Fault tree analysis is a graphical technique for determining the root causes of system-level failures. It employs boolean logic to combine a series of lower-level events. It is essentially a top-down approach to identifying the component level failures (basic event) that result in the system level failure (top event). Fault tree analysis comprises two components: "events" and "logic gates," which connect the circumstances to determine the cause of the top undesired event. Fault tree analysis is simpler than Failure Mode and Effects Analysis (FMEA) because it focuses on all potential system failures caused by an unwanted top event. FMEA analyses all possible system failure modes, regardless of severity.