Michael Burns and William M. Cavage

A series of aircraft flight and ground tests were performed by the Federal Aviation Administration (FAA) and the Boeing Company to evaluate the effectiveness of ground-based inerting (GBI) as a means of reducing the flammability of fuel tanks in the commercial transport fleet. Boeing made available a model 737-700 for modification and testing. A nitrogen-enriched air (NEA) distribution manifold, designed, built, and installed by Boeing, allowed for deposit of the ground-based NEA into the center wing tank (CWT). The fuel tank was instrumented with gas sample tubing and thermocouples to allow for a measurement of fuel tank inerting and heating during the testing. The FAA developed an in-flight gas-sampling system, integrated with eight oxygen analyzers, to continuously monitor the ullage oxygen concentration at eight different locations. Other data such as fuel load, air speed, altitude, and similar flight parameters were made available from the aircraft data bus. A series of ten tests were performed (five flight, five ground) under different ground and flight conditions to demonstrate the ability of GBI to reduce fuel tank flammability.

The CWT was inerted with NEA to approximately 8% oxygen concentration by volume for each test. The aircraft condition was then set (fuel load, wind condition, and flight condition), and the oxygen concentration in the CWT was continuously monitored. Results showed that, under quiescent conditions, the oxygen concentration in the fuel tank remained somewhat constant, keeping the CWT inert (below 10 to 12% oxygen by volume) for relatively long periods of time. However, due to the cross venting configuration of Boeing aircraft, certain wind conditions created cross venting within the CWT which allowed for significant increases in the oxygen concentration. Some flight conditions also contributed to cross venting and created high oxygen concentrations within the fuel tank. A modification to the vent system prevented cross flow within the CWT and created a significant increase in the amount of the time the tank remained below 10% oxygen, even at low to moderate fuel loads.

Timothy R. Marker and John W. Reinhardt

This report describes full-scale fire tests conducted by the Federal Aviation Administration (FAA) to investigate the effectiveness of several types of water spray systems against in-flight cargo compartment fires. Currently, commercial transport cargo compartments are protected with Halon 1301 fire suppression systems. Water spray is being considered as an alternative agent for Halon 1301 which is no longer being produced because of its ozone depletion potential. A dual-fluid (air/water) nozzle system, two types of high-pressure, single-fluid design systems, and a second dual-fluid (water/nitrogen) nozzle system were evaluated. The in-flight fire scenarios included simulated bulk-loaded fires, containerized fires, flammable liquid fires, and aerosol can explosions. The majority of tests were conducted inside a wide-body DC-10 cargo compartment; additional tests were conducted in a B727 narrow-body compartment. Several tests utilizing one of the high-pressure, single-fluid design systems were conducted according to the Minimum Performance Standard (MPS) for aircraft cargo compartments which standardizes and specifies the fire test performance for halon replacement agents. Parameters such as activation temperature, spray duration, nozzle configuration, and flow rate were varied during the tests to determine the impact on water usage and suppression. The tests determined that the systems were capable of suppressing class-A and class-B cargo fires for extended periods, using varying amounts of water. Water spray systems require additional development and evaluation to become a viable replacement for Halon 1301 because of the weight (agent) penalty associated with the systems tested. Also, the capability of water spray against cargo fires involving aerosol cans needs further investigation.

Thomas L. Reynolds, Delbert B. Bailey, Daniel F. Lewinski, and Conrad M. Roseburg

The purpose of this technology assessment is to define a multiphase research study program investigating Onboard Inert Gas Generation Systems (OBIGGS) and Onboard Oxygen Generation Systems (OBOGS) that would identify current airplane systems design and certification requirements (Subtask 1); explore state-of-the-art technology (Subtask 2); develop systems specifications (Subtask 3); and develop an initial system design (Subtask 4). If feasible, consideration may be given to the development of a prototype laboratory test system that could potentially be used in commercial transport aircraft (Subtask 5). These systems should be capable of providing inert nitrogen gas for improved fire cargo compartment fire suppression and fuel tank inerting and emergency oxygen for crew and passenger use.

Michael Burns and William M. Cavage

This report documents a series of experiments designed to determine the quantity and purity of nitrogen-enriched air (NEA) required to inert a vented aircraft fuel tank. NEA, generated by a hollow fiber membrane gas separation system, was used to inert a laboratory fuel tank with a single vent on top designed to simulate a transport category airplane fuel tank. The tank ullage space could be heated as well as cooled and fuel could be heated in the bottom of the fuel tank to provide varying hydrocarbon concentrations within the ullage space.

Several inerting runs were performed with varying NEA gas purities and flow rates. The data was nondimensionalized in terms of NEA purity, volume flow rate, and fuel tank size to provide one universal inerting curve. Changing temperatures and hydrocarbon concentrations appear to have little effect on the amount and purity of NEA needed to inert the test specimen. A model of ullage washing developed by the Federal Aviation Administration Chief Scientific and Technical Advisor for fuel systems design, based on the volume exchange of gases of different concentrations, was compared with data obtained from the test article. Also, an exact solution based on uniform and instantaneous mixing was derived and compared with the test data. Both the model and exact solution showed good agreement in both trend and magnitude with the data obtained during the testing.

Michael L. Ramierz

This work has been conducted as part of the Federal Aviation Administration's (FAA) efforts to develop fire-resistant materials for commercial aircraft cabins. Polymers based on 2,2-bis-(4-hydroxyphenyl)-1,1-dichloroethylene (bisphenol C, BPC) have thermal and physical properties of bisphenol-A polymers but have an order of magnitude lower heat release in flaming combustion. This is due to a thermal degradation mechanism that yields only char and nor combustible gases in a fire. Two thermoplastics and one 'thermoset BPC-based polymer were studied to establish the decomposition mechanism of these materials. Thermal gravimetric analysis, differential scanning calorimetry, infrared spectroscopy, chromatography, and mass spectrometry were used separately and in combination to characterize the thermal degradation mechanism. Results showed that the major volatiles are hydrogen chloride (HCI) and the degradation products of the linking group. The rearrangement through stilbenes and acetylenes is responsible for the high char yield when burned.