title: The effects of consecutive night shifts and shift length on cognitive performance and sleepiness: a field study.
abstract: BACKGROUND
  The aim of this study was to evaluate the effects of consecutive night shifts (CNS) and shift length on cognitive performance and sleepiness.
  
  
  METHODS
  This study evaluated the sleepiness and performance of 30 control room operators (CROs) working in 7 nights, 7 days, 7 days off (7N7D7O) and 30 CROs working in 4 nights, 7 days, 3 nights, 7 days off (4N7D3N7O) shift patterns in a petrochemical complex on the last night shift before swinging into the day shift. To assess cognitive performance, the n-back test, continuous performance test and simple reaction time test were employed. To assess sleepiness, the Karolinska sleepiness scale was used.
  
  
  RESULTS
  Both schedules indicated that the correct responses and response times of working memory were reduced (p = 0.001), while intentional errors and sleepiness increased during the shift work (p = 0.001). CNS had a significant impact on reaction time and commission errors (p = 0.001).
  
  
  CONCLUSIONS
  The main duty of CROs at a petrochemical plant is checking hazardous processes which require appropriate alertness and cognitive performance. As a result, planning for appropriate working hours and suitable number of CNS in a rotating shift system is a contribution to improving CRO performance and enhancing safety.
authors.affiliation: a Ergonomics Department , Hamedan University of Medical Sciences , Iran.
authors.forename: Rashid
authors.initials: R
authors.lastname: Haidarimoghadam
authors.affiliation: a Ergonomics Department , Hamedan University of Medical Sciences , Iran.
authors.forename: Reza
authors.initials: R
authors.lastname: Kazemi
authors.affiliation: a Ergonomics Department , Hamedan University of Medical Sciences , Iran.
authors.forename: Majid
authors.initials: M
authors.lastname: Motamedzadeh
authors.affiliation: b School of Public Health , Hamedan University of Medical Sciences , Iran.
authors.forename: Rostam
authors.initials: R
authors.lastname: Golmohamadi
authors.affiliation: c Department of Biostatistics and Epidemiology , Hamedan University of Medical Sciences , Iran.
authors.forename: Alireza
authors.initials: A
authors.lastname: Soltanian
authors.affiliation: d Department of Psychology , Buali Sina University , Iran.
authors.forename: Mohamad Reza
authors.initials: MR
authors.lastname: Zoghipaydar
mesh_terms: D000328:Adult; D002617:Chemical Industry; D003071:Cognition; D005260:Female; D006801:Humans; D007492:Iran; D008297:Male; D008568:Memory; D011581:Psychological Tests; D011930:Reaction Time; D012892:Sleep Deprivation / Q000209:etiology / Q000523:psychology*; D013647:Task Performance and Analysis; D000066477:Work Performance; D014940:Work Schedule Tolerance / Q000523:psychology*; D055815:Young Adult
keywords: consecutive night shift; performance; sleepiness