Urban Tunnel Fires Research Articles

A Monte Carlo simulation study on probability distribution of urban tunnel fire

Urban tunnel traffic has its inherent charateristics, such as frequently periodical traffic congestion/blocking, tidal phenomenon, large traffic flow and population, complicated traffic confluences and cross-flowing intertwined sections. Unlike ordinary roads, the potential fire scenarios are quite different and the consequences of fire are extremely severe in urban tunnel. The study adopts theoretical calculation, formula derivation, traffic survey, random sampling simulation to explore the probability distribution of urban tunnel fire. MATLAB is used to realize the numerical simulation of a million fire scenarios under different working conditions. The results identify the major factors affecting two-lane tunnel vehicle ignition model and three-lane model respectively. The probability of six combustion scales (, , , , and ) is higher than that of others, and with the increase of combustion scale, the probability decreasing exponentially. The ratio of truck to bus has a significant impact on the probability of large-scale fire. And truck fire and bus fire have a risk of igniting vehicles in adjacent lanes. The research results provide a basis for the design parameters of evacuation safety in practical engineering.

Numerical investigation on fire accident and evacuation in a urban tunnel for different traffic conditions

A fire outbreak in a urban tunnel with congested traffic may pose a great danger to all tunnel users. The main threat to human life in an urban tunnel fire is thick toxic smoke quickly filling large parts of the tunnel. It hinders evacuation and may even lead to lethal intoxication. Due to the potentially rapid development of the fire, people trapped will need to evacuate on their own. Thus, tunnel safety systems must support their self-rescue efforts. In this paper, several scenarios of fire accidents in a real urban tunnel are numerically investigated. The scenarios differed in road traffic state, fire power and fire detection time. To make them realistic the entire sequence of events during a tunnel fire was numerically modeled. First, the formation of congestion is examined using VISSIM software, then fire development is simulated by Fire Dynamic Simulator and finally, the evacuation process is modeled by PATHFINDER software. All data needed to build these numerical models correspond to real conditions of the selected urban tunnel under the Martwa Wisła river in Gdansk (Poland). The outcomes of the work suggest the number of threatened people may be very large even under common circumstances. In the worst case over a half of people trapped inside may come into contact, at least temporarily, with factors threatening health or live.

The effect of technical installations on evacuation performance in urban road tunnel fires

Tunnels are separated from the ground by structural linings, and are enclosed and unfamiliar for occupants. In tunnel fires, occupants are faced with a dangerous environment and they need to evacuate. Conveying and obtaining information about the evacuation is the key issue for evacuees. Since tunnels typically have low lighting and little connection outside the tunnel, technical installations are the only approach to deliver information to occupants in order to guide their fast and safe evacuation. This is particularly an issue for urban road tunnels with large occupants’ flow in a large underground space. The present study explores the effect and role of technical installations (alarms, information signs, and lighting) on people’s evacuation performance in urban tunnel fires, through field experiments, questionnaires and interviews. Theory of affordance (sensory affordance, cognitive affordance and functional affordance) is taken into consideration and provides an integral evaluation for technical installations. Technical installations are useful in helping occupants notice the emergency, finding exits and guiding path, and information signs are regarded as the most powerful among those three. Besides, this experiment points out some side effect from alarms and ambiguity of signs which will result in serious consequence potentially. This study leads to guidance on improvement of technical installations on evacuation planning and procedures on urban road tunnels.

A simplified mathematical model for estimating gas temperature and velocity under natural smoke exhaust in sloping city tunnel fires

In the previous study, the prediction of gas temperature and velocity in the naturally-ventilated inclined tunnels under traffic blockage has been well concerned (Y. Zhou et al., Sustain. Cities Soc. 45, 2019, 258–270). In this paper, we continue to pay attention to the estimation of internal gas temperature and velocity under natural smoke extraction in both single-slope and gable-slope tunnel fires, a more hazardous scenario. A series of simplified mathematical models based on the equations of continuity, energy and pressure balance was proposed to estimate the gas temperature and velocity in sloping tunnel fires, in which the influences of fire source location, tunnel slope and tunnel geometry were taken into account. In addition, corresponding numerical simulations based on full-size tilted urban tunnel fires were performed using Computational Fluid Dynamics (CFD) method. The results show that the variation trends between CFD and analytical results are basically the same, and the iterative values of gas temperature and velocity coincide well with the simulations. A fast and convenient method for the estimation of gas temperature and velocity in sloping tunnel fires has been proposed, and the results of this work can provide a reference for the optimal design and management of natural smoke extraction systems, and help to ensure the fire safety of single-slope and gable-slope city tunnels.

A Simple Method to Improve Smoke Exhaust Effectiveness of a Shallow-buried Urban Tunnel Fire with Natural Ventilation

ABSTRACT In order to improve the natural ventilation performance of a shallow-buried urban tunnel under the influence of external wind blowing above the shaft, a new method with installing a jet fan downstream of the shaft was proposed and a set of simulations were conducted to validate its effectiveness. The detailed smoke spread characteristics, such as mass flow rate, temperature, and velocity vector, were analyzed together with varying the ambient wind speed above the shaft, the longitudinal wind speed in the tunnel, and the velocity of the jet fan. Results show that under the coupled push effect of the longitudinal wind upstream of the fire and the airflow of jet fan downstream of the shaft, the block effect of the strong ambient wind on the vertical flow of smoke through the shaft can be overcome completely. In the tunnel, almost all the fire-induced smoke is confined between the fire and the shaft, and smoke can only be exhausted from the shaft. The findings can be a reference for tunnel ventilation design.

Performance evaluation on fixed water-based firefighting system in suppressing large fire in urban tunnels

Operating fixed water-based firefighting systems (FFFS) might affect the performance of other parts of an integrated tunnel safety system, particularly the longitudinal ventilation system. The interaction of the water spray discharged from two FFFS (with and without foam), with the longitudinal ventilation system in a new city tunnel under construction was studied by full-scale burning tests. Results of the study under large fires up to 20 MW in diesel pool fires or wood pallet fires are reported in this paper. The impact of longitudinal ventilation, the activation sequences of the ventilation system and the fixed fire-fighting system, and the performance of the two FFFS in suppressing vehicular fires with and without shields to fire sources were evaluated. Results are expected to be useful for drafting appropriate fire codes on fire suppression systems for controlling urban tunnel fires.