Evaluation of Fatigue and Workload among Workers Conducting Complex Manual Assembly in Manufacturing.

OCCUPATIONAL APPLICATIONSWe conducted a study to evaluate fatigue and workload among workers performing complex assembly tasks. We investigate several predictors of fatigue, including subjective workload estimates, sleep duration, the shift being worked, and production levels. High levels of fatigue were reported in one-third of the shifts evaluated. The main predictors of high fatigue were workload estimates, working evening shifts, and baseline fatigue. Among the six dimensions of workload, only mental demand and frustration were predictors of high fatigue. Mental demand was also rated highest. Participants reported less than seven hours of sleep in 60% of the nights evaluated. These results suggest that managers and supervisors should consider cognitive workload as a key contributing factor to fatigue in complex manual assembly. Similarly, work schedule planning should consider shift duration, start times, and end times, because of the negative influence on fatigue and the potential disruptions on sleep among workers.

TECHNICAL ABSTRACTBackground: General fatigue and mental workload have been studied extensively in safety-critical contexts; wherein human performance degradation can lead to catastrophic outcomes. In the manufacturing sector, the physical demands of a job have received most of the attention because of the presence of biomechanical loads and the incidence of musculoskeletal disorders. However, in complex manual assembly, cognitive and chronobiology aspects of work can contribute to fatigue and degrade worker performance.Purpose: We aimed to evaluate self-reported levels of fatigue and workload among a group of workers performing complex assembly tasks. We also sought to investigate several predictors of fatigue, including workload estimates, sleep duration, the shift being worked, and production levels.Methods: Fourteen assembly line workers participated in a two-week study. They evaluated their levels of fatigue at the beginning and end of each shift using the Samn-Perelli Fatigue Scale. They also evaluated their workload according to the NASA-TLX scale at the end of each shift.Results: High levels of fatigue (fatigue score ≥ 5) were reported in approximately one-third of 114 work shifts evaluated. Binary logistic regression indicated that fatigue scores at the beginning of the shift, NASA-TLX scores, and working evening shifts were significant predictors of high levels of fatigue. Among the six dimensions measured by NASA-TLX, only mental demand and frustration were predictors of high fatigue. Mental demand was also rated highest by the workers. Participants reported less than seven hours of sleep in 60% of the nights evaluated.Conclusions: These results suggest that cognitive load can contribute to fatigue in complex manual assembly work. Circadian and homeostatic processes related to shift duration, start times, and end times are also potential contributing factors. Similarly, existing work schedules may be contributing to sleep disruptions among workers.

Ergonomic risk assessment with DesignCheck to evaluate assembly work in different phases of the vehicle development process.

Occupational hazards exist, if the design of the work situation is not in accordance with ergonomic design principles. At assembly lines ergonomics is applied to the design of work equipment and tasks and to work organisation. The ignoring of ergonomic principles in planning and design of assembly work leads to unfavourable working posture, action force and material handling. Disorders of the musculoskeletal system are of a common occurrence throughout Europe. Musculoskeletal disorders are a challenge against the background of disabled workers. The changes in a worker's capability have to be regarded in the conception of redesigned and new assembly lines. In this way ergonomics becomes progressively more important in planning and design of vehicles: The objective of ergonomic design in different stages of the vehicles development process is to achieve an optimal adaptation of the assembly work to workers. Hence the ergonomic screening tool "Design Check" (DC) was developed to identify ergonomic deficits in workplace layouts. The screening-tool is based on the current ergonomic state of the art in the design of physical work and relevant EU legal requirements. It was tested within a federal German research project at selected work stations at the assembly lines at Dr.-Ing. h.c. F. Porsche AG / Stuttgart. Meanwhile the application of the screening-tool DC is transferred in other parts of the Porsche AG, Stuttgart. It is also realized as an ergonomic standard method to perform assembly work in different phases of the vehicle development process.

Influences of mechanical exposure biographies on physical capabilities of workers from automotive industry - a study on possible dose-response relationships and consequences for short and long term job rotation.

This paper describes a field study in production areas of a vehicle manufacturing plant, where 106 male workers (aged from 20 to 63 years) were examined and interviewed by the authors. Aim of study was to identify relationships between specific physical worker capabilities and doses of mechanical exposures using self-developed standardized questionnaires as well as a battery of work-specific tests. The dependent variables are different "physical capabilities", classified using a five-point rating scale with regard to the grade of limitation of the respective capability. Independent variables are "age" and specific "mechanical exposures". Several exposures were combined and multiplied with their respective durations in order to determine doses on three different body regions - back, shoulder-neck and upper limbs. There are significant positive correlations between "age" and "dose of mechanical exposure on back/shoulder-neck/upper limbs region". The analysis of the relationship between dose of exposure and different capabilities to lift or reposition loads (with variable weight) shows weak significant correlations for all three body regions. Data analysis shows no significant correlations between any dose of mechanical exposure and capabilities to work in awkward body postures.These results should be considered in age management programs when scheduling future employee assignments to workplaces, especially for production systems where manual handling tasks are dominant.

Procedimiento de análisis ergonómico de tareas- AET / Procedure in job ergonomics analysis

El principal objetivo de esta publicación es efectuar una aproximación al procedimiento de análisis ergonómico de tareas AET con respecto a sus bases teóricas, la metodología empleada, su campo de aplicación, así como también observar las actividades individuales del hombre con respecto a su rol tanto en los conflictos humanos, como en los aspectos económicos y técnicos del trabajo

Procedimiento de análisis ergonómico de tareas- AET / Procedure in job ergonomics analysis

El principal objetivo de esta publicación es efectuar una aproximación al procedimiento de análisis ergonómico de tareas AET con respecto a sus bases teóricas, la metodología empleada, su campo de aplicación, así como también observar las actividades individuales del hombre con respecto a su rol tanto en los conflictos humanos, como en los aspectos económicos y técnicos del trabajo (AU)