Low-pressure conditions, as experienced in space applications, are considered benign for many electronic components. However, for switching devices the probability of failure may be significantly greater than at normal atmospheric pressure due to arcing-at-break processes. This study was stimulated by a relay failure in a 60-V power bus in a spacecraft module, and it was intended to analyze failure modes and the probability of their occurring under lowpressure conditions. The effects of gas pressure, power bus voltage, and load current on arc duration and probability of arc flashover have been investigated. It was shown that arc duration mostly depends on switching power and gas pressure, significantly increasing when power is rising and pressure is decreasing. Failure analysis indicated two major mechanisms in low-pressure conditions: (1) contact damage (excessive erosion and/or microwelding) and (2) arc flashover to a grounded case and/or grounded coil post. For a relay operating in a vacuum, the effect of leak rate on the time to failure at low-pressure conditions is discussed.