The fire plume spilled from a window is believed to be one of the main fire sources with respect to a building façade fire, which happened previously in China. To have a deep understanding of vertical temperature distribution at window opening is of significance. In the current contribution, a series of compartment fire tests under over-ventilation were conducted with a 1.35 m × 1.35 m × 1.35 m compartment to clarify the critical discontinuity position (HD) by varying window opening sizes, opening aspect and heat release rate (HRR). Temperature history at the window openings were recorded by a thermocouple net. A theoretical calculation method of HD is detailed according to the compartment configuration. It is found that the critical discontinuity area is observed apparently along the window opening height, which has a big temperature difference. By the comparison of experimental and theoretical results, the constant comprehensive coefficient of 1.68, 1.92 and 3.85 of 300 kW, 600 kW and 900 kW are got for an engineered empirical prediction model are proposed, respectively. It provides an insight for the understanding of critical temperature discontinuity and reference for engineering calculations.

The minimum fire extinguishing concentration is a key index for the development of next generation chemical clean fire extinguishing gases, which is usually got by the cup-burner. The fire suppression performance of low concentration of chemical gas is hard to be understood by the available methods. In this work, the fundamental acknowledgement of steady flame surface attacking mechanism by halon functional group is newly discussed by conducting a series of bench scale tests with a cylindrical channel under a varied fluorinated gases. The characteristics of flame propagation under differentiated air atmosphere environmental conditions is obtained. The influence of fluorine-containing gas flow rate on flame propagation speed is clarified. A dimensionless relationship including atomic radius, bond length, polarization degree, molar mass and molar volume are proposed to describe the influence of low concentration of fluorine-containing gas on flame propagation speed. It provides an insight for the understanding of the flame inhibition performance of low concentration halogenated gas.

Due to its huge oil storage capacity and high operating temperature, the UHV (ultra-high-voltage) converter transformer is prone to high-temperature hot oil fire. As the main fire extinguishing system for oil fires, the low-expansion foam fire extinguishing system with the functions of cooling and isolating air can be targeted for extinguishing UHV transformer fires. To evaluate the technical feasibility of low-expansion foam extinguishing agents in oil-immersed transformers, this paper explores the suppression effect of three low-expansion foam extinguishing agents with different concentrations for hot oil fire under different conditions through the experiment model with a combustion area of 1 m2. By analyzing the effects of different foam generation mode, supply intensity, foam types and fire conditions on extinguishing efficiency and fire development trend. According to the experimental results, when low expansion foam must be used to extinguish fires, it is recommended to select AFFF or AFFF/AR to extinguish a hot oil fire oil-immersed. Meanwhile, the foam monitor or bubble gun with a good foaming effect can avoid boiling overflow of hot oil to a certain extent. The results can provide scientific guidance for fire fighting and rescue of large oil-immersed transformer fires, and a reliable reference for the selection of high-efficiency low-expansion foam extinguishing agent.

Compared with traditional fuel vehicle fires, new electric vehicle fires have a fast flame propagation rate and higher smoke toxicity. Thus, higher requirements need to be implemented when designing tunnel fire protection. In this study, a horizontal highway tunnel with a rectangular cross-section is taken as the research scenario, and the FDS numerical simulation method is used to study the effects of different blocking ratios and key parameters of the water mist system in a rectangular tunnel under longitudinal ventilation on the smoke temperature and flow state near the fire source area. The results indicate that the average velocity of smoke in the vicinity of the fire source in the tunnel is mainly related to the cross-sectional size of the obstruction, and changing the spray angle does not affect the state of the smoke flow field. The relationship between the cross-sectional size of the blocked vehicles in the tunnel and the spray angle is proposed. In addition, when the blocking ratio reaches 25%, the back-layer length of smoke corresponding to the subsequent blocking ratio remains basically unchanged. Setting a reasonable spray angle can significantly reduce the CO mass fraction in the tunnel, while the visibility of the tunnel will also decrease. Using the dimensionless analysis method, a critical velocity correction model based on the blocking ratio factors is proposed. These research results provide a theoretical reference for the design of longitudinal ventilation and smoke exhaust for new energy-electric vehicles in highway tunnels.

Transformers, being the largest oil-bearing equipment, are susceptible to high-temperature hot oil fires and large-area flowing fires that can be challenging to extinguish. To investigate the effectiveness of compressed air foams (CAFs) agents in extinguishing fires in ultra-high voltage (UHV) converter transformers, this work examines the fire suppression capabilities of three typical CAFs agents. A test model of a hot oil fire in a transformer with a burning area of 1 m2 was constructed for this purpose. The fire test was conducted by heating the transformer oil using an electric heating system, and the test process was monitored using an unmanned aerial vehicle. The results indicate that three CAFs agents used in the tests are capable of extinguishing a 1 m2 transformer hot oil fire without causing boiling over phenomenon. 1% MJBP CAFs is the fastest with a fire extinguishing time of 168 s, and is even more efficient when the gas to liquid ratio is 9:1. CAFs have the advantage of uniformity and stability, making it suitable for extinguishing hot oil fires in extra high voltage transformers as it does not cause boiling fires during firefighting.

The application of abrasive water jets for wire surface treatment is discussed. It is found that the roundness of wire improves with the increase of standoff distance and nozzle numbers. The analysis shows that when the wire moves fast, the abrasive water jet only peel off a thin layer from the wire surface but as the tractive speed slows down, the abrasive water jet cut deep slots on the wire.