Shift work is not a new phenomenon. Scherrer (1981) reported that in ancient Rome, transportation of goods had to be performed at night in order to reduce traffic congestion. However, it is only during the last century, after Edison’s invention of the lamp, that shift work has become widely adopted in industry. This is concomitant with several trends in industry and society:

1. Process industries. Many modern industries such as power plants and steel works cannot close at night.