To draw lessons from historical chemical accidents and guide the practice of chemical safety production management，a method for identifying critical factors in chemical accidents based on text mining and improved DEMATEL method was proposed. Firstly，text mining technology was used to fully mine the text information of 1 627 chemical accident investigation reports，based on which 14 chemical accident influencing factors were extracted according to related literature，laws and regulations. Then，the fuzzy DEMATEL method based on alpha-level sets was used to calculate the performance levels of the factors affecting chemical accidents. Finally，the correlations between critical factors and other factors were analyzed and the mechanism of chemical accidents was revealed. The results show that 8 chemical accident influencing factors are identified as the critical factors，i.e.，extreme weather，regulations，technical procedures，hidden danger investigation，risk control，education and training，supervision and management，and operation management. These 8 critical factors have direct impact on the influence factors such as facilities and equipment，material reactions，occupational quality，job responsibilities，emergency management，and safety investment，which eventually lead to chemical accidents.

In order to address the difficulty to quantifying the emergency coordination ability of related organizations during the formation of urban flood emergency plans，a method to evaluate the robustness of inter-organizational networks for urban flood emergency response considering cascading failure was proposed. First，the inter-organizational networks for flood control emergency plans in Beijing，Shanghai and Shenzhen were established，and attack strategies and evaluation indexes of network robustness were proposed. Secondly，network characteristic statistical parameters are computed，and the network topology properties were analyzed. Then，the natural connectivity was selected as the robustness indicator to evaluate the network robustness under node single-attack strategy and continuous attack strategy. Finally，the robustness of networks under different attacks was compared，and the key organizations that have a great influence on robustness were found. The results indicate that inter-organizational networks of urban flood control emergency plans in Beijing，Shanghai，and Shenzhen have small-world and scale-free characteristics. Under single attacks of nodes，compared with the case of non-cascading failures，the robustness of inter-organizational networks is weaker considering cascading failures. Organizations with a large number of failure nodes are key to making the networks robust. Under continuous attacks，networks are strongly robust to random attacks，but weakly robust to deliberate attacks，where organizations with high degree values are key to making networks robust.

In order to ensure the safety of the construction and operation of the karst water inrush tunnel，based on the elastic beam model，double cusp mutation model of the instability of the karst water inrush roof under dynamic disturbance was established by using the catastrophe theory. Considering the surrounding rock properties，hydrostatic pressure，dynamic disturbance and other factors，the instability mechanism and failure conditions of the roof of karst water inrush tunnel were analyzed，the discriminant equation of its instability mutation was established，and the minimum safe thickness of the roof was solved by Matlab software programming. At the same time，in order to avoid the irrationality of the theoretical formula of the mutation when the hydrostatic pressure was too large，the minimum safe thickness of the hydrostatic pressure was calculated separately，and the greater value of two calculated values was taken. The results show that whether the waterproof rock mass remains stable is determined by the factors the internal and external factors of rock mass. The minimum safe thickness of the rock mass increases with the increase of the span of the rock mass，and decreases with the increase of the elastic modulus of the rock mass. When the vibration frequency is constant，the greater the blasting load，the greater the minimum safe thickness of rock mass. When the blasting load is constant，the greater the frequency of blasting vibration，the smaller the minimum safe thickness of rock mass. The greater the hydrostatic pressure，the greater the minimum safe thickness of rock mass. The engineering example shows that this method of calculating the safety thickness of the roof of karst tunnel is feasible and highly accurate.

In order to improve the accuracy of fire water cannon jet trajectory prediction and overcome the difficulty of traditional parabolic theory to describe the phenomenon that "when the initial velocity is constant，the range increases with the increase of jet flow"，first of all，the Euler method was used to establish a one-dimensional mass conservation equation along the trajectory of the water jet in the air，axial momentum conservation equations and the radial momentum conservation equations. Then，assuming that the axial velocity distribution of the water column and air column was in the shape of "bowler hat"，the established conservation equations were derived and analyzed，and the fire water cannon water jet trajectory calculation model was established. Finally，based on three conservation equations，the numerical computation process of the jet trajectory model was given and verified with the collected experimental data. The results show that the error of this model is less than 10%.

To investigate the features and causation factors of fire accidents in SRBE，118 fire accidents were studied using method of mathematical statistics. Firstly，accident features were mined in terms of the temporal and spatial attributes of accidents，the three elements of fire and the severity of injuries. Then，based on the improved HFACS-SRBE accident causation model，methods such as Chi-square test，OR and Cramer's V were used to analyze the correlations and their strength between the causal factors. The results show that 14:00-16:00 is the most prone to fire accidents and casualties. The main location of fire accidents is in the ship area，accounting for 33.90%. 59.19% of the ignition source comes from the ignition operation. Ratio of no injuries，slight and minor injuries，serious injuries and deaths is 61:54:3. Through the test of correlations and their strength，it is determined that 15 groups of adjacent level causal factors are correlated，and 26 complete accident causation chains are obtained. Covers communication and coordination→inappropriate operation plans→bad psychological state→decision-making errors is the accident causation chain with the greatest strength of correlation leading to the occurrence of fire accidents in ship repair and building enterprises.

To further improve the fire extinguishing efficiency of environmentally friendly foam extinguishing agents，surfactants of the sodium alpha-olefin sulfonate (AOS) and phosphate betaine silicone surfactant (PBSS) and foam stabilizers of inorganic salts and polysaccharides were used to propose environmentally friendly foam extinguishing agents. The effects of inorganic salt and polysaccharide mixtures on surface tension，foaming capability，and foam stability were analyzed. Then the foam stabilization mechanism of the foam stabilizer mixtures was investigated. The results indicated that the inorganic salt and polysaccharide mixtures greatly improved the physicochemical properties of the foam extinguishing agents. The foam fire extinguishing agent mixture by 0.025% xanthan gum，0.125% gelatin，and 0.1% MgCl₂ showed the best overall performance with a surface tension of 24.34 mN/m，an initial foam height of 118.81 mm，and a 25% liquid drainage time of 132.1 s. The foam stabilizing mechanism of the foam stabilizer was attributed to the formation of hydrogen bonds between xanthan gum and gelatin，which greatly enhanced the surface strength of the foam liquid film，thereby effectively slowing down the drainage rate and bubbles coarsening of foam. Moreover，the Mg²⁺ was adsorbed around the AOS/PBSS head group due to electrostatic interaction，which impaired the electrostatic repulsion between the head groups and increased the concentration of surfactant，further improving foam stability.

In order to reduce the safety problems caused by leakage of hydrogen-blended natural gas during the distribution，based on fluid mechanics and porous media theory，a three-dimensional numerical model of leakage and diffusion of urban buried hydrogen-blended natural gas pipeline was established by Fluent software. The effects of hydrogen blending ratio，leakage aperture，pipeline pressure，pipeline buried depth and soil type on the leakage of hydrogen-blended natural gas and the vertical diffusion distance of the lower explosion limit of methane and hydrogen were analyzed. The results show that the larger the proportion of hydrogen blending，the smaller the leakage of hydrogen-blended natural gas，and the longer the time it takes for the methane explosion lower limit contour to diffuse to the surface，while the opposite is true for hydrogen. Secondly，the leakage amount is about twice as much as 5 mm when the leakage aperture is 10 mm. The leakage amount is about twice as much as 10 mm when the leakage aperture is 20 mm. The larger the leakage aperture，the shorter the time required for the lower explosion limit of methane and hydrogen to reach the surface. Thirdly，the greater the pipeline pressure，the greater the leakage of hydrogen-blended natural gas and the faster the diffusion speed，and the higher the risk coefficient. Besides，when the buried depth of the pipeline is 1.1m，the leakage is largest，followed by 1.4 m and 0.8 m. The shallower the buried depth，the shorter the time required for the lower explosion limit of methane and hydrogen to reach the surface. Finally，the soil type has an important influence on the leakage and diffusion of hydrogen-blended natural gas. When the soil type is silty sand，the leakage and diffusion rate of hydrogen-blended natural gas are the largest，followed by loam and finally clay.

To improve the synergistic explosion suppression and flame retardant efficiency of inert gas-water mist，based on spectral experiments，theoretical analysis and numerical simulation methods such as Fluent and CHEMKIN-PRO were used to study the changes in elementary reactions and typical free radical (H· and ·OH) molar fractions during the explosion suppression and flame retardant process of N₂ water mist at different injection positions and pressures. The results showed that staggered injection of N₂ and fine water mist had better synergistic explosion suppression and flame retardant effect than convection and parallel injections. For case of simulated pipeline，good explosion suppression and flame retardant effect were found only when the spray pressure of N₂ and water mist was 4.5 and 2 MPa，respectively. Furthermore，the maximum value of mole fraction for H· and ·OH was 0.006 4 and 0.006 9，respectively. The spray pressure can be applied to the actual methane explosion fire area based on scale effect. Moreover，the H· and ·OH mole fractions can be used as monitoring parameters during the operation of the current automatic fire extinguishing system in the fire protection area，and their changes can be used as a reference for fire extinguishing process.

To effectively prevent and control coal mine underground belt conveyor fire accidents and ensure the safety of lives and property of coal mine workers，the fire causes，combustion characteristics，smoke flow characteristics，monitoring and early warning technologies，and prevention measures of mine belt conveyor fires were systematically analyzed. Then，further prospects were proposed based on the current research status. The results showed that the main causes of belt conveyor fire were friction temperature rise，electrical equipment failure，and open flame. There were some limitations for the tunnel fire model and corresponding numerical simulation parameters used to study the fire combustion and smoke flow characteristics of belt conveyors，the actual working conditions and environmental parameters of the transportation tunnel should be comprehensively considered. Although there were monitoring and early warning systems for belt conveyor fires in China，they had some limitations. It was necessary to introduce emerging technologies such as 5G，big data，and artificial intelligence，and combine them with hardware detection and personnel management to improve the coal mine belt conveyor fire prevention and control system，and then comprehensively promote the construction of safety and intelligent in coal mine.

In order to realize the effective rescue of various complex rail transit accidents，the present situation and development trend of the existing rail fire rescue systems at home and abroad were analyzed through a literature search first. Then，the applicability of road and rail dual-purpose vehicles in mountain urban rail transit systems and the feasibility of modular transformation were summarized and analyzed. Finally，a new fire and rescue rail transit system was proposed，which was suitable for mountain urban rail characteristics. The results show that the designed road and rail dual-purpose fire rescue vehicle meets the requirements of track fire rescue. The system is adopted with a high-intensity modular and prefabricated design concept. It is equipped with a fire extinguishing and smoke exhaust system for controlling various fire conditions，a traction winch，emergency power generation，medical supplies，and other emergency rescue equipment，which can deal with the rescue work of track accidents in a closed and heavy smoke environment. The loss caused by accidents is significantly reduced.