Ergonomic assessment of natural rubber processing in plantations and small enterprises

Evaluación ergonómica del procesamiento del caucho natural en plantaciones y pequeñas empresas

Sandra Velásquez
Grupo BIOMATIC- Biomecánica, Materiales, TIC, Diseño y Calidad para el Sector cuero, plástico, caucho y sus cadenas productivas, Centro de Diseño y Manufactura del Cuero, SENA. Antioquia, Colombia
E-mail: smvelasquez@sena.edu.co

Sebastián Valderrama
Grupo BIOMATIC- Biomecánica, Materiales, TIC, Diseño y Calidad para el Sector cuero, plástico, caucho y sus cadenas productivas, Centro de Diseño y Manufactura del Cuero, SENA. Antioquia, Colombia
E-mail: svalderrama1@misena.edu.co

Diego Giraldo
Grupo de Materiales Poliméricos, Universidad de Antioquia. Medellín, Colombia.
E-mail: dhernan.giraldo@udea.edu.co

Recibido: Diciembre 21 de 2015
Aceptado: Marzo 10 de 2016
Eje temático: INGENIERÍA DE PROCESOS / PROCESS ENGINEERING

Abstract

This exploratory study used OWAS (Ovako Working Posture Analysing System) to analyze the working postures of natural rubber tappers and rubber industry workers. A community of natural rubber farmers of Tarazá and five small companies of Medellín and Itagüí, all of them allocated in Antioquia-Colombia, participated in this study. Processes were analyzed in-situ and videotapes of activities were recorded for carrying out a movement study. For an overall distribution of trunk postures, OWAS identified that a bent and twisted trunk posture which fell into action category 4, was the major poor posture for rubber tappers and rubber industry workers. This study also identified that latex tapping, latex collection, mixing in two roll mills and metallic molds operation were the four activities in which the major working posture risks were observed. It was found that reduction of posture risks in natural rubber production chain requires designing and implementing plans considering organizational culture, socio-economic and sociodemographic factors of natural rubber farmers and small rubber manufacturing industries, besides the use of some useful tools that reduce the handling of heavy loads.

Keywords: Ergonomic assessment, natural rubber industry, OWAS, posture.

Resumen

Este trabajo presenta un estudio exploratorio que usa la metodología OWAS (Ovako Working Posture Analysing System, por sus siglas en inglés) para analizar las posturas de heveicultores y operarios de la industria del caucho durante sus actividades laborales. El estudio se realizó en pequeñas plantaciones de una asociación de cultivadores de caucho en Tarazá, y en cinco pequeñas empresas de Medellín e Itagüí, en Antioquia-Colombia. Se analizaron los procesos in-situ, tomando registros mediante videos para posteriormente efectuar un análisis de los movimientos. Se encontró que los mayores riesgos ergonómicos para los heveicultores y los operarios de pequeñas y medianas industrias de caucho son la generación de trastornos musculoesqueléticos (TME) en la columna vertebral y la Back, con un nivel de riesgo 4. Se encontró también que el sangrado de los árboles, la recolección del látex, el mezclado en molino abierto de rodillos y la manipulación de moldes fueron las cuatro actividades en las cuales se presentan los principales riesgos de postura. Al final del trabajo se proponen recomendaciones para evaluar y reducir los riesgos de postura en pequeñas empresas de la cadena productiva del caucho natural. Se identificó que la reducción de los riesgos de postura in la cadena productiva del caucho natural requiere diseñar e implementar planes que consideren la cultura organizacional y factores socioeconómicos y sociodemográficos de los cultivadores de caucho natural y pequeñas industrias fabricantes de artículos en caucho, además de la utilización de algunas herramientas que reducen la manipulación de cargas pesadas.

Palabras clave: Evaluación ergonómica, industria del caucho natural, OWAS, postura.

1. Introduction

Work-related ergonomic risks are a major problem in public health (Stock et al., 2011). Physical/ergonomic factors during working time such as combination of mechanical loading and postures (Butler & Kozey, 2003), discomfort of the lower extremities of workers in occupational environments, (Reid et al., 2010), awkward postures during work time (Burdorf et al., 1993; Choobineh et al., 2007; Scuffham et al., 2010), lifting loads (Andersen et al., 2007), manual material handling (Meksawi et al., 2012), standing or walking prolonged periods (Andersen et al., 2007; Balasubramanian et al., 2009), long working hours (Raanaas & Anderson, 2008), torsion of the trunk (Sbriccoli et al., 2004; Hartman et al., 2005), repetitive or monotonous work (Guo, 2002; Juul-Kristensen & Jensen, 2005), are associated to some work-related musculoskeletal disorders (WMSDs), specially to lower back pain (Petit et al., 2016).

Prevalence of WMSDs varies by occupation, gender and country, being higher among unskilled workers like farmers (Holmberg et al., 2003; Punnett et al., 2005; Singh et al., 2015), forestry workers (Gallis, 2006), construction workers (Savinainen & Nyberg, 2012) and manufacturing processes operators (Punnett et al., 2005).

While natural rubber is grown and processed for industrial purposes since the late XIX century, there are still ergonomic issues without addressing with regard to heveiculture, as it is called this economic activity consistent in harvesting, tapping, collecting and processing natural rubber. In Thailand, having the largest natural rubber production in the world (Meksawi et al., 2012) found that natural rubber processing includes activities with high risk of developing WMSDs. (Bensa-ard et al., 2004) stated that natural rubber farmers had high risk of developing back pain and to a lesser degree carpal tunnel syndrome, possibly as an effect of awkward and highly repetitive postures.

Natural rubber production and consumption exhibit constant growth, and some projections estimate that this will continue for at least the next decade, so it is appropriate to consider associated occupational health risks to begin mitigate them (Warren-Thomas et al., 2015). In the case of Colombia, heveiculture has increased significantly in the last decade but it is estimated that 90 % of farmers have crops of 5 hectares or less, that is small plantations (Confederación Cauchera Colombiana, 2015). These natural rubber-producing areas are located in regions with unsatisfied basic needs in infrastructure, education and health which make relevant an intervention with regard to ergonomic risks associated with their work.

Natural rubber production chain ends with its transformation in industries generally located in urban centers, where rubber is mixed with chemical additives and/or synthetic rubbers and vulcanization process takes place for obtaining parts with the elastic properties and chemical resistance that characterize rubber products (Confederación Cauchera Colombiana, 2015). 61% of companies dedicated to manufacture rubber parts in Colombia have technology ranked among poor and regular, 32% have technology fair to low, and only 7% have technologies considered between normal and excellent (Cámara de Comercio de Medellin, 2014). This study also indicates that approximately 80% of these enterprises are micro and small enterprises, recalling that these organizations are more likely to operate in ergonomic risk conditions (Unnikrishnan et al., 2015). Musculoskeletal problems among workers of rubber factories were reported in the lower back, knees and upper back due to awkward postures and manual material handling (Choobinehi et al., 2007). Risks related to exposure to the chemicals substances used in rubber industry have been reported by Andjelkovich et al. (1988), but this work is focused on working postures and posture risks of workers in Antioquia (Colombia) who perform operational tasks in small plantations of natural rubber and small rubber factories. Postural hygiene for these activities is analyzed by OWAS method (Ovako Working Posture Analysing System) and some improvement actions to mitigate them are proposed.

2. Methodology

Processes characterization in plantations and small industries was carried out at first. Processing of rubber latex was analyzed in small plantations of ASCULTICAUCHO (Asociación Comité de Cultivadores de Caucho) in Santa Clara, municipality of Tarazá (Antioquia). This region represents 8 % of the cultivated area in Colombia, recalling that is the area of Antioquia with the highest amount of cultivated land and natural rubber workers. Characterization of natural rubber processing was carried out by analyzing the working postures of three workers separately during four visits every three months, regarding this work is aimed to identify working postures. Workers are males between 17 and 26 years old, they received some type of training in natural rubber processing in the last five years and have worked for at least three years in those activities.

Mixing and vulcanization processes were characterized in five small businesses in the Valle de Aburrá, industrial capital of Antioquia and the second most industrialized area of Colombia, considering that 80 % of rubber factories in Colombia are micro and small businesses. All the workers included in this study were males between 23 and 34 years old, without any type of training in natural rubber manufacturing. In all the cases they learned its skills by working in rubber industries.

According to interviews and Confederación Cauchera Colombiana (2015), in Colombia all rubber workers of small plantations and small rubber factories perform its activities in the same way that was observed in this work.

Information was collected through direct observation (in situ), photographs and videos were useful recording in detail each activity, with special attention to the operator's movements. Each process was recorded four times, analyzing the movements from the videos and images using the open source software Kinovea®.

Activities involving ergonomic risks were identified and aspects related to postural hygiene for theseactivities were analyzed by OWAS method, because this method is of easy implementation by small companies and does not requires specialized instructions to be used. OWAS method allows a simple analysis of the posture based only on the observation of the activity (Wahyudi et al., 2015), seeking to reduce musculoskeletal loads during activities in the workplace and make it safer and more productive (Lee & Han, 2013). Wintachai & Charoenchai (2012) used OWAS method finding that working postures in rubber sheet manufacturing contained high OWAS scores. Positions codes used in this work and description of risks that were observed are presented in Table 1.

Table 1. Posture codes and risks description of OWAS method

To analyze control and handling of loads the methodology developed by the National Institute for Occupational Safety and Health of the United States (NIOSH) was used, because it has been demonstrated that it is reliable in several manufacturing activities (Hafeezah et al., 2013). NIOSH Lift Index® application for Apple was used for obtaining the risk level for each activity in rubber processing. Potential WMSD that can be generated if the ergonomic hazards are not evaluated properly were identified. Then, preventive and corrective measures to minimize the probability of occurrence of MSDs were established.

3. Results and discussion

In this section, the characterization of activities is presented as the first set of results. Then, the identification of postural risks and finally the OWAS scores are calculated.

3.1 Characterization of processes

3.1.1 Natural rubber processing at plantations

Once Heveas brasiliensis plantation has been established and it is suitable for exploitation, tapping takes place; this activity consists in make an incision in the tree's bark with a knife, letting the latex flow from the lactiferous vessels of the tree to a gatherer cup. The worker performs this action during between 12 and 20 seconds for each tree in the plantation. This procedure was carried out between 400 and 600 times a day according to the crop size that the worker had in charge that day.

Farmers reported that tapping usually began when the circumference of the tree trunk reached 50 cm, and then divided the circumference in two or three sections. A single section can bleed for 6 years and then the next section can start be tapped. The cuts started at a height of 150 cm from the base of the tree and continued down until nearly ground level, as shown in Figure 1. The first cut is carried out from the left to the right in a downward direction, along a path that forms an angle of 30° to the horizontal by using a pattern made of a plastic film. When the cut of section reaches the base of the tree, it is necessary starts to bleed a new section, beginning again at a level of 150 cm above ground level.

Figure 1. Natural rubber processing for obtaining sheets

It was observed that when performing the incision, worker's forearms and wrists must maintain a degree of flexion while the trunk was leaning forward and lateral rotated. The level of flexion or rotation depended on the height of the level of bleeding. After finished the tapping of all the trees located on each tree and gather the latex in drums to on the plantation and when latex stopped to drop into facilitate their transport to the latex treatment area the cups, the worker collected the latex of each cup where next activity is carried out, as shown in Figure 1.

During this study, each worker transported 15 to 25 Kg drums by walking between 1 and 2 Km from the plantation to a zone where rubber sheets are manufactured. The distance that was traveled by the worker depended of the location of the plantation where he ended the collection of latex. Collected latex was filtered to remove impurities and subjected to dilution using an aqueous solution of acetic or formic acid.

After a coagulation period of one day, rolling of rubber until transformation to rubber sheets on manually operated equipment took place. The worker passed the coagulated material 7 to 10 times between two metal rollers in which the worker diminished gradually the gap until sheets of 1.5 to 2 mm thick are obtained.

After a drying period of seven to ten days, dried sheets of natural rubber were obtained. These sheets are raw materials for rubber industries.

3.1.2 Rubber articles manufacturing

Natural rubber sheets were mixed with the ingredients selected by the manufacturer according to the desired properties for the product, by passing the materials by an open roll mill. The mixture was cut in pieces that were incorporated to a mold, where parts were manufactured by applying heat and pressure in a molding press. Mixing and molding are shown in Figure 2.

Figure 2. Rubber parts manufacturing processes a) y b) Mixing in open rolls mill, c) and d) compression molding

In the case of micro and small rubber factories from Antioquia, their mills, molding presses and molds varied in structural configuration and automation level but broadly have low and old automated technologies, which increase the level of ergonomic risk.

Tables 2 and 3 describe ergonomic risks rolling of rubber to obtain sheets, mixing, identified during in-situ work and analysis of and molding; manual handling of heavy loads the videos, for the natural rubber processing at in activities like latex collection, mixing and plantations and small industries, respectively. molding; repetitive movements during latex It can be seen that the main risks are associated tapping, latex collection and mixing, and with awkward postures in activities like rubber mechanical entrapment risk during rolling of tapping, latex collection, filtering and dilution, rubber to obtain sheets.

Table 2. Postural risks in natural rubber processing for obtaining sheets

Table 3. Postural risks in manufacturing of rubber parts in small factories

3.3 OWAS analysis

Table 4 presents OWAS analysis natural rubber processing at plantations and Table 5 presents the same type of analysis for manufacturing rubber parts. In both processes it can be seen that there are level 4 risk activities, such as bleeding and collecting cups in the case of work in plantations, and mill cleaning in the case of rubber articles manufacturing. WMSDs like musculoskeletal injuries at back level, spine deviation and cramps can occur in both processes. Other activities have lower risk levels, creating risks of WMSD as described above, but also with the possibility of causing upper limb and muscle fatigue.

Table 4. OWAS analysis for natural rubber processing for obtaining sheets

Table 5. OWAS analysis for rubber mixing and molding

According to the risk levels that were identified, OWAS method establishes that it is necessary to perform corrective action immediately for activities such as tapping, latex collecting and handling of molds because its OWAS codes were 4, and for other activities such as filtering and dilution, mixing and mold handling is relevant implement corrective actions as soon as possible because its OWAS codes were 3.

According to OWAS analysis and literature review, it is recommended to carry out some actions seeking to reduce work-related ergonomic risks:

* Design and implement improvement plans specifically aimed to reduce the ergonomic risks in natural rubber production chain, considering organizational culture, socio-economic and sociodemographic factors of natural rubber farmers and small rubber manufacturing industries. To create awareness between workers and employers is a key component of these plans, as was stated in the studies of Singh et al. (2012) and Unnikrishnan et al. (2015).

* Since latex tapping and collection cannot be automated, it is inevitable trunk tilting and leg bending when workers perform those activities. It is required to design and implement an active pauses program at appropriate intervals during workday.

* For mixing in open rolls mills it is recommended that the worker uses a bench according to the height of the mill, reducing the lifting of the arms above the shoulder level. Frequent stretching and active pauses are also necessary.

* A redistribution of workplaces and the use of height adjustable tables in molding process areas could reduce postural risks in rubber industries. Furthermore, handling molds closer to the center of gravity of the worker could reduce posture risks related to musculoskeletal disorders mainly in the spine, and in the low back area.

* It is recommended the use of mechanical aids such as carts for lifting and transportation of drums in plantations and molds in rubber industries. In the case of rubber industries, wheeled tables or to seek help from co-workers could decrease ergonomical risks related to manual handling of loads in the workplace.

4. Conclusions

In this exploratory study, ergonomic risks in small plantations and small industries belonging to the natural rubber production chain were identified by using the OWAS method. It was observed that several activities of natural rubber processing required movements that can cause work-related musculoskeletal disorders in back and legs. The risks arise in awkward postures, repetitive movements, manual handling of loads and mechanical entrapment of hands. OWAS analysis identified level 4 risks for two activities in plantations, i.e. latex tapping and collection, and two activities in small rubber industries, i.e. mixing in open rolls mills and mold handling.

According to OWAS analysis and literature review, it is recommended to carry out some corrective and other preventive actions seeking to reduce work-related ergonomic risks. Since few ergonomic studies are available on the natural rubber chain production, it is appropriate to carry out new studies involving other ergonomic evaluation techniques to complete the results found in this work. It is important to note that small plantations and rubber industries are more exposed to posture risks because the lack of education in ergonomic issues.

It was identified that workers are unaware of the risks associated with their tasks, so some education in ergonomic aspects could avoid habits that are potentially harmful to their health and welfare. Considering that physiological disorders caused by ergonomic risks do not appear immediately, which hinders further analysis and control implementation to minimize the consequences of those risks, it is appropriate to act preventively in the case of a growing economic activity like is the case of natural rubber exploitation in Colombia and other regions where heveiculture is important for the economy of smallholders and small rubber industries.

The assessment presented in this work can help mitigating the ergonomic risks in production chains similar to natural rubber.

5. Acknowledgments

The authors thank the administration of the Department of Antioquia for financing the project "Improving productivity for development and increased competitiveness in the natural rubber chain through an applied research program and innovation in the Department of Antioquia - BPIN code 2013000100162", which allowed the development of this work.

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