“On straight shifts or fixed shifts, each crew has its own set of hours that do not change…there are two basic fixed schedules. The first is a set of three 8-hr shifts that comprise the total hours available during the day. A standard schedule is 7:00 a.m. to 3:00 p.m., 3:00 to 11:00 p.m., and 11:00 p.m. to 7:00 a.m. The second basic schedule is a 12-hr schedule, which runs from 6:00 a.m. to 6:00 p.m. and from 6:00 p.m. to 6:00 a.m.” (Oexman, Knotts, & Koch, 2002, p. 153).

Oexman, R.D., Knotts, T.L., & Koch, J. (2002, December). Working while the world sleeps: A consideration of sleep and shift work design. Employee Responsibilities and Rights Journal, 14(4), 145 - 157.