Nuclear reactor which produce delayed neutrons have half lives for their decay by neutron emission that range from milliseconds to as long as several minutes, and so considerable time is required to determine exactly when a reactor reaches the critical point. Keeping the reactor in the zone of chain-reactivity where delayed neutrons are "necessary" to achieve a critical mass state allows mechanical devices or human operators to control a chain reaction in "real time"; otherwise the time between achievement of criticality and nuclear meltdown as a result of an exponential power surge from the normal nuclear chain reaction, would be too short
Chain of events (accident analysis) Chain of events (accident analysis) In accident analysis, a chain of events (or error chain) consists of the contributing factors leading to an undesired outcome. In aviation accidents and incidents, these contributing actions typically stem from human factor-related mistakes and pilot error, rather than mechanical failure. A study conducted by Boeing found that 55% of airline accidents between 1959 and 2005 were caused by such human related factors, while only 17% of accidents were caused by mechanical issues with the aircraft. The Tenerife airport disaster, the worst accident in aviation history, is a prime example of an accident in which