Effectiveness of Halon Alternatives in Suppressing Dynamic Combustion Processes

Abstract

C 3 F 8 is shown to require the least storage volume among twelve fluorocarbons for suppressing a quasi-detonation. CF 3 I performs the best of the gaseous suppressants evaluated in a spray burner. Two experimental facilities are described as part of an effort to identify suitable replacements for CF 3 Br in aircraft applications. A turbulent spray burner simulates the hazard associated with a ruptured fuel line in an engine nacelle or dry bay. A deflagration/deto nation tube evaluates the ability of a gaseous agent to attenuate the pressure build-up and Mach number of a quasi-detonation.Halon 1301 (CF 3 Br) is no longer produced in the U.S., forcing the manufacturers, owners, and users of aircraft to search for an alternative fire suppressing agent (/). A research program was established at NIST to focus specifically on engine nacelle and dry bay protection. The nacelle is the portion of the airframe which surrounds the jet engine. The engine system certification process requires that enough agent be available to maintain a minimum concentration (6% by volume for halon 1301) throughout the nacelle for a 0.5 s time interval to ensure that the fire will be extinguished and not relight. Dry bays refer to normally closed spaces adjacent to flammable liquid storage areas that are vulnerable to anti-aircraft fire. The entire suppression sequence occurs in under 100 ms in the dry bay.The experiments described here are two of dozens that were developed (2) to identify the best chemicals for subsequent full-scale aircraft fire extinguishment evaluation at Wright-Patterson Air Force Base. The discriminating factors elucidated by the test protocols were lumped into four categories: (i) agent dispersion charac teristics, (ii) required storage volume, (iii) environmental factors, and (iv) operational issues. The results presented in this paper are limited to the flame suppression studies which directly impact the estimate of agent storage volume required on board the aircraft. However, the dispersion character of the different agents in cold-flow 3