Wood stack fire tests to evaluate the influence of extinguishing medium and driving pressure on fire extinguishing efficacy of forest trees

•Hydrogel extinguishing agent and CAF can effectively extinguish woodpile fires.•Compared with CAF,hydrogel extinguishing agent has higher extinguishing efficiency.•Increasing driving pressure to improve cooling efficiency of extinguishing agent.•Cooling efficiency of CAF reaches the highest at a certain driving pressure range. In order to explore efficient fire extinguishing agents for forest fires and further enhance fire prevention and extinguishing technology, an outdoor fire extinguishing test platform for burning wood stacks is constructed to simulate fire extinguishing scenarios in an open-air environment. Comparative analysis of fire extinguishing performance of hydrogel extinguishing agent and compressed air foam (CAF), and exploring cooling effect of fire extinguishing agent on internal high temperature of wood stacks under three driving pressures of 0.45 MPa, 0.55 MPa and 0.65 MPa. Test results show that both hydrogel extinguishing agent and CAF can effectively extinguish woodpile fires. Hydrogel fire extinguishing agents are more efficient in extinguishing fires by comparing extinguishing time and agent dosage. CAF in the early stages of firefighting, there is a momentary enhancement of flame, which leads to an increase in temperature of wood stacks and heat radiation fluxes. In contrast, hydrogel fire extinguishing agents can quickly reduce temperature and heat radiation flux of wood stacks, and cooling effect is significant; When driving pressure is increased from 0.45 MPa to 0.65 MPa, the flame extinguishing time gradually decreases. Analyzing cooling capacity in terms of consumption of extinguishing agent, hydrogel extinguishing agent increases about 40 %, while cooling capacity of CAF increases only about 22 %; Hydrogel's cooling efficiency is better than CAF, and increasing driving pressure helps to improve agent cooling efficiency. Among them, CAF needs to be within a specific gas driving pressure range, which can minimize negative effect of gas driving pressure and enhance its cooling efficiency.