Opposed-Flow Flame Spread and Extinction in Electric Wires: The Effects of Gravity, External Radiant Heat Flux, and Wire Characteristics on Wire Flammability

Abstract

Combustion of electric wires is the most probable cause of fire in human space activities. Therefore, the fire performance of electric wires in microgravity conditions must be thoroughly analyzed. This study investigates the opposed-flow flame spread and its limits in electric wires preheated by external radiation, under both normal gravity and microgravity, to understand their fire performance when exposed to external heat sources in such gravity conditions. The experiments were performed on low-density polyethylene (LDPE)-insulated copper (Cu) wires having an outer diameter of 4 mm and differing in core diameter (2.5 and 0.7 mm, corresponding to insulation thicknesses of 0.75 and 1.65 mm, respectively). Both standard and black LDPE insulations were used to study the effect of radiation absorption on the wire preheating and subsequent flame spread. The comparison of the flame spread limits revealed that the wire with the thicker Cu core was less flammable under both normal gravity and microgravity; in particular, its flammability further decreased in the case of microgravity, in contrast with thinner electric wires (~1 mm outer diameter), which exhibited higher flammability in the same gravity condition. These results suggest that different mechanisms, for thicker and thinner wires, determining the critical conditions to sustain flame spread under microgravity. This study provides valuable information about the fire performance of electric wires in space gravity.

Effect of reduced ambient pressures and opposed airflows on the flame spread and dripping of LDPE insulated copper wires

“…Several previous studies have investigated the effect of these parameters on wire burning, including various wire characteristics [6]- [9], environmental conditions [6], [10]- [17], and geometries [8], [18], [19]; however, there are only a limited number of studies examining the effect of ambient pressure, specifically sub-atmospheric, on flame spread [15], [19]- [22]. This research is important because it has previously been found that low pressure environments can approximately mimic results found in micro-gravity environments [16], [17], [21].…”

Upward flame spread and self‐induced buoyant blow‐off over two‐sided thin fabric at different inclination angles

“…[24][25][26] The one-side blowoff always occurred in the narrow strip fabrics with an adequate flame length, which was explained as the small Damköhler number caused by self-induced buoyant flow. The blow-off mechanism of a spreading flame has been widely investigated under downward or opposed force flow configurations [27][28][29][30][31][32] ; while a few findings of blow-off in upward spread flames in air stream due to limitation of sample length. Alternatives are used with an adjustable concurrent force flow to reduce the ratio of chemical time and residence time.…”

Introduction to Special Issue on Spacecraft Fire Safety

“…Unique space fire experiments have been conducted in the International Space Station [5,6], unmanned spacecraft [7], and a satellite [8] to understand the long-term micro-gravity combustion and fire phenomena. The fire dynamics small and thin fuels are also explored through ground-based microgravity experiments using drop towers [9] and parabolic flights [10][11][12][13][14]. In addition, combustion and fire experiments under reduced pressures [15][16][17] and a narrow channel [18] are applied to lower the influence of buoyancy and simulate low-gravity environments on Earth.…”

“…Proper material selection for spaceflight requires a thorough knowledge of fire and flammability behavior in varied gravity. Thus, the critical conditions for flame ignition and extinction in microgravity are extensively explored under different ignition protocols [12], oxygen concentrations [11][12][13], airflow rates [13] and radiant heat fluxes [11], and for flame retardant materials [13].…”

“…Thus, microgravity also provides an ideal environment for fundamental combustion research [4]. Unique phenomena for flame spread in microgravity over thin paper [9], thick plastic plates [7,10,18], cylindrical rods [8,17], spherical fuels [5] and electrical wires of different thicknesses [11,12,14,20] are observed, and the influence of airflow speed, direction, and oxygen concentration on flame stability are investigated.…”