A comparative study of drainage characteristics in AFFF and FFFP compressed-air fire-fighting foams

Abstract

Drainage measurements are commonly used for assessing the quality, water-retention ability and stability of aqueous foams used in fire-fighting applications. A new experimental technique is proposed in this paper, for measuring the drainage rate of liquid from compressed-air fire-fighting foams. The procedure outlined here provides advancement in precision over that prescribed by the standard for low expansion foams (NFPA 11, Standard for evaluating low expansion foams, NFPA, Quincy, MA, 1998). A comparative analysis of drainage characteristics in two commonly used Class B fire-fighting foams was undertaken, from theoretical and experimental perspectives: (i) aqueous film forming foam and (ii) film forming fluoroprotein foam. It is demonstrated that even though both the foam solutions exhibited similar fundamental physical properties, the disparities in surface rheological properties cause the resulting foams to have remarkably distinct drainage and coarsening characteristics. In addition, a drainage model is outlined, which allows the explicit prediction of the time evolution of liquid holdup profiles and drainage rates in fire-fighting foams. The existing drainage model is extended to simulate fire-fighting foams made from protein based and synthetically produced surfactants.