One human action in every thousand results in an error that can comprise the safety of personnel.
Such critical situations often occur under time pressure, perhaps because the whole process needs to be stopped to rectify the fault on a plant.
Defeating an interlocking device can also be included here, when the complex procedure of restarting the plant can be avoided by removing a part that has become stuck during operation. Scientific studies show: half of all fatal industrial accidents can be attributed to operator behaviour!