Browsing by Author "T'Ien, James"
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Item Fire Safety Implications of Preliminary Results from Saffire IV and V Experiments on Large Scale Spacecraft Fires(50th International Conference on Environmental Systems, 7/12/2021) Urban, David; Ruff, Gary; Ferkul, Paul; Easton, John; Owens, Jay; Olson, Sandra; Meyer, Marit; Fortenberry, Claire; Brooker, John; Graf, John; Casteel, Michael; Jomaas, Grunde; Toth, Balazs; Eigenbrod, Christian; T'Ien, James; Liao, Ya-Ting; Fernandez-Pello, Carlos; Meyer, Florian; Legros, Guillaume; Guibaud, Augustin; Smirnov, Nikolay; Fujita, OsamuThe spread and growth of flames over large solid fuel samples and their effect on the pressurized spacecraft were studied inside Cygnus spacecraft while in orbit after departing the International Space Station. These experiments were developed by NASA�s Advanced Exploration Systems Division in the Human Exploration and Operations Mission Directorate. The ignited materials consisted of poly-methyl methacrylate (PMMA), cotton fabric and a cotton/fiberglass fabric blend. The samples were all 40 cm wide and with various lengths ranging from 18 cm for the PMMA samples to 50 cm for the fabrics. The overall results from these tests and their impact on the spacecraft are presented with emphasis on the fire safety implications of the results. The experiments included, a post-fire cleanup system, vehicle internal volume measurements, and transport of acid gases (HCl and HF). Measurements included video images, flame spread rate, flame temperatures and radiant heat output; energy release through oxygen calorimetry; distributed measurements of CO2 concentration and temperature at six locations in the spacecraft; CO2, CO, O2, HF and HCl concentrations; vehicle pressurized volume; and aerosol concentrations. Details of the flame growth and spread are discussed in other papers as are details of the post-fire cleanup system performance. The fire events had a measurable impact on the vehicle pressure, temperature, and carbon dioxide concentration. However, despite having heat release rates up to 10 kW, the average vehicle conditions did not rise to unacceptable levels. The combined results of the experiments provide significant new understanding of the impact of sample and flow duct height on flame spread and growth in addition to an improved perspective of the impact of a fire event on a spacecraft.Item Flammability Limits from BASS-II Testing in Microgravity Compared to Normal Gravity Limits(49th International Conference on Environmental Systems, 2019-07-07) Olson, Sandra; Ferkul, Paul; Fernandez-Pello, Carlos; Miller, Fletcher; Wichman, Indrek; T'Ien, JamesNormal gravity flammability limits are often reported as downward spread limits (Limiting Oxygen Index), or upward spread limits (NASA Test 1, UL 94V). In microgravity, the comparable limits are opposed flow and concurrent flow. During BASS-II experiments in the Microgravity Science Glovebox on the ISS, PMMA (polymethylmethacrylate) rods, sheets, and slabs, and cotton-fiberglass fabric sheets were burned in microgravity with a variety of oxygen concentrations and at different flow speeds in both opposed and concurrent flow directions. Flame extinctions occurred under conditions indicating that materials can burn at a lower oxygen concentration in microgravity compared to normal gravity. Flames at very low velocity shrink to small spherical sections at the ends of rods, or to small nearly circular disks (a.k.a. flamelets) above flat samples. These spherical/circular flames sometimes oscillate prior to extinction. At high velocity, flames quickly grow but the stabilization zone thins and then fails as the flow time becomes too short for the reactions to occur in that hot flame stabilization zone. The flame blows off, often after a few oscillations. At the other extreme, the flames always quenched when the fan was turned off. This shows that the first line of fire defense on the ISS, to turn off all ventilation systems when a fire is detected, is an excellent mitigation strategy for the ISS. Previous quiescent testing at elevated oxygen concentrations, however, suggests that ventilation may not be necessary for a flame to survive under conditions that may be present in high oxygen low pressure atmospheres in spacecraft or in partial gravity environments, so this mitigation strategy may not be applicable in future exploration missions. The role of heat losses, sample dimension, and near-limit phenomena are discussed. A normal gravity test method is suggested that can account for partial gravity flammability, where more research is needed.Item Laboratory Evaluation of Nomex® IIIA as a Flammability Barrier Material in a variable oxygen and pressure atmosphere(46th International Conference on Environmental Systems, 2016-07-10) Shang, Wei; T'Ien, JamesMany flammable materials are used in home, building and transportation applications (automobile, airplane, spacecraft, etc). Despite they may fail in standard tests, they are employed because of their other desirable performance functions. One way to alleviate the potential fire hazard of these useful materials, is to use a barrier fabric that wraps around the subject. Nomex® is known to be non-flammable in normal air. It has been used extensively in spacecraft as a barrier fabric. However, with the possibility of using enhanced oxygen at reduced pressure in future space exploration vehicle, it is desirable to test the effectiveness of Nomex® as a barrier material in these new atmospheres. In this study, we tested Nomex® IIIA as a barrier fabric for flexible polyurethane foam samples in a range of atmospheres (pressure ranges from 6 to 18 psia and oxygen concentration up to 46%) in a small environmental chamber. Two polyurethane samples sizes were used (8x5.08x2.54cm and 8x5.08x1.27cm). The samples are wrapped around by the Nomex® fabric. An electric Ignition coil with a prescribed power and duration is placed on the top of the samples. The distance the flame spread downward is recorded. If the flame does not spread beyond the ignition zone, it is considered as non-flammable. A flammability boundary of the low oxygen limits (LOI) vs. pressure is determined. The oxygen limit is higher at reduced pressure, as expected. But, quantitatively, the measured LOI’s are higher not only than that of the stand-alone polyurethane foam sample but also higher than that of the stand-alone Nomex® sheet. The wrapping combination by the barrier Nomex® is found to be a surprisingly effective way to reduce the flammability of the polyurethane foam.Item Results of Large-Scale Spacecraft Flammability Tests(47th International Conference on Environmental Systems, 2017-07-16) Ferkul, Paul; Olson, Sandra; Urban, David; Ruff, Gary; Easton, John; T'Ien, James; Liao, Ya-Ting; Fernandez-Pello, A. Carlos; Torero, Jose; Eigenbrod, Christian; Legros, Guillaume; Smirnov, Nickolay; Fujita, Osamu; Rouvreau, Sebastien; Toth, Balazs; Jomaas, GrundeThe preliminary results for two flights of the Spacecraft Fire Experiment (Saffire), conducted on an orbiting spacecraft, are presented. These experiments directly address the risks associated with our understanding of spacecraft fire behavior at practical length scales and geometries. The result of this lack of experimental data has forced spacecraft designers to base their designs and safety precautions on 1-g understanding of flame spread, fire detection, and suppression. However, low-gravity combustion research has demonstrated substantial differences in flame behavior in low-gravity. Over the past several years, NASA and an international team of investigators have worked to address open issues in spacecraft fire safety. NASA’s Spacecraft Fire Safety Demonstration Project was developed with a goal to conduct a series of large-scale experiments in true confined spacecraft environments that represent practical spacecraft fires. The first two flights are complete and examined spread over a large thin sheet of flammable fuel (cotton/fiberglass 41 x 94 cm) and over 9 samples (5 x 30 cm) of various materials (silicone (4), PMMA (2), cotton/fiberglass (2) and Nomex®) that addressed the conditions of NASA STD 6001 Test 1 (material flammability). These experiments were performed on two separate unmanned ISS re-supply spacecraft after they had delivered their cargo and had begun their return journeys to Earth (destructive reentry). Preliminary flame spread rates and flammability assessments are presented for the conditions studied with comparison to prior data. A computer modeling effort is underway to complement the experimental effort. In addition, conceptual development has begun for three more flights that will include fire detection and suppression objectives to the program.