Tunnel Fire Accidents Research Articles

Fire-Retarding Asphalt Pavement for Urban Road Tunnels: A State-of-the-Art Review and Beyond

AbstractWith the rapid urbanization and development of metropolises, urban road tunnels have been constructed at an increasing rate, significantly alleviating urban traffic pressure, and improving urban resilience. Fire hazards have become a major threat to modern road tunnels due to the growing popularity of electric vehicles and high-density transportation of goods, particularly flammable materials. Asphalt pavements, as an essential component of road tunnels, may release harmful effluences and smoke under high temperatures, exacerbating the fire and adding risk to life safety. It is hence critical to investigate fire-retarding asphalt materials and their potential use in urban road tunnels pavements. This paper provides a comprehensive review of fire-retarding asphalt pavements for urban road tunnel pavements. The review covers tunnel fire generation mechanisms, evaluation methods, flame retardants for asphalt pavements, and recent developments in flame retardant technologies. By investigating these aspects, this paper aims to better understand the flammability of asphalt mixtures and asphalt pavements in urban road tunnels, promote the research of flame-retardant technology, and ultimately reduce the damage and loss caused by asphalt road tunnel fire accidents. Additionally, this study identifies the limitations of current research and provides an outlook for future research to contribute to the resilience of urban road tunnel structures and the longer service life of asphalt pavement in semi-closed road tunnels.

Evaluating Tunnel Users’ Literacy on Expressway Tunnel Fire Safety: Questionnaire Analysis and Policy Decisions

The number of tunnel fire accidents has increased with the scale of expressway tunnel construction and traffic flow. Due to the severity of tunnel fires, improving tunnel fire safety and reducing fire accident hazards has become a societal concern. It is essential to explore and evaluate tunnel fire safety literacy among the population. In this study, an online and on-site questionnaire survey was conducted in Hunan Province, China. A total of 1990 questionnaires were collected, of which 1573 were valid. Overall statistical analysis, descriptive statistics, and correlation analysis were performed on valid questionnaires. The results show that the overall level score rate of awareness of drivers and passengers regarding tunnel fire safety was only 0.43. In total, 58.42% of people were unaware of the pedestrian cross passages in expressway tunnels, and 68.40% were unable to recognize them. Similarly, 46.47% of people were unable to recognize evacuation signs in expressway tunnels. In addition, 39.29% of people chose the wrong evacuation behavior. The percentage of people who were aware of the correct usage of firefighting facilities in expressway tunnels was below 50.00%. Correlation analysis results show that tunnel users’ demographic characteristics significantly affected their cognition of expressway tunnel escape methods. This study shows that tunnel users’ emergency escape knowledge regarding tunnels is relatively low. Corresponding countermeasures were proposed to guide policy decisions for enhancing tunnel fire safety.

An experimental investigation into the fire behaviors and smoke characteristics of continuous spill fires in road tunnels

Continuous fuel spill fires are a common accident scenario which needs to be considered for the safe operation of tunnels, given the potential threat posed to trapped persons. In this paper, a series of continuous spill fire experiments on a concrete surface were studied using a 1/8 reduced-scale tunnel model. Gasoline was used as the discharge fuel and the discharge rate varied from 1.5 to 5.2 ml/s. The burning area, steady regression rate, smoke front arrival time, and ceiling temperature were analyzed. The results show that the burning area spreads slowly following an initial rapid spill stage, with the spread process following a pattern of exponential decay. The steady regression rate is found to be approximately 63% of that of pool fires for the same burning area. At the same heat release rate, the smoke front moves faster for spill fires than pool fires because of the larger burning area, and a correlation is built to predict the smoke front arrival time. Finally, a ceiling temperature rise prediction model is developed which considers the spread and burning processes of the fire. The results are of practical importance in the quantitative risk assessment of liquid fuel fire accidents in tunnels, and their implications for personnel evacuation.

A survey of fire accidents during the process of highway tunnel operation in China from 2010 to 2021: Characteristics and countermeasures

China has the largest number of highway tunnels in the world and the most rapid development in this scope. Along with the advancement of highway tunnels, fire incidents continue increasing, causing significant damages to life and property safety. The knowledge of characteristics of highway tunnel fire accidents is essential for the fire authorities to update their safety policies on tunnels and also useful for the scholars to carry out basic and applicable researches. Previous studies have been performed on fire accident statistics in highway tunnels before 2016. The dataset after 2016 are unknown. To solve this problem, the present study examined total 256 fire incidents in Chinese highway tunnels during 2010–2021 based on police-reported database. The results showed that the fire number in 2017–2021 is almost three times that in 2010–2016. The fires occur more in spring and summer. The majority of fires occur in the long and extra-long tunnels (80%), in the one-way tunnels (90%), in the curved tunnels (70%), in the interior zone of tunnels (67.2%) and in the low altitude areas (60%). The top two burning vehicle types are heavy goods vehicles (HGVs, 38.1%) and passenger cars (37.2%). A total of 81.2% of fatalities in highway tunnel fires are associated with HGVs. The head of vehicle (41.8%), tire (25.3%) and goods (15.3%) are the top three causes of fire. Despite the fact that 92.7% of cases are single fire category while spread fire category only accounts for 7.3%, the spread fire has a more than 7 times higher casualty rate than the single fire. Based on the results, some useful fire safety measures for highway tunnels are proposed. It is hoped that this work could provide some data supports and references for tunnel fire safety and relative policy-making.

Risk analysis of people evacuation and its path optimization during tunnel fires using virtual reality experiments

The number of urban tunnels has been increasing rapidly, accompanied by frequent tunnel fire accidents owing to the complex tunnel structure and large traffic flow. In this study, a full-size tunnel virtual reality (VR) scenario and computational fluid dynamics (CFD) construction model were established to investigate the evacuation behavior and corresponding risk of people in the early stage of vehicle fires considering four scenarios: normal circumstance, without VR agents, without emergency evacuation signs, and without fire extinguishers. Firstly, the cumulative values of CO, CO2, and temperature along the evacuation path were monitored using CFD. Secondly, the smoke toxicity was calculated using the N-GAS model, and the total risk value was computed based on the analytic hierarchy process which was defined as “smoke hazard: temperature hazard = 7:3.” Thirdly, a multiple regression model was created based on accident data. Finally, to minimize accidents, the design of the evacuation path was optimized using the established mathematical model and A* algorithm to verify the effectiveness of the risk assessment model. The results show that the effects of VR agents, emergency evacuation signs, and fire extinguishers on the evacuation behavior of people are mutual influence. This study combined time and route in the VR evacuation experiments to overcome the limitations of the existing control and VR experiments in quantifying the evacuation results. This research can be utilized to improve emergency evacuation plans and emergency response decision making. Furthermore, it can broaden the application of VR in the field of tunnel lifecycle safety management.

Experimental study on flame tilt angles of two unequal fires in a longitudinal ventilated tunnel

In historical tunnel fire accidents causing major casualties and property losses, the special fire phenomenon of multiple fires burning was usually accompanied. Other than the longitudinal ventilation in tunnel, the interaction burning of multiple fires will also make the flame tilt. Flame tilt angle is an important parameter to characterize the magnitude of acting forces on fires and it determines the possibility of ignition and flame spread. Former studies were mainly focused on multiple equal fires with same sizes, very limited attention has been paid on multiple unequal fires. Due to the different air entrainment mechanisms, the proposed correlations for flame tilt angle of multiple equal fires might be unsuitable for the multiple unequal fires. This paper presents an experimental study on flame tilt angles of two unequal square gaseous fires of propane in a 1/10 scale tunnel with longitudinal ventilation. Two square burners with different side lengths were located parallel and along the longitudinal centerline of tunnel. The effects of heat release rate of each burner, the burner edge spacing and the ventilation velocity were explored. Using the image processing method, the flame heights and tilt angles of upstream fire and downstream fire were determined. The results showed that due to the shielding effect of upstream fire acting on the downstream fire, the flame height of downstream fire is larger than the upstream fire, while the flame tilt angle of downstream fire is lower than the upstream fire. In addition, the flame heights of upstream and downstream fires are reduced with increasing the ventilation velocity, while the flame height of downstream fire is weakly affected by the separation distance. As the ventilation velocity increases, both the upstream and downstream flame tilt angles increase first and then maintain unchanged. The separation distance has little influence on the upstream flame tilt angle, while it affects the downstream fire more. Among the impact factors, the longitudinal ventilation plays a leading role of the flame tilt behaviors of two fires in tunnel. Based on the force analysis, it is found that the pressure thrust between two fires is much smaller than the buoyancy force and ventilation force. As a result, different correlations for predicting the flame tilt angles of two unequal fires in tunnel are developed based on the coupling effect of buoyancy force and ventilation force of each fire.

Highway Tunnel Fire Traffic Control Plan

Tunnel fire accidents occur from time to time, due to its special structure, will cause huge losses, this paper by studying the division of tunnel fire, put forward the principles and specific measures of traffic control, and carry out zoning control of tunnel fire traffic, and prepare a plan for the traffic control of the affected area and the fire tunnel area.

Experimental study on multiple fire hazards in a naturally ventilated tunnel: Assessment of the flame interaction and extension of two unequal fires

The catastrophic tunnel fire accidents are usually accompanied with multiple fires burning. This work experimentally studied the temperature-determined flame extension below the ceiling induced by two unequal square gaseous fires in a 1:10 scale tunnel with natural ventilation. The two fires were parallel and both placed along the longitudinal centerline of tunnel. The heat release rate (HRR) of each burner and the burner spacing were changed. The measured ceiling gas temperatures were used to obtain the flame length and tilt angle. Results showed that for small fire groups, the spacing has a small effect on the flame length. For large fire groups, the variation law of flame length of the small fire with spacing is different from that of the large fire. The flame tilt angle is analyzed to illustrate the variation of flame length. A normalized parameter α representing the spacing effect and the equivalent burner size concerning the weight of the burner perimeter is introduced to modify the HRR of each burner. Then a new model for flame length of two asymmetric fires with large HRRs in a tunnel is developed. The model for flame length with small HRRs is proposed based on the single fire assumption. Regarding the two merging fires as a virtual fire source, the model for flame length of virtual fire is established. Then the critical merging criterion is proposed based on the normalized spacing and HRR. Regarding the two fires with zero spacing as a single circular fire source, the point source model is adopted to calculate the overall flame outward radiation, and the personal safety distances under different HRRs in tunnel are further determined. The present results can be well used to predict the flame lengths of two unequal fires in tunnel and provide some useful references for personal evacuation, fire rescue and risk assessment in tunnels.

Performance of ceiling jet induced by dual unequal strong plumes in a naturally ventilated tunnel

• Thermal property of two unequal flames in a naturally ventilated tunnel is studied. • Temperatures induced by the small plume decay faster than that of the large plume. • A new model for maximum ceiling temperature of two unequal plumes is proposed. • Correlations for ceiling temperature decay profiles of dual plumes are developed. The catastrophic tunnel fire accidents are usually accompanied with multi-source burning. Ceiling gas temperature in tunnel is an important parameter in monitoring the daily operation process and unexpected combustion process. Previous studies are mainly focused on single fire or multiple equal fires in tunnel, while multiple unequal fires burning is common in real tunnel fires. Till now, the law of asymmetrical temperature distribution of multi-source below a ceiling is unknown. This paper aims to experimentally study the thermal performance of two unequal fire sources of propane in a naturally ventilated tunnel. A total of 90 experimental tests were conducted. The side lengths of two burners are fixed at 10 cm and 15 cm. The heat release rate (HRR) of each burner are changed with the HRRs ratio of 1–6. And the spacing between two sources along the longitudinal centerline of tunnel varied from 0–45 cm. Analysis shows that there is only one peak temperature with small spacings, while two peak temperatures appear with large spacings. Then the impingement point position and the maximum ceiling gas temperature of each burner are illustrated. The force analysis is adopted to explain the variation of impingement point position. A parameter α is innovatively introduced to characterize the promoting effect of spacing on maximum temperature at small spacings. Then a new normalized HRR is proposed to establish a unified model for the unequal maximum temperature rises below the ceiling of both sources, which indicates that the maximum temperature rise increases with the normalized HRR and then it maintains at 754 K. By introducing the plume radius, models for asymmetrical temperature decay profiles on both sides of two plumes below the ceiling are proposed, which shows that the temperature in the upstream of the small burner decays faster than that in the downstream of the large burner. The proposed models for maximum temperature and temperature decay profiles can be used to predict the ceiling gas temperatures of two unequal fires in tunnel.

Based on ISM—NK Tunnel Fire Multi-Factor Coupling Evolution Game Research

A tunnel is a complex network system with multiple risk factors interacting. At present, the cause analysis of tunnel fire accidents focuses on exploring risk sources and risk assessment, ignoring the interaction between risk factors. A single model has certain limitations. By proposing the concept of the multi-factor coupled evolutionary game of tunnel fire, integrating the natural killing model (NK) and the explanatory structure model (ISM), the evolutionary game of multi-factor coupling of tunnel fire is studied from the perspective of micro and macro analysis, qualitative and quantitative research, the coupling relationship and effect between risk factors are discussed, 100 tunnel fire accidents and 158 tunnel fire literature at home and abroad are analyzed, and 40 typical tunnel fire risk factors and 31 coupling types of fire cause factors are extracted. Using the combined ISM-NK model, a seven-level network model of tunnel fire accident risk coupling is constructed, and the degree of coupling of various types of risk factors is evaluated. The hierarchical network cascade model revealed that 4 of the 40 typical tunnel fire risk factors were the underlying risk factors, 23 shallow layers were the risk factors and direct influencing factors, and 13 were the middle-risk factors and indirect influencing factors. The NK model shows that with the increase of coupling nodes, the frequency of tunnel fire accidents also shows an upward trend, and the subjective risk factor coupled with tunnel fires have a higher frequency than the objective risk factors.

Parameters that affect tenability conditions during fire emergency in metro tunnels

Underground spaces are characterized by special conditions and complexity, as well as by severe consequences in the event of an accident. Although the frequency of fire accidents in tunnels or metro stations is low, in worst cases they may lead to severe fatalities and damages. In order to have a more accurate prediction of fire impacts, most safety standards enforced worldwide suggest the development of special risk analyses. This needs to be made having in mind fire characteristics, geometrical and ventilation parameters so as to have an accurate view of the thermal and smoke propagation within the underground space. In this paper a parametric analysis is carried out, varying input values, crucial for fire risk analysis, like fire curve and heat release rate maximum (HRRmax), as well as ventilation and tunnel geometry. Key factors like visibility conditions, temperature and CO concentration are recorded through the fire dynamic simulation (FDS), in order to determine the conditions inside the metro tunnel. Furthermore, the fractional effective dose (FED) that occupants might receive in a period of time, in different positions inside the tunnel, is calculated. Based on the above, detailed data on the prevailing conditions are gathered and conclusions can be drawn regarding the influence of each parameter’s evolution on the tenability conditions inside the tunnel. Hence, the analysis can illuminate key issues to consider for performing an accurate risk analysis in an underground environment.

Studies and Prospects of Technologies for Monitoring Highway Tunnel Fire

Because the tunnel fire poses a great threat to the personal and property safety of the trapped people, it is urgent to monitor the tunnel fire in real time, which will help the emergency rescue and evacuation of the tunnel fire accidents. This paper summarizes the studies of technologies for detecting highway tunnel fire and traffic accidents, and discusses the prospect of monitoring the fire of tunnel vehicles through video images.

Inherent fire safety engineering in complex road tunnels – Learning between industries in safety management

Road tunnels in Norway are becoming increasingly complex, and several long subsea tunnels are either under construction or planned for the near future. The Office of the Auditor General in Norway recently stated that there is a need to improve fire safety in road tunnels. By systematically examining safety management in an industry dealing with high risks on a daily basis and combining this with knowledge gained through investigations of tunnel fire accidents and existing research on tunnel fires, this paper aims to identify some areas for improvement in the fire safety engineering of complex road tunnels. The ‘inherently safer’ philosophy is used as a starting point for safety management, and there appears to be some potential for improvement within tunnel fire safety engineering, when taking into account parameters and uncertainties regarding fire growth, heat release rates, smoke stratification toxicity, and time available to escape with different ventilation strategies.

Use of mobile fans during tunnel fires

Smoke control is a key issue in tunnel fire accidents. While jet fans have been widely used in road tunnels, mobile fans provide a good complement, due to its flexibility to operate, especially if there are no fixed jet fans present. To confirm the feasibility of a mobile fan system, full scale fire tests were conducted in Kalldal tunnel in Sweden, with fire size in the range of 1–2.6 MW and a mobile fan placed at the tunnel portal. In the tests, it takes about 4–5 min to establish full flow in the opposite direction and the final flow velocity can reach 1.5–1.9 m/s. To describe the transient behavior of flow development inside tunnel, a one-dimensional lumped theoretical model has been developed. The model takes into account the pressure losses of external wind, the stack effect of fire and friction losses over tunnel walls and two portals. The model is validated using the data from Kalldal tunnel fire tests. Results show that the model can well predict the initial and final steady state velocity, but underestimates the flow development. The model gives prediction on the safe side.

Study on Fire Accidents in Tunnels

This paper provides a collection of information on 156 tunnel fire accidents at home and abroad and analysis of their time and spatial distribution, accident causes and effects. The study shows: most tunnel fires occur in summer; tunnel fire accidents are frequent in economically developed areas of eastern and southern China as well as mountainous areas in southwestern and northwestern China; long tunnels and super long tunnels experience more fire accidents which occur mostly at tunnel entrance/exit; most tunnel fires are caused by spontaneous combustion of vehicles and traffic accidents; cars and trucks are the most frequently seen models in tunnel fires; consequences of tunnel fires include casualties, vehicle damage, damages to tunnel structure and facilities and traffic interruption. At the end of the paper, appropriate measures and advice are proposed for tunnel fire accidents based on the above analysis results.

Statistical analysis of fire accidents in Chinese highway tunnels 2000–2016

Statistical analysis of tunnel fire accidents (TFAs) in China 2000–2016 as related to causes, characteristics, and consequences are discussed in this study with average frequency, time and locations, vehicle types, and regional distribution features revealed. Analysis results indicate that over half of TFAs in China result from vehicle technical problem. The average prevalence of TFAs has increased yearly since 2000 with the majority of incidences occurring in the summer and winter seasons and the autumn season experiencing the least. Fire accident prone locations tend to be at entrance and exit points of highway tunnels with heavy goods vehicles experiencing the largest proportion of TFAs at 58.2%. Countermeasures focusing on improving tunnel safety are recommended.

Smart Disaster Response in Vehicular Tunnels: Technologies for Search and Rescue Applications

Recently, the number of tunnels is increasing due to urbanization, and fire accidents in tunnels are likewise increasing. In particular, in a long tunnel of more than 1 km it is very difficult to track the exact location of a fire, accident vehicles, and the fire brigade, as well as whether a fire occurred. In this paper, we analyze various types of accidents that may occur in tunnel fires and propose detection, search, and rescue techniques to cope with them. For early detection of accidents, we propose various sensors using Internet of Things (IoT) technology and sensor networks to connect them. These sensors can detect not only a fire but also the position of the vehicle in which the fire is occurring in real time. We also propose a robotic system and operation technique that can be controlled by a fire fighter for more precise search operation. For rescue procedures, localization and tracking technology for fire fighters and robots is proposed. Finally, the efficiency of the proposed system was verified through actual performance tests, including simulations of actual placement and operation in tunnels. Through the construction of the equipment in an actual tunnel 1.9 km long, we show that the proposed system is good enough to cope with fire accidents, in terms of the delivery ratio of the collected data, fire recognition ratio, localization accuracy, and response delay.

Intelligent Ventilation and Emergency Evacuation of Underwater Tunnel under fire Conditions

With the development of traffic cause, the number of underwater tunnel increased year by year. The tunnel fire accidents at home and abroad in recent years have caused a large number of casualties and property losses. The layout form of underwater tunnel is special, in the event of fire, the consequence will be unimaginable. The study of ventilating control and fire evacuation of underwater tunnel is urgent and necessary. Propose the Fuzzy PID ventilation algorithm and intelligent control mode of emergency evacuation signs from the perspective of keeping wind speed zero around fire point and induction of personnel escape. Write the PLC program and simulate the emergency evacuation signs’ automatic control under the condition of tunnel fire.

DPT 실험을 이용한 고온노출된 강섬유보강콘크리트의 인장강도 평가

Steel fiber-reinforced concrete (SFRC) is widely used for tunnel lining structure such as shot-crete in NATM tunnel and segment in TBM tunnel. In tunnel fire accidents, structural performance of a lining is very important because the lining is the structure that directly exposed to fire. In this study, the effects of high temperatures, mix ratios and types on failure pattern, DPT tensile strength and coefficient of variation were investigated through Double Punch Tests (DPT) of SFRC subjected to high temperatures. In the results, it is confirmed that the residual DPT tensile strength increases as for SFRC and this is more in SFRC with higher mix ratio. But, the equation for evaluation of DPT tensile strength does not involve the number of failure surfaces SFRC specimens subjected to high temperatures, therefore, it is required to investigate more fracture energy in DPT tests.

Fire Dynamics Simulator (Version 4.0) Simulation for Tunnel Fire Scenarios with Forced, Transient, Longitudinal Ventilation Flows

In this study, a series of sensitivity analyses were conducted to evaluate a computational fluid dynamic (CFD) model, Fire Dynamics Simulator (FDS) version 4.0, for tunnel fire simulations. A tunnel fire test with a fire size on the order of a 100 MW with forced, time-varying longitudinal ventilation was chosen from the Memorial Tunnel Ventilation Test Program (MTVTP) after considering recent tunnel fire accidents and the use of CFD models in practice. A careful study of grid size and parameters used in the Large Eddy Simulation (LES) turbulence model—turbulent Prandtl number, turbulent Schmidt number, and Smagorinsky constant—was conducted. More detailed analyses were performed to refine the smoke layer prediction of FDS, especially on backflow (i.e., a reversed smoke flow near the ceiling). Also, energy conservation was checked for this scenario in FDS. A simple guideline is given for smoke layer simulations using FDS for similar tunnel fire scenarios.