Work method used to fill dialysis bag.
An ergonomic intervention method based on QOC Matrix the workers’ voice was implemented in a study case. The diagnosis and analysis developed are used in improvement proposals for workstation redesign. The workers’ voice resulting from reports of the employee’ complaints and symptomatology was the base for a standardized method that comprises: (a) QOC questionnaire application, (b) risk factor categorization, (c) determination of unsafe and unhealthy ergonomic metrics, (d) figuring out the task content impact in the workers’ body, and (e) work system diagnosis. Since workers’ voice, the risk identification made included: (1) the task content linked to work method: repetitiveness associated with the sensor activation using the fingers and the repetitive movements include twist and the stretch of wrist, (2) workplace design regarding container height and injuries caused in wrists and elbows due to hits, (3) task developed regarding risk time exposition and workers position, and (4) workplace design regards to housing collector distance from filling area linked to workers position adopted for reach bags. Improvements included redesign of the workstation with a system of 90° exit discharge curve, one elevation system, and a photoelectric sensor in filling nozzle for automatic filling. As an improvement result, the activity called bags provision was eliminated from the task.
- musculoskeletal disorders
- ergonomic intervention
- risk factors
Physical and ergonomic risks cause musculoskeletal disorders (MSDs). Physical risks are external loads associated with long periods of exposure during tasks performed. The external loads are caused by awkward postures, manual material handling, repetitive motion, and force exerted. All of them are known as ergonomic risk factors (ERFs), which impact on health and well-being of workers [1, 2]. Ergonomics comprises a set of techniques directed to adequacy of the work to the people, optimizing human well-being and performing the overall system [3, 4]. Elements of work system are: workplace, tasks performed, tools manipulation, products and materials manipulation, work organization, and work environment [5, 6]. During the interaction of a person with the work system, unsafe and unhealthy elements must be changed or redesigned. The Mexican Ministry of Labor and Social Safety (STPS) defines that if one of this interaction is incorrectly designed, the work task requirements will become ERFs that can lead to musculoskeletal disorders and occupational illness .
In Mexico, the real number of musculoskeletal disorders (MSDs) developed by workers is unknown due to three main causes: (1) workers are afraid of being dismissed by employers if they report symptoms of illness , (2) employers have historically evaded the law and they have not usually implemented safety and health standards in workplaces , and (3) authorities have improperly followed up safety inspections. Therefore, the negligence triggered apathy to assure abatement of risk conditions and has caused omissions, contributing to under-reporting risk conditions and work accidents . Despite under-reporting risk factors, the concern of Mexican authority is the upward trend of developing MSDs (within the industrial and service sectors), as established in the First Forum on Safety and Health at Work, carried out in Mexico City in August 2015, where the ergonomic risk factors are identified as a main problem due to their impact on workers’ health and their economic costs . The increase in cases (73% on average) in 8 years (2009–2017), informed by the Mexican Institute of Social Safety (IMSS) [12, 13], reported a cumulative total of 20,523 cases, identifying dorsopathies as the most prevalent work disease with 6752 cases (32.9%) followed by enthesopathies with 3490 cases (17.01%) and carpal tunnel syndrome with 3280 cases (15.9%) (Figure 1).
To abate this health problem, the government has issued a mandatory rule called Federal Rule for Safety and Health at Work (Reglamento Federal de Seguridad y Salud en el Trabajo) . It includes employer obligations to find, to report, and to reduce ergonomic risks presented inside facilities. Thus, the question is: how employers can follow the law taking in to count that (a) ergonomic aspects are ignored for a long time, (b) ergonomic risks are seldom identified, and (c) an ergonomic intervention is not commonly carried out.
Based on the latter, it is important to define that an ergonomic intervention includes a diagnosis and analysis about the work system, which results in making improvement proposals . If a proposal is carried out (elimination of ergonomic risk factors), a reduction of reports from employees’ complaints must be observed.
In this chapter, an ergonomic intervention method based on QOC Matrix the workers’ voice is carried out in a study case, the diagnosis and analysis developed were used to propose a workstation redesign as improvement proposals. Reports of the employees’ complaints and symptomatology suffered represent the workers’ voice. Improvement proposal should be standardized, to warranty workers’ complaint reduction. Methods include: (a) QOC questionnaire application, (b) risk factor categorization, (c) determination of unsafe and unhealthy ergonomic metrics, (d) figuring out the task content impact in the workers’ body, and (e) work system diagnosis.
2. Methods and tools
2.1 QOC Matrix the workers’ voice (QOCMWV)
QOC Matrix-the workers’ voice (QOCMWV) [16, 17] is an interactive ©Microsoft Excel spreadsheet. It uses decision support system (DSS)  that helps people to apply ergonomic parameters to identify and categorize the risk factors and fix them through ergonomic intervention.
It involves a questionnaire that encloses in each question criteria from: ergonomic ISO standards, Mexican safety and health standards, OSHA and NIOSH recommendations, among others used as evaluation parameters. During an ergonomic risk assessment, workers have to choose the option that answer questions according to their perception about workstation and tasks developed; the results got are called workers’ voice.
The questionnaire was organized in to five sections: (1) work area with two subdivisions: (a) workplace design and (b) task content, (2) manual material handling, (3) work organization, (4) work environment, and (5) psychosocial aspects. Metrics for intervention and specific risk factors are obtained because of its implementation. Metrics are proportions (%) that define the level of risk. Specific risk factors are dimensional relations worker-workstation, repetitiveness, load manipulated, and exposition time. The results are represented in Pareto charts.
2.2 Pareto charts
Pareto chart is a frequency distribution (or histogram). It was used for arranging risk factors by category. Pareto method and rules of 70/30 (Pareto principle)  can identify crucial areas from the intervention standpoint. When the Pareto principle is determined, the common effect of workers’ answers that a relative few of the contributors (risk factors)—the vital few—accounts for the bulk of the effect (MSDs). The vital few identification is easier when the tabular data are presented in graphic form that encloses the next main elements :
Risk factors to the total effect, ranked by the magnitude of their contribution
Magnitude of each risk factor is expressed as a percentage of total
Sum of magnitude of all contributors is expressed as a total percentage.
3. Case study
The QOCMWV survey was implemented in three automatic high-speed lines designed for filling dialysis bags with a liquid mixture and produces 110,000 bags daily. The production time comprised three shifts of 8 h, with 16 operators in each line by shift. Activities were developed on standing posture. Workers took a lunch time of 0.5 h, in the middle of the work period. Ergonomic risk factors like manual material handling, repetitive movements, awkward postures, and force exerted were identified as a part of task performance. In Table 1, the work method developed by a worker is presented.
Because of exceeding permissible exposure limits by operators, the company has received a preaction for probable occupational disease ST-9 (official document) issued by the IMSS, to the medical treatment for work-related injuries and diseases. In a preanalysis, the following percentage of cases suffered by workers was found: 30% epicondylitis, 20% hand tendinitis, and 10% shoulder injury.
4. Method for ergonomic intervention
The method used for implementing the ergonomic intervention was applied as follows:
Step 1: the workers’ voice was collected through applying QOC questionnaires.
Step 2: the results of workers’ voice were the base to categorize ergonomic risk factors, through a Pareto chart in three cases of intervention:
effects caused in workplace by unsafe and unhealthy elements,
effects caused in work task by unsafe and unhealthy elements,
task content impacts in the workers’ body.
Step 3: once the risk factors were identified, an ergonomic work system diagnosis was carried out.
Step 4: project improvements were determined to abate risk factors identified.
5. Results and discussions
5.1 Work system diagnosis
Questionnaire QOCMWV was applied to 48 operators and three supervisors from each shift. (In Figure 2, an example of part of assessment is shown.) Workers tested the work system, and the task was chosen from options. Options were represented by letters that symbolized a level of comfort, for example, “S” for comfortable. Each option was associated with a color to show the risk , as shown in Table 2.
|S = Yes||Comfortable||Green||No risk|
|NT = Not at all||Not at all comfortable||Yellow||Risk|
|N = No||Uncomfortable||Red||High risk|
In Mexico, the workforce is people who have basic studies in the best case; therefore, workers’ training is difficult in ergonomics issues. Therefore, the survey made to the workers focuses in their filings, complaints, and motivations . The matrix results were organized through three Pareto chart.
5.2 Categorization of ergonomic risk factors
5.2.1 Unsafe elements of work system components
Figure 3 shows the work system elements evaluated. According to Pareto principle, the cumulated frequency symbolizes “the vital few” (see Section 2.2). Therefore, this percentage was considered as the workers’ voice index. Unfortunately, the Pareto principle was not presented in the first chart (rule of 70/30) as is observed in Figure 3, due to which there were small differences between opinions about unsafe and unhealthy work system elements. Workplace and task content received 18 complaints, each one representing only 37% of cumulate frequency, and materials handling and psychosocial factors received 17 complaints, each one representing only 35.06% of cumulate frequency, the 70% was to reach until the fourth bar and not in the first three bars, as established by the Pareto rule. Hence, there was no main work system element identified as workers’ voice to be improved during the intervention.
The unusual behavior got in the Pareto chart was explained by the workers’ complaints in this manner; workplace design: the workers suffered continuous little hits in wrists and elbows, caused by the container height and the housing collector distance from filling area, arm overstretching in the moment of taking set bags, and awkward position during the filling bag process. Task content and materials handling: as the speed of line was too fast, and they have to handle huge materials quickly and exhaustively. Aspects were confirmed with the results got in the second Pareto chart.
5.2.2 Unsafe and unhealthy ergonomic metrics
In the second Pareto chart, the ergonomic metrics about the task were evaluated, see Figure 4. The chart bars symbolize the task metrics, which was assessed by the QOCMWV by comparing the process parameters vs. international standards. In this chart, the Pareto principle was more clearly presented (rule of 70/30). Unfavorable environment received 23 complaints, repetitiveness received 20 complaints, and body position received 19, thus representing only 64% of cumulate frequency, close to 70%. Hence, unfavorable environment, repetitiveness, and body position were identified as workers voice to be improved during the intervention.
The chart results due to the unfavorable environment of the task were tied with the workplace design, and then at least 41 opinions from the 48 workers had complaints about work place design; in the same way, task content was linked with repetitiveness; then, at least 40 from the 48 workers had complaints about task content. Thus, workplace design and task content were identified as workers’ voice.
5.2.3 How task content impacts workers´ body
In the third Pareto chart, the task content impact in the workers’ body was assessed. The chart bars that represent the human body parts were exposed to injury due to ergonomic hazards and unsafe conditions. Once again, the Pareto principle was not presented in the third chart (rule of 70/30) as observed in Figure 5. However, the upper limbs (as a whole) were identified as affected by the repetitive works developed.
5.3 Diagnosis to determine the incompliances regarding ergonomic rules
The results of the diagnosis about incompliance of ergonomic rules inside the work system are mentioned below.
5.3.1 Identification of risks
The task content about work method:
Repetitiveness associated with the sensor activation using the fingers
The repetitive movements include twist and the stretch of wrist
Workplace design regards to container height:
Injuries associated with wrists and elbows hits
Task content regards to task duration about workers’ position
Workplace design regards to housing collector distance from filling area about workers’ position adopted for reach bags.
5.3.2 Symptoms found
Wrist pain and swelling caused by repetitive little hits
Elbow pain and swelling caused by repetitive little hits
Shoulder pain regarding arm overstretching position adopted to reach bags
Back pain regarding task duration and workers' position adopted to reach bags.
5.4 Improving proposal work station redesign
5.4.1 Transport system of bags
In order to eliminate the 92 repeated overstretching positions taken by the workers during task performance (Table 1), redesign of the workstation was proposed (see Figure 6). Improving proposal included a transport system of a 90° exit discharge curve, which will position in the right way the bags are directed into the base container. Regarding poor design of container height and the distance between the collector and the worker, a slide elevator system was added, which included an optical sensor with two main functions. First one consists in detecting each bag to move the elevator system down when each bag is deposited in the container base, the second one refers to moving up the container base added to the elevator system when a determinate quantity of bags is counted, allowing the workers to reach without additional efforts to the bags. Additionally, a synchronization of the conveyor system was suggested, improving the productivity and decreasing the overwork driving to the human factor.
5.4.2 Photoelectric sensor implementation in filling nozzle
For reducing repetitiveness in the activation sensor (Table 1) during filling bag (right hand), a photoelectric sensor was implemented. It will automatically activate the filling nozzle. This implementation allowed eradicating the twist and stretch movements generated at wrist (see Figure 7).
The assessment and diagnosis method based on QOCMWV was developed and implemented, with the objective of improving the labor relationship, between workers and employers as well as their working conditions. The standardized method allows obtaining relevant diagnosis about hazards and ergonomic risks factors present in the work system, which leads to musculoskeletal disorders. The study shows that the QOCMWV: (a) improves the worker-employer understanding about origin of ergonomic problems present in working areas, (b) identifies the main unsafe and unhealthy areas and work system components, (c) supports the decision-making about improvement projects focused on risk elimination, (d) the workers´ fear of being dismissed by employers if they report symptoms of illness was diminished because the survey was anonymous. However, the workers’ voice (complains) and the employers´ opinion in many cases were contradictory. Thus, it is necessary for new studies to implement strategies to balance the differences in opinion.
We appreciate the enthusiastic participation of the employees who take part in the evaluation as well as the company contribution in the development of this study.