Iranian Journal of Ergonomics

Investigating the Effect of Carbon Dioxide in the Air on the Feeling of Thermal Comfort, Cognitive Function, and Heart Rate of Healthcare Workers while Working

Karen Fatahi

Objectives: The primary aim of this study is to examine the impact of carbon dioxide (CO₂) concentrations in the air on thermal comfort, cognitive performance, and heart rate among healthcare workers while they engage in their duties within therapeutic environments. These settings are often characterized by high occupancy, inadequate ventilation, underground locations, limited natural light, and exposure to pollutants.
Methods: In this laboratory-based research, 20 employees from a specialized clinic were randomly assigned into two groups of ten. They were exposed to varying levels of CO₂at a controlled temperature of 25°C: one group experienced 1100 ppm with adequate ventilation, while the other was subjected to 1800 ppm without ventilation. Key parameters, such as heart rate, thermal comfort (assessed using the ASHRAE standard questionnaire), and cognitive performance (measured through the MOCA test) were recorded. The collected data were analyzed using multivariate analysis of covariance (MANCOVA).
Results: The statistical analysis revealed significant effects of cognitive performance and CO₂levels (1800 ppm vs. 1100 ppm) on thermal comfort (F(1,15)=13.257, P<0.05 and F(1,15)=16.694, P<0.05). Furthermore, both the CO₂levels and the gender of participants significantly influenced the heart rate of healthcare workers in their work environments (F(1,15)=53.381, P<0.05 and F(1,15)=9.642, P<0.05). Specifically, individuals exposed to 1800 ppm of carbon dioxide reported a thermal dissatisfaction score that was 0.878 units higher and exhibited a heart rate that was 9.25 beats per minute greater compared to those exposed to 1100 ppm.
Conclusion: The findings underscore the importance of continuous air quality monitoring in workplace settings. Such measures can enhance thermal comfort levels, improve cognitive performance, and mitigate health risks for healthcare workers engaged in their professional activities.

Investigating the Effective Factors in the Positioning of the Vehicle’s Multimedia with the Approach of Mitigating the Reflection While Nighttime Driving

Milad Karimi

Objectives: Nowadays, using digital displays in vehicles has become very common. Therefore, the reflection display screen issue as a virtual image on the vehicle's side windows at night is a controversial item in the ergonomics position of the designed display. Given the high importance of visual tasks, it is necessary to consider ergonomics considerations during vehicle design to achieve an optimal display position.
Methods: In the current study, by identifying the factors affecting the placement of the central display inside the vehicle and assigning level values for them, using the design of experiment statistical method with the full factorial approach, 243 runs were obtained from the combination of the identified factors using MINITAB (version 18) software. By implementing all the extracted runs, the amount of reflection from the central display on the side windows was subjected to statistical analysis of variance (ANOVA).
Results: Significantly effective factors (including their interactions) on the response of the reflection of the virtual image on the critical vision zone and the total reflection on the driver's right and left side windows were identified. In addition, the amount/direction of the factors' effect on the responses was analyzed using a linear regression model.
Conclusion: During the interior design process of the vehicle and display packaging, the factors identified in this study can be used as a control tool to reduce or eliminate the concern of the amount of display reflection on the side windows to prevent driver's ergonomics problems during nighttime driving.

A Study on the Status of Cognitive Failures and Their Relationship with Individual Factors and Personality Traits among Midwives Working in Kermanshah Province

Mahsa Mashayekhi

Objectives: Cognitive failures are important for reducing accidents and improving performance, and they depend on multiple factors. Given that this issue has received less attention among midwives, the present study aimed to determine the status of cognitive failures concerning individual factors and personality traits among midwives.
Methods: This cross-sectional study was conducted in the summer of 2024 on 211 midwives working in Kermanshah province in Iran. The samples were selected using a convenience sampling method. In addition, a standard three-part questionnaire was used. The first part included demographic information, and the second and third parts included questions from the Cognitive Failures Questionnaire and the short form of the NEO Personality Inventory. Moreover, data were analyzed using the SPSS (version 24) software.
Results: The mean age and work experience of the midwives participating in this study were 36.22±8.03 years and 10.38±7.85 years, respectively. The overall scores for cognitive failures in memory, action, and attention were 16.79±3.04, 17.41±2.80, and 16.30±3.62, in respective order. The results revealed a positive relationship between age, work experience, and body mass index (BMI) with cognitive failures and a negative relationship between exercising and cognitive failures. Neuroticism, agreeableness, and openness were positively related to cognitive failures, while conscientiousness was negatively related to cognitive failures.
Conclusion: The status of cognitive failures in the action dimension was more unfavorable than the other two dimensions. Some individual and personality traits were directly, and others inversely related to cognitive failures. Further research in this area is necessary.

Investigating the Association of Noise Exposure with Occupational Stress and Work Ability among Workers of a Food Processing Plant

Mansour Mahmood Aghbash

Objectives: Numerous factors such as job types and conditions, work organizations, and individual characteristics affect work ability of the workers. Furthermore, occupational stress is not solely influenced by individual characteristics; a stressful work environment is also a significant source of stress. Noise has been recognized as one of the major occupational hazards that adversely affects work condition in many industries. In the present study, the association of noise exposure with occupational stress and work ability of the workers in a food processing plant was investigated.
Methods: This descriptive-analytic study was performed on 142 workers of a food processing plant in various work groups. The OSIPOW questionnaire results were utilized to measure occupational stress and the work ability of the workers was determined by Work Ability Index (WAI) questionnaire. Noise exposure of the workers was calculated as a measure of 8-hour time weighted average. The association between noise exposure and work ability was analyzed using Pearson and Spearman correlation tests. Multiple regression test was utilized to analyze the simultaneous effect of variables. Moreover, one-way analysis of variance (one-way ANOVA) was used to analyze the mean difference of independent variables.
Results: The findings demonstrated a significant positive association between noise exposure and stress level across various work groups (P<0.001). Furthermore, a significant negative relationship can be found between noise exposure and work ability of the workers (P<0.001). A simultaneous analysis of variables influencing occupational stress and WAI showed that noise had the most effect. Although occupational stress levels were not significantly different across working groups, mean difference of WAI was significant.
Conclusion: Based on the obtained findings, higher levels of noise exposure may contribute to increased occupational stress and decreased work ability among workers.

Effect of Tonal Noise and Irrelevant Background Speech on Neurophysiological Based on Personality Traits: An Experimental Study

Mohsen Aliabadi

Objectives: The present study aimed to investigate the effect of tonal noise and background speech on neurophysiological parameters and noise annoyance based on personality characteristics.
Methods: In this experimental study, 25 male students were exposed to four scenarios of tonal noise, irrelevant speech, and broadband noise as a reference in a simulated laboratory environment. The LF/HF index and galvanic skin response were recorded before and during exposure to the noise. The level of noise annoyance was determined at the end of each test session using the noise annoyance questionnaire according to ISO 15666.
Results: Repeated measures analysis of variance (RMANOVA) indicated that the difference between the values of neurophysiological indices and noise annoyance in different noise exposure scenarios was significant (P<0.05). The effect of different tonal sound levels on galvanic skin response and noise annoyance was significant (P<0.05). In addition, the effect of 65 dB tonal sound level and 55 dB speech sound level on the LF/HF index was reported to be significant (P<0.05). Also, the effect size of 1.919 in exposure to 65 dB tonal sound level had the highest value compared to other noise exposure scenarios for the noise annoyance variable.
Conclusion: Exposure to different levels of tonal noise and irrelevant speech leads to disruption of individuals' neurophysiological parameters and noise annoyance in individuals regarding some of their characteristics and personality traits.

Evaluation of Musculoskeletal Disorders, Mental Workload, General Health, and Occupational Stress Among Office Employees

Azim Akbari

Objectives: Administrative employees are often at risk of developing musculoskeletal disorders due to prolonged computer use. Additionally, frequent interactions with clients expose them to a high mental workload and job stress. The present study aimed to assess the prevalence of musculoskeletal disorders, mental workload, general health, and job stress among administrative employees to improve their working conditions.
Methods: The present work followed a cross-sectional descriptive-analytical method and was conducted on the administrative employees of an engineering company in 2021. Finally, 119 individuals participated in the study using the census method. Demographic information questionnaires, as well as Rapid Office Strain Assessment (ROSA), Cornell, NASA Task Load Index (NASA-TLX), General Health Questionnaire (GHQ), and Health and Safety Executive (HSE)-UK job stress checklists were used to collect data. Data analysis was performed using the SPSS software, employing descriptive statistics, independent t-tests, and one-way analysis of variance (ANOVA).
Results: According to the posture assessment with the ROSA method, the average final ROSA score was 4.33±1.03. Examination of mental load with the NASA-TLX indicated that 78% had a high mental load. In addition, according to the GHQ questionnaire, the average final general health score was 24.4±11.73. Moreover, based on the HSE-UK occupational stress questionnaire, more than 80% (103 people) of employees were under severe stress, and 12% (15 people) were under critical stress. A significant relationship was observed between occupational stress, body mass index (BMI), and age (P<0.05).
Conclusion: The implementation of intervention and control measures to improve musculoskeletal disorders, workload, general health, and job stress seems to be essential.

The Impact of Eccentric Contraction Caused by Lowering the Load from Different Heights on Postural Control Strategies in Low Back Pain Patients and Healthy People

Majid Shahbazi

Objectives: Balance control is a crucial issue in patients with low back pain. Despite existing studies, the mechanism of balance control in patients with low back pain, especially under different loading conditions at various heights, remains unclear. Therefore, this study aimed to investigate the effect of height on balance during loading.
Methods: In this cross-sectional study, 54 low back pain patients and 20 healthy male individuals participated. Balance control was assessed using a force plate system. The participants were randomly instructed to lower the load from above the head to waist level and from waist level to the ground. The load was approximately 10% of the participants' body weight. The P value was established 5% level of significance.
Results: The results showed that during lifting from above the head to waist level and from waist level to the ground, there were significant differences (P<0.05) in variables such as medial-lateral and anterior-posterior velocity, total mean velocity, and center of pressure displacement in the anterior-posterior direction between the two groups. Intra-group comparisons of variables in healthy individuals and low back pain patients indicated significant differences (P<0.05) in all variables except anterior-posterior velocity in healthy individuals. Both groups exhibited increased postural sway while lowering at a lower height.
Conclusion: The present study demonstrates that both healthy individuals and low back pain patients display less balance when loading at a lower height with a flexed lumbar spine, indicating that considering these findings could contribute to rehabilitation, determining occupational conditions, and preventing workplace-related accidents.

Relationship between Organizational Culture with Employees Job Performance in Health Centers (Based on Denison Model)

Yadollah Hamidi

Objectives: Health centers are the first level to provide care, and job performance is important to achieving the goals of the health systems. One of the factors that affects job performance is organizational culture. Therefore, the present study aimed to determine the relationship between organizational culture and employee job performance.
Methods: The present cross-sectional study (descriptive-analytical) was conducted on 210 employees in one of the health centers of Kermanshah province using the census method in the years 2021-2022. Standard questionnaires were used to collect information, including the Denison Standard Organizational Culture Questionnaire and the Employee Job Performance Evaluation Questionnaire. The collected information was entered into SPSS (version 25) software and analyzed with statistical tests. A significance level of less than 0.05 was considered.
Results: There is a direct and significant relationship between the dimensions of organizational culture and employee job performance (P<0.05). Age and work experience had an inverse relationship with the dimensions of employee job performance (quality of work and initiative). Gender had a significant relationship with the organizational leadership dimension, and marital status had a significant relationship with initiative (P<0.05).
Conclusion: Organizational culture has a direct and significant relationship with the dimensions of employee job performance; therefore, by improving organizational culture, we can witness effective and sustainable changes in job performance. In addition, some demographic variables are also related to the level of employee job performance, and organization managers should pay attention to these variables when hiring.