Fault tree analysis is a top down analysis of an undesired system state to determine the best ways to reduce risk. It uses Boolean logic to combine contributing events, giving overall probabilities of failure. Fault trees are used primarily in high-risk industries such as aerospace, nuclear, and chemical. However, it can also be used in software to review and harden systems against failures. Walking through a fault tree Suppose we’re concerned with the uptime of our Software as a Service (SaaS).