any method of organizing work in shifts whereby workers succeed each other at the same work stations according to a certain pattern, including a rotating pattern,and which may be continuous or discontinuous entailing the need for workers to work at different times over a given period of days or weeks, a) continuous (4 or 5 shift crews work 24 hours a day, 7 days a week); b) semi-continuous (3 shift crews/no daily break in production but stoppage during weekends); c) discontinuous (2-shift crews/no night work)