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Evaluacion ergonomica del procesamiento del caucho natural en plantaciones y pequenas empresas.

Ergonomie assessment of natural rubber processing in plantations and small enterprises

1. Introduction

Work-related ergonomie risks are a major problem in publie health (Stock et al., 2011). Physieal/ergonomie factors during working time sueh as eombination of meehanieal 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 (Confederacion 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 (Confederacion 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 (Camara 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 (Asociacion Comite de Cultivadores de Caucho) in Santa Clara, municipality of Taraza (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 Aburra, 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 Confederacion 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[R].

Activities involving ergonomic risks were identified and aspects related to postural hygiene for these activities 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.

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[R] 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[degrees] 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.

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 on the plantation and when latex stopped to drop into the cups, the worker collected the latex of each cup located on each tree and gather the latex in drums to facilitate their transport to the latex treatment area 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.

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

3.1.3 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.

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.

6. Referencias

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Sandra Velasquez ([seccion]) *, Sebastian Valderrama *, Diego Giraldo **

* Grupo BIOMATIC-Biomecanica, Materiales, TIC, Diseno y Calidad para el Sector cuero, plastico, caucho y sus cadenas productivas, Centro de Diseno y Manufactura del Cuero, SEN. Antioquia, Colombia.

** Grupo de Materiales Polimericos, Universidad de Antioquia. Antioquia, Colombia.

([seccion]) smvelasquez@sena.edu.co, svalderrama1@misena.edu.co, dhernan.giraldo@udea.edu.co

(Recibido: Diciembre 21 de 2015--Aceptado: Marzo 10 de 2016)

Caption: Figure 1. Natural rubber processing for obtaining sheets.

Caption: Figure 2. Rubber parts manufacturing processes a) y b) Mixing in open rolls mill, c) and d) compression molding
Table 1. Posture codes and risks description of OWAS method.

Body             Assigned posture code
area
                1                      2

Legs   Sated                  Standing with both-
                                legs straight

Back   Erect                  Leaning forward or
       Both arms be-            backward
Arms     low shoulder         One arm above and
         level                  one below the
                                shoulder level
Load   < 10Kg                 Between 10Kg and
                                20Kg

       Risk Description

Risk   Description

1      Normal and natural posture without
         harmful effects on the musculoskeletal
         system
2      Posture with harmful effects on the
         musculoskeletal system.
3      Posture with harmful effects on the
         musculoskeletal system.
4      The burden caused by this posture has
         extremely harmful effects on the
         musculoskeletal system.

Body          Assigned posture code
area
               3                 4

Legs   Stand with the      Stand with the
         weight on           knees bent
         one leg

Back   Rotated or tilted   Leaning back
         laterally           with twist
Arms
       Both arms above
         shoulder level
Load    > 10Kg

       Risk Description

Risk   Description

1      Normal and natural posture without
         harmful effects on the musculoskeletal
         system
2      Posture with harmful effects on the
         musculoskeletal system.
3      Posture with harmful effects on the
         musculoskeletal system.
4      The burden caused by this posture has
         extremely harmful effects on the
         musculoskeletal system.

Body          Assigned posture code
area
            5             6            7

Legs   Standing or   Kneeling       Walking
         crouched      on one or
         with one      both knees
         knee bent
Back
Arms
Load

Risk   Action

1      No action is required
2      Corrective actions are required in
         the near future.
3      Corrective actions are required as
         soon as possible.
4      Corrective actions are required
         immediately.

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

Activity         Postural risk

                 Awkward postures

                 * Mechanical loading is not symmetrically applied
                   due to the slope of the incision, because the
                   worker must cut the tree's bark using its
                   deft hand.
Tapping          * The height above the floor at which the incision
                   is done varies with the time of exploitation of
                   the tree and tree diameter. Often the worker
                   must perform the activity in a squatting
                   position, with constant bending of the knees
                   and trunk tilt with sporadic rotations. The
                   level of stress generated also depends on the
                   height of the worker. The activity is executed
                   taking the knife with both hands, but the
                   deft hand applies the most demanding force that
                   is required by the tool.

                 Repetitive movements

                 * The worker repeats the activity between 400 and
                   600 times every day. The activity takes between
                   2 and 4 hours, according to the slope of the
                   terrain and the size of the plantation.

                 Risks associated with manual handling of loads in
                   the workplace

                 * Unbalanced lifting that increases the load to
                   the back. Once filled, buckets weigh between 10
                   and 15 kilograms; the worker carry one bucket
                   with an arm. Drums filled weigh between 15 and
                   25 kilograms; the worker can carry one drum with
                   an arm or with each arm when transportation of
                   two drums is needed.

Latex            Awkward postures
  collection
                 * The height above the floor at which the
                   incision is done varies with the time of
                   exploitation of the tree and tree diameter.
                   Sometimes the worker must squat to perform
                   the activity, i.e. bending the knees is
                   frequent. The level of stress generated also
                   depends on the height of the worker.

                 Repetitive movements

                 * The worker collects between 400 and 600 cups
                   every day. The activity takes between 1 and
                   1.5 hours, according to the slope of the
                   terrain and the size of the plantation.

                 Awkward postures

Manufacturing    * Filtering and dilution are carried out at
  of rubber        ground level. Sometimes the worker
  sheets           must squat to perform the activity and
                   bending of the knees occurs, but sometimes
                   the activity is carried out by tilting the
                   trunk, with or without twisting of the
                   trunk. Mechanical loading is not symmetrically
                   applied.

                 Mechanical entrapment risk

                 * Mechanical entrapment of fingers can occur at
                   the open rolls or at the gears that generates
                   the movement of the rolls.

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

Activity                 Postural risk

Mixing at    Awkward postures
open rolls
mill         * Mechanical loading is not symmetrically
               applied due to the height of the space
               where rubber enters for rolling.
             * The level of stress depends on the size
               of the mixtures, the height of the mill
               and the height of the worker.

             Repetitive movements

             Two repetitive movements were observed:

             * When ingredients enter to the space
               betwwen rolls, an overload is applied
               on hands and the back. Mixtures weight
               varies between 1 and 13 Kg.
             * During the collection of ingredients
               that fall into the tray the worker must
               bend down to pick up the materials, and
               rise again to incorporate them into the
               mix at the top of the mill. Risks
               associated with manual handling of
               loads in the workplace
             * The level of stress depends on the size
               and the weight of the mixtures, which
               varies between 1 Kg and 13 Kg, and the
               height of the mill.

Molding      Awkward postures

             * The worker must carry the molds from
               the working tables to the molding press,
               and then transport them back to extract
               the finished product. The activity is
               carried out by twisting of the trunk.
               Occasionally, tilting of the trunk is
               required. The tables were molds are
               handled are also used for placing tools,
               polishing products, preparing pieces of
               the mixture to be incorporated to the
               molds or temporarily placing finished
               products, then the height and position
               of the table vary into the company.
               For this reason, mechanical loading on
               the back is unbalanced.

             Risks associated with manual handling of
               loads in the workplace

             * For manufacturing small pieces, it was
               observed that molds of 500 gr are
               handled every five minutes. Molds of

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

                                      Postural risk

Process                Activity       Aspect   Code

Tapping and          I. (Tapping)      Back     4
  latex                                Arms     1
  collection

                                       Legs     6

                                       Load     1

                   II. (Collection)    Back     4

                                       Arms     1

                                       Legs     5

                                       Load     1

Sheet              I. (Filtering       Back     3
  manufuncturing     and dilution)     Arms     1

                                       Legs     5

                                       Load     1

                   II. (Rolling for    Back     2
                     obtaining
                     rubber sheets)    Arms     1
                                       Legs     4
                                       Load     1

                                          Postural risk

Process                Activity       Risk    Possible WMSDs s
                                      level

Tapping and        I. (Tapping)         4     * Back symptoms
  latex                                       * Deviation of
  collection                                    the spine
                                                (lordosis or
                                                scoliosis)
                                              * Muscle
                                                contractures,
                                                sciatalgia,
                                                frequent muscle
                                                spasms
                                              * Tendinitis,
                                                tenosynovitis,
                                                and carpal
                                                tunnel syndrome
                   II. (Collection)     4     * Pain associated
                                                with the
                                                compression of
                                                the lumbar
                                                vertebrae (lower
                                                back pain)
                                              * Deviation of
                                                the spine
                                                (lordosis or
                                                scoliosis)
                                              * Cervical
                                                tension syndrome
                                              * Rotator cuff
                                                tendinitis
                                              * Muscular fatigue
Sheet              I. (Filtering        3     * Back symptoms
  manufuncturing     and dilution)            * Deviation of
                                                the spine
                                                (lordosis or
                                                scoliosis)
                                              * Muscle
                                                contractures,
                                                sciatalgia,
                                                frequent
                                                muscle spasms
                                              * Pain associated
                                                with the
                                                compression of
                                                the lumbar
                                                vertebrae
                                                (lower back pain)
                   II. (Rolling for     2     * Hand sprain or
                       obtaining                hand fracture
                     rubber sheets)           * Amputation of
                                                fingers or hand

Table 5. OWAS analysis for rubber mixing and molding

Process     Activity            Postural risk
                                Aspect Code

Mixing      I. (Incorporation       Back        2
  in open     of ingredients        Arms        1
  rolls       to the mill)          Legs        2
  mill                              Load        2
            II. (Mixing until       Back        2
              ingredients are       Arms        1
              dispersed in          Legs        4
              the rubber            Load        2
              matrix)
            III. (Extraction        Back        2
              of the mixture)       Arms        1
                                    Legs        4
                                    Load        2
            IV. (Mill               Back        4
              cleaning)             Arms        2
                                    Legs        4
                                    Load        1
Molding     I. (Molds               Back        4
              handling)             Arms        1
                                    Legs        2
                                    Load        3

Process     Activity             Risk    Possible WMSDs s
                                 level

Mixing       I. (Incorporation     2     * Back symptoms
  in open      of ingredients            * Deviation of
  rolls        to the mill)                the spine
  mill                                     (lordosis or
                                           scoliosis)
                                         * Muscle
                                           contractures,
                                           sciatalgia,
                                           frequent
                                           muscle spasms
             II. (Mixing until     3     * Pain associated
               ingredients are             with the
               dispersed in                compression of
               the rubber                  the lumbar
               matrix)                     vertebrae (lower
                                           back pain)
                                         * Deviation of
                                           the spine
                                           (lordosis or
                                           scoliosis)
                                         * Muscle
                                           contractures,
             III. (Extraction              sciatalgia,
               of the mixture)             frequent
                                           muscle spasms
                                    3    * Pain associated
                                           with the
                                            compression of
                                           the lumbar
                                           vertebrae
                                           (lower back pain)
                                         * Deviation of
                                           the spine
                                           (lordosis or
                                           scoliosis)
             IV. (Mill                   * Pain associated
               cleaning)                   with the
                                           compression of
                                           the lumbar
                                           vertebrae (lower
                                           back pain)
                                         * Deviation of
                                           (lordosis or
                                           scoliosis)
                                   4     * Cervical
                                           tension
                                           syndrome
                                         * Rotator cuff
                                           tendinitis
                                         * Muscular fatigue
                                         * Back symptoms
                                         * Deviation of
                                           the spine
                                           (lordosis or
                                           scoliosis)
Molding      I. (Molds             3     * Muscle
 handling)                                 contractures,
                                           sciatalgia,
                                           frequent
                                           muscle spasms
                                         * Pain associated
                                           with the
                                           compression of
                                           the lumbar
                                           vertebrae
                                           (lower back pain)
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Title Annotation:INGENIERIA DE PROCESOS
Author:Velasquez, Sandra; Valderrama, Sebastian; Giraldo, Diego
Publication:Ingenieria y Competividad
Date:Dec 1, 2016
Words:4902
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