Analysis of Thermal Stress and Ergonomic Risks in the Oil Industry in Ecuador

This study employed four methods: WBGT, REBA, OCRA, and SWOT analysis to assess thermal stress and ergonomic risks among oil industry workers in the parish of San José de Ancón, Province of Santa Elena. In addition, reference surveys were conducted with oil company operators, and with the entire process mentioned above, strategies were developed to mitigate these problems. The methodological process (Figure 1) included the use of the WBGT index to assess thermal conditions and the REBA and OCRA tools to analyse ergonomic risks, such as postures and repetitive movements. In addition, SWOT surveys were conducted with workers from two contracting companies to develop an occupational safety management framework, identify risks, and establish measures to reduce accidents and improve safety.

1.png

Figure 1. Scheme of the methodological phases of the case study

2.1 Selection of the work environment

The study focused on an oil field located in San José de Ancón parish, in the province of Santa Elena (Figure 2), where contractor companies provide services. The oil industry, a key sector for the economic development of the area, is the main activity in this area, which has a population of 7,918 inhabitants [30]. The criteria used to select the work area were as follows:

1. Geographical location and climatic conditions: The terrain, characterised by being a semi-arid region with extreme temperatures, high humidity, and direct exposure to the sun without sufficient shade, creates an environment prone to both thermal stress and ergonomic risks.
2. Work area: The company conducts activities such as the construction of containment basins, the assembly of metal structures, welding, and the maintenance of oil infrastructure, with civil engineering work standing out for its high physical effort, which involves forced postures and repetitive movements.
3. Duration and exposure time: Workers perform their tasks in shifts of 8 to 12 hours.
4. Number of workers: In the study area, there are currently two active contracting companies providing services to the oil industry, which employ a total of 10 workers.

2.png

Figure 2. Geographical map of the study area

One of the activities within the civil engineering field is the construction of oil counter wells, a process illustrated in the diagram (Figure 3).

3.png

Figure 3. Identification of ergonomic and thermal risks in the construction of oil counter wells

2.2 Assessment of thermal stress and ergonomic risk factors

In this phase, three methods (WBGT, REBA, OCRA) were employed to assess the risks associated with working in environments characterised by high temperatures and significant physical exertion. This assessment is essential for determining the level of risk and preventing serious injuries [31].

2.2.1 Calculation of the WBGT index

WBGT is an environmental indicator that quantifies the level of heat stress to which people are exposed in work environments with heat exposure [32]. Two data sources were used to calculate the WBGT index: first, daily satellite meteorological data from the ‘Santa Elena’ station (code M1170), provided by the National Institute of Meteorology and Hydrology (INAMHI, acronym in Spanish) [33]. Second, in situ measurements obtained through the WBGT mobile application (version 2.0), developed by the company Everade [34]. Both measurements were taken in March, with one set taken in the morning and another in the afternoon.

The WBGT required three primary parameters: natural wet bulb temperature (T_nwb), which reflected the influence of heat and humidity. Black globe temperature (T_g), which measures the thermal radiation of the environment. Air temperature (T_a), which represented ambient heat without humidity or radiation [35]. The case study was conducted in the oil industry, where activities were carried out outdoors. Therefore, Eq. (1) proposed by Gourzoulidis et al. [36] was used, which allows the WBGT to be evaluated in outdoor environments.

$\mathrm{WBGT} _{\text {outdoor }}=0.7 \mathrm{~T}_{\mathrm{nwb}}+0.2 \mathrm{~T}_{\mathrm{g}}+0.1 \mathrm{~T}_{\mathrm{a}}$                 (1)

where,

T_nwb = Natural wet bulb temperature.

T_g = Globe temperature.

T_a = Air temperature.

This study did not include direct measurements of globe temperature (Tg); therefore, it was estimated using Eq. (2) [37].

$\begin{gathered}\mathrm{T}_{\mathrm{g}}=0.009624(\mathrm{SR})+1.102\left(\mathrm{T}_{\mathrm{a}}\right)-0.00404(\mathrm{RH}) -2.2776\end{gathered}$                  (2)

where,

RH = Relative Humidity.

SR = Solar Radiation.

T_a = Air temperature.

To estimate T_nwb without a specialized instrument, the following Eq. (3) was used.

$\mathrm{T}_{\mathrm{nwb}}=\mathrm{T_\mathrm{pwb}}+0.25\left(\mathrm{T}_{\mathrm{g}}-\mathrm{T}_{\mathrm{a}}\right)+\mathrm{e}$                  (3)

where,

T_pwb = Psychrometric wet bulb temperature.

e = Measurement error or correction.

T_a = Air temperature.

T_g = Globe temperature.

Once the WBGT value was calculated, it was compared with the limits set out in ISO 7243 [38]. Table 1 classifies the WBGT index into five risk levels. At less critical levels (low, minimal, and moderate), monitoring and hydration were required. However, at high and very high levels, immediate measures such as breaks, reduced workload, and continuous monitoring were taken to prevent thermal stroke.

Table 1. WBGT reference values source [36]

2.2.2 Calculation of the REBA method

The REBA method consisted of groups A and B, which analysed different parts of the body to calculate the ergonomic risk. Group A evaluated the positions of the worker's trunk, neck, and legs, assigning scores to each of these parts. These scores were correlated to obtain the A value, to which the load handled by the worker was added, resulting in the final score that measured the total physical effort involved in the work tasks. The components of group A are described below:

• Trunk: Four flexion postures were considered: neutral (score 1), flexion or extension up to 20° (score 2), flexion between 20° and 60° or extension greater than 20° (score 3), and flexion greater than 60° (score 4).
• Neck: Scored according to the angle of flexion or extension: flexion between 0° and 20° (score 1), and flexion greater than 20° or extension (score 2).
• Legs: The assessment was based on posture and load: sitting, walking, or standing with a distributed load (score 1). Standing with an undisturbed load and unstable posture (score 2).
• Load or force: The weight of the load and the sudden force in the task were assessed: 0 points for loads < 5 kg, 1 for 5-10 kg, and 2 for > 10 kg.

Group B evaluated the movements of the arm, forearm, and wrist, assigning scores to each part. The B value was obtained by correlating the scores for the upper limbs, reflecting the interaction between these parts. The final score was calculated by adding the B value and the type of grip, thus measuring the physical effort associated with upper limb movements. The components evaluated in this group are detailed below:

• Arm: The score varied according to the angle: 1 for 20° of extension or flexion, 2 for 20° to 45°, 3 for 45° to 90°, and 4 for more than 90°, indicating greater risk.
• Forearm: A score of 1 was assigned for flexion between 60° and 100°, and 2 for flexion < 60° > 100°.
• Wrist: A score of 1 was assigned for neutral movement or flexion/extension between 0° and 15°. If 15° was exceeded, the rating was 2. In all cases, if the wrist position was inadequate, 1 point was added.
• Grip quality: A score was assigned according to the quality of the grip: 0 for good, 1 for fair, 2 for poor, and 3 for unacceptable.

The C score was obtained by combining the values of the A and B scores. An additional point was added to this score if significant muscular effort was identified, such as prolonged immobility, repetitive movements, or unstable postures. This yielded the final REBA score (Table 2), which allowed for the classification of risk levels and the establishment of necessary corrective actions: the higher the score, the greater the identified risk.

Table 2. REBA score source [39]

2.2.3 Calculation of the OCRA method

The OCRA method was used to assess exposure to risk from repetitive movements in the upper limbs [40]. The OCRA method was calculated as the ratio between Actual Technical Actions (ATA) and Recommended Technical Actions (RTA). To determine ATA [41], workers' activities were directly observed to identify and count technical actions. Then, the frequency per minute and the duration of repetitive work were calculated, and finally, the ATA was obtained by multiplying both values. To calculate the RTA value, the following Eq. (4) was used [42]:

$R T A=\left[C F \times\left(F_f \times F_p \times F_a\right) \times D\right] \times F_r$                   (4)

where,

CF = Standard frequency constant (30 actions/min).

F_f = Force factor applied during the task.

F_p = Posture factor adopted during the task.

F_a = Additional factors (physical conditions such as vibration or use of tools).

D = Duration of the repetitive task (min).

F_r = Recovery multiplier factor (considers breaks and rest periods).

The quantification of the physical load perceived by the worker was performed using the force factor (F_f), derived from the Borg scale [43]. This scale, with a range from 0.5 (low effort) to 5 (maximum effort), indicates that the greater the effort, the lower the F_f value. In the work tasks (manual excavation, removal of wood from the formwork, preparation of the mixture, and application of the plaster), three representative levels of effort were selected:

• Medium effort: 2.5 on the Borg scale, corresponding to an F_f of 0.55.
• High effort: 3.5 on the Borg scale, corresponding to an F_f of 0.35.
• Very high effort: 4 on the Borg scale, corresponding to an F_f of 0.20.

The posture factor (F_p) assessed the left and right upper limbs, considering the movements of the shoulders, elbows, wrists, and fingers [44]. Postures were classified into three effort ranges: 4-7 (F_p = 0.70, moderate effort), 8-11 (F_p = 0.60, high effort), and 12–15 (F_p = 0.50, very high effort). As the ranges increased, the posture became more forced, and the F_p decreased, indicating a greater physical effort and increased risk of injury. This factor enabled the quantification of postural load and the identification of physical risks associated with forced postures. Additional factors (F_a) represented risks, such as the use of vibrating tools and lifting or pushing loads. When the assigned value was 0 (F_a = 1, no impact), no additional effect on risk was considered. In contrast, a value of 4 (F_a = 0.7, indicating a moderate impact) suggests that one or more additional factors had a significant effect. The higher the assigned value, the lower the F_a, indicating a greater effect of these factors on the risk. This factor allowed the assessment to be adjusted according to additional physical conditions.

Table 3. Risk assessment and recommended actions based on the method OCRA [41]

The recovery factor (F_r) was assigned according to the number of hours without adequate rest. If the worker had no rest hours, their factor was 1. As the hours without rest increased, the F_r decreased, reflecting a lack of recovery. This study focused on the range of 6 hours without adequate rest (F_r = 0.25, high risk), which indicated a high level of fatigue and a significant reduction in the worker's performance capacity.

Table 3 presents the risk levels based on the values obtained using the OCRA method to assess workload. Based on these values, the risk level and recommended actions are defined, as detailed above.

2.3 Proposed prevention and safety measures

Surveys were conducted among a population of 10 workers from two contracting companies in the oil sector. The survey enabled the collection of suggestions to propose strategic guidelines aimed at improving working conditions. The survey consisted of 12 questions: 11 multiple-choice and one open-ended (Table S1), which addressed aspects related to posture, repetitive movements, and exposure to thermal. This type of mixed survey is valuable for obtaining quantitative and qualitative data [45].

The SWOT analysis identified internal and external factors related to ergonomics and thermal stress in the work environment. Regarding internal factors, the strengths evaluated included knowledge of good practices, use of protective equipment, and working conditions (questions #1, #3, #5, #6, and #11). The weaknesses identified focused on the lack of active breaks (questions #2, #4, and #7). In terms of external factors, the threats included exposure to high temperatures and poor posture (questions #8, #9, and #10).

This study assessed thermal stress and ergonomic risk factors among workers engaged in outdoor activities at two oil companies. It was found that workers face a high risk of thermal stress, particularly in the area of well construction. This is due to prolonged periods of sun exposure associated with the type and duration of the tasks they perform. Similarly, according to Umar and Egbu [50], activities involving exposure to extreme thermal conditions have a profound impact on occupational health, exposing workers to physiological risks, injuries, and even occupational fatalities.

It was identified that, in the area of counter-well construction, workers faced high risks of thermal and ergonomic stress. It is due to prolonged periods of sun exposure associated with the type and duration of the tasks they perform. According to Benson et al. [18], this trend was confirmed in the oil and gas sector, with ergonomic risks (30%) identified as the most common, followed by physical risks (26%). Prolonged exposure to the sun and the physical demands of the tasks create an environment with multiple risks that can affect workers' health in both the short and long term [51].

In this study, WBGT values of up to 34.6℃ were recorded during the morning shift, exceeding the 29.76℃ reported at an oil terminal in Iran [52]. The difference observed between the two studies could be attributed to environmental factors, underscoring the need for thermal assessments tailored to specific regions and times of day [53]. These temperatures impact occupational health, necessitating measures such as breaks, hydration, and the proper use of protective equipment to mitigate risks in this vulnerable sector [54]. Additionally, heat stress poses a significant risk, particularly near heat tolerance limits [55].

The thermal stress assessment revealed that WBGT indices in the morning (31.6℃ to 34.6℃) were high due to the high solar radiation, low relative humidity, and low wind speed recorded at the site. This thermal behaviour coincides with that reported in a study conducted at an oil company in Indonesia, located in a tropical climate region, where WBGT values above 28℃ were recorded during the hours of highest solar radiation [56]. It demonstrates that heat stress is a recurring and well-documented challenge in the oil industry, highlighting the urgency of standardising mitigation strategies in these environments [57, 58].

This study evaluated ergonomic risks (REBA and OCRA methods) in activities such as formwork assembly, manual soil compaction, and painting. These activities indicated medium and high-risk levels, especially in the upper extremities and lower back, due to the adoption of forced postures. These findings align with those reported by Li et al. [59], who emphasise the importance of implementing occupational health and safety management in construction projects to reduce the incidence of musculoskeletal injuries. It is also recommended to improve job design, train staff, and implement measures to limit excessive loads, static postures, and prolonged exertion to reduce ergonomic risks in construction [60].

In the oil industry, research has demonstrated that repetitive tasks and poor posture pose a significant risk to workers' musculoskeletal health. For example, using the OCRA method, a study at an oil plant found that 72% of jobs presented a high ergonomic risk due to repetitive movements, resulting in frequent discomfort in the lower back and shoulders [61].

Manual soil compaction performed during counter-pit construction presented a high risk (REBA = 9) to workers. Similarly, a study conducted in other areas of the same oil industry reported a very high risk (REBA = 11) for lathe operators [62]. Despite differences in tasks and work environments, ergonomic risks are a constant challenge in the oil industry.

According to the survey, 70% of workers in the oil industry reported that repetitive tasks cause greater physical exhaustion, which in turn increases the risk of injury. These results are consistent with those reported by Wang et al. [15], who noted that musculoskeletal disorders associated with repetitive tasks significantly impact the health and well-being of operation and maintenance workers in this industry.

This study demonstrated that heat stress is a factor that intensifies ergonomic risks due to prolonged exposure to high temperatures. Additionally, this risk is triggered by factors such as fatigue and a reduction in the body's ability to maintain proper posture and perform controlled movements. These conditions contribute to an increased risk of musculoskeletal disorders in the workplace [63].

Occupational risk management proposals were developed based on input from workers and a SWOT analysis. For example, one risk factor is posture during the workday, especially in activities such as excavation or mixture preparation, as these involve greater physical effort. Additionally, the implementation of periodic ergonomic programmes that include active breaks adapted to the job is recommended, as well as optimising the work environment through assistive technologies (such as ergonomic hand tools). Preventive strategies must be adapted to each work environment, as working conditions, physical demands, and the tools used vary according to the different positions and characteristics of the workplace. This adaptation allows for the design of more precise and effective interventions to protect the health and well-being of workers [64].

This study identified the following lines of research: evaluating the relationship between thermal stress and ergonomic risks in various work sectors, considering variations in work environments, activities performed, and worker characteristics. Additionally, the implementation of prevention programs tailored to these factors could be crucial in improving both occupational health and safety and productivity. Finally, the influence of environmental factors on thermal stress.