meaning of "sudden and accidental"

"sudden and accidental" meaning in Insurance Dictionary

An exception towards 1973 comprehensive basic responsibility (CGL) air pollution exclusion preserved protection with respect to air pollution incidents which were "abrupt and accidental." Prolonged litigation tested whether the term unexpected meant just unexpected, as some dictionary meanings specify, or whether or not the term fundamentally has actually a-temporal element—referring to a brief time frame, or being similar to all at one time. Many of courts fundamentally followed the latter view.