Iran Occupational Health

Background and aims: The job safety is one of the necessary aspects of efficiency in humane resource manangement of every organization, and if organizations enable to reduce the rate of job accidents and undesirable stress, then performance of workers become more efficient. Hence, job rotation is as good as a rest to increase efficiency. The aim of this research is to design an appropriate job rotation system in order to reduce job risks in terms of ergonomic risks of jobs.

 Methods: This research is aimed to design a job rotation system by using a mathematical modeling approach in which in addition to satisfying employer needs, it reduces ergonomic risk of jobs. The research method in this research is application in terms of goal, and is mathematical descriptive in terms of method, which includes: (1) problem extraction, (2) modeling, (3) model solving, (4) model verification, and (5) model implementation. The aim is to all of the risksis assigned to n workers such that maximum risk of all workers are minimized (problem extraction). According to conditions and constraints of system, the problem is modeled as a linear programming model. The parts of this model includes objective function of minimization of maximum job risk of human resource, structural constraints of problem (each job should be assigned just to one worker at any time, and each worker should occupy just one job), parameters (n workers, n jobs at time interval T, jobs risks), and variables (job assignment at time intervals to workers) (modeling). Since the model is a linear programming model, the Lingo optimization software and coding in it is used to solve optimally (model solving and verification).

Results: The optimal model of job rotation system was evaluated in semi-industrial work-station where dissatisfaction of workers from ergonomics problems has been reported (model implementation). This mathematical linear model is constructed with 144 decision variables, 57 constraints and a objective function. The model is implemented by Lingo software and the results include 138 zero optimal variables and 6 one optimal variables. These results provide an optimal sequence of assignment and workers job rotation that can be used to make most moderate state of job risks and divide the job risks in a logical proportion among all workers. The optimal assignment of jobs to workers implies the reduction of job risks for all workers to 1.25 (calculated value for optimal objective function).

Conclusions: The main output of this research is a optimal plan for job assignment in a work plan of a production system which not only considers job conditions but also minimizes ergonomic risk of jobs  and also leads to job satisfaction due to moderate job risk. The results demonstrate outstanding effect of job rotation on setting of job risk among workers at an appropriate level, and improvement on workers' satisfaction.