Performances of Flame Retardants in Microgravity: Insights from Opposed Flame Spread over Electrical Wires

Fire safety is a critical consideration for space exploration. Flame retardants are a straightforward solution to improve the fire resistance of flammable material critical to the success of space missions, but their performances in microgravity conditions can differ from ground-based evaluations due to altered heat and mass transfer. Understanding the behavior of flame retardants in microgravity is essential for designing effective fire safety strategies for spacecraft. This study examines the opposed-flow extinction limits of flames spreading over low-density polyethylene (LDPE) samples. The parabolic flight experiments consider both monophasic cylindrical samples and electrical wires featuring a Nickel-Chrome core. The samples are loaded with three flame retardant systems, i.e. Ammonium Polyphosphate/Pentaerythritol (AP), Red Phosphorus (RP), and the commercial Intumescent Adeka (AD). and RP works by combining gas-phase free radical inhibition and solid-phase charring, while AP and AD rely on intumescence and expand upon heating to form a thermal barrier that slows down pyrolysis. Experimental results reveal that the presence of AP and RP in a sample significantly increases the extinction limits, while AD-loaded samples show no notable improvement compared to pure LPDE samples. The presence of a metal core markedly enhanced the performance of AP, highlighting the need to consider the use of fire retardant as part of a complex assembly. These findings illustrate the varied performance of flame retardants in microgravity and highlight the importance of selecting materials based on their mechanisms and compatibility with specific applications. This research contributes to the development of fire-safe materials tailored for the unique challenges of space exploration.