Dependence of dry powders inerting concentration on internal fire parameters

Purpose. Pulse extinction of a standardized fire (heptane) in a combustion chamber with a dry powder based on sodium bicarbonate (hydrocarbonate) and sodium carbonate is considered. The minimum dry powder concentration for extinction of internal fires with different parameters is determined. Dependences of powder fire-extinguishing properties on average volumetric temperature of а mock-up room and on combustible liquid temperature are obtained. Methods. The authors carried out a series of laboratory experiments in order to obtain dependence of minimum and optimal values of inerting concentration at various temperatures of internal environment and standardized fire (combustible liquid) temperature. Findings. Dependences of minimum dry powder concentration on temperature parameters of a standardized fire are obtained. The highest value of minimum inerting dry powder concentration turned out to be in the temperature range of gas-air medium from 20 to 35 °С, and the lowest values were at temperatures above 40 °С. A similar picture was observed when determining the values of minimum inerting dry powder concentration on the combustible liquid temperature. The highest value of minimum inerting powder concentration turned out to be in heptane temperature range approximately from 48 to 80 °С. Research application field. It is advisable to include study results in the educational process, as well as in research work in order to develop recommendations for choosing a rational method for supplying powder to fire area in rooms with different fire load. Conclusions. Based on the numerical value of inerting concentration in analyzing extinguishment efficiency for all cases of temperature changes in the mock-up room, the authors found an ambiguous behaviour pattern of minimum fire extinguishing dry powders concentration. This is explained by the fact that as the combustible liquid is burning out, combustion products (CO2 and H2O) are accumulating in the room and oxygen concentration decreases. It is also possible that at higher temperatures the decomposition of the powder into inhibiting gases occurs faster, which leads to less losses and a decrease in the inerting concentration. These facts require a more detailed study.