Iran Occupational Health

Background and aims: In manual assembly industries, productivity could increase by scientific study, correct and accurate identification of activities and the time required for implementing each activity - with respect to the health, safety and human wellbeing. Although the positive effect of engineering interventions on the efficiency of production is evident, but its impact on the productivity of labor is unknown. The aim of this study is to evaluate the influence of assembly lines redesign based on the engineering techniques on the productivity and ergonomic factors such as musculoskeletal disorders, working posture and fatigue.

Methods: This study was carried out in hob gas assembly plant with 30 men worker. Work-study (Method study: Flow Diagrams and Flow Process Chart Motion &Time study: MTM-1) as engineering techniques and Body Map questionnaire, REBA analysis and MFI questionnaire as ergonomics analysis were applied. According to the engineering techniques (Work Study), interventions implemented in order to improve assembly process. After 12 weeks, work-study and ergonomics analysis carried out again to determine the effectiveness of the redesign on productivity and ergonomic factors.

Results: Redesign led to reduce activities time to 8.8 minute and productivity increased 21%. After redesign, prevalence and severity of musculoskeletal disorders increased in the most parts of the body. Nevertheless, no improvements found in working postures and total fatigue.

Conclusion: Although productivity increased by engineering techniques, but these interventions could result in more exposure of operators to musculoskeletal disorders. In designing assembly lines, routine engineering methods are better to applied together with ergonomic design principles.