The influence of foaming agent concentration on the wetting ability and foam expansion rate when dosing in automatic sprinkler systems

Abstract

Purpose. To determine the dependence of the wetting ability and expansion ratio of foam on the concentration of the foaming agent (wetting agent) for extinguishing fires, and also establish the concentration limits of the foaming agent at which the fire extinguishing solution meets the requirements of technical regulations and technical documentation of the manufacturer for the expansion ratio of foam and the wetting ability indicator. Using the example of a model room, to perform a hydraulic calculation of an automatic fire extinguishing sprinkler installation and analyze the possibility of maintaining the required concentration of foam concentrate using a pressure-type dosing device with a washer.

Methods. The general methodology of the work included the theoretical (analysis, synthesis, comparison) and experimental research methods. Wetting ability of the foaming solution and the expansion rate of generated foam were determined experimentally using the test method described in STB 2459-2016. Processing of experimental data was performed using regression analysis, as well as establishing the uncertainty of measurements.

Findings. In the result of experimental studies, it was found that the concentration of foaming agents (wetting agents) OPS-0,4 by more than 0.67 % and SP-01 by more than 0.77 % in the extinguishing solution can lead to an increase in the expansion rate of foam formed at the outlet of the automatic fire sprinkler system by more than 5, and consequently, cause the deterioration of the effectiveness of the fire extinguishing. For this reason, in sprinkler fire extinguishing system (FES), the dosing device must provide a certain minimum (operation of one dictating sprinkler) and maximum flow rate of the foam agent to maintain a concentration sufficient for effective extinguishing. Using the example of a model room measuring 12.5×7.7 m, it is shown that when using a pressure-type dosing device with a washer having a fixed hole diameter for introducing the foam agent into the supply pipeline of the unit, an excess of the concentration of foaming agent SP-01 brand recommended by manufacturers by more than 7.7 times occurs when opening three of the twenty-four sprinklers of the ceiling section of the FES. Based on this, it is necessary to conclude that when designing sprinkler FES, it is necessary to carry out a detailed calculation of the dosing of the foaming agent when the sprinklers are sequentially activated in the section, or to use dosing devices capable of automatically adjusting the dosing depending on the water flow in the supply pipeline.

Application field of research. Designing of automatic FES using sprinklers.