilities. [3] PIARC (2008): Road Tunnels: Assessment of Fixed Fire Fighting Systems. ISBN [4] Kratzmeir S, (2008); Substitution. Promising results challenge for the future. IWMA/COSUF conference on Fire Suppression in Tunnels 2/ Munich