Fire and Materials最新文献

Tunnel fire is one of the major challenges that cannot be ignored in the safe operation of tunnels. Considering the structural characteristics of tunnel fires, it is feasible to use longitudinal ventilation coupled with multi-point centralized smoke exhaust in subway tunnel engineering. Combining common slope tunnels, it is of great significance to investigate the ceiling temperature characteristics of such tunnels. Experimental testing was conducted. The results indicate that there is a strong linear relationship between the ceiling maximum temperature and the tunnel slope. A prediction formula for the ceiling maximum temperature of a sloping subway ventilation tunnel with a multi-point centralized smoke exhaust mode has been proposed. Based on the double exponential addition temperature decay model, the decay trend upstream and downstream of the exhaust vent was discussed. The constant coefficient remains basically unchanged; the decay index coefficient is linearly related to the tunnel slope, and the reduction coefficient is linearly related to the smoke exhaust volume. A tunnel ceiling temperature decay model with a multi-point centralized smoke exhaust mode affected by tunnel slope was proposed.

Highway tunnel fires caused by traffic accidents can lead to multiple simultaneous fires, which are more destructive and difficult to control compared to single fires. This study conducts a series of experimental tests to examine the smoke backlayering length, maximum gas temperature rise beneath the tunnel ceiling, and other critical parameters of dual source fires. The experiments were carried out in a 1:10 reduced-scale model tunnel with longitudinal ventilation, varying burner separation distances and burner dimensions. The results indicate that the smoke backlayering length in dual source fires is influenced by the longitudinal ventilation speed, heat release rate, and burner separation distances, while the maximum temperature rise beneath the ceiling decreases with increasing burner separation distances. A function incorporating burner separation distance and burner dimensions was proposed to predict the smoke backlayering length, based on the prediction model for a single fire source and the experimental data for dual fire sources. Additionally, based on the single fire source theory, a prediction model for the maximum temperature rise beneath the ceiling with dual fire sources was established. These findings provide a theoretical basis for risk prevention in tunnel fires involving multiple fire sources.

To study the explosion suppression mechanism of nonpremixed inert gas, this paper uses CFD software Simtec to simulate the suppression process of methane explosion by nonpremixed nitrogen in a square tube. The closed square tube includes three sections: ignition section, suppression section, and combustible gas mixture section. The results show that the critical explosion suppression length increases first and then decreases with the increase of methane concentration. When the methane concentration is 11%, the critical explosion suppression length is the biggest, which is 1.6 m. With the increase of the length of the suppression section, the overpressure curve first changes from a high-pressure single peak to a double peak and finally to a low-pressure single peak. After ignition, the nitrogen in the suppression section moves to the right with the flame under the driving effect of thermal expansion of combustion products. When the flame propagates near the suppression section, the nitrogen section stops moving right. Then, under the disturbance of the explosion wave, the suppression section is stretched. When the length of the suppression section is less than the critical explosion suppression length, the flame passes through the suppression section to ignite the combustible mixture, causing a secondary explosion. If the suppression length is greater than the critical explosion suppression length, the flame will gradually extinguish in the suppression section. The feasibility of suppression explosion by nonpremixed inert gas was verified, and the suppression mechanism of nonpremixed inert gas is inertial isolation rather than dilution.

This paper investigates the inhibitory effects and mechanisms of different powder inhibitors on corn starch explosion flame propagation. The results indicate that ABC powder exhibits the strongest suppression effect, followed by Al(OH)₃ powder and dolomite powder. Increasing the inerting ratio progressively suppresses the flame acceleration characteristics of corn starch explosion. The addition of 25 wt.% ABC powder significantly inhibits flame propagation, reducing the average flame propagation velocity by 83.6% and the maximum propagation velocity by 91.7% compared to the uninhibited condition. Compared to Al(OH)₃ and dolomite powder, ABC powder has a lower initial thermal decomposition temperature, a broader pyrolysis temperature range, and greater endothermic efficiency. The thermophysical properties of the powder inhibitors show good consistency with their explosion suppression effectiveness. The inhibitors generate NH₃, H₂O, SO₂, and N₂, which effectively reduce both the laminar burning velocity and heat release rate of corn starch pyrolysis gases. The competition between H + O₂ = O + OH and H + CH₃(+M) = CH₄(+M) dominates the combustion reactions of pyrolytic gases from corn starch. The CO₂, H₂O, and NH₃ generated by the thermal decomposition of inhibitors do not alter the fundamental reactions governing combustion. However, the generated SO₂ introduces two additional key inhibitory elementary reactions: H + SO₂(+M) = HOSO(+M) and H + O₂(+M) = HO₂(+M).

The insulation of electrical cables, exposed to external heat in a high-temperature environment, undergoes thermal decomposition and carbonization, resulting in the loss of insulation performance. Cables without insulation protection were prone to short circuits. Short circuits were one of the common ignition sources in electrical fires. However, research on the ignition of energized wires by arcs was not clarified. In this study, the standardized cone heater was used to simulate high-temperature conditions in order to investigate the occurrence of short circuits in energized cables within a high-temperature environment, as well as the characteristics and correlations of the combustion. The intensity of thermal exposure was accurately controlled through adjustments to the heat flux emitted by the cone heater. The short circuits in thermally exposed cables could be classified as a single arc or multiple arcs based on the fluctuations observed in voltage and current upon the occurrence of an arc. The results indicated that the minimum heat flux leading to a short circuit was 22 kW/m². A short-circuit arc became inevitable once the heat flux surpassed 25 kW/m². Notably, when the heat flux exceeded 26 kW/m², the probability of multiple short circuits within the conductor escalated significantly, reaching 83.7%. Compared to a single arc, multiple arcs exhibited a shorter initial occurrence time, a longer duration, and a higher probability of igniting cable insulation. The spread distance of combustion due to multiple arcs was primarily concentrated within the range of 23–28 cm. Furthermore, the maximum and minimum arc energies generated by multiple arcs were approximately three times higher than those generated by a single arc, respectively. This research provided valuable information for evaluating the fire hazards associated with different short circuits and determining the fire causes.