A “normal accident” is an emergent disaster, arising from a complex and highly technical system whose components are tightly coupled, meaning that the state of one component significantly affects others. Perrow wrote that in simple mechanical systems, a high degree of reliability can be achieved through the use of independent and redundant components, but as system complexity increases, especially when human organizations are involved, true redundancy among the components ceases to exist, and failures or errors may trigger a “cascade” that propagates through the system until disaster occurs. Cascades are, by their very nature, difficult or impossible to fully predict until they occur.

• Admiral Cloudberg paraphrasing Charles Perrows 1984 book ‘Normal Accidents’