Multiobjective Optimization of Mg(OH) 2 -Gel Dry Water for Engineering: Pressure-Tailored Fire Suppression via Structural-Cooling Balance

China’s rapid urbanization has amplified both the complexity of urban fire hazards and the demand for sustainable public safety solutions. Conventional fire extinguishing agents, however, suffer from inefficient performance and environmental pollution, underscoring the critical need for high-efficiency and eco-friendly alternatives. In this study, eight kinds of dry water (DW) were prepared by gel structure strengthening and gradient magnesium hydroxide modification. The effects of composition, particle size and pressure on the fire extinguishing performance were systematically analyzed, and the optimal injection pressure of the modified DW was determined. The results show that Mg(OH)₂-Gel-DW-B has the best overall performance, the outflow rate is 3.71 mL/s, the bulk density is 0.452 g/mL, and the particle size is mostly less than 300 μm. The gel structure makes the particle damage rate <12% under 1.4MPa pressure; The fire extinguishing efficiency of 200–400 μm particles is significantly higher than that of fine/coarse particles. Mg(OH)₂-Gel-DW-B cooling rate is 20.5% and 35.5% higher than ABC/BC dry powder. When the pressure increases from 1.0MPa and 1.2MPa to 1.4MPa, the Mg(OH)₂-Gel-DW-B damage rate increases by 96.06% and 62.39%, and the cooling rate decreases by 20% and 16.36%. Combined with the powder diffusion time difference <1s, the optimal injection pressure is determined to be 1.0 ~ 1.2MPa. The research provides the key theoretical support for the engineering application of environmental protection fire extinguishing agent.