Failure analysis, or fault tree analysis, uses Boolean algebra, probability theory, and reliability theory to analyze the complex relationships between hardware, software, and humans to determine potential system failures. The end product is a visual diagram representing potential or existing failures. It was first developed in 1962 by HA Watson and has been adapted for use in various industries. Fault analysis software is now widely available and can help prevent accidents by identifying root causes.
Failure analysis, also known as fault tree analysis, is a method used to determine the various chains of effects that could cause a system to fail, compromising safety or stability. Engineers often use failure analysis for safety or hazard assessment. In failure analysis, the complex relationships between hardware, software and humans are analyzed with methods derived from Boolean algebra, probability theory and reliability theory. The end product of failure analysis is a logical visual diagram representing any potential failure a system could experience or existing failures that have already occurred and why they have occurred.
The top of a fault tree diagram shows the final failed state of the system, while events branching out below show the states of any separate system components that could possibly allow for the final state. The lines and shapes connecting the components show the logical relationship. For example, if a closed valve or unavailable pump could cause a loss of cooling, a pointed dome shape representing “or” would connect these two possible causes to the final state. If both the closed valve and the unavailable pump were needed to cause the cooling loss, however, a rounded dome representing “e” would be used. The next level in this hypothetical fault tree diagram would show which components could cause the valve to close or the pump to be unavailable.
HA Watson of Bell Laboratories first developed failure analysis in 1962, while working for the US Air Force to create a launch control system for an ICBM. The Boeing company recognized the benefits of this system and adapted it for use in commercial aircraft design. Failure analysis gained national attention after the Apollo 1 launch pad fire on January 27, 1967, when NASA hired Boeing to design a new safety program for Project Apollo.
Failure analysis then made its way into the nuclear power industry, where it was used to analyze the Three Mile Island Nuclear Power Plant accident on March 28, 1979. The nuclear power industry probably did more to the development of fault tree theory and software than any other group, according to Fault Tree Analysis—A History by Clifton A. Ericson II. Now, a variety of industries, including automotive, railways and robotics, use this method.
Currently, fault analysis software is widely available and useful for creating and evaluating fault tree diagrams. Ideally, failure analysis is intended to help prevent accidents or serious incidents by identifying the root causes and improving users’ understanding of the system. This method can also be useful for analyzing incidents after they happen and determining what went wrong.
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