Proportioning accuracy of foam concentrate testing in periodic control of foam fixed extinguishing systems

Abstract

The proper concentration of foam concentrate in water solution is a key factor in the effectiveness of fire-fighting foams produced using all currently used foam systems. The standard method for measuring the concentration of foaming agent, used to control the operation of the foam systems, is conductivity method. In this study, the applicability of the refractive index of the solution and the conductivity method was tested. The research found that the conductivity method can be used to determine the actual concentrations of all types of foaming agents in the solutions made from tap water, or water of similar electrical conductivity, of approx. 0.5 ÷ 0.8 mS/cm. Conductivity meter must be equipped with temperature compensation system. Measurement uncertainty is estimated to be ± 0.1 vol. % under optimal conditions for this method. In the case of water with high electrical conductivity, also refractometric method gives good results. In the case of solutions made with tap water and foaming agents working concentrations of 3% and more acceptable uncertainty in the measurements provides portable digital refractometer without temperature stabilization. In other cases, obtaining sufficient accuracy requires sample temperature stabilization during the test.