Microgravity flammability limits of ETFE insulated wires exposed to external radiation

The present work studied the normal gravity (1 g) and microgravity (μg) flame spread limits (LOC) of ETFE insulated copper wires exposed to an external radiant flux. Experiments with sample wires of a 0.50 mm copper core and 0.30 mm ETFE insulation thickness were conducted in oxygen concentrations ranging from 20% to 32% and external radiant fluxes from 0 to 25 kW/m2. Microgravity experiments conducted in parabolic flights showed that μg reduced the Limiting Oxygen Index of the material. The addition of an external radiant flux further extends the Limiting Oxygen Concentration (LOC) for flame spread over ETFE insulated wires. Microgravity reduced heat losses and allowed the flame to propagate in lower oxygen concentrations. The addition of an external radiant flux further compensates for lower flame temperatures in reduced oxygen concentrations and further extends the LOC of the material. Limiting Oxygen Index (LOI) results obtained with ETFE were also compared to available results with PE and show that μg conditions have a larger impact in ETFE than PE. The results of this work are relevant given that the flammability of materials is routinely tested without considering the effects of environmental variables and according to the results presented in here may not be indicative of the absolute flammability limits.