Normal Accidents: Living with High-Risk Technologies: Difference between revisions

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 ===[[Complex]] interactions and [[tight coupling]]===
 First, some definitions.
-*'''Complexity''': Perrow anticipates the later use of the concept of “[[complexity]]” — a topic which is beginning to infuse the advocacy part of this site — without the benefit of [[systems analysis]], since it hadn’t really been invented when he was writing, but to describe interactions between non-adjacent subcomponents of a system that were neither intended nor anticipated by the designers of the system. Complex interactions are not only unexpected, but for a period of time (which may be critical, if the interacting components are [[tightly coupled]]) will be incomprehensible''. This may be because the interactions cannot be seen, being buried under second-order control and safety systems, or even because they are not ''believed''.  If your  — ''wrong'' — theory of the game is that the event in question is a [[ten sigma event]], only expected once in one hundred million years, then you may have a hard time believing it could happen in your fourth year of operation, as the partners of [[Long Term Capital Management]] may tell you.
+*'''Complexity''': Perrow anticipates the later use of the concept of “[[complexity]]” — a topic which is beginning to infuse the advocacy part of this site — without the benefit of [[systems analysis]], since it hadn’t really been invented when he was writing, but to describe interactions between non-adjacent subcomponents of a system that were neither intended nor anticipated by the designers of the system. Complex interactions are not only unexpected, but for a period of time (which may be critical, if the interacting components are [[tightly coupled]]) will be ''incomprehensible''. This may be because the interactions cannot be seen, buried under second-order control and safety systems, or even because they are not ''believed''.  If your  — ''wrong'' — theory of the game is that the risk in question is a [[ten sigma event]],  expected only once in one hundred million years,  you may have a hard time believing it could be happening in your fourth year of operation, as the partners of [[Long Term Capital Management]] may tell you.
 :''These represent interactions that were not in our original design of our world, and interactions that we as “operators” could not anticipate or reasonably guard against. What distinguishes these interactions is that they were not designed into the system by anybody; no one intended them to be linked. They baffle us because we acted in terms of our own designs of a world that we expected to exist—but the world was different.''<ref>{{br|Normal Accidents}}, p. 75. Princeton University Press. Kindle Edition. </ref>
 *'''[[Linear interactions]]''': Contrast these [[complex interactions]] with much more common “[[linear interactions]]”, where parts of the system interact with other components that precede or follow them in the system in ways that are expected and planned. In a well-designed system, these will (of course) predominate: any decent system should mainly do what it is designed to do and not act erratically in normal operation. Some systems are more complex than others, but even in the most linear systems are susceptible to some complexity — where they interact with the environment.<ref>Perrow characterises a “complex system” as one where ten percent of interactions are complex; and a “linear system” where less than one percent or interactions are complex. The greater the percentage of complex interactions in a system, the greater the potential for system accidents.</ref>