r. shahidi

The permissible exposure time to vibration for the operator is one of the key factors in maintaining the operator's health while optimizing machinery and equipment. The tractor studied was the ITM475, manufactured in Iran. The purpose of this study was to calculate the operator's permissible vibration exposure time while using the tractor to ensure the driver can maintain good bodily health.

In this study, experiments were conducted using a 3-axis vibration meter based on the ISO 2631 standard. The obtained data were analyzed through a factorial experiment using 18 treatments and 3 replications. The factors studied were engine rotation speed (at three levels of 1000, 1500, and 2000 rpm), road type (dirt and asphalt), and gear position (at three levels of 1, 2, and 3).

Various total vibration models were obtained for the tractor, and their determination coefficient varied from 90.11% for gear No. 3 on an asphalt road to 100% for gear No. 1 on an asphalt road and gear No. 2 on a dirt road. The maximum whole-body vibration, and consequently the minimum permissible exposure time, was observed for gear No. 3 at an engine rotation speed of 2000 rpm on a dirt road, which was 1.49 and 1.16 hours, respectively.

The maximum whole-body vibration experienced during an 8-hour tractor-driving session was measured at 0.85 m s-2. It is important to note that the permissible exposure time decreases as vibration levels increase, and it reaches a limit of 1.16 hours. To ensure drivers adhere to these permissible exposure times across various driving conditions, measures must be implemented to reduce tractor vibration and minimize its transmission to the driver. By reducing overall tractor vibration and minimizing its impact on the driver, it becomes possible to increase the permissible exposure time for drivers.

Exposure to hand- arm vibrations is one of the occupational risk factors for employing dentist manual tools. This study aims to determine the exposure level to vibration and its related health effects in dentists employed in academic clinics.

This study was conducted on 30 dental practitioners as a case group and 30 employees at the clinic who were not exposed to vibration as a control group. Hand-arm vibration was measured using the SVANTEK 106 vibration meter in accordance with ISO 5349 standard. The level of musculoskeletal complications was determined using the hands grasping and finger grip strengths and finger dexterity. The level of neurosensory disorder was determined by the monofilament test. Data were analyzed using SPSS 16 software.

The mean of equivalent exposure level to vibration for 8 working hours was 0.65 m / s2 for dentists which are lower than the national exposure limit. Feeling of needle punching was the most commonly reported symptom (47.5%) among dentists. The levels of handgrip strength, fingers' strength and dexterity of dominant hand were decreased 22 % (p<0.05), 8% (p<0.05) and 2 % (p>0.05), respectively in case group compared to control group. The fingers sensory threshold of dentists was higher than the control group and in the dominant hand of the case group was higher than their non-dominant hand (p<0.05).

Despite the low level of exposure to vibration, a level of disability was observed in the physical and neurosensory function of dentist’s hand. The prevalence of neurosensory disorder was also more than musculoskeletal symptoms.