The input design constraints applied to the Extra-Vehicular Activity (EVA) spacesuit pose a significant challenge for mitigation of the fire hazard. In order to minimize fatigue and increase comfort of the crewmember operating the suit, the suit pressure is lowered below sea level conditions with typical EVA suit designs operating with 4.3 psia (29.7 kPa). With the lowered operating pressures and the use of closed loop life support, the suit requires elevated concentrations of oxygen typically >95%. At these oxygen concentrations, nearly the entirety of the suit internal materials are flammable. This leaves one remaining possible control leg of the fire triangle: ignition sources. Since the Gemini and Apollo programs, this has been a risk that has under constant reassessment with focus on improved mitigation. After the Apollo I fire, an arc ignition method was developed and used to quantify ignition thresholds for in-suit materials resulting in a current limit for powered in-suit devices applied to all suit designs that followed. After the discovery of a frayed spacesuit biomed cable on STS-113 during the Shuttle Program, the previous arcing method was repeated with additional methods developed to extend the testing further. One of those methods was Wire-break Ignition Testing in which the current in a single strand of wire was progressively taken higher preheating the material in proximity with a resultant break and the application of a reasonably repeatable arc to ignite the material all while exposed in the selected environment. This method was used to test a suite of spacesuit materials providing relative performance with respect to ignition with this particular configuration for application of energy. Leveraging the previous data and extending it further to consider more and recent materials coupled with lowering energy levels via smaller wire gauges is the subject of this paper.
Campbell et al. (Sun,) studied this question.