Fire suppression is essential to the readiness and effectiveness of nearly all Department of Defense (DoD) weapons systems. The fire suppressant agent Halon 1301 (CF3Br) has high ozone depletion potential and has been out of production since January of 1994. Near-term alternative compounds compromise system needs and make phase-out of CF3Br difficult due to serious weight and volume penalties, as well as operational and financial impacts.
The objective of the Next Generation Fire Suppression Technology Program (NGP) was to develop and demonstrate technology for economically feasible, environmentally acceptable and user-safe processes, techniques, and fluids that meet the operational requirements currently satisfied by Halon 1301 systems in aircraft.
This research was driven by evolving environmental constraints, while maintaining safety and cost-effectiveness, in developing new technologies for fire control in the engine nacelles, dry bays, and fuel tanks of existing and future aircraft. The NGP consisted of six components: (1) New Fire Suppressant Chemistry, which identified new families of high-efficiency agents; (2) Suppressant Screening Tests to develop methods to estimate rapidly the performance, hazard, and environmental properties of suppressants using only small amounts of chemical; (3) New and Improved Aerosol Suppressants, which involved the identification of candidate agents for those applications where a residue is acceptable; (4) Improved Suppressant Storage and Delivery, in which techniques were developed to obtain the highest efficiency of each new technology; (5) Viability of New Suppression Technologies, which developed methods for ascertaining the performance of new agents at real scale and evaluated the total cost of implementing candidate retrofit fire suppression technologies; and (6) Fuel Tank Inertion, which developed new techniques for quenching deflagrations in fuel tank ullage.
NGP research has produced a comprehensive view of the fire suppression process, involving both the chemical properties of the agent and the transport process, from the storage source to the flames. A suite of screening tests were developed or adapted to identify rapidly those chemical agents meriting further pursuit. Several new chemicals, including bromoalkenes and a partially fluorinated ether, show acceptable fire suppression efficiency, low atmospheric lifetime, and low toxicity. NGP research also produced a physiologically-based pharmacokinetic (PBPK) model for short-term inhalation of volatile halogenated hydrocarbon suppressants (extendable to other types of agents), enabling a more accurate calculation of safe exposure times and levels. Researchers also created a validated model for the transient delivery of two-phase agents through the complex distribution plumbing that exists in aircraft. The team quantified the relationships between the extinguishing concentration and the agent injection period for different clutter geometries and determined the optimal properties for liquid droplet suppressants. These combined results have led to the initiation of models that enable the optimization of effective agent distribution and efficient flame suppression. To ensure the effectiveness of new technologies, prototype instrumentation was developed for monitoring the concentrations of fuel, oxygen, agent, and hydrogen fluoride gas (an undesirable byproduct of some agents) during real-scale fire suppression tests.
This program identified and demonstrated alternatives to Halon 1301 that will enable DoD weapons system managers to make prudent decisions to eliminate the use of a key ozone-depleting substance in a manner that offers minimal fiscal and operational barriers to implementation.