Acoustical role of ear canal in exposure to the typical occupational noise levels.

Background: Exposure to noise associated with injuries has become a public health issue in recent years. This study aimed to show the role of the acoustical structure of the ear canal on the typical occupational sound pressure levels at different frequencies. Methods: This cross-sectional study was done on 20-30-year-old participants. White noise was used at 3 levels, including 75, 85, and 95 dB as the stimulus sound pressure levels (SSPLs). The speakers had a 1.5-meter distance from the participants and at the height of 87 centimeters from the lab ground and were located in front of the participants. The SSPLs were measured outside (cavum part of the external ear) and inside the right ear of each participant. Measurements were done at the total sound pressure level and in the 1/1 octave frequencies. The duration for each measurement was 10 seconds. The independent sample t test was used for the statistical analysis, and the equality of means were rejected at p<0.05. Results: There were 30 (50%) males out of the 60 participants. The mean ± SD for the age of all the participants was 23.29±2.93 years. The total sound pressure level difference between the inside and outside of the ears of male and female participants was statistically significant (p<0.001) at the stimulus sound pressure levels. The peak resonance was observed in the frequencies 2000 Hz and 8000 Hz for males and 8000 Hz for females. Conclusion: The ear canal can amplify the sounds and increase the sound pressure levels. This amplification was found to be greater for males than for females.

Designing an adjustable ergonomic laptop desk and its evaluating by RULA and NERPA methods.

BACKGROUND: Using a computer may lead to pain in wrists, neck, and back. In addition, adopting various body postures like sitting cross-legged, semi-fowler's position, and putting the laptop on the leg may lead to the development of persistent and irreversible discomfort. OBJECTIVE: The purpose of this research is to design and build an adjustable ergonomic laptop desk based on the anthropometric characteristics of students in the age range of 20 to 30 years and to evaluate its efficiency using RULA and NERPA methods. METHODS: This cross-sectional study conducted on 108 students, in which an adjustable and portable ergonomic desk designed and built based on 10 anthropometric dimensions of students and the length and width of 10 different laptop models. Two assessment methods, RULA and NERPA, were used. Wilcoxon statistic test and SPSS version 26 software used for data analysis. RESULTS: The dimensions of the desk were calculated in three positions, and the desk was made with the ability to adjust height, width and tilt, each with two degrees of freedom. The statistical analysis comparing score of RULA and NERPA in two situations without using a desk and using an ergonomic laptop desk had a significant difference (P-value <  0.001). Comparison of RULA and NERPA scores showed that NERPA evaluated the low ergonomic risk level better than RULA method. CONCLUSIONS: Due to the ability to adjust the designed desk, the changes in RULA and NERPA score in all three modes, it indicates the effectiveness of the table in improving the body posture of users when using a laptop.

The Effect of Sleep Quality and Mental Fatigue on the Learning Rate of Shift Workers with Fast Shift Work Rotation.

Background: Modern industrial societies are always prone to errors and accidents due to complex devices, multitasking, and shift work jobs. Therefore, behavioral tests in learning and memory are necessary to evaluate employees' perceptions to examine the brain's information processing and the physiological and psychological aspects of memory disorders. Materials and Methods: In this study, the effect of fast shift rotation, sleep quality, and mental fatigue on individuals' learning and memory was investigated using a maze device. Participants were divided into two groups (regular daytime workers and shift workers). The quality of sleep was assessed using the Pittsburgh Sleep Quality Index (PSQI), and the rate of mental fatigue was evaluated using a checklist published by the Japan Industrial Safety and Health Association. Results: Learning time and the number of learning errors at the beginning and end of the morning shifts and night shifts had a significant relationship (P value <0.0001). However, there was no meaningful relationship between sleep quality and time and the number of learning errors in day workers and shift workers. Conclusion: The results indicated that although shift workers experience rapid shift rotation, they are still exposed to this circadian sleep change's side effects such as general physical fatigue, sensory-neurological fatigue, poor perceived sleep quality, daily dysfunction, difficulty in learning, and memory. They show a significant difference compared to people working on a regular workday.