Espacios. Vol. 34 (12) 2013. Pág. 2
Determination of the Lifting Index (LI) of NIOSH equation in milkings manual activity in rural properties in COMCAM region, Brazil
Determinación del Índice de Elevación (IL) de la ecuación en manual de actividad de ordeños NIOSH en propiedades rurales de región COMCAM, Brasil
Recibido: 23-08-2013 - Aprobado: 21-10-2013
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Ergonomics, when applied to manual labor, both in light and heavy activities, seeks to ensure the worker’s health, as well as increase productivity, use of time and the overall quality of the procedures.
Agricultural activity, considered inherently risky both by climatic and economic aspects as well as dangers to the health and security of the rural workers in Brazil, due to the inadequacy of their work activities, is showing increasingly different characteristics from urban labor (Popija; Ulbricht, 2005).
Milk production is included within the context of agricultural activity, and it forms the building block for milking activities. Agricultural work is very risky and many accidents happen while executing the several types of activities involved in it. “It is an area where the work effort has decreased, but is still very heavy and many workers suffer from various Musculoskeletal Disorders” (Falzon, 2007, p. 538).
As it involves one of the areas of ergonomics, there is a concern with the physical workload, it is inserted within the specialization field of physical ergonomics, which refers to anatomical, anthropometric, physiological and biomechanical characteristics of human beings insofar as they relate to physical activity. (Másculo, 2008; Merino; Teixeira, 2010).
This area of specialization in Ergonomics includes: working postures, handling of materials (application of force and physical efforts), repetitive movements, work related musculoskeletal injuries, layout of the workplace, occupational health and safety and its application is given by assessment tools created during the development of ergonomics.
Among the tools for evaluating physical workload is NIOSH equation. Considering that many studies make use of this equation in its methodologies and that among other assessment tools indicated by Stanton (2005), this proved to be the most used.
The application of the NIOSH Lifting Equation provides the Lifting Index (LI) which represents an estimate of the physical stress associated with the lifting activities being evaluated in this study.
Therefore, it is of paramount importance that studies are made on rural activities, so that we can improve the quality of life of the rural worker.
Considering what has been shown so far, this study aims to evaluate the Lifting Index (LI) and the incidence of lower back pain of workers in relation to the milking activities at Comunidade dos Municípios de Campo Mourão/PR (COMCAM), Brazil. The choice of the search region is due to the significant presence of family farms, to which milk is an important economic activity.
Biomechanics studies the efforts made by the worker, the handling, lifting and carrying of loads, the use of spinal cord and upper limb actions as working tools (Couto, 2007).
This study focuses on the work activities, the application of forces as well as their consequences for workers, since many unfit processes working environments cause muscle tension, pain or discomfort, fatigue, and can lead to the development of occupational diseases.
2.1 Lifting of Loads
Despite increased automation and mechanical tools in various sectors of the Brazilian economy, with consequent reduction of the heavy lifting, and technological advances in medicine for diagnosis and treatment, the inability to work caused by low back pain remains an important issue.
With respect to agricultural and livestock breeding activities, the manual lifting of loads is still used frequently. In milking activity in the region of COMCAM, which is the region being evaluated, it was noted that it is still necessary for workers to move milk containers with approximately 50 liters into cooling tanks or even freezers, loading bags of silage for livestock feeding, among other activities that are performed manually (Oliveira et al., 2011).
To Couto (2007), rural workers who work in non-mechanized processes perform physically heavy work.
According to Stål, Hansson and Moritz (1999), epidemiological studies conducted by the Swedish University of Agricultural Science in Swedish farms indicated that the activity of farmers is high risk with respect to WMSDs, most of the agricultural work is associated with lifting and carrying heavy loads and inadequate postures.
The cargo handling is responsible for the majority of muscle trauma in workers. This activity is a major cause of back pain because the lifting loads in general does not meet ergonomic conditions, being as related to the total weight, grip points, height of the surfaces, among others (Kromer; Grandjean, 2005).
The diseases and disorders related to the spine and paraspinal regions emerge through pain to become chronic, enough to make absence from work increasingly longer and more frequent, which may lead to disability of the worker. The disturbances due to overload, usually in the lower spine, represent most of all occupational disorders. One should also consider that more than half of the total disorders are from overload, "two-thirds of overload disorders involve the lifting of loads and around 20% involves pulling and pushing loads" (KROMER; GRANDJEAN, 2005, p. 103).
It is worth noting that there is an appropriate calculus for assessing loads of the workers, known as the NIOSH equation (developed by the National Institute for Occupational Safety and Health, USA), which proposes to assess the risk involved in activities that involve manual lifting of loads (NIOSH , 1994).
To Dul and Weerdmeester (2004) and Couto (2007) the Equation of NIOSH in relation to the Recommended Weight Limit (RWL), considers as base the weight of the load that nearly all healthy workers could lift for a substantial period of time without increasing the risk of developing back pain (Couto, 2007).
To Marras (2000), the high prevalence of MSDs and spinal injuries can occur when the physical overload is excessive, or when the physical capabilities of workers are tiring due to individual or occupational factors.
This research paper used the method of qualitative and quantitative approach, characterized as an exploratory study using a case study.
To achieve the objectives of the present study, the technique of literature search was employed, performing searches on the Internet, scientific articles and specialized books.
The data collection instrument chosen was questionnaires divided into two parts:
a) General and Occupational Data
This part was developed according to Ulbricht (2003), serving as a theoretical support. There were changes on some issues, the instrument was then adjusted and adapted thus getting a questionnaire in the final version.
This questionnaire had basic information to evaluate the profile of milkers, in the form of 22 questions.
b) Identification of Musculoskeletal Symptoms
To evaluate the musculoskeletal symptoms, and adapted version of the Nordic Standard Questionnaire (NSQ) of Kuorinka (1987) was used.
To collect the data, we conducted random visits on dairy farms.
Ethic precautions were taken for the application of questionnaires, and information kept confidential. The milkers were identified by codes consisting of a number (from 1 to 9.), accompanied by two letters according to the production system adopted: manual milking (Ma), mechanical milking with bucket (Mb), milking machine connected to the milking ducts (Md), milking machine connected to ducts in the milking parlor (gap) (Mdf) and mechanical milking with bucket in the milking parlor (gap) (Mbf).
For better accuracy of data from each questionnaire in regards to the gathered results, the method of structured interviews in the form of a questionnaire was opted for. Thus, the filling of the questionnaires was performed by the researchers, due to the fact that the sample of the population had, in most cases, low levels of education.
For the evaluation of the workload that the workers perform during the activity, the National Institute for Occupational Safety and Healt - NIOSH (1994) equation was used, which proposes to evaluate the risks involved in activities involving manual lifting (NIOSH, 1994) .
To Dul and Weerdmeester (2004) and Couto (2007) the NISH equation in relation to the Recommended Weight Limit (RWL), considers as base the weight of the load that nearly all healthy workers could lift for a period of up to eight hours a day without increasing the risk of work-related back pain (NIOSH, 1994).
The RWL that the worker is able to lift safely is up to 23 kg in the best conditions, being multiplied by six coefficients. Thus the RWL is obtained by the following equation.
RWL = Cc x FH x FV x FD x FA x FF x FP (1)
RWL = 23 x [25/H] x [1-(0,003|V-75|)] x [0,82 + (4,5/D)] x [1 – (0,0032 A)] x FF x FP (2)
RWL - Recommended Weight Limit
CL – Constant Load, which is 23 Kilograms in this excercise;
HF = Horizontal Factor (in centimeters), which is 25/H;
VF = Vertical Factor (in centimeters), which is [1-(0,003?V-75?)];
DF = Distance Factor (lifting/minute), is [0,82 + (4,5/D)];
AF = Asymmetry Factor (degrees), is [1 – (0,0032 A)];
FF = Frequency Factor, value is obtained by NIOSH’s (1994) Table 5.
FP = Grip Factor, value is obtained by NIOSH’s (1994) Table 7.
Each of these coefficients in the equation is determined from the value of each variable found in specific activity.
As soon as the RWL is retrieved for the activity, comparisons are made between the discovered value and the real weight of the cargo (RW). This relationship provides the Lifting Index (LI), and represents an estimate of the physical stress associated with the physical activity being assessed. Thus, an estimate of the level of physical stress is defined by the following equation:
LI = RW/RWL (3)
LI – Lifting Index;
RW – Real Weight of the load (in kilograms);
RWL – Recommended Weight Limit (in kilograms).
With the results the equation of LI, ergonomic hazards can be identified in Table 1.
Table 1 – Interpretation of the biomechanical risk and risks to the spinal cord based on LI
Fonte: Couto (2007, p. 70).
As per the information in Table 1, it is known that the activities or tasks with a LI of less than 0.7 do not present any risk and those with a LI larger than 2.5 show a high risk not only in the lumbar region of the spine, but in its entirety.
The RWL and the LI are based on the concept that the risk of low back pain (pain in the lumbar region) and generally spine-related pain increases directly proportional to the increases of the lifting demand. According to Teixeira, Okimoto and Gontijo (2011), inasmuch as LI increases, the risk of LBP also increases. The shape of the risk function is unknown because there is not a sufficient number of studies on epidemiology to establish the relationship between the LI and the risk of low back pain.
The study was conducted in six dairy farms totaling nine milkers, but only one property with two dairy milkers had lifting activities that did not enter the restrictions of the equation of NIOSH.
The weight lifting activities that were considered as restricted were: activities executed in one or two milkers with only one hand; the use of a wheelbarrow or shovel; lifting the milk container on the shoulders of the milker; and the use of a crane.
4.1 Description of the Evaluated Activity
In a dairy property, the worker performs the daily milking of animals, cleaning of the facilities, equipment and utensils and feeding of livestock. In these activities there is constant lifting of cargo manually, such as buckets (approximately 12 to 40 kg) milk containers (approximately 40 to 50 kg) bag with silage or animal food (approximately 60 kg ), among others.
However, the activity of lifting loads entails possibility that it would cause a musculoskeletal injury, back injury or injuries in other segments of the spine and superior limbs.
According to the study proposal of checking if the working conditions for the lifting of milk containers is being performed within normal limits of tolerance based on the limit cargo load to be handled or if there is a muscle overload to the lifting, the National Institute for Occupational Safety and Health - NIOSH (1994) equation was applied, which will be presented in the following sections.
4.2 Sample Profile and Identification of Musculoskeletal Symptoms
Seven male and two female milkers were evaluated. The average age of the nine milkers was 43 years, the average service time of 22 years and two of them had started the activities since one year only, the other started the activities since childhood.
With respect to BMI, five participants were overweight and all complained of pain and / or discomfort.
As for the pain and / or discomfort in the musculoskeletal system, the complaints were:
The average age is 42.66 years and the majority of the milkers have little education and are owners or part of the family, these being from the family agriculture.
The weekly schedule is on average 82.66 hours, indicating a high workload, compared with the urban work (average 44 hours / week).
As for the pain and/or discomfort in the musculoskeletal system, 100% of milkers reported complaints, and the highest prevalence with 77.77% (7) in the lumbar region, 44.44% (4) in the region of the shoulder girdle (shoulder) with irradiation in the upper limbs (arms, forearms and wrist), 22.22% (2) in the neck and lower limbs (hip, knees and legs), respectively, and 11.11% (1) in the thoracic region.
4.3 Data in Regards to the Load Lifting Evaluation – NIOSH Equation
By applying the equation for calculation of RWL, this equation uses known or readily measurable variables, like weight to be transported, the distance of the load relative to the individual, frequency of the task, among others. Thus, there can be an estimate of the recommended weight to be transported by workers without risk of injury or discomfort.
Thus, we analyzed the lifting of milk containers (steel) with a capacity of 50 liters of milk in dairy activities.
Table 2 shows the measurements of the variables of the activity in which the milker performs lifting of the milk container on a short wall with a different height as to where the cooler is, these measurements were calculated on the field.
Table 2 – Data for the calculus of NIOSH equation – Milker 2 Mb
Figure 1 illustrates the analysis of the activity of lifting the milk container from its origin, in this case, the floor of the hose (milking site) and the destination, the short wall (floor with differentiated height) where the cooling tank is fixed.
Figure 1 - Lifting of milk container from origin (a) to the short wall of destination (b) – Milker 2 Mb
The results found for RWL were 17.066, ie, this value is the ideal weight for lifting the load in the conditions the milker executes it (varying distances), and since the actual weight is 59 kg, the Lifting Index (LI) calculated was 3.457.
Table 3 presents the measurements of another lifting activity that milkers execute. After milker 2 Mb lifts the milk container to the short wall, the milker 1mA performs the lifting of the milk container to the cooler tank, as milk is stored for conservation thereof.
Table 3 – Data for the calculus of NIOSH equation – Milker 1 Ma
As Figure 2 illustrates, for letter (a) the origin of the lifting and the letter (b) the destination, in this case, pouring milk inside the cooling tank.
Figure 2 –Lifting of milk container Origin (a) in the cooling tank Destination (b) - Milker 1Ma
Subsequently, we applied the measured variables presented in tables 1 and 2 in NIOSH (1994) equation. To facilitate the calculations, these were performed by means of specific software.
As a result, Table 4 presents the summary of values ??for both RWL and LI of the two milkers from the analyzed farm.
Table 4 – Summary of the results found for RWL and LI values
Thus, the results of the situations of lifting loads were greater than two, there is ergonomic high risk (max risk) for the milkers, with the variables presented and the values ??for both RWL and the LI in the two analyzed activities, this should be considered as unacceptable. Since the milkers should not execute the lifting of these loads, immediate changes should be required in the methods of this activity, since the lifting of loads constitutes a high risk for spine and limbs, indicating an incidence of low back pain and risk of overuse injuries.
Therefore, returning to the data presented, in regards to pain and / or discomfort in the musculoskeletal system have a higher prevalence of spinal pain in the past 12 months in the lumbar region with 77.77% (7). Having been the most remembered, this is probably the most recurrent among the milkers. Thus, cross-referencing this information with the results of lifting situations of cargoes superior to the LI, this shows that the activities of lifting milk containers, presents an overload scenario, imposing a biomechanical load the worker above the recommended.
This study allowed us to observe a relationship to the work posture adopted, regarding the activity of lifting loads and the presence of pain in various segments of the human body, particularly in the lumbar spine, showing that there is a relationship of incidence of low back pain associated with manual lifting of loads in the activity of milking.
The evaluated activities were observed with the application of the NIOSH equation based on the values ??found for the Lifting Index (LI), the activities of lifting of loads showed high ergonomic risks for milkers, due to unfavorable condition of different variables, principally with respect to the weight of the load. Pointing, thus, overloads in the musculoskeletal system of the milkers, there being the need for change, since they are exposed to high risk for spine and limbs, indicating an incidence of low back pain and risk of overuse injuries.
The loading of cargo by milkers, plus the expense of muscle strength for loading (cans, buckets and containers), used as support, body parts like the arms and shoulder girdle, and some containers have no place to grip and are slippery, missing loops or handles for the fingers and when there are handles, they are very thin, so the grip quality is poor, as ranked by NIOSH (1994), which can cause diseases by additional load on the joints and / or muscles.
Thus, it can be concluded that the constraining postures and the lifting of cargo carry biomechanical and spinal risks for the workers.
We conclude, therefore, that the work in dairy farming requires the proper conduct of the wide variety of tasks performed by rural workers, more organization and planning with respect to work schedules, needs and gaps in the workplace adaptations of milking, so that the postures are not as constraining
To reduce the burden of this task, it was recommended:
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