In current urban societies, it is estimated that approximately 20% of the population does not work traditional working hours, and this percentage is tending to increase due to economic, demographic, and technological changes that have occurred in the last decades (Presser, 1999;Rajaratnam, 2001). From the middle of last century, researchers have reported (Bjerner, 1948;Andersen, 1970;Akerstedt, 1981) that working in shifts affects the health of workers; even then, it was shown that shift workers complained about fatigue and sleepiness. Around 81% of the workers complained about night shifts in contrast to only 4% for afternoon shifts (Bjerner, 1948). Production and distribution of electrical power from nuclear stations requires 24 h operation. Therefore, as in other sectors, the security of the whole operational system depends on the efficiency and the ability of the worker to execute tasks with remarkable accuracy and attention. However, because this type of energy is government-controlled, access to research in this area is mostly difficult; therefore, there is a scarcity of scientific publications related to the health of these shift workers. The objective of this chapter is to describe aspects related to sleepiness, particularly excessive day sleepiness, with respect to its origins and consequences as well as the forms of minimization and preventive strategies that can be adopted by companies that use shifts and night work. Such practices may reduce the number of accidents related to fatigue and sleepiness that occur inside and outside the work environment.
Sleep and shift workAlthough sleep functions are not completely known yet, it was assumed for several decades that brain activity was widely reduced or absent during sleep (Saper, 2005;Tufik et al. 2009). However it is important to emphasize that even during sleep, the brain is 80% active, such 16 www.intechopen.com
Nuclear Power 338that sleep is an active process of neuronal reorganization rather than just a process of diminishing wakefulness (Hobson, 2007). Currently, it is accepted that the wakefulness-sleep cycle in human beings is coordinated by two processes that interact among themselves: the homeostatic process (process S) and the circadian process (process C) (Borbely, 1982; Borbely, 1999). The homeostatic process reflects the duration of wakefulness and can be monitored by slow-wave activity (Dijk, 1990), while the circadian process occurs during a 24-hour time frame and sets the rhythms of several physiological activities. Both processes interact to consolidate sleep (Czeisler, 1980). The first systematic classification of sleep stages was described in the Standard Manual organized by Rechtschaffen and Kales (1968), where sleep was divided into NREM sleep (stages 1, 2, 3, and 4) and REM sleep. REM sleep alternates with NREM in intervals of 70 to 110 minutes that are repeated 4 to 6 times a night, depending on the total time slept (Silva, 1996). The duration of REM sleep episodes in humans progressively increases over a sleeping period, with lo...