Roger R. Rosa

Extended workshifts and excessive fatigue

SUMMARY  Studies of overtime have pointed to fatigue as a potential factor producing, for example, a three‐fold increase in accident rate after 16 h of work, increases in back injuries, hospital outbreaks of bacterial infection, or nuclear‐power plant safety compromises. Fatigue has been measured more directly in studies of scheduled long workshifts, where performance decrements in both work‐related tasks and laboratory‐type behavioural tests have been observed, and significant loss of sleep and increases in subjective sleepiness have been reported. Analyses of accidents or injuries during scheduled extended workshifts, however, have produced equivocal results. Factors which could compound the fatiguing effects of extended workshifts, such as workload, noise, chemical exposure, or duties and responsibilities outside of the workplace, rarely have been studied systematically. It is concluded that extended workshift schedules should be instituted cautiously and evaluated carefully, with appropriate attention given to staffing levels, workload, job rotation, environmental exposures, emergency contingencies, rest breaks, commuting time, and social or domestic responsibilities.

Promoting alertness with a short nap during a night shift

The use of a short (< 1 h) nap in improving alertness during the early morning hours in the first night shift was examined under laboratory conditions. The study contained four experimental, non‐consecutive night shifts with a nap of either 50 or 30 min at 01.00 or 04.00 hours. An experimental night shift without a nap served as a control condition. Each experimental shift was followed by daytime sleep. Fourteen experienced male shift workers went through all of the experimental conditions. The results showed that the naps improved the ability to respond to visual signals during the second half of the night shift. Physiological sleepiness was alleviated by the early naps, as measured 50 min after awakening, but not at the end of the shift. Subjective sleepiness was somewhat decreased by the naps. The naps produced sleep inertia which lasted for about 10–15 min. Daytime sleep was somewhat impaired by the 50 min naps. The study shows that a nap shorter than 1 h is able to improve alertness to a certain extent during the first night shift.

Extended workdays: Effects of 8-hour and 12-hour rotating shift schedules on performance, subjective alertness, sleep patterns, and psychosocial variables

Abstract A newly instituted 3-4 day/12-h rotating shift schedule was compared to the previous 5-7 day/8-h schedule using standard laboratory-type measures of performance and alertness, and a questionnaire on sleep patterns and other personal habits. After seven months adaptation to the new schedule, there were decrements in the laboratory-type tests of performance/alertness which could be attributed to the extra 4 h of work per day. There were also reductions in sleep, and disruptions of other personal activities during 12-h workdays. However, increases in self-reported stress were attenuated by the shortened workweek. These results are discussed in terms of trade-offs between longer workdays and shorter workweeks.

Long workdays versus restdays: assessing fatigue and alertness with a portable performance

A test battery designed to assess psychological/behavioral fatigue was used to compare restdays to a workweek of five 12-hr days at a data entry job simulation. Across both workdays and restdays, the battery was presented at regular intervals to test for fatigue effects and diurnal variations. Increased data entry errors across the workday and the workweek as well as subjective reports of increased tiredness on workdays indicated that the work regimen was fatiguing. Test battery performance paralleled those results. On workdays, as compared with restdays, grammatical reasoning was faster but less accurate; digit addition was slower; simple, dual, and choice reaction times were slower; and hand steadiness decreased. The results demonstrated the sensitivity of the battery to long hours of work. The results are discussed in terms of work-rest differences, changes across the workweek, diurnal variations, and cognitive demand.

Performance and alertness on 8 h and 12 h rotating shifts at a natural gas utility

An 8 h/5-7 day shift schedule was compared with a newly instituted 12 h/2-4 day schedule in this, our second worksite study of extended workshifts. Workers completed a performance/alertness test battery, and a questionnaire on sleep patterns and other personal habits, 2-4 times a week on all shifts. After 10 months adaptation to the 12 h shift schedule, there were decrements in performance/alertness attributable to the extra 4 h on the extended shift. There were also reductions in sleep across the workweek which were most apparent on 12 h night shifts. The results are consistent with our first worksite study of 12 h shifts and indicate extra caution should be exercised when scheduling critical activities for extended workshifts, especially extended night shifts.

Performance, alertness, and sleep after 3·5 years of 12 h shifts: A follow-up study

Abstract Control room operators at a continuous processing plant have been working a 12 h/3–4 day rotating shift schedule for over 3 years. After 7 months on this schedule, our initial assessment indicated decrements in performance and alertness, and a mild to moderate sleep debt, when the 12 h shift schedule was compared to the previously-worked 8 h shift schedule. In an effort to track long-term adaptation to the schedule, we conducted a 3 & 5 year follow-up evaluation using the same set of measures. Long-term follow-up testing revealed persistent decrements in performance and alertness attributable to 12 h shifts, and 1–3 h reductions in total sleep time after 12 h night shifts. Little deterioration in performance or alertness was observed across the workweek, which suggested day-to-day recovery from the extended workshift. The popularity of the 12 h shift schedule at this worksite indicates that the workers are willing to tolerate extra fatigue to derive other benefits from this schedule.

The business cycle and the incidence of workplace injuries: Evidence from the U.S.A.

INTRODUCTION The current study explored the association between the business cycle and the incidence of workplace injuries to identify cyclically sensitive industries and the relative contribution of physical capital and labor utilization within industries. METHOD Bureau of Labor Statistics nonfatal injury rates from 1976 through 2007 were examined across five industry sectors with respect to several macroeconomic indicators. Within industries, injury associations with utilization of labor and physical capital over time were tested using time series regression methods. RESULTS Pro-cyclical associations between business cycle indicators and injury incidence were observed in mining, construction, and manufacturing but not in agriculture or trade. Physical capital utilization was the highest potential contributor to injuries in mining while labor utilization was the highest potential contributor in construction. In manufacturing each effect had a similar association with injuries. CONCLUSION The incidence of workplace injury is associated with the business cycle. However, the degree of association and the mechanisms through with the business cycle affects the incidence of workplace injuries was not the same across industries. IMPACT ON INDUSTRY The results suggest that firms in the construction, manufacturing, and mining industries should take additional precautionary safety measures during cyclical upturns. Potential differences among industries in the mechanisms through which the business cycle affects injury incidence suggest different protective strategies for those industries. For example, in construction, additional efforts might be undertaken to ensure workers are adequately trained and not excessively fatigued, while safety procedures continue to be followed even during boom times.

Some effects of 8- vs. 10-hour work schedules on the test performance/alertness of air traffic control specialists

Abstract A 10 h 4 d rotating shift schedule worked by some Air Traffic Control Specialists (ATCSs) was compared to the more traditional 8 h 2-2-1 rapidly rotating schedule. Measures of performance and alertness were obtained from a group of 52 ATCS at an en route ATC center on tasks in the NIOSH fatigue test battery. Additional information on sleep patterns, mood, and somatic complaints was also gathered. Results confirm that tests comprising the NIOSH battery are sensitive to fatigue and diurnal variations associated with a rotating shift schedule. Test performance of ATCSs on the 10 h shift did not differ from those on the 8 h schedule for any of the parameters, when comparing the initial 4 d of the work week. Test performance was notably poorer on the night shift that occurred on the final (fifth) day of the 2-2-1 8 h schedule. For both schedules, there was evidence of changes in alertness on some of the NIOSH performance measures within work days and across days of the week. Changes in test performance and mood ratings corresponded to the decline in self-reported sleep time across the work week. Relevance to industry The increased emphasis on compressed work weeks within industry and other settings has raised a number of issues concerning how longer work days impact sleep, fatigue, mood, and performance. There have been relatively few attempts to systematically utilize field studies to gather relevant data so that managers have a scientific basis for decision-making. This study is one example of an approach to developing a more effective data base for decision-making regarding both a rapidly rotating shift schedule and a compressed work schedule.

Assessing muscular fatigue with a portable tremor measurement system suitable for field use

The utility of a portable tremor measurement system for detecting muscle fatigue was evaluated. Static arm extension was used to induce fatigue. A probe containing two accelerometers, held in the extended hand, recorded horizontal and vertical tremor oscillations in the 1- to 18-Hz range. Several summary amplitude and frequency measures were then derived to analyze hand/arm tremor in the unfatigued and the fatigued states. Large increases from unfatigued to fatigued states were observed in all of the amplitude measures in both axes. Summary frequency measures were far less sensitive to fatigue. Correlations between consecutively measured observations revealed high levels of reliability (r τ .80) in all of the amplitude measures, but not in the frequency measures. The most robust index of fatigue was the total power in the entire 1- to 18-Hz spectrum. The other amplitude measures, however, are suitable for examining the effects of fatigue in isolated portions of the spectrum.

Effects of Auxillary Load on Vigilance Performance in a Simulated Work Environment

The effects of extra-task demands and long hours of work on the performance of simultaneous (comparative judgment) and successive (absolute judgment) type vigilance tasks were assessed in a simulated work environment. For three consecutive 12 hour days, subjects engaged in four 1-hour vigilance sessions interspersed with work at a heavy-load (20 codes/rain) or a light-load (10 codes/min) data entry task. For both types of vigilance tasks, performance efficiency varied inversely with the auxilary workload confronting the subjects. In addition, the quality of vigilance performance improved over the work week in the context of the light auxilary workload and declined in the context of the heavy load. Subjects reported becoming more drowsy, strained and fatigued and experienced more somatic complaints over the work day and the work week. These mood effects were maximal with the successive task and a heavy auxiliary workload, suggesting that in order to maintain performance standards in the successive task, subjects expended more processing resources which led to a greater cost in fatigue and strain.