When Charles Perrow published Normal Accidents in early 1984, the catastrophes at Bhopal and Chernobyl and the crashes of the Challenger and the Exxon Valdez were still in the future. Yet Perrow's warnings about the dangers of complexity and tight coupling in large technological systems were borne out perfectly by these disasters. "Normal accident theory" gained credibility. When today's investigators examine disasters, they look for, and often find, unexpected interactions between design flaws, human errors, self-defeating "safety" mechanisms and broken or deluded organizations.

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