Assessment of the Joint Effect of the Use of Fire Extinguishers by Several Operators

The study is dedicated to the investigation of improving the efficiency of fire extinguishing due to the joint action of the grouped use of fire extinguishers. Based on experimental data and mathematical modeling, the author has demonstrated how the fire-extinguishing powder jet configuration impacts the suppression of combustion. The experiments were carried out on model fire seats using nonane as a fuel, where the key parameters were the area of the fire seat, pressure in the device, and the nozzle diameter. The critical mass of powder, determined as the minimum quantity not sufficient without increasing the charge by 10 %, was equal to 2·10⁻³ kg. The investigation encompassed three jet configurations: parallel, counter, and angular. The parallel configuration ensured the increase in particle concentration in the jet crossing area; the counter configuration ensured the formation of a stable powder cloud inside the fire seat; and the angular configuration ensured the optimal distribution of particles due to combined coating. A comparison with metal grids at the input speed of 0.1–3 m/s has shown that the grids with 0.1 mm cells and high speed are most efficient, whereas large cells (5 mm) did not ensure fire extinguishing due to the insufficient heat sink area. The results of experiments have revealed that the joint use of two fire extinguishers decreased the required powder mass by 32 %. The highest efficiency has been achieved for the angular configuration, which is associated with the even distribution of particles. For the quantitative assessment, a joint action coefficient (1,6875) reflecting the increased effect during group work has been introduced. Based on that, a probabilistic model allowing for the calculation of the success of fire extinguishing depending on the number of fire extinguishers and operators has been developed. For example, with two fire extinguishers and two operators, the probability of suppression of an ignition reaches 99.9 %. The analogy between a powder cloud and metal grids has been experimentally determined. The innovation of the study is the introduction of a quantitative parameter of joint action of several fire extinguishers, which is useful for efficiency forecasting.