As part of the National effort to identify effective replacements for halon fire suppressants, NIST has been investigating whether highly effective thermal agents are feasible. Thermal agents are defined as those that obtain their effectiveness solely by heat extraction and dilution. Excluded from investigation are species that directly or indirectly disrupt the combustion chemistry such as halons, which derive much of their effectiveness by the release of bromine atoms that catalytically remove hydrogen atoms in the flame zone. A NIST Internal Report is available describing the findings of the first year of this investigation. A thorough search of NIST thermodynamic databases was performed to identify molecular species that might be particularly effective thermal agents. Detailed chemical kinetic modeling of laminar opposed jet diffusion flames was used to predict extinguishing concentrations and provide insights into extinguishment mechanisms. Methane flames burning in air diluted with the known thermal agents nitrogen (N2), argon (Ar), helium (He), carbon dioxide (CO2), and water (H2O), as well as artificial surrogate agents, were considered. These findings were summarized during the 1999 HOTWC meeting. The third part of the study was an analysis of the interaction of liquid droplets with surfaces in order to characterize the physical properties desirable for liquid agents. The database search identified two chemicals that were predicted to be particularly effective at extracting heat from a flame zone. The first was methoxy-nonaflurobutanc (C4F9OCH3), also known as HFE7100, which was one of the highest rated thermal agents on both mass and molar bases. The boiling and freezing points are 334 and 138 K, respectively. Extinguishing molar concentrations in air for the gas were reported as 6.1% in a cup-burner test using heptane fuel and in a "micro cup-burner" test burning butane. No measurements of the effectiveness of this compound when released as a liquid were available.
Citation: Special Publication (NIST SP) - 984-4
NIST Pub Series: Special Publication (NIST SP)
Pub Type: NIST PubsReport Number:
halon alternatives, laminar flames, diffusion flames, extinguishment, liquids, burners, reaction kinetics, flame extinguishment, halons