Ergonomic Risk By: Repetitive Movements, in the Operators of a Crude Oil Production Plant

Subjective Representation by Survey

The technique of the Standardized Nordic Questionnaire (SQN) [8], which determines the MSDs in each of the operators from the outset, allows the results to be obtained and evaluated quickly and effectively. The analysis of the CNE was carried out by professionals and researchers in the field of ergonomics with the support of students from the industrial engineering career, UTN, trained in the subject of Ergonomics and qualified with 120 hours of theoretical and practical academic learning, coordinated by the Director of the research project. The questions were related under a dialogic context that allows the validity in each one of the consultations made to the operators, which agreed to affirm the semantic effectiveness. However, for the analysis of each of the data, the refinery’s macro-processes were taken into account (Figure 1.) for each production area, while in Table 1, the areas and personnel to be evaluated are defined.

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Population of Analysis

The analysis carried out, determines the number of operators according to the areas of crude oil production, and several centers of oil production (CPF). The sample (finite), determines the method of application, as the set of elements or individuals, that, congregate the necessary typologies of study of the working population of the CPF; “which really will be carried out in study, considering a subset of the population” (Gallego, 2004). For the stages of the sample calculation, it was established according to the number of operators, with a ratio of 150, with a margin of error of 4.0%, and a reliability of 95%. In Table 2, the calculation of the finite sample is established according to the Vallejo method (Vallejo, 2012).

N p q n d N p q Z Z

2

2 2 * * * $$ v = \frac {N ^ {*} Z _ {\alpha} ^ {*} p ^ {*} q}{d ^ {2} * \left(N - 1\right) + Z _ {\alpha} ^ {2} *} $$ (1) α ( ) * 1 * * n= sample size N= population size

2 Z α = confidence level value p= punctual estimation q= probability against

When taking the result of the sample calculation (150 workers), in table 3 and graph 1, they are analyzed by sex and age in the areas and processes of the CPF.

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Graph 1: Quantitative diagram.

Method of Evaluation by Work Cycle

OCRA checklist as a starting tool: The OCRA method considers various aspects of identifying the risk factor for postural dysergonomic exposure, establishing a preliminary analysis, based on ISO 11228-3 [10]. The first part of the analysis, the observation and monitoring of each posture by the extremes, analyzes and identifies the factor, the strength, repetitiveness (in strength), (harmful) postures of type of movement and the long journey by work cycles that make possible an absence by recovery time in the operator. Application in the operators: To establish a value by the Check List OCRA Index (ICKL) and identify and classify the risk factor as: optimal, acceptable, very light, light, medium or high, the use of an equation is required [11].

$$ I C K L = \left(F R + F F + F F z + F P + F C\right) ^ {*} M D $$

FR= For the recovery factor. FF= By the frequency factor. FFz= By the force factor. FP= By the posture and movement factor. FC= Because of the additional risk factor. FD= By the cycle time multiplier.

Net Time per Cycle / Repetitive Work

It is essential to determine the net repetitive work time (TNTR) and the network cycle time (TNC) for the operators before calculating the ICKL. The TNTR is the time during which the operator performs the repetitive activities or tasks, that is, the length of the working day at the site, less breaks, non-repetitive tasks, rest periods and other downtime [11].

$$ T N T R = D T - \left(T N R + P + A\right) $$

DT= For the duration in minutes of the shift in a day. TNR= For the non-repetitive working time. P= By the duration in minutes of the breaks while occupying the position A= For the length of the lunch break in minutes. At the same time, the TNC, is the net time per work cycle if we only consider the repetitive tasks executed at the job under examination.

60* TNTR TNC NC   =    

NC= By the number of work cycles performed at the position These TNTR and TNC calculations are derived by calculating the factor and multiplier from the ICKL equation.

The first instance to be analyzed is, if the tasks per work cycle are performed by repetitive motion [12].

The OCRA method, 2005- Occupational Repetitive Action (OCRA) establishes a criterion for determining risk exposure and MSD associated with repetitive movements by the upper limbs [13].

Therefore, the risk factor recommended by the International Ergonomics Association (IEA) is considered by assessment: repetitiveness, due to inadequate or static postures, forced movements and forces, the lack of rest both for recovery periods, assessing along the work cycles or activity time by the worker. On the other hand, other influential factors during the task can be considered such as vibrations, which can influence the worker’s condition due to exposure to cold and other factors. The following terms need to be understood: [14].

• Working time: daily work cycle in which the operator performs various tasks.
• Task: work or work activity whose operation objective is specified.
• Cycle: is the sequence of actions and techniques, to the movement both physical and mechanical of short, medina and long repetitive continuation in the same way again and again.

Exposure calculation process: For the exposure index, it corresponds to the sum of actions performed by both upper and lower limbs in repetitive tasks by cycles within the working day, indicated in the following equation: [15].

$$ I E = \frac {A _ {e}}{A _ {r}} \tag {2} $$

e r IE= Exposure Index Ae= Existing repetitive movements in the shift Ar= Number of existing tasks When analyzing the actions in the work area, it is not recommended to use for evaluations in the use of the PVD11. Therefore, walking or visualizing does not demand any mechanical action or cycles by the upper extremities.

To determine the calculation: A_r it is necessary to perform an analysis by means of an equation:

$$ I E = \sum_ {n} \left[ C F * \left(F o _ {m i} * P o _ {m i} * \mathrm {R e} _ {m i} * A d _ {m i}\right) * D _ {i} \right] * R c _ {m} * D u _ {m} $$ n= For each of the cycles of tasks to be carried out, by repeated movement.

1  Display Screens

CF= Per constant to the frequency of operations to the task (X). Fomi= By the force factor in the task (X). Pomi= By the posture factor in the task (X). Remi= By the repetitiveness factor in the task (X). Admi= By the factor in additional elements in the task (X). Di= By the duration in each task for repetition in minutes. Rcm= By the factor of the lack of period in the recovery per day. Dum= By factoring in the multiplier at the time of the function by the cycle or its usual duration in the repetitive task.

Frequency Constant (CF): In the frequency due to repetition, the risk factor is higher, consequently, the final value of the index, CF=30 per share, per minute to the reference value is considered as a high grade variable.

Repeatability Factor (Rem): In determining the OCRA methodology, other existing aspects of the same actions repeated by an average of 50% per work cycle are considered. However, when taking the times by the lesser of 15 seconds, it is by means of the multiplier to 0.70, taking into account the multiplier by 1.

In figure 2, it represents different aspects of the movement of postural biometry by repetition, both in the upper and lower extremities:

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According to studies, the OCRA index presents a high percentage with the appearance of musculoskeletal diseases of the upper limb in jobs exposed to this type of risk [15]. From the beginning, all assessments were taken to preserve confidentiality and study information in each of the areas and jobs in the operators evaluated. Likewise, in the cases where possible MSDs were determined, occupational physicians, ergonomists and students, who in each clinical occupational evaluation placed the operators, determined the occupational psychopathology by cycles and work times.

Initial Data Frequency

Based on the Nordic Questionnaire (NQ) of Kuorinka [8], an analysis was performed by postural biometry in each work station of the plant operators, with the objective of establishing the validity and reliability of the assessment due to dysergonomic exposure, taking into account factors of both pathological origin and the appearance of a clinical occupational picture (CCO). In graph 2, the different pathological factors present in the last 12 months are determined:

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Graph 2: Pathological exposure, according to the results of the CNE.

OCRA Checklist Frequency

In Figure 3 and graph 3, the Frequency by OCRA Checklist,

are related to the representative MSDs in the operators:

Graph 3: The identification of MSDs by the OCRA Checklist, determines the specific exposure risks in the operators, according to the work cycles in the last 14 days. The CCO of pain, represented high risk by postural biometry in: 5% of neck, 5% of lower back, while 4% as: discomfort in the right shoulder, elbow, forearm, right and left arm, hips and Achilles’ heel, the estimate is a moderate risk [16, 17, 18].

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Frequency of OCRA Analysis

When determining the results of the measurement analysis, the 18 operational areas of the CPF are established in stages for both preventive action to the risk factor, in this way, the results are determined to the estimate, as presented in Table 4, where the score given the valuation of the OCRA method, However, in Table 4, the relationship between the consequences and the work cycles on the health exposure of the workers in the production plant will depend on the occupational medical actions of the company’s occupational health and safety unit.

Based on the weighting and hierarchy of the risk index (RI) and as a disposition for the application to both preventive actions, starting from Very High Risk (VHR) to Very Low Risk (VLR), these results start in relation to the OCRA Checklist shown in Figure 4.

With these results, the laboratory technician’s work area has an unacceptable level of risk. Mild with an evaluation of 12.5, according to the Checklist’s risk index in an interval of 11.1 to 14, in the area of the API welder’s assistant, the risk level is unacceptably high with an evaluation of 49.0, outside the IE22 range of >22.5.

In Graph 4, it shows the exposure assessment according to the OCRA Checklist, both in the upper extremities and in other workplaces. However, in the more OCRA-defined analysis, the exposure and work cycle consequences represent the lack of control in both upper and lower extremity movements.

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Graph 4: OCRA Risk Index Checklist.

2  Index Exposure

Once the analysis by the OCRA Checklist has been elaborated, we proceed to the methodological development of OCRA, which, allows us to make the VLTs for their exposure by cycles and rest breaks, these results in table 6, allow us to reflect the operators with greater risk of exposure as in the case of the laboratory technician, with a level Without Risk of estimation to the IE of 1.34, for the right arm and 1.01, in the left arm. However, for the assistant on the right side of the road, the level is High Risk, with an estimated IE value of 5.11, for the right arm and 3.47 for the left arm, in Table 5.

It is really an approach to the physiological context of the operator due to his/her exposure in each cycle of the task to be performed, that is, the variety of certain consequences both psychological and biological, which, when related, can produce an alteration to health, creating a BCC, disability or death. However, by insisting on a clinical-pathological or epidemiological approach to the solution of problems caused by MSDs or SCIs, in accordance with the results of the OCRA Method, the situation among the specific health- disease aspects of the operators is analyzed, identifying their difficulties during or after each cycle. Therefore, to establish the measurement of these factors of dysergonomic risks by MSD, they are prioritized and hierarchized, as a previous step

3  Ergonomics and Occupational Hygiene

4  Northern Technical University 5  Threshold Limit Values (TLV)

to achieve the fundamental purpose of the preventions to the health, that allows us to improve with specific measures and determined terms, to the state of health of all the operators; in the table 6, (elaborated in the laboratory of EHO3-UTN4 03/2020), the most frequent pathologies with form to the TLV5 are defined.

In Figure 4, the clinical pathology or epidemiological table by Occupational Risk Factor (ORP) of symptoms due to pain in the body, and based on the analysis of the Nordic Questionnaire (NC) and its Clinical Functional Assessment (CFA), the estimate by case of pathologies or clinical picture due to pain, is personified in the last 14 days (n=150).