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Journal ArticleDOI

Fire Safety in Spacecraft

01 Sep 1996-Fire and Materials (Wiley)-Vol. 20, Iss: 5, pp 235-243
TL;DR: In this article, the authors review the findings of microgravity-combustion research that are relevant to techniques of spacecraft fire safety and further illustrate the practical applications of some fire-safety requirements and design features of the Shuttle and those in progress for the International Space Station.
Abstract: Fire prevention, detection, and suppression requirements for spacecraft are based on those established for terrestrial and aircraft systems. In the weightless (or microgravity) environment of an orbiting spacecraft, however, the buoyant upward flow typical of fires in terrestrial environments is nearly absent; and this feature profoundly influences fire characteristics and responsive safety strategies. This paper reviews the findings of microgravity-combustion research that are relevant to techniques of spacecraft fire safety. These practical applications are further illustrated by descriptions of some fire-safety requirements and design features of the Shuttle and those in progress for the International Space Station.
Citations
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Journal ArticleDOI
01 Jan 2009
TL;DR: In this paper, two kinds of sample wires, made by nickel-chrome (NiCr) and iron (Fe) as core metal, are used in the experiment to study the electric fire spread along a single wire harness in sub-atmospheric pressure.
Abstract: Flame spread along the single wire harness (thin-metal wire with coating of polyethylene film) in sub-atmospheric pressure has been examined experimentally to gain better understandings of the electric fire in the aircraft and space habitats. Two kinds of sample wires, made by nickel-chrome (NiCr) and iron (Fe) as core metal, are used in this study. Ambient gas is fixed as air and total pressure is varied from atmospheric to sub-atmospheric (100–20 kPa). As the pressure decreases, flame shape changes from typical “teardrop” to “oval” and flame becomes less-luminous irrespective of the materials of the wire. It turns out that the dependence of the spread rate on pressure varies with the materials of the wire; when the pressure decreases, the spread rate of NiCr-harness monotonically increases, whereas that of Fe-harness mostly remains as constant. From the simple thermal-length analysis, it is proposed that there are two modes in the spread depending on the controlling factor; one is “wire-driven mode” (the spread is mainly governed by the thermal input through the wire) and the other is “flame-driven mode” (the spread is mainly governed by the thermal input from the flame). Observed two cases (NiCr- and Fe-harness) would be categorized to the latter and former modes, respectively.

110 citations

Journal ArticleDOI
01 Jan 1998
TL;DR: In this article, an experimental study of flame spread over ETFE (ethylene-tetrafluoroethylene)-insulated wires has been performed in microgravity to obtain basic data on the fire safety of wire insulation.
Abstract: An experimental study of flame spread phenomena over ETFE (ethylene-tetrafluoroethylene)-insulated wires has been performed in microgravity to obtain basic data on the fire safety of wire insulation. Three samples with different wire diameters, d w (0.32–0.51 mm) and the same insulation thickness, δ (0.15 mm) were investigated. The effects of the parameters thought dominant for wire combustion in fires: the ambient oxygen concentration, wire initial temperature, T i , wire diameter, d w , pressure, and dilution gas were investigated in the microgravity experiments. A series of comparative experiments were also conducted at normal gravity. The results show that flame spread rates in microgravity are higher than vertically downward spread rates at normal gravity when oxygen concentration is greater than 30% O 2 . However, with wire preheating, the spread rate in microgravity is higher than the downward spread rate at normal gravity even at lower O 2 concentrations. The increase in flame spread rates in microgravity became larger with decreases in d w . The effect of pressure on the flame spreading appeared very small, and lower pressure caused extinction of the flames in microgravity. The increase in flame spread rates in microgravity was especially large with CO 2 dilution, and this must be taken into account when selecting extinguisher gas. The microgravity experiments with CO 2 dilution gave rise to a new unsteady flame spread phenomenon for flame spreading over the wire: this phenomenon involves discontinuous flames partly occurring ahead of the spreading flame front.

93 citations

Journal ArticleDOI
01 Jan 2015
TL;DR: In this article, the flame spread rate (FSR) over polyethylene (PE) insulated copper (Cu) wires with inner core diameter (dc) of 0.30mm, 0.50mm 0.80mm and insulation thickness (δp) with inclination angles ranged from −90° to +90°.
Abstract: This paper reveals experimentally the flame spread rate (FSR) [both upward (concurrently) and downward (opposed)] over electric wire with high thermal conductivity metal core at different inclination angles, which is new in view of that previous works about such inclination effect are mainly focusing on the material (wood, PMMA……) where the conductivity through media itself is not so important. Polyethylene (PE) insulated copper (Cu) wires with inner core diameter (dc) of 0.30 mm, 0.50 mm 0.80 mm and insulation thickness (δp) of 0.15 mm, 0.30 mm are studied with inclination angles ranged from −90° to +90°. Their behaviors are examined in both naturally normal (Hefei city with altitude of 50 m; 100 kPa) and a reduced (Lhasa city with altitude of 3650 m; 64 kPa) ambient pressure atmosphere. Results show that with increase in inclination angles from −90° to 90°, the FSR first decreases and then increases (“U” trend) with its value being lowest at nearly horizontal condition (0°) in both pressures, which is quite different from what we normally know for other materials with low thermal conductivity. Two characteristic lengths, the flame base width (Wf) and the pyrolysis zone length (Lp), are found to account for this special variation behavior with their variation trend with inclination angle being consistent with that of FSR. A simplified heat balance analysis concerning core thermal conduction effect is performed to calculate the FSR in relation to these two characteristic lengths, thermal conductivity of the metal core as well as the effective convection heating of the wire by the flame base. The calculated FSR are shown to be in fairly good agreement with the measured values at different inclination angles for different inner core (wire) diameters in both ambient pressures.

78 citations

Journal ArticleDOI
Osamu Fujita1
01 Jan 2015
TL;DR: In this paper, the authors introduce fire safety standards for flammability evaluation of solid material intended for use in a spacecraft habitat, and the difference between the limiting value in microgravity and the indices given by the standard test methods on the ground is discussed.
Abstract: This paper introduces fire safety standards for flammability evaluation of solid material intended for use in a spacecraft habitat. Two types of existing standards include material evaluation by pass/fail criteria corresponding to Test 1 of NASA STD 6001B and evaluation by a flammability index such as maximum oxygen concentration (MOC) corresponding to the improved Test 1. The advantage of the latter is the wide applicability of the MOC index to different atmospheres in spacecraft. Additionally, the limiting oxygen index (LOI) method is introduced as a potential alternative index for the evaluation using the improved Test 1 method. When criteria based on an index such as MOC or LOI are applied for material screening, the discrepancy of the index to the actual flammability limit in microgravity such as minimum limiting oxygen concentration (MLOC) is essential information for guaranteeing fire safety in space because material flammability can be higher in microgravity. In this paper, the existing research on the effects of significant parameters on material flammability in microgravity are introduced, and the difference between the limiting value in microgravity and the indices given by the standard test methods on the ground is discussed. Finally, on-going efforts to develop estimation methods of material flammability in microgravity according to normal gravity tests are summarized.

74 citations

Journal ArticleDOI
01 Jan 2013
TL;DR: In this article, an ignition-to-spread model is developed to systematically explain electrical wire ignition and the following transition to spread, and experiments show that additional heating times after flash are required in order to fully pass the transition and achieve a spreading flame.
Abstract: Ignition of electrical wires by external heating is investigated in order to gain a better understanding of the initiation of electrical-wire fires. An ignition-to-spread model is developed to systematically explain ignition and the following transition to spread. The model predicts that for a higher-conductance wire it is more difficult to achieve ignition and the weak flame may extinguish during the transition phase because of a large conductive heat loss along the wire core. An experimental study was performed using several sample wires with different core metals, diameters and coating thicknesses of polyethylene. A coil heater was adopted as the ignition source, and both the heat flux and heating time were selected as the main parameters to identify the flashpoint and spread point of wire fires. Experiments show that additional heating times after flash are required in order to fully pass the transition and achieve a spreading flame, agreeing with model predictions. Finally, the effects of different heating lengths, environmental pressures, and oxygen concentration on wire ignition are discussed, which may be useful for upgrading the design and standards of future fire-safe wires.

61 citations

References
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Journal ArticleDOI
TL;DR: In this article, the authors consider the opportunities for enhanced fundamental combustion understanding from experiments where effects of buoyancy are eliminated, and the new challenges of fire safety considerations in non-buoyant (spacecraft) environments.

182 citations

Journal ArticleDOI
TL;DR: In this article, a flame spread map is presented which indicates three distinct regions where different mechanisms control the flame spread process: near-quenching region, very low characteristic relative velocities, a new controlling mechanism for flame spread - oxidizer transport-limited chemical reaction - is proposed.
Abstract: Microgravity tests varying oxygen concentration and forced flow velocity have examined the importance of transport processes on flame spread over very thin solid fuels. Flame spread rates, solid phase temperature profiles and flame appearance for these tests are measured. A flame spread map is presented which indicates three distinct regions where different mechanisms control the flame spread process. In the near-quenching region (very low characteristic relative velocities) a new controlling mechanism for flame spread - oxidizer transport-limited chemical reaction - is proposed. In the near-limit, blowoff region, high opposed flow velocities impose residence time limitations on the flame spread process. A critical characteristic relative velocity line between the two near-limit regions defines conditions which result in maximum flammability both in terms of a peak flame spread rate and minimum oxygen concentration for steady burning. In the third region, away from both near-limit regions, the flame spread behavior, which can accurately be described by a thermal theory, is controlled by gas-phase conduction.

142 citations

01 Jul 2005
TL;DR: In this paper, the authors summarize the life support functions and processes used onboard U.S. and U.R/Russian space habitats and provide additional information on the ECLS systems.
Abstract: Human exploration and utilization of space requires habitats to provide appropriate conditions for working and living. These conditions are provided by environmental control and life support systems (ECLSS) that ensure appropriate atmosphere composition, pressure, and temperature; manage and distribute water, process waste matter, provide fire detection and suppression; and other functions as necessary. The tables in appendix I of NASA RP 1324 "Designing for Human Presence in Space" summarize the life support functions and processes used onboard U.S. and U.S.S.R/Russian space habitats. These tables have been updated to include information on thermal control methods and to provide additional information on the ECLS systems.

113 citations

01 Dec 1987
TL;DR: In this article, a flame spreading over a thermally thin cellulose fuel was studied in a quiescent microgravity environment, and two different extinction limits were found in microgravity for the two thicknesses of fuel.
Abstract: A flame spreading over a thermally thin cellulose fuel was studied in a quiescent microgravity environment. Flame spread over two different fuel thicknesses was studied in ambient oxygen-nitrogen environments from the limiting oxygen concentration to 100 percent oxygen at 1 atm pressure. Comparative normal-gravity tests were also conducted. Gravity was found to play an important role in the mechanism of flame spread. In lower oxygen environments, the buoyant flow induced in normal gravity was found to accelerate the flame spread rate as compared to the microgravity flame spread rates. It was also found to stabilize the flame in oxidizer environments, where microgravity flames in a quiescent environment extinguish. In oxygen-rich environments, however, it was determined that gravity does not play an important role in the flame spread mechanism. Fuel thickness influences the flame spread rate in both normal gravity and microgravity. The flame spread rate varies inversely with fuel thickness in both normal gravity and in an oxygen-rich microgravity environment. In lower oxygen microgravity environments, however, the inverse relationship breaks down because finite-rate kinetics and heat losses become important. Two different extinction limits were found in microgravity for the two thicknesses of fuel. This is in contrast to the normal-gravity extinction limit, which was found to be independent of fuel thickness. In microgravity the flame is quenched because of excessive thermal losses, whereas in normal gravity the flame is extinguished by blowoff.

41 citations

Journal ArticleDOI
TL;DR: In this paper, it is shown that a reversal of the limiting oxygen indices from normal gravity and microgravity is possible using a stagnation-point diffusion flame adjacent to a spherical solid-fuel surface.

34 citations