Enhanced Effectiveness of Liquid Thermal Fire Extinguishing Agents

Abstract

This paper describes the findings of a study designed to identify and characterize super-effective thermal fire-fighting agents as possible halon replacements. Two existing thermodynamic databases have been searched in order to identify chemical compounds, which are predicted to extract large amounts of heat from a combustion zone. Additional substances that are not well represented in these databases were included. Compounds having high (1) heats of vaporization, (2) liquid-phase heat capacities, and (3) total heat absorption due to phase changes (if applicable), heating of a liquid (if applicable), and heating of the gas phase to combustion temperatures were identified. Two compounds, methoxy-nonaflurobutane (HFE7100) and lactic acid, were identified as being especially interesting. Both agents and water were tested in the Dispersed Liquid Agent Fire Suppression Screen (DLAFSS) apparatus. Lactic acid was tested in mixtures with water at various concentrations. The acid/water mixtures were found to be less effective than water alone, indicating that the lactic acid was reacting and releasing heat that more than compensated for the heat extraction. HFE7100 and water were also tested in a screening apparatus known as the Transient Application Recirculating Pool Fire (TARPF) that incorporates a flame stabilized behind a bluff body in a turbulent oxidizer flow. The agent failed to extinguish a propane flame when it was released at nominal mass fraction in air twice as high as the extinguishing mass fraction measured in the DLAFSS. This observation is attributed to ineffective mixing and entrainment of liquid droplets into the flame. A simple thermodynamic analysis under-predicts the performance of the liquid thermal agents in the DLAFSS. Additional studies of the effectiveness of fire extinguishing agents released as liquids should be performed with a focus on confirming and understanding their enhanced performance relative to that expected based on simple heat extraction.