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2015 | Buch

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Tunnel Fire Dynamics

verfasst von: Haukur Ingason, Ying Zhen Li, Anders Lönnermark

Verlag: Springer New York

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

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Über dieses Buch

This book covers a wide range of issues in fire safety engineering in tunnels, describes the phenomena related to tunnel fire dynamics, presents state-of-the-art research, and gives detailed solutions to these major issues. Examples for calculations are provided. The aim is to significantly improve the understanding of fire safety engineering in tunnels. Chapters on fuel and ventilation control, combustion products, gas temperatures, heat fluxes, smoke stratification, visibility, tenability, design fire curves, heat release, fire suppression and detection, CFD modeling, and scaling techniques all equip readers to create their own fire safety plans for tunnels. This book should be purchased by any engineer or public official with responsibility for tunnels. It would also be of interest to many fire protection engineers as an application of evolving technical principles of fire safety.

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Inhaltsverzeichnis

Frontmatter

1. Introduction

Abstract

An introduction to the main differences between open fires, building fires and tunnel fires is given as the basis for better insight into the physics of fires in tunnels. An overview is given of what type of fires is to be expected in different types of tunnels and what consequences such fires may have. A short description of mitigation systems commonly used to increase the fire safety in tunnels is also given and their main features are put into the context of fire dynamics. Finally, the major fire incidents that have occurred are summarized and analysed in order to understand the main reasons for their different consequences.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

2. Fuel and Ventilation Controlled Fires

Abstract

The effect of ventilation on fire development is one of the most important phenomena to understand in tunnel fire safety engineering. Ventilation controls the combustion process and is usually the phenomenon that engineers find most difficult to comprehend. Tunnel fires are considerably different from compartment fires in the way flashover occurs and develops; misconceptions about the effects of ventilation in tunnel fires are clarified in this chapter. The difference between fuel-controlled fires and ventilation-controlled fires is shown and explained. This chapter lays out the basics for understanding the role of ventilation interactions with other combustion phenomena and in fire development. This chapter is based partly on theory, but also includes experimental data obtained by the authors.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

3. Tunnel Fire Tests

Abstract

This chapter gives a detailed overview of numerous large-scale fire tests carried out in different types of tunnels. Some important model scale tunnel fire tests are also included. The information given, sets the level of knowledge from this type of tunnel fire testing. The reason for doing tests is to obtain new knowledge about different phenomena. Although the focus is on large-scale testing, the fundamental knowledge is obtained both from large-scale and intermediate size tunnel testing as well as laboratory testing (For example, scale models). The aim is usually to investigate some specific problems such as influence of different ventilation systems on smoke and temperature distribution along the tunnel, the fire development in different type of vehicles, and the effect of heat exposure on the integrity and strength of the tunnel construction.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

4. Heat Release Rates in Tunnels

Abstract

An overview of heat release rates (HRRs) for different vehicles driving through tunnels is presented. The focus is on understanding fire development and the influences of tunnel conditions on the HRR. The HRR describes the fire development in the form of energy release given in megawatts (MW) over a given time period. The chapter presents the basic theory of burning of fuels and summarizes the HRR for different types of vehicles, solid materials, and liquids. Influences of different physical parameters such as tunnel construction or ventilation on the HRR are addressed. The HRR is also given as a value per square metre of exposed fuel surface area.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

5. Fire Growth Rates in Tunnels

Abstract

An overview of fire growth rates (FGR) for different vehicles travelling through tunnels is presented. The emphasis is on understanding the governing physics of fire growth rates. This includes ignition sources, geometry and type of the fuel, and the effects of the longitudinal ventilation flow. The FGR related parameters are decisive for tunnel fire safety. It dictates how fast the fire in different materials develops and influences the situation inside a tunnel in very different ways. The chapter gives a good understanding of the main mechanism behind the FGR of different types of vehicles and different solid materials. The effects of windbreaks on the FGR are explored.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

6. Design Fire Curves

Abstract

An overview of design fires in tunnels is given. Design fires are obtained from guidelines or standards, or exclusively for a specific tunnel project. They can be represented as a single constant design value or as a time dependent fire curve, either given in form of heat release rates (HRRs), temperatures or combustion products. Various ways exists to represent a design fire curve for tunnels. These can include different growth rates or combinations of growth rates with constant levels of design maximum values coupled to a decay period. The different type of design fire curves are put into the context of fire development in vehicles and tunnel fire dynamics. Mathematical representations of design fire curves are presented and discussed. An example of a new concept for creating a design fire curve is presented.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

7. Combustion Products from Fires

Abstract

Knowledge of the different species produced during fires is of great importance for estimating the toxicity of the fire gases. In this chapter the main combustion products from different types of fires are presented. This includes carbon monoxide (CO), carbon dioxide (CO₂), hydrogen chloride (HCl), sulphur dioxide (SO₂), volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs), total amount of hydrocarbons (THC) and soot/smoke, but yields also for some other species are presented. Results from measurement during fire tests in vehicles and tunnels are summarized and discussed. The importance of the ventilation conditions (equivalence ratio) on the productions of different species is described and relations for different yields and ratios are given and discussed.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

8. Gas Temperatures

Abstract

Gas temperature is of great importance for assessment of heat exposure to tunnel users and tunnel structures, estimation of fire detection time and possibility of fire spread, and to design ventilation systems. In this chapter, the theory of fire plumes in ventilated flows is presented with a focus on the maximum ceiling gas temperature and its position in tunnel fires. The maximum ceiling excess gas temperature can be classified into two regions, depending on the ventilation velocity. Each can be divided into two subregions. The first subregion exhibits a linear increase which transits into a constant period, depending on the fire size, ventilation, and effective tunnel height. The position of the maximum ceiling gas temperature is directly related to a dimensionless ventilation velocity. A theoretical analysis of the upper smoke layer is presented and correlations for the distribution of ceiling gas temperature along the tunnel are given to support this analysis. Finally, a one-dimensional model of average gas temperatures in tunnel fires with longitudinal ventilation is presented.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

9. Flame Length

Abstract

In a large tunnel fire, the flame impinges on the ceiling and then extends along the tunnel ceiling. When the longitudinal ventilation rate is high, flames only exist on the downstream side of the fire source, while under low ventilation rate, flames exist both upstream and downstream of the fire source. In a large tunnel fire the horizontal distance between the fire source and the flame tip is defined as a flame length. A theoretical model of flame length in a large tunnel fire is proposed in this chapter. A large amount of data relevant to the flame length from model- and large-scale tunnel fire tests are used to verify the model. The results show that the downstream flame length increases approximately linearly with the heat release rate (HRR) but is insensitive to the longitudinal ventilation velocity. The flame length under high ventilation rate approximately equals the downstream flame length under low ventilation rate. As the longitudinal ventilation velocity decreases, the upstream flame length increases and so does the total flame length. Dimensionless equations that correlate well with test data are proposed.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

10. Heat Flux and Thermal Resistance

Abstract

Heat flux is a major issue that must be considered for evacuation, fire spread, and structure protection in tunnel fires. The three heat transfer mechanisms: convective, radiative, and conductive heat transfer are described with a focus on correlations related to tunnel fires. The Reynolds–Colburn analogy is introduced as a basis for calculation of convective heat transfer. Characteristics of the absorbing, emitting, and scattering gases are summarized, together with radiation between multiple surfaces. Analytical solutions for heat conduction into tunnel walls are summarized for different types of simplified boundary conditions. The overall heat transfer from flames and gases to the tunnel structure involves all three heat transfer mechanisms; their correlations are illustrated using an electrical circuit analog. Simple models for calculating heat flux in small and large tunnel fires are presented with a focus on radiation. Correlations for incident heat flux are proposed and verified for small and large fires in tunnels, taking radiation from both flames and smoke into account.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

11. Fire Spread

Abstract

Fire spread is a very important issue during fires in tunnels. The elongated geometry of a tunnel with a relatively low ceiling height makes the flames and hot gases follow the ceiling over long distances, increasing the risk for fire spread. The use of ventilation in the tunnel as well as different types of vehicles, commodities, and materials influences the fire spread. This chapter contains both a summary of traditional ignition and fire spread theory and experiences especially related to situations in tunnels with risk for fire spread. Different aspects of spread and burning of liquids are presented and discussed.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

12. Smoke Stratification

Abstract

The phenomena and formation mechanisms of smoke stratification and engineering solutions to estimate smoke stratification in tunnel fires are described. Smoke stratification is an important issue for evacuation and fire fighting in tunnel fires. Smoke released from a fire contains some hazardous combustion products. If the smoke stratification in a tunnel section dissolves, tunnel users in this region could be in great danger. In no ventilation or very low ventilation conditions, smoke exists on both sides of the fire, and good stratification could exist at the early stages but generally not after the fire becomes larger. For a ventilation velocity slightly lower than the critical velocity, smoke backlayering and good stratification exist upstream of the fire, however, the smoke stratification downstream becomes worse. Under high ventilation rates, all the smoke flows towards the downstream side and stratification is difficult to maintain even at a short distance downstream. The theory of the smoke movement along the tunnel is introduced. An empirical model of smoke stratification in tunnels with longitudinal ventilation is also presented.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

13. Tunnel Fire Ventilation

Abstract

Ventilation is the most common measure to mitigate the effect of fire and smoke in a tunnel. Various normal ventilation systems for removal of heat and contaminants from the tunnels are introduced at first. In case of a tunnel fire, fire ventilation systems are required to control smoke flows and create paths for evacuation and firefighting. The fire ventilation systems used in tunnels mainly include longitudinal ventilation systems and smoke extraction ventilation systems, which are discussed in great detail in this chapter. Two key parameters for tunnels with longitudinal ventilation, that is, critical velocity and back-layering length are investigated in full details. For smoke extraction systems, sufficient fresh air flows are required to be supplied from both sides to prevent further smoke spread. Further, fire ventilation systems in tunnel cross-passages and rescue stations are discussed. A simple model of longitudinal flows is introduced for calculation of longitudinal ventilation velocity in a tunnel fire.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

14. Visibility

Abstract

Visibility is very important for evacuation during a fire and, therefore, a very important parameter for fire safety in a tunnel. There are different methods for estimating the visibility in smoke-filled spaces, using mass-specific extinction coefficient or the mass optical density. For both methodologies there are experimental values available for some materials of interest. First, the mass extinction coefficient methodology is presented and at the end compared and correlated to the mass optical density methodology. Values of these parameters for selected materials are presented and conversion of values for one of the parameters into the other is discussed. Finally, the effect on the walking speed during egress is discussed.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

15. Tenability

Abstract

One of the most important issues during a fire in a tunnel is the possibility for a safe escape. During an evacuation, tunnel users may be exposed to toxic gases, radiation, high temperatures and dense smoke. In this chapter the most important consequences of exposure to gas components, radiation and convective heat are presented. Examples of asphyxiant and irritant gases and the effect on evacuating people are presented. Different models for estimating time to incapacitation and other endpoints due to exposure are discussed.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

16. Fire Suppression and Detection in Tunnels

Abstract

The basic concepts of fire suppression systems are depicted. There are mainly two water-based fire suppression systems used in tunnels, that is, water spray systems and water mist systems. The main differences are the water density, pressure, and droplet size. The extinguishment mechanisms are explored and the critical conditions at extinction are discussed. Further, suppression of realistic fires is discussed considering both the water flow rate and the total water flow rate used for fire suppression. A summary of fire suppression tests carried out in tunnels is presented followed by a short discussion of tunnel fire detection.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

17. CFD Modeling of Tunnel Fires

Abstract

Computational fluid dynamics (CFD) modeling has been widely used for performance-based tunnel fire safety design in engineering applications. A CFD tool divides a computation domain into a large number of small cells, and solves a set of differential equations with sub-models using different solution algorithms. The CFD users need to not only efficiently use CFD tools, but also to understand the embedded mechanisms. The basics of CFD modeling are introduced including controlling equations, different turbulence models, and numerical methods. Sub-models important for tunnel fires are then described, that is gas phase combustion models, condensed phase pyrolysis models, fire suppression models, wall functions, and heat transfer models. Despite the rapid development and completeness of these models related to fire phenomena, many limitations exist which should be always kept in mind by the users. Recommendations for CFD modeling of tunnel fires are presented.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

18. Scaling Technique

Abstract

Physical scaling has been successfully applied throughout the development of fire safety science in the past several decades. It is a very powerful and cost-effective tool to obtain valuable information concerning, for example, fire characteristics, smoke movement, smoke control, fire development, and fire suppression. Typical scaling techniques that have been developed are summarized in this chapter to provide a theoretical benchmark and support for further development of more advanced scaling methods. Different scaling techniques are introduced although the focus is on the Froude scaling method which is the most common one used in fire safety science. Scaling of convective heat transfer, radiative heat transfer, and heat conduction is investigated as well as scaling of water sprays, response time of sprinklers, and combustible materials.

Haukur Ingason, Ying Zhen Li, Anders Lönnermark

Titel: Tunnel Fire Dynamics
verfasst von: Haukur Ingason
Ying Zhen Li
Anders Lönnermark
Copyright-Jahr: 2015
Verlag: Springer New York
Electronic ISBN: 978-1-4939-2199-7
Print ISBN: 978-1-4939-2198-0
DOI: https://doi.org/10.1007/978-1-4939-2199-7

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