a disaster happens when you miss a step or do something wrong.
A disaster can happen at any time. The trigger depends on the kind of disaster.
Patria disaster happened in 1940.
Westfield disaster happened in 1871.
PEPCON disaster happened in 1988.
Ryongchon disaster happened in 2004.
Flixborough disaster happened in 1974.
Kaprun disaster happened in 2000.
Feyzin disaster happened in 1966.
Kyshtym disaster happened in 1957.
Spyros disaster happened in 1978.
Abbeystead disaster happened in 1984.
Niamiha disaster happened in 1999.