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This study proposes a heat release rate (HRR) estimation method for a carrier loaded with fuel cell vehicles (FCVs) trapped in a tunnel fire. The carrier is divided into several parts, and the HRR is estimated by adding the HRRs of all system parts (carrier and FCVs). The HRR of one FCV was compared with that of a gasoline vehicle. The thermal fume behavior in longitudinally inclined tunnel fires was also investigated. Even a modest inclination hastened the thermal fume propagation of the FCV fires. Of relevance to the prevention of tunnel fire disasters, the thermal fume behavior differed between FCV and gasoline fires. For safety assessment of tunnel fires, the thermal fume behaviors of an FCV fire and gasoline vehicle fire in a tunnel were investigated by the proposed method. In the case of no longitudinal inclination, the thermal fume of the FCV fire arrived earlier than that of the gasoline vehicle fire (by 1 min at x = 200 m and over 4 min at x = 250 m) because of the emitted hydrogen gas. At 2% longitudinal inclination, the thermal fume of the FCV fire propagated to the downstream side 4 min before that of the gasoline vehicle fire. At 4% longitudinal inclination, the thermal fume propagated 50 m downstream of the initial fire after 10 min. Therefore, after the hydrogen emission, the thermal fume of the FCV fire traveled faster than that of the gasoline vehicle fire. The proposed HRR estimation method can contribute to the risk analysis of various types of tunnel fires. • HRR of a carrier loaded with FCVs in a tunnel was estimated. • Thermal fume of FCV and gasoline vehicle fires in inclined tunnel was investigated. • Inclination caused faster thermal fume propagation of FVC fires was clarified. [ABSTRACT FROM AUTHOR]

Tunnel fires create dense black smoke that covers ceiling lights and darkens tunnel spaces. The present study investigates experimentally the evacuation speed in a full-scale tunnel filled with smoke and clarifies the relation between the extinction coefficient (up to 1.6 m −1 ) and normal walking speed. In this study, participants were exposed to smoke in a full-scale experimental tunnel that was darkened by turning off the ceiling lights, and the extinction coefficient was varied from 0.18 to 1.6 m −1 . The maximum, minimum, and mean normal walking speeds were almost constant up to 1.0 m −1 but decreased slightly at higher extinction coefficients. At 0.30 m −1 , the maximum emergency-evacuation speed through the dark tunnel is less than that when the ceiling lights are on and corresponds to 2.6 m/s, thereby indicating a fast walking speed even at small extinction coefficients. However, the maximum emergency-evacuation speeds at coefficients exceeding 0.48 m −1 for light and dark conditions are almost identical. The minimum and mean emergency-evacuation speeds decrease at extinction coefficients of approximately 1.0 m −1 . Additionally, normal walking speed and emergency-evacuation curves are calculated from the current experimental results to compare the effect of ceiling lights with that of a darkened space. The results indicate that the normal walking speed and emergency-evacuation speed are influenced by the darkened space. [ABSTRACT FROM AUTHOR]

A series of fire experiments was conducted using a 1:12 scale model of a shallow urban road tunnel with roof openings to clarify the flow structure of smoke and fresh air during a fire with a longitudinal external wind blowing above the roof openings. The model tunnel consisted of two road tubes separated by a pillar-type median structure. Five fire test cases were conducted by changing the heat release rate as the experimental parameter. When the smoke produced by a fire in the tunnel tube was exhausted by natural ventilation through the roof openings of the tunnel tube, fresh air was sucked in from the roof openings of the opposite tunnel tube. The flow of exhausted smoke and sucked-in fresh air created a complex three-dimensional flow structure inside the tunnel tubes. Stratified smoke that had formed under the ceiling of the tunnel tube was disturbed by the flow of sucked-in fresh air and was diffused on the upstream side of the fire. Compared to the condition without a longitudinal external wind, when a longitudinal external wind blew over the tunnel with the pillar median structure, the smoke spreading distance on the upstream side was longer than that without the external wind due to the diffusion of smoke. On the other hand, the smoke spreading distance on the downstream side of the fire was shorter than that without the external wind due to the improved smoke extraction performance by the Venturi effect of the longitudinal external wind. Furthermore, the smoke spreading distance on the downstream side was nearly constant and independent of the heat release rate of the fire, within the scope of our experimental conditions. [ABSTRACT FROM AUTHOR]

The present paper proposes a safe evacuation method using underground evacuation tunnels for urban area evacuation owing to a wide-area fire disaster that may occur in the aftermath of a major earthquake. To survey the effectiveness of the evacuation tunnels, evacuation completion time was estimated using wide-area evacuation simulations. It was discovered that evacuation completion time for underground tunnels was one hour faster than that of evacuation above ground (even with the widening of the surface roads) if tunnel usage was appropriately controlled so that vulnerable people (i.e., elderly people and children) used it while others evacuated above ground. Moreover, an estimation of the construction cost of evacuation tunnels in a metropolitan area indicated that one could be built at the same, or even lower, cost than that of the road widening above ground. [ABSTRACT FROM AUTHOR]

This study proposes a quantitative method for assessing road tunnel fire safety based on a numerical simulation of in-smoke evacuation. Considering evacuation in tunnels which is a long and large but single and simple space; evacuees are generally in the same space as the fire source but evacuation direction is almost one dimension, a new one-dimensional evacuation simulation was developed wherein the self-determined evacuation necessity detection factors were modeled. Using expedited 1D evacuation simulations, random number results from 2000 simulations determined the mean number of sufferers. To evaluate the influence of smoke on evacuees, various smoke environment (SE) levels were defined as a function of time and longitudinal location using a simplified smoke distribution derived from 3D CFD. The number of people surrounded by thick smoke within 10 min of fire ignition was used as an evaluation index for tunnel fire safety. The proposed method was tested under various longitudinal gradients, large heat release rate, and pre-evacuation time scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] • Evacuation and normal walking speeds in smoke-filled tunnels with obstacles. • Analyzed effects of number and arrangement (aligned and random) of obstacles. • Investigated effects of varying smoke extinction coefficient. • Emergency evacuation speeds decreased with an increase in smoke density. • Obstacles significantly influenced average and maximum walking speed values. We experimentally investigated the evacuation walking speed distributions in a smoke-filled tunnel with obstacles such as a car in the evacuation route. Based on the extinction coefficient, the smoke levels were categorized into four: 0 (no smoke), I (0.01–0.5 m−1), II (0.5–1.0 m−1), and III (>1.0 m−1). The probability density functions of the evacuation walking speed for the different smoke levels were fitted to gamma, normal, and lognormal distributions. Based on the statistical results, the relationship between the probability density function of the evacuation walking speed and the smoke density was investigated. The influence of obstacles was significant on the average and maximum walking speed values and minor on the minimum walking speed values. [ABSTRACT FROM AUTHOR]

Among tunnel fire safety strategies, evacuation speed in smoke, which is the basic evacuation performance characteristic, is one of the most important factors when assessing safety. An evacuation experiment in a full-scale tunnel filled with smoke has been done in order to clarify the relation between extinction coefficient up to Cs = 1.0 m −1 , which includes Cs = 0.4 m −1 as a Japanese road tunnel fire prevention standard, and evacuation speed. The maximum, minimum and mean values of normal walking speeds are almost constant regardless of the extinction coefficient. As for the emergency evacuation speeds, the maximum speed is largely influenced by extinction coefficient, decreasing rapidly from 3.55 m/s at Cs = 0.30 m −1 to 2.53 m/s at Cs = 0.75 m −1 while the minimum and mean speeds are almost constant with a slight decrease as Cs increases. The maximum evacuation speed trends in the present experiments and those in Frantzich and Nillson (2003, 2004) and Fridolf et al. (2013), lie on the same decreasing logarithmic curve as a function of extinction coefficient. [ABSTRACT FROM AUTHOR]

Fire experiments using a 1:12 scale model tunnel were conducted to evaluate effects of a transverse external wind on the performance of roof openings in a shallow urban road tunnel under fire conditions. A particular focus was placed on clarifying the characteristics of the spread of smoke in the tunnel under the condition of a transverse external wind blowing above the roof openings. Two types of median barriers, pillars and walls, were examined as dividing structures in the model tunnel, and the heat release rate was selected as the experimental parameter. The following conclusions were obtained. Compared to conditions with no external transverse wind, in the model tunnel with the pillar median structure, the smoke spreading distance was shortened when the transverse external wind was in the positive direction, and the distance remained the same when the wind was in the negative direction; in the model tunnel with the wall median structure, the smoke spreading distance was shortened when the wind was in the positive direction. Furthermore, the smoke spreading distance in each case was constant and independent of the heat release rate of the fire under the scope of the experimental conditions used in this study. [ABSTRACT FROM AUTHOR]

Abstract: The characteristics of the spread of smoke were investigated for a fire occurring in a shallow urban road tunnel with roof openings in its ceiling. In this type of tunnel, the smoke produced by a fire is ventilated through the openings in the ceiling given the natural buoyancy of hot smoke. A fire experiment was conducted using a 1/12 scale model tunnel to ascertain whether natural ventilation via the roof openings was sufficient to maintain a safe evacuation environment for tunnel users. The distance from the fire to the tip position of the spreading smoke and the thickness of smoke layers along the ceiling were investigated by changing the heat release rate and using two types of median structure as experimental parameters. The two types of median structure dividing the tunnel into two road tubes were pillars and walls. It was clarified that the smoke spreading distance was constant and independent of the heat release rate of the fire under our experimental conditions. Moreover, it was confirmed that the thickness of the smoke layers in the tunnel thinned out quickly due to the natural ventilation. [Copyright &y& Elsevier]

• We measured the perfectly darkened walking speed using eye-mask in real tunnel. • Walking speed was approximately lognormal, gamma and normal distributed. • Two female participants gotten lost their route and suspended the walking. • We compare with the past researches and the minimum values. • Tunnel wall could be guide role and support to walk in the tunnel. When a serious tunnel fire occurs, dense smoke obscures the ceiling lights and pedestrians must evacuate the darkened tunnel with limited visibility. The precise walking speed in such situations has never been clarified, although indoor walking speeds in darkness are said to be 0.325 m/s for subjects unfamiliar with the environment and 0.705 m/s for subjects familiar with it (Togawa, 1955). The walking speed in a dark tunnel is extremely slow in evacuation situations and must be determined accurately to assess tunnel fire safety. Therefore, this study conducted full-scale tunnel experiments to measure the walking speeds of participants wearing blindfolds. The tests were conducted in the disused ex-Tonokuchi tunnel in Fukui, Japan, in 2016 and 2017. Age and gender were confirmed to have a small influence on walking speed. The results clarified that participants' walking speeds were approximately lognormally distributed within a 95% interval (using the 2.5th and 97.5th percentiles of the distribution as endpoints, which are 0.24 and 0.88 m/s with a mean value of 0.49 m/s). Two female participants became lost and gave up trying to evacuate, which generated a cancellation rate of 0.6% of the total number of evacuees. [ABSTRACT FROM AUTHOR]

Particles of a thermo-sensitive gel were observed in a polymer solution. Gels of N -isopropylacrylamide (NIPA), which generally have a volumetric transition temperature of around 32 °C in pure water, were synthesized as porous media. The swelling ratio, mass ratio of a gel in the swollen state to that in the dry state, was measured in water as well as in an aqueous polymer solution of polyacrylamide at various temperatures. The observation in the polymer solution, where temperatures varied vertically between 10 °C and 40 °C from bottom to top, showed that gel particles repeatedly moved up and down. [ABSTRACT FROM AUTHOR]

• We conducted the full-scale tunnel experiments for investigation of the emergency evacuation speed. • Evacuation speed distribution was investigated statistically. • Evacuation speed was approximately lognormal, gamma and normal distributed. • We investigated the evacuation speed curve with smoke. A series of experiments was performed to investigate the evacuation speed distribution in a darkened smoke-filled full-scale tunnel where participants are expected to perform urgent evacuation, the results of which provide fundamental patterns for evacuating pedestrian traffic in the event of tunnel fires. The extinction coefficient was divided into levels, namely, 0 (no smoke), I (0.01–0.5 m−1), II (0.5–1.0 m−1), and III (>1.0 m−1), the probability distribution of evacuation speeds of which were found to approximate gamma, and lognormal distributions, as reported by Seike et al. (2020) considering zero-visibility tunnel conditions. The results of the statistical analysis were used for determining the relationship between emergency evacuation speed and extinction coefficient of up to Cs = 2.2 m−1 through a set of formulations, which agree that the evacuation speed decreases with greater values of extinction coefficient. Based on the comparison between the present experimental results and that of the Swedish group, it was considered that the evacuation speed decreased rapidly at around Cs = 4 m−1, after which it approached Seike et al.'s (2020) values asymptotically. [ABSTRACT FROM AUTHOR]

To understand time gaps during bus evacuation to conduct high-quality risk analysis of tunnel fires, this study collected time gaps from the Hsuehshan tunnel fire in Taiwan, experimental bus evacuations, and observed bus alighting. Based on the analysis of Hsuehshan tunnel fire, two situations were manifested: one wherein the bus passengers alighted normally as if it was a usual bus experience with no urgent requirement to evacuate (evacuees one to seven) and another associated with an urgency to evacuate (evacuees 8–19). We applied the results of the analysis in the Hsuehshan tunnel fire incident to investigate the time gaps from experiments and observations by dividing it into two groups: non-urgent and urgent. Statistical analyses were performed to investigate suitable probability distribution curves to describe the time gap distributions. The lognormal and gamma distributions show relatively good performance in approximating time gap data in non-urgent and urgent situations. Moreover, when comparing the time gaps of bus evacuation during the Hsuehshan tunnel fire accident, the urgent and non-urgent group time gaps corresponded to the assorted Stage II (52%) and Stage I (65%) of the Hsuehshan tunnel fire, respectively. • Time gaps of bus evacuation during a tunnel fire were investigated. • Bus-alighting time gaps were clarified as two main types (non-urgent and urgent). • Time gaps can be approximated by lognormal or gamma distribution. • Time gap distribution was compared with time gaps in an actual incident. [ABSTRACT FROM AUTHOR]

Industrial fires are undeniably the most dangerous type of fires for firefighters, and the master stream from water monitor is one of the safest means to deploy defensive or offensive strategies against such fires. However, few studies pay attention to the efficacy of the master stream. To address this issue, we extracted and analyzed numerical data from physical master streams. The proposed methods comprising of digital image processing (DIP) and large-scale particle image velocimetry (LS-PIV), which were conducted in the full-scale discharge in order to obtain coordinate trajectory pattern as well as the instantaneous and mean vector-velocity fields. The flow vectors in the different zones of the master stream were compared using KAZE feature detection. This study thus offers more extensive and detailed experimental data to validate computational fluid dynamics (CFD) simulations and opens an avenue for future fire-safety research. • Measure the velocity field of master stream with safety and cost-effectiveness. • Validate CFD simulation program with extensive and detailed experimental data. • Performance-based design for fixed water monitor adjacent to the storage tanks. [ABSTRACT FROM AUTHOR]

We examined the exhaust performance of a hybrid ventilation strategy for maintaining a safe evacuation environment for tunnel users in a tunnel fire. The hybrid ventilation strategy combines the longitudinal ventilation strategy with the point ventilation strategy which is a type of transverse ventilation strategy. The model tunnel developed by this study was scaled to 1/5 the size of a full-scale tunnel. The model-scale experiment was performed taking into consideration Froude's law of similarity. Measurement items were the distribution of temperature and concentration of smoke inside the tunnel, longitudinal wind velocity, mass flow of smoke in the point ventilation duct, and the heat release rate of the fire source. The following main conclusions were obtained. The smoke height was constant even when varying the extraction rate of smoke from the ceiling vent. The backlayering length and critical velocity of the smoke flow in the hybrid strategy could be predicted by the methodology developed by using the longitudinal strategy. The hybrid strategy maintained a safe evacuation environment on both sides of the tunnel fire. [ABSTRACT FROM AUTHOR]