Software and system safety: promoting a questioning attitude

System safety is an accepted approach to help understand and manage hazards and risks in complex systems in order to prevent accidents. Many different industries use system safety analyses and methods to help reduce the potential for harm to people, property, and the environment. When used correctly, system safety methods can provide tremendous benefits, focusing resources to reduce risk and improve safety in complex systems. Because computing systems are increasingly being used to control critical functions and supply safety decision information, software may directly or indirectly contribute to an accident. Therefore, software must be included as part of an organization's system safety efforts to manage hazards and risks. However, for many organizations, software is not effectively incorporated into the system safety process, and questions are not asked about whether the analyses are appropriate for complex, automated systems. This paper will summarize several accident reports and use those reports to illustrate potential failures in the system safety process with respect to software and computing systems. Lessons learned will be discussed, and some essential questions in software safety will be presented. This discussion is intended to provide insights to help promote a questioning attitude that can improve software safety and system safety efforts.