Ventilation in Tunnels Fires in the UK - Literature review Example

Ventilation in tunnel fires Name Institution Instructor Date Abstract Ventilation in tunnels fires has taken a dynamic facet in the manner in which fires could be handled in tunnels. This has called for a proactive action in the European nations more so, in the UK to come up with strategies that would ensure the risks have been reduced. There have been setbacks that have promoted catastrophic actions. These are attributed to poor designs which primarily rely on simple fire actions scenarios rather than, the actual occurrence of such incidences. Both the experimental and numerical studies have been conducted in order to ascertain the extent in which the action of ventilation of fire in tunnels takes place. Simulator models are used in the numerical studies whereas the experimental studies give the computational dynamics of the fluid model of the initial and the boundary conditions. Furthermore the studies indicate that, back layering does not necessary occur at cases which are simulated meaning that, the ventilation strategies used are more efficient in eliminating smoke out of the tunnel. Apparently, studying in the manner that, back layering takes place would enhance the manner in which evacuation would be handled. The evacuation systems in the tunnels are still the main safety systems that may be used to control the amount of smoke and provide proper means in which evacuation may take place. This paper gives a critical review of the related literature on ventilation tunnel fires with regards to UK standards. Key words: Back layering, critical ventilation velocity, smoke, tunnel fire Introduction A number of accidental fires have been experienced in recent years in UK in several rail and road tunnels globally. Many of these fires have grown rapidly to disastrous situation and have claimed many lives. During the action of ventilating the tunnel fires, it is apparent that some hot products such as smoke and fire emanate from combustion as noted by Carvel and Beard (2004). The trend tends to flow in the opposite direction which forms a challenging basis in the manner in which the evacuation of underground processes and fire fighting methods may be conducted. Such actions have been studied by the critical ventilation velocity that is capable of simulating on the reverse layers that are formed (Sabaei, 2006). This has called for a lot of literature on matters concerned with ventilation of tunnel fires. In scenario where there is an unventilated tunnel, the hot air that arises from combustion would lead to the formation of plume due to the entrainment of the nearby cold air that has a different velocity as compared to the surrounding hot air. As argued by Chen (2003), ventilating the tunnel ensures that, the stream that exists between the ceiling and the plume that is rising by back layering. The cause of these fires and their rapid growth are yet to be adequately understood. This paper review describes number of these accidents and analyzes experimental research that has caused the tunnel fire behaviour. Detailed review of methodology and analysis of results of fire dynamics have been presented. In different analysis it was found that, the rate of heat release of heavy vehicles fire can be increased greatly by longitudinal ventilation, e.g. by almost a factor of five having longitudinal velocity of about 3ms. Ventilation causes great increase in the heat rate of large fires, but can cause decrease in rate of heat release of the small car and pool fires. The analysis has found that, the rate of heat release varies with the tunnel width and fire object width. Geometry of the tunnel can also increase the rate of heat release significantly. In recent years there has been an increase need of improving transport network causing an increased rate of construction of tunnels. Advancement in engineering has ensured that tunnels constructed are longer than 50km such as the Totley, Disley, wood head and Standege tunnels. A critical review of `The influence of tunnel geometry and ventilation on heat release rate of fire, by Richard Oswald Carvel and Beard, A. 2004 This paper gives an overview of the influence of the longitudinal ventilation on the size of the fire in tunnels and the tunnel geometry influence on the size of the fire. The author utilizes discrete methodology to split span of possible values of k, which is a variable used in describing the effect that ventilation have on the size of the fire to a number of ranges. Bayesian method was used in the study to aid decision based on limited information because it is scientifically sound and is adaptable in different situations (Carvel and Beard, 2004). It was also used to refine probability estimates based on different experimental data sets. This technique is used because it gives an approximate understanding of longitudinal ventilation on fires in tunnels. The author employed the Bayesian methodology aids in estimating estimate particular tunnel size. The results from the experiment gave the perfect tunnel configuration. Prior probability distributions were devised based Bayes’ postulate and the estimates of the panel experts in fire safety engineering fields. This study found that fires that occurred inside tunnels burned with much heat release than fire in open air. Rate of heat release of some fires were observed to be much greater than similar fires in open air. Bayesian methodology predicted geometrical factor with great influence on degree of the rate of heat release enhancement. Distance from the walls of the tunnel to the fire object had much influence on the rate of heat release for fires in the tunnel. Rate of heat release enhancement, width of the tunnel and the fire width were related according to an equation shown below. Ø=24 Where WF= the width of object fire; WT=the tunnel width while ø = the ratio of the rate of heat release in a tunnel outside of a tunnel. Results from this study were used to build mathematical description of different processes used in tunnel fires. Many equations presented were derived from observation empirically from experimental fire tests which attest with those derived by Colella and Rein (2011). In conclusion the equations were used to predict aspects associated with fire behaviour under different circumstances. Moreover, the results from experimental fires test carried out in tunnels were used as evidence useful in enhancing or reduce different hypothesis related to this influences. A critical review of `Tunnel Fire Protection’ as noted in NFPA 502 bridges This paper was based on NFPA 502 bridges, road tunnels and limited access highway standards 2004 edition. The aim of this paper was prepared was to provide conversion document from standards to practical systems tested in the fire safety research laboratories. This enables the engineers and designers to select the best fire solution that is suitable to their project. Method used in this paper is based on selection of different tested prompt constructions. To meet the requirement of the methodology, the paper point’s outs that the department should be contacted further for more comprehensive information on this field as noted in NFPA (2008). The research based on this paper was undertaken in both real laboratory conditions and disused tunnels. As a result of the data obtained from different tests, series of temperature/time curves for diverse exposure was developed. This study found out that different standard fire test for which various specimen of construction are based on, exposure is founded on temperature/cellulosic curve defined in different national standards such as, ISO 834, ASTM, DIN 4102 and AS 1530 (Choi, 2005). The study found out that the curve presented was based on the rate of burning in general construction materials and contents of the tunnel. Different factors influenced the design of the tunnel as presented. Duct functionality when the duct is being used as an air duct to supply fresh air. The design of the duct should be in such a way that it maintains its functionality when exposed to fire for in and outside the tunnel. System integrity and thermal insulation must be maintained at all times during incidences of fire in the tunnel. Installation of the duct for extraction of smoke should be designed in such a way that, it has capability of coping with elevated temperatures in the duct to ensure that system integrity is maintained throughout the duration of fire exposure. A critical review of `Fire Development and Critical Velocity’ by Wu, Y at Sheffield University in UK The aim of this paper was to examine the combustion characteristics of different fire zones under ventilation condition by establishing fundamentals changes on the status in which fire burns when the rate of heat release is at critical level. The paper is build based on combustion theory to analyze fire development under ventilation. The methodology used in this study was based on semi-empirical equations that were obtained from Froude Number preservation together with experimental data. Though, these methods gave effective and simple semi-empirical solutions essential in determining critical velocity, Froude number modelling could not explain the reason why there was super critical velocity. Relationship between fire development and critical velocity were analyzed in this paper by proper examination of the status of fire burning. Aerodynamic and combustion theory were developed to analyze different stages of fire development in order to reveal changes in physical conditions that could result to correlation between rate of heat release and critical ventilation velocity. Plume theory was used to explain super critical velocity. This theory was extended to provide a description of fire plume in tunnels. The results from this study shows that plume theory can be used to show that critical velocity is interlinked with development of fire in tunnels. Development of inside the tunnel was found to be controlled through fuel-controlled mode or ventilation controlled mode. Results from CFD simulation showed that at low rate of heat release, there is a very high level of oxygen level in downstream exit while the oxygen level drops significantly in combustion zone. Results from this paper also indicates that the average level of oxygen decreases as the rate of heat release increases, causing large area of the zero oxygen level in combustion zone leading to elongation of the frame showing absence of excess air in combustion zone. A critical review of `Design of Tunnel ventilations for fire emergencies’ by G. Rein, F. Colella, R. Borchiellini, V. Verda, R. Carvel, T. Steinways and J. L. Torero March 2010 The paper presented a fast modelling approach essential in simulation of tunnel ventilation flows in the event of fire emergencies. The authors have given a high cost of computational fluid dynamics; inaccuracies of simplistic zone and complexity in the models were avoided by effective combination of CFD (3D) and mono dimension (1D) modelling techniques as noted by Colella and Rein (2010). The multi-scale method was used to simulate systems for tunnel ventilations such as vertical shafts, jet fans and portal. It was used in this presentation to take into account effects of the fire in transient and in steady state. The authors have applied the methodology by analyzing the tunnel of about 7m in diameter and about 1.2km in length. The paper has analyzed different scenarios with varying number of operating jet fans. It is evident that, the authors applied a more efficient method of Bernoulli formula in the generation of the 1D network. This was designed to account for transient fluid phenomenon, effects of buoyancy and thermal phenomenon. Their main reason was handle complexity in typical layout of the modern tunnels ventilation systems based on topological representation. CFD modelling was done using commercial code FLUENT. The two ventilation scenarios that were considered in this paper based on time dependent simulation. The fire growth curve was designed characterized by a slow rate of growth, followed by a higher rate of fire growth (Choi, 2005). Results from this study shows that subcritical ventilation conditions must be properly chosen in order to capture all back-layering with CFD domain. Through time dependent calculations, fire effluents were found to form long back layering at early stages but was contained in CFD domain. A critical review of ` The fire growth rate in a ventilated tunnel fire’ by Li, Y. and Ingason, H., 2011 This paper aims to prepare a bridge the gap between techniques and knowledge regarding tunnel fire safety. It covers knowledge and consistency in various fields trying to prevent occurrence of fire in tunnels. The authors have employed the methodology that ranges from hard methodology whereby, there is agreement between actors to soft systems methodologies. In hard methodology considerable knowledge was used in decision making process. This method proceeded from problem presented to solution in orderly manner. Though, these approaches were suitable for different situations, it was not suitable in the tunnel fire safety. Essential features in the soft system approach showed existence of different views among those involved and due to lack of reliable knowledge system. Essentially, between the soft and hard spectrum methodologies is the intermediate methodology. Intermediate methodology was used in decision making in tunnel fire safety methods (Li and Ingason, 2011). This method contained iteration loop which does not depend on time and effort in different stages. Based on the developed methodology, risk based approach was a necessity in constructing models related to tunnel fires. The results from this study showed that fire risk in tunnel is mostly due the work of different systems that involve operation, design, and tunnel use and emergency response involving designed and none designed parts which were also supported by Kunsch (2002). Designed part took account of non designed part. The analysis found out that what need to be regarded as satisfactory ranges of risk of fire with regard to property loss, fatality and disruption should be based on what ought to be regarded as acceptable for upgraded tunnel range. There was a need of an overarching probabilistic framework, within deterministic and probabilistic model. A critical review of ` Calculation and design of tunnel ventilation systems using a two-scale modelling approach’ by Borchiellini, R. Carvel, R., Torero, L., Verda V., 2009. This paper was prepared by with a major aim of evaluating tunnel ventilation system in controlling spread of smoke in time of emergency to provide condition for evacuation simulation in double tube tunnel. Numerical Model was used in calculating temperature and flow fields, that is, smoke concentration in the event of fire inside tunnel space using CFD software package. According to assumed physical situation, high length of the tunnel and certain identical segment was used to develop a 3 dimension space model for three geometrically diverse tunnel segments. This technique seems to give an accurate evacuation time in the tunnel. The basic geometrical differences showed the distances between evacuation and ventilators hallways. Cars were generated in the tunnel virtual space away from the evacuation hallway. Amount of heat released was defined according to PIRAC recommendation. Mathematical Model was used in calculating temperature and flow field of air within the tunnel. Equation k-e turbulent model was used in the analysis. Universal turbulent model was used because of its reliability in predicting flow fields (Borchiellini, Carvel, Torero, Verda, 2009). Four basic balanced equations were used in describing a non-stationary incompressible flow of the fluid for control volume. The results from this study concluded that apart from mutual distance from an axial ventilator from evacuation opening, there was a great difference when the distance in an axial ventilator was formed in an evacuation opening. When the ventilation system worked on maximum rate of flow in tunnel ventilation, smoke and combustion products could not be able to penetrate evacuation hallway in case fire is caused by passenger vehicles. Maximum air velocities in this paper were reached in the zone that was most required. In conclusion, the ventilation system was found to operate at a maximum rate of flow that was designed in the tunnel ventilation. To prevent smoke penetration, it was a requirement to increases the rate of airflow in the ventilators. By analysis of the obtained results it was realized that velocity obtained through numerical simulation were 20% lower than those recommended by PIRAC. This was a suitable technique in ascertaining the flow of tunnel ventilation. A critical review of ` Critical velocity and burning rate in pool fire during longitudinal ventilation’ by Roh, J., Ryou, H. and Kim, D., 2007 This paper aims at addressing the types of sprinkler systems, types of tunnel ventilating systems and their influences in achieving fire emergency goals. The paper also covered new design challenges in the current fire prevention systems in achieving tenable environment for occupancy evacuation. The author employed the methodology that was based on analysis of tunnel ventilation systems as a tunnel fire safety system that can be used to provide tenable environment solution and system that can be used to control smoke in the event of fire. Illustration of common ventilation and FFSS benefits have been adequately presented in supporting fire fighting procedures and providing a system of cooling down of the tunnel in the event of fire (Roh, Ryou and Kim, 2007). Analysis of fixed suppression was carried out in this paper to present method that could be used support early evacuation, activate after evacuation strategies and support property protection. From the experiment, the results from this study shows that, there are many benefits associated with tunnel ventilation, which includes; control of smoke and gases, provision of tenable evacuation solution, cooling down of the tunnel in the event of fire and supporting fire fighting procedures. Though there are many advantages associated with tunnel ventilation presented in this study, there are some main concerns that arose this are tunnel ventilation significantly increases the rate of fire growth and supports further spread of fire. A critical review of ` Critical ventilation velocity for tunnel fires occurring near tunnel exits by Tsai, K., Yee-Ping, L. and Shin-Ku, L., 2001. The main aim of this paper was on large scale fire tests of rate of heat release, gas concentration, temperature, smoke, velocities and radiations. Different methods were used in this study and includes; Extrapolation of different values of different tests on tunnel conditions Measurement of different parameters like loss rate and the rate of fuel flow Calorimetric method was used to calculate rate of heat release due to the fact that common fuels most of time releases about the same energy amount per Oxygen consumed. Method used by carvel was used because of its ability to estimate different probabilities based on very little information. Observed periods of oscillations in this paper were explained using acoustic approach and frequency analysis approach based on impedance analysis. Result from this study showed that non-hazardous cargo show different rate of heat release and the temperature mainly related to hazardous goods. Highest rate of heat release and gas temperature are presented as being higher than those in guidelines of fire design. Close correlation was presented between maximum rate of heat release and energy content in passengers cars. The paper has also used Runehamar test to show that fire in HGV can be spread about a distance of 100m downstream in a tunnel (Tsai, K., Yee-Ping and Shin-Ku, 2001). Based on different test results it was emphasized that incident operations during the initial outbreak of fire is very important. A critical review of `Smoke and Fire Control in Road Tunnels’ by Ahmed Kashef Lougheed, G. Bénichou, N. And Debs, A., 2005 This paper aims to analyze and evaluate effectiveness of emergency ventilations to control smoke and fire in the road tunnels. The study was carried out to validate operation instructions based on experimental and numerical studies. Numerical studies used dynamic simulators to investigate fire and smoke models for ventilation in tunnels. Experimental study was used to give initial conditions for computational fluid dynamics model. The authors employed the experimental methodology in this study by carrying out a research at National Research Council in evaluating performance in case of fire experimental and numerical approach. This article is based on parameters that were performed using 20mW heat source in the tunnel (Kashef, Lougheed, Bénichou, and Debs, 2005). Fire test and airflow measurement were undertaken in North Roadway La-fontanel tunnel to establish ventilation scenarios. Test fires were carried out using propane burner system concluding that the measured data helps to control temperatures producing enough airflow velocity. From the experiment, it is evident that the results presented in the paper showed that numerical analysis on phenomenon occurring in simulated cases and when ventilation strategies are effective in clearing fire and smoke from the tunnel. It also gives recommendation on improving performance of strategies and increased level of safety used as evacuation means. The results also show that, there is a need to introduce configuration change on the side vent dampers (Choi, 2005). The four cases that were investigated examined capacity of fans VA201, VA103 and percentage opening in lower and upper side vent. A critical review of ` Fire dynamics simulator. Simulation for tunnel fire scenarios with forced, transient, longitudinal ventilation flows’ by Kim, E., Dambsey, N. And Woycheese, J., 2008 The aim of this paper was to review requirements on ventilation during the road tunnel emergencies and provided recommendation on how limited grade separation and how it can be amended in the light of current knowledge. The experimental methodology in this study was used to determine design scenarios based on risk. In the quantitative risk assessment (QRA) taken, design was based on return periods within design life (Kim, Dambsey, and Woycheese, 2008). Three basic methods were used to provide longitudinal ventilation Injectors that direct jets in the tunnel Jet fans that are mounted along tunnel crown Push-pull axial arrangement fans in the chambers. The results in this study entailed actual tunnel fire incidents and vehicle fire tests. This paper showed that fires sizes in major tunnels are larger than fire used in design purposes. Results suggest that tunnel ventilation may sometimes take longer to clear smoke and dense gas from the tunnel and thus rapid detection and an emergence response is a requirement. Results indicate specification of the minimum capacity of exhaust per lane meter is not enough by its own and thus location of extract and the size of the extract openings must be addressed for effective smoke control. References Avillo, A., 2002 Fireground strategies: Fire engineering. Tulsa, OK: Penn Well. Azuma T, Gunki S, Ichikawa, A. and Yokota. M., 2004. Effectiveness of a flame sensing type fire detector in a large tunnel. Marseilles. Borchiellini, R. Carvel, R., Torero, L., Verda V., 2009. Calculation and design of tunnel ventilation systems using a two-scale modelling approach. Journal of building and environment, 44(3), pp.2357-2367. Carvel, O., and Beard, A., 2004. "The influence of tunnel geometry and ventilation on the heat release rate of a fire." Fire technology, 40(1), pp. 5-26. Chen. F. 2003. "Smoke control of fires in subway stations "Theoretical and computational fluid dynamics." Theoretical and computation Fluid Dynamics 16:349-368. Choi, S., 2005. "Experimental investigation on smoke propagation in a transversely ventilated tunnel." Journal of fire sciences, 23(6), pp.469-483. Chow, K. and Ng, M., 2003. "Review on fire safety objectives and application for airport terminals." ASCE Journal of Architectural Engineering 9{2).pp.47-54. Colella, F., and Rein, G., 2011. "Time-dependent multiscale simulations of fire in longitudinally ventilated tunnels." Fire safety science, 10(2), pp.359-372. Fire Engineering, 2003. CIBSE Guide. London: CIBSE. Harvey, N., and Fuster, T., 2009. Design fire heat release rate selection – Impacts for road tunnels. New Jersey: BHR Group. Kashef, A., Lougheed, G. Bénichou, N. And Debs, A., 2005. Investigation of effectiveness of emergency ventilation strategies in the event of fires in road tunnels. ASHRAE Transactions 11(1), pp.1-14. Kim, E., Dambsey, N. And Woycheese, J., 2008. Fire dynamics simulator. Simulation for tunnel fire scenarios with forced, transient, longitudinal ventilation flows. New York: Worcester polytechnic institute. Kim, J., Sung-Wook,Y. and Ji-Oh Y., 2006. "A study on the smoke control characteristic of the longitudinally ventilated tunnel fire using PIV." Tunnelling and underground space technology, 21(3), pp.302. Kunsch, J., 2002. ‘‘Simple Model for Control of Fire Gases in a Ventilated Tunnel’’, Fire Safety Journal, vol. 37(2), pp.67–81. Li, Y. and Ingason, H., 2011. "The fire growth rate in a ventilated tunnel fire." Fire safety science, 10(3)347-258. NFPA, 2008. NFPA 502 Standard for Road tunnels, Bridges, and Other Limited Access Highways. London: Quincy. Roh, J., Ryou, H. and Kim, D., 2007. "Critical velocity and burning rate in pool fire during longitudinal ventilation." Tunnelling and underground space technology, 22(3), pp.262-271. Sabaei, J., 2006. Fire Engineering: Prevention, protection and suppression of building fires. Tsai, K., Yee-Ping, L. and Shin-Ku, L., 2001. "Critical ventilation velocity for tunnel fires occurring near tunnel exits." Fire safety journal. Wu, Y.2003. Smoke control in tunnels with slope using longitudinal ventilation effect of tunnel slopeon critical velocity. Luzern. Read More

Geometry of the tunnel can also increase the rate of heat release significantly. In recent years there has been an increase need of improving transport network causing an increased rate of construction of tunnels. Advancement in engineering has ensured that tunnels constructed are longer than 50km such as the Totley, Disley, wood head and Standege tunnels. A critical review of `The influence of tunnel geometry and ventilation on heat release rate of fire, by Richard Oswald Carvel and Beard, A.

2004 This paper gives an overview of the influence of the longitudinal ventilation on the size of the fire in tunnels and the tunnel geometry influence on the size of the fire. The author utilizes discrete methodology to split span of possible values of k, which is a variable used in describing the effect that ventilation have on the size of the fire to a number of ranges. Bayesian method was used in the study to aid decision based on limited information because it is scientifically sound and is adaptable in different situations (Carvel and Beard, 2004).

It was also used to refine probability estimates based on different experimental data sets. This technique is used because it gives an approximate understanding of longitudinal ventilation on fires in tunnels. The author employed the Bayesian methodology aids in estimating estimate particular tunnel size. The results from the experiment gave the perfect tunnel configuration. Prior probability distributions were devised based Bayes’ postulate and the estimates of the panel experts in fire safety engineering fields.

This study found that fires that occurred inside tunnels burned with much heat release than fire in open air. Rate of heat release of some fires were observed to be much greater than similar fires in open air. Bayesian methodology predicted geometrical factor with great influence on degree of the rate of heat release enhancement. Distance from the walls of the tunnel to the fire object had much influence on the rate of heat release for fires in the tunnel. Rate of heat release enhancement, width of the tunnel and the fire width were related according to an equation shown below.

Ø=24 Where WF= the width of object fire; WT=the tunnel width while ø = the ratio of the rate of heat release in a tunnel outside of a tunnel. Results from this study were used to build mathematical description of different processes used in tunnel fires. Many equations presented were derived from observation empirically from experimental fire tests which attest with those derived by Colella and Rein (2011). In conclusion the equations were used to predict aspects associated with fire behaviour under different circumstances.

Moreover, the results from experimental fires test carried out in tunnels were used as evidence useful in enhancing or reduce different hypothesis related to this influences. A critical review of `Tunnel Fire Protection’ as noted in NFPA 502 bridges This paper was based on NFPA 502 bridges, road tunnels and limited access highway standards 2004 edition. The aim of this paper was prepared was to provide conversion document from standards to practical systems tested in the fire safety research laboratories.

This enables the engineers and designers to select the best fire solution that is suitable to their project. Method used in this paper is based on selection of different tested prompt constructions. To meet the requirement of the methodology, the paper point’s outs that the department should be contacted further for more comprehensive information on this field as noted in NFPA (2008). The research based on this paper was undertaken in both real laboratory conditions and disused tunnels. As a result of the data obtained from different tests, series of temperature/time curves for diverse exposure was developed.

This study found out that different standard fire test for which various specimen of construction are based on, exposure is founded on temperature/cellulosic curve defined in different national standards such as, ISO 834, ASTM, DIN 4102 and AS 1530 (Choi, 2005).

Read More