siamak pourabdian

With the increasing presence of individuals, particularly women, in the workplace, it becomes imperative to prioritize the well-being of employees. Numerous interventions exist to enhance working conditions, and one such intervention is the incorporation of music. This research aims to investigate the correlation between music exposure and the working memory of female operators employed in a medical infusion set assembly company.

The study involved the assessment of 81 employees from the assembly unit of a company specializing in the production of infusion sets. The current research is an interventional study, the data of which were collected by the method of interview and cognitive tests (N-back test). The evaluation was conducted under two conditions: with background music and without background music. The research focused on assessing the working memory and productivity (task performance) of the participants.

The mean age of the participants in this study was 37 ± 33.09 years, with a mean work history of 0.2 ± 1.3 years. Furthermore, 56.7% of the participants were married. The results of the study showed that productivity was significantly better in the music-playing mode (P = 0.005). Furthermore, the results of the N-back test significantly showed an increase in correct answers in the condition of playing music (P < 0.05).

The integration of background music in the workplace emerges as a beneficial factor, contributing to enhanced working memory and improved performance among female employees.

Drivers have a significant role in transporting and moving goods using heavy vehicles. These drivers are exposed to various complications including hearing loss, due to long journeys and constant exposure to road noise. Considering the importance of preventing hearing loss, this study was conducted to determine the occupational exposure of truck drivers to noise and its effect on noise‑induced hearing loss.

This cross‑sectional‑analytical study was conducted on 692 truck drivers of 16 types of heavy vehicles in Iran. The hearing status of the truck drivers was measured in the right and left ears using a Welton 1300 clinical audiometer in a soundproof room based on the guidelines provided by the American Speech–Language–Hearing Association. The equivalent sound pressure level (LAeq) in the truck driver’s cabin was measured by a sound meter with a CEL‑440 analyzer model and according to the standard (ISO 9612 1997) in A‑frequency weighting. Finally, using SPSS V‑26, the prevalence of hearing loss, the amount of hearing loss in different frequencies, and its relationship with exposure to noise in different frequencies were investigated.

The mean ± standard deviation LAeq in the examined truck was determined as 75.89 ± 5.98. The highest average LAeq was related to the frequency of 500 Hz with 62.76 dBA. The average LAeq was generally higher at lower frequencies (250, 500, and 1000). The prevalence of hearing loss in the right and left ears was estimated at 59.98% and 64.74%, respectively. The highest average hearing loss in the right and left ears was related to 6000 and 8000 Hz frequencies. There was a statistically significant difference between the LAeq inside the truck’s cabin with hearing loss compared to people without hearing loss in the right and left ears (P < 0.001). A statistically significant relationship between LAeq at different frequencies in different truck brands with hearing loss at different frequencies in the right and left ears was observed in the majority of trucks in reverse (P < 0.05). A significant relationship was observed between age and work experience with hearing loss in the right and left ears (P < 0.001).

Truck drivers suffer from a high level of hearing loss which is very similar to any industrial worker with high frequencies such as 4000 and 6000 Hz. Despite the lack of frequency relation between noise and hearing loss, increasing age, work experience, and noise exposure, regardless of frequency, can lead to increased hearing loss in these truck drivers, especially in the left ear. The appropriate cabin design, regular maintenance of vehicles, use of personal protective equipment, reduction of driving hours, and periodic annual examinations of drivers are suggested to prevent further progress of hearing loss in them.

Choosing the suitable hearing protection for workers as part of the Hearing Conservation Program was introduced as a final measure. This study aimed to investigate the absorption and transmission loss of common earmuffs at one third octave band frequencies using the impedance tube method.

An analytical-experimental study was carried out on absorbers of four earmuff models. The transmission loss of the absorbers was measured using the impedance tube by the transfer function method, in accordance with the ISO 10534-2 standard. Data analysis was conducted using the paired-samples t-test and analysis of variance (ANOVA) with SPSS software.

The highest and lowest mean transmission losses measured in absorbers were 27.5 dB and 0.3 dB, respectively. The results showed a significant difference in the mean transmission loss between absorber A and absorbers B, C, and D, as well as between absorber B with absorbers A and D, across all measured frequencies (P < 0.05). Moreover, the results showed a significant difference in all frequencies before and after in absorbers A, B, and C (P < 0.05).

When comparing earmuff absorbers, it is evident that their performance in transmission loss and efficiency varies across different frequencies. In addition, most of the earmuffs examined in the study showed a decrease in transmission loss at low frequencies as the frequency increased. However, above2 kHz, an increasing trend in transmission loss was observed. These results need to be noted when choosing suitable hearing protection for workers in industries.

Using a hearing protection device is one of the ways to control noise pollution in the industry. The purpose of the present study is to evaluate the changes in the sound absorption coefficient of some commonly used earmuffs in laboratory conditions at various sound levels and frequencies.

In this study, four earmuff models, including TASCO2550, AKHAVAN (VENUS-740), 3M optime98, and Parkson ABZ, were prepared. The absorber of the earmuffs was then cut to a diameter of 3 cm and a thickness of 1.2 cm. The absorption coefficient of each sample was measured using an impedance tube and VA-Lab4 software at three sound levels of 75, 85, and 95 dB. Finally, the data were analyzed using SPSS software.

There was no significant difference in the average absorption coefficient between sound levels of 75, 85, and 95 dB. However, in middle and high frequencies, the average absorption coefficient increased. TASCO2550 earmuff absorbent samples showed the highest absorption coefficient at frequencies of 2000-2500 Hz. While AKHVAN (VENUS-740) and 3M optime98 absorbent samples showed the highest average absorption coefficient at the frequency of 4000 Hz. Also, The Parkson ABZ absorbent sample had the highest average absorption coefficient at a frequency of 5000 Hz. In general, The TASCO2550 earmuff absorbent sample showed the highest absorption coefficient, while the 3M optime98 absorbent sample showed the lowest absorption coefficient.

By selecting an earmuff with efficient absorber, we can increase sound absorption rate to achieve the desired results of reducing noise pollution.

In addition to having auditory effects, sound also has nonauditory effects. Acoustic Annoyance is one of the nonauditory effects of sounds which are construed as psychoacoustic characteristics. The study at hand was undertaken to investigate the psychoacoustic characteristics of absorbents used in common earmuffs.

In this study, four earmuffs prevalent in industries were used. The psychoacoustic characteristics of loudness and sharpness were measured and analyzed in sound levels of 75, 85, and 95 dB using an impedance tube and Va-Lab 4 software with and without absorbers. The results were analyzed with SPSS-26 software.

Results showed that the highest and the lowest increase in loudness were attributed to the EM-101 and the EM-104, respectively. In addition, with the increase in the sound level, the loudness increased. Furthermore, in 85 dB, there was no significant relationship between loudness and earmuff absorber only in the case of the earmuff EM-103. Furthermore, the highest and the lowest increase in sharpness were, respectively, attributed to the EM-101 and the EM-103. Only in the samples of EM-103 and EM-104 earmuffs at the level of 75 dB, there was no significant relationship between sharpness and earmuff absorber.

Earmuffs used in industries showed different performances against the loudness and sharpness of the sound. In other words, the quality and the structure of earmuff absorber play noteworthy roles in decreasing the qualitative parameters of sound.

Backround:

 Noise is one of the most important occupational and environmental health hazards. Exposure to loud noise can cause irrevocable hearing damage and loss of hearing. The aim of this study was to determine the efficiency of two samples of earmuff and earplug in low frequency noise reduction in comparison to subjective method.

All the procedures of the work were done using the simulated human ear canal and the required microphone in the eardrum. At the octave frequencies, that is 31.5 and 63.5, 125, 250, 500, 1000, 2000, 4000, and 8000 Hz, and intensities of 85‑90 dB, one stage was done by using the individual’s subjective response relative to the received sound before and after using the ear protector.

The sound levels before and after the protection were significantly different in both the model and humans (P < 0.05). However, at 315 Hz frequency, the rate of attenuation is increased by 4 dB after placing the earplug and 14 dB after placing the earmuff, showing a reduction of 18 dB.

This study verifies the increasing protection by simultaneous application of earplugs and earmuffs. Because of the laboratory evaluation of ear protectors, it is possible not to justify the proficiency of ear protectors in a subjective method.

 Today, low back pain (LBP) is one of the major challenges among occupational health professionals in various jobs. The objective of this study was to investigate the relation between work limitation and functional disability with LBP in Iranian nurses. 

 Overall, 400 subjects were examined systematic random sampling in this cross-sectional-comparative study. Participants were divided into the case (195 persons with LBP) and control (205 persons without LBP) groups. Data were collected using a comprehensive questionnaire including demographic information form, Nordic Musculoskeletal Questionnaire, Oswestry Disability Questionnaire, and Work Limitation Questionnaire. The collected data analyzed using SPSS statistical software version 20. 

 Findings showed that age, marital status, and family history were significantly associated with LBP (P < 0.001). The most common cause of back pain among nurses was work-related LBP (56.9%) and genetics (heredity) (30.2%). Furthermore, the mean score of functional disability and work limitation in the case group was higher than the control group (P < 0.001). 

 Although, based on statistical analyzes, the frequency distribution and mean score of functional disability, work limitation, and all subscales in the group with LBP were higher than the group without LBP, it seems that back pain does not put nurses in working functional disruptive conditions.

The aim of this study was to investigate the level of noise exposure and its relationship with job stress, changes in blood pressure and heart rate among woodworking workshop workers.

In this cross-sectional-analytical-descriptive study, 140 employees of a lumber workshop in Mazandaran province were selected and divided into case and control groups. Demographic information of employees was collected by questionnaire. Systolic and diastolic blood pressure were measured using mercury sphygmomanometer. Heart rate of the case and control groups was measured by Beurer pulse meter. The results were analyzed using SPSS software.

The results of noise measurements showed that the mean noise exposure in workers from 8-hour shifts was 92.11 dB and among non-exposed group was 74.48 dB. The mean systolic and diastolic blood pressure in the control and exposure groups were 124, 126, 80 and 82, respectively. Also, the mean heart rate of the studied groups was 74.9 and 75.83 beats per minute, respectively. There was no significant difference in systolic and diastolic blood pressure and heart rate between the two groups, (p> 0.05).

Based on thefindings, the rate of systolic and diastolic blood pressure, as well as the heart rate and stress levels were higher in the exposed group as compared with the control group; however, the difference between systolic, diastolic blood pressure and heart ratebetween the two groups was not statistically significant. There was a significant difference in stress. It was found to be consistent with the results of some previous studies

Low‑frequency noise is produced from different sources in the working environments such as pumps. Thus, the aim of this study was to investigate the effect of low‑frequency noise on precision and focusing of the studied subjects.

This cross‑sectional–interventional study was performed on 13 students of Isfahan University of Medical Sciences. The precision of individual subjects was evaluated using the mental arithmetic test. The sound sources with frequencies of 125, 250, and 1000 Hz at 75, 85, and 95 dB sound pressure levels. Also, the rate of precision was measured before the exposure (time “zero”), and at 45 and 90 min. SPSS (Ver. 26) software was used to analyze the data.

Comparison of the precision scores of the individuals between the frequencies of 125 and 250 Hz at the sound pressure level of 75 dB and at 45 min (P = 0.032). And 90 min (P = 0.006). And also, the frequencies of 250 Hz and 1000 Hz at the time of 45 min. At the sound pressure levels of 85 dB (P = 0.019). And 95 dB (P = 0.043) and at the time of 90 min. At the sound pressure levels of 85 dB (0.027). And 95 dB (P = 0.009) demonstrated a significant difference.

We concluded that low frequency noises could reduce the person’s precision. While for 125 Hz noises, just increasing of the exposure time was effective on the precision reduction. But for 250 Hz noises, both parameters increasing including exposure time and sound pressure levels, was effective.

A review of the existing literature shows the importance of mental health in preventing traffic accidents. Therefore, the current study aims to determine the mentioned mental disorders in relation with the history of accidents among truck drivers.

This cross‑sectional study was done with two groups of truck drivers (with and without a history of accidents) in Iran. 56 people with a history of accidents and 410 people without a history of accidents participated in this study. At first, using questionnaires, the demographic information of the participants including age, education level, cigarette use, and addiction to drug was collected. Then, the mental disorders of the participants were evaluated by a 71‑question, short form of the multidimensional Minnesota Multiphasic Personality Inventory (MMPI). The evaluated disorders are the HS or hypochondria, D or depression, HY or hysteria, Pd or social mental deviation, Pa or paranoia, Pt or mental weakness, Sc or schizophrenia, and Ma or hypomania. The tests used for data analysis include descriptive tests and Chi square.

Man–Whitney U test showed that status of mental disorders, as revealed by the MMPI questionnaire, had a significant difference between the two groups with and without history of driving accidents (P ˂ 0.001). The results showed that mental disorders of depression, hysteria, social mental deviation, paranoia, schizophrenia, and hypomania in individuals with history of driving accidents led to meaningful differences from individuals without history of driving accidents (P ˂ 0.048).

The results of the current study showed that generally, individuals with history of driving accidents had significantly more mental disorders than people without history of driving accidents.

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.

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.

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. 

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.

 Low-frequency sounds are generated from many sources in both the occupational and nonoccupational environments. Hence, the aim of this study was to investigate the effect of low-frequency noise (LFN) on the working speed and the rate of annoyance of the subjects under study. Materials and 

 This cross-sectional/interventional study was performed in the sound and vibration laboratory of Isfahan University of Medical Sciences in 2019. Simple random sampling was used to select the subjects. In this study, the working speed of the subjects was evaluated using mental arithmetic test and the rate of the perceived annoyance was measured using ISO 15666 in Likert format (0–11) due to exposure to noise sources. Mann–Whitney U-test was used to analyze the data. 

 There was a significant statistical difference in the rate of the individuals' working speed Between 0 and 90 min at the frequency of 125 Hz and the sound level of 95 dB (P = 0.029). There was a statistically significant difference between the frequencies of 125 and 1000 Hz at the sound pressure level of 85 dB and the 45 min time (P = 0.001) and 90 min (P = 0.001) as well as at the 95 dB sound pressure level at 45 min (P = 001) and 90 min (P = 0.001). 

 The results of the present study showed that increasing sound pressure levels and the exposure time in both LFN and high-frequency noises, increased the working speed and the amount of perceived annoyance in individuals.

The widespread use of cell phones has led to an increase in concern about the effect of radiofrequency radiation on the physiology of the human body. This study was conducted to determine the different reaction temperatures of different brain tissue in exposure to mobile radiofrequency waves.

This was an experimental study. The cow's brain tissue was examined in a chamber at three depths of 2,12 and 22 mm and at a distance of 4 mm and 4 in the cell phone from the tissue for 15 min of the radiofrequency radiation of the mobile phone during exposure and after the exposure was discontinued. . Luteron thermometer was used to measure tissue temperature.

During the exposure to the brain tissue at a distance of 4 mm from the mobile phone, the temperature increase at 22 mm depth was more than the depths of 2 and 12 mm, so that the tissue temperature at 2, 12 and 22 mm depths was 29 ° C 0 /, 0.3 / 0 and 0/37 respectively. Also, the temperature of the brain tissue at 4 cm intervals was greater than the other depths with increasing tissue depth. An increase in tissue temperature was also associated with increased brain tissue depth after exposure to mobile phones. The temperature of the depth of 22 mm of texture increased during exposure to higher temperatures.
 

Mobile radiofrequency waves not only increased the temperature of the tissue at all depths of the brain but at higher depths (22 mm), brain tissue was higher than the temperature of mobile radiofrequency waves.

 In developing countries, pesticide poisoning, regardless of occupational exposure or deliberate actions, is one of the major public health problems. To determine the impact of occupational exposure to pesticides on workers' health status, this study evaluated the consequences of pesticide exposure and its effects on hematological indices.

 Eighty workers of pesticide production factories were studied in two experimental and control groups during 2018–2020. Data were collected using demographic, occupational, health questionnaires, and blood analysis. The collected data were analyzed using SPSS software (ver. 23), Chi-square, and U Mann–Whitney test considering a significance level of 0.05. 

 The age range of subjects was 23–56 years (mean = 36.21 ± 6.744). A significant difference was observed between studied groups in terms of marital status, education level, and work shift. In addition, levels of erythrocyte sedimentation rate (ESR) (P = 0.036), white blood cell (WBC) (P = 0.009), uric acid (P = 0.033), and alkaline phosphates (P < 0.001) were significantly different between the two studied groups. The results showed a significant difference between the hematology Index level of toxin production workers and workers in administrative and service units. 

 As expected given the type of their job, a significant difference was observed between studied groups in terms of marital status, education level, and work shift, use of safety equipment, as well as residency. Furthermore, levels of ESR, WBC, uric acid, and alkaline phosphates were significantly different. It seems that pesticide toxins exposure in the poison-production industry causes hematological changes, which may be dangerous in a long time

Prevalent use of mobile phones has led to increasing worries about the effect of radiofrequency waves on the physiology of human body. This study was aimed to determine the mobile phones radiofrequency waves’ impact on different brain tissue depth and brain tissue temperature. In this empirical research, a cow’s brain tissue was placed in a compartment and the effects of radiofrequency waves of the mobile phone were analyzed during and after radiation, in three different brain tissue depths of 2, 12, and 22 mm, in 4 mm and 4 cm distances of the tissue to a mobile phone, for 15 min. Lutron thermometer was used to measure the tissue temperatures. Data were analyzed using Lutron software. The rate of temperature increasing in 22 mm depth was higher than 2 and 12mm depths. The results also showed that during radiation of the brain tissue in 4 mm distance by the mobile phone, the tissue temperatures in 2, 12, and 22 mm depths were increased 0.29 ˚C, 0.31 ˚C, and 0.37 ˚C, respectively, relative to the base temperature (tissue temperature before radiation). Moreover, the brain tissue temperature in 4 cm distance was more sensitive than other depths. There was also a direct relationship between brain tissue depth and tissue temperature increase after mobile phone radiofrequency waves’ radiation. The temperature in 22 mm depth increased with higher speed. Not only radiofrequency waves of mobile phones increased the tissue temperature in all depths of the brain tissue, but also the higher temperature was observed in the 22 mm tissue depth. In fact, the radiofrequency wave’s thermal affect was higher in higher depths.

Exposure to hand–arm vibrations higher than permissible standard rates can have destructing effects on workers’ health. Pneumatic hammers are among the tools that are used in civil and industrial projects, transferring high vibration acceleration to the workers. This study has considered the probable effects of hand–arm vibrations on the performance of blood coagulationfactors in the workers using this tool and exposed to high vibration acceleration.

Five new workers without any experience in exposure with hand–arm vibrations were selected for this interventional study. Blood sample was taken from each worker before they started working for the required analysis. Sampling was repeated in two other stages in 2‑month intervals from the frst sampling, whereas the workers were then experienced in working with pneumatic hammers. Measuring the vibration of the pneumatic hammer was done according to ISO 28927‑10 standard.

 The point of measuring the vibration acceleration was selected close to the hand, in accordance with the standard. Regarding the exposure time of the workers, the amount of vibration acceleration was obtained 15.54 m/s2. Activated partial thromboplastin times of four samples in the second and third stages have shown increases in comparison to the frst stage in that respect. On the other hand, a number of red blood cells, white blood cells, and platelets did not show a consistenttrend in the three stages.

The considered samples showed longer time for blood coagulation as compared to the reference time. Thus, it can be concluded that the main reason is the acceleration in three different coordinate axes of x, y, and z. Hence, the values beyond permissible standard rate of hand–arm vibration in 8 h shifts affect the blood parameters, among which the considered coagulation parameters in this study showed more tangible changes in that respect.

Noise is one of the most common stress-inducing factors in a workplace and can cause many detrimental effects. Regarding this, the present study was conducted to investigate the effects of exposure time to noise and sound pressure level on mental fatigue and release of noradrenaline in the human body under lab situations. This study was conduced on 10 students of Isfahan University of Medical Sciences, Isfahan, Iran, during 4 consecutive days. The subjects were exposed to the noise levels of 85 and 90 dB on the first (0.5 h)/second (1 h) and third (0.5 h)/fourth (1 h) days, respectively. They solved 20 mathematic questions before and after exposure to noise every day, and then marked their fatigue severity on a visual analog scale. In addition, blood samples were collected before and after exposure to noise. The data were analyzed in SPSS software (verion 20). The noradrenaline level estimated after 0.5 h exposure to 90 dB was significantly different with the level obtained after 1 h exposure to the same sound level (P=0.037). However, no significant difference was observed for other exposure durations. Furthermore, the mental fatigue degrees evalauted before exposure to the sound pressure levels of 85 and 90 dB were significanty different form those measured after exposure to these pressure levels in all situations. As the findings indicated, the elongation of time exposure to noise led to the elevation of mental fatigue; however, it resulted in no change in the level of noradrenaline. Furthermore, the rise of noise level from 85 to 90 dB did not lead to the elevation of mental fatigue and noradrenaline release. Consequently, it seems that increased exposure time to noise is more important in causing mental fatigue than the sound pressure level in a short period of time.

Analyzing the possible negative effects of using cell phones on the users’ health is an important and vital affair due to rapid growth and extensive use of these devices on human communications and interactions. The aim of this study was to determine the effect of increasing the distance of cell phones to brain tissue on the temperature of the central and gray matters of brain due to the heat generated by radio frequency waves.
This study was an experimental study. A cow’s brain tissue was analyzed in a compartment with three thicknesses of 2, 12, and 22 mm, in the distances of 4 mm and 4 cm from a cell phone for 15 min. Lutron thermometer was used to measure the tissue temperature, and the data analysis were done by Lutron and MATLAB software packages.
The tissue temperature was increased while confronting with a cell phone in distances of 4 mm and 4 cm in all the three thicknesses of 2, 12, and 22 mm. The tissue temperature was higher after removing the confrontation at 4 mm distance as compared to the distance of 4 cm.
During confrontation and after that with the cell phone, reducing the distance of brain tissue and the cell phone increased the tissue temperature intensely. In fact, by increasing the cell phone distance from brain tissue, the thermal effect of radiofrequency waves was reduced.

Worries have recently been increased in the absorption of radiofrequency waves and their destructing effects on human health by increasing use of cell phones (mobile phones). This study performed to determine the thermal changes due to mobile phone radio frequency waves in gray and white brain tissue.
This study is an empirical study, where the thermal changes of electromagnetic waves resulted from cell phones (900 MHZ, specific absorption rate for head 1.18 w/kg) on the 15 brain tissue of a cow were analyzed in a compartment with three different thickness of 2 mm, 12 mm, and 22 mm, for 15 min. The Lutron thermometer (model: MT‑917) with 0.01°C precision was used for measuring the tissue temperature. For each thickness was measured three times. Data analysis is done by Lutron and MATLAB software packages.
In confronting of the tissue with the cell phone, the temperature was increased by 0.53°C in the 2 mm thickness that is the gray matter of the brain, increased by 0.99°C in the 12 mm thickness, and also increased by 0.92°C in the 22 mm thickness. Brain temperature showed higher rates than the base temperature after 15 min of confrontation with cell phone waves in all the three thicknesses.
Cell phone radiated radio frequency waves were effective on increasing brain tissue temperature, and this temperature increase has cumulative effect on the tissue, being higher, for some time after the confrontation than the time with no confrontation.

Earplug as one of the protective equipment of the auditory system has different function at different frequencies. Thus, in this study, by simulating a model of human ear canal, protective effectiveness of earplug in sound attenuation was checked at different frequencies and different lengths of the ear canal.
In this cross-sectional descriptive-analytical study, in one side of the simulated ear canal, a microphone was used as the sound receiver, and earplug was embedded in the other end of the ear canal. After playing the pink noise through the speaker, the insertion loss (IL) of earplug at one octave frequency and at different lengths of placement of earplug in simulated ear canal (12.8, 17.5, 25.5, and 31.1 mm) was examined and the results were recorded using Labview software.
Findings: The result of insertion loss of earplug at one octave frequencies showed that in comparison with other distances, the insertion loss of earplug at 25.5 mm in low frequencies (below 500 Hz) was higher, and at this distance, the frequency at 4000 Hz reached the highest rate.
The highest rate of insertion loss was achieved for low frequencies at 25.5 mm. The average length of the human ear canal is 2.5 cm; so, in human hearing system, the highest levels of environmental sound attenuation are at the this distance. Due to the maximum insertion loss of earplug at this distance and at 4000 Hz, producing protective device from absorbent substance for this frequency is suggested.

Effects of vibration appear as mechanical and psychological disorders, including stress reactions, cognitive and movement disorders, problem in concentration and paying attention to the assigned duties. The common signs and symptoms of hand‑arm vibration (HAV) in the fingers and hands may appear as pins and needles feeling, tingling, numbness, and also the loss of finger sensation and dexterity. Laboratory Virtual Instrument Engineering Workbench programming software designed for occupational vibrations measurement was used to calculate HAV acceleration. Hole steadiness test is designed to measure involuntary movement of people. V‑Pieron test is designed for one of the other aspects of the psycho motor phenomena of steadiness by moving the stylus across a V‑form ruler. The two points test was an experiment of touch acuity, which used a caliper by placing the two styli very close on the pad of finger knuckles. The temperature of finger skin is also measured simultaneous to the above tests. Wilcoxon test indicated that a significant decrement in hand steadiness occurred after gripping a vibrating handle for 2 min (P ≤ 0.003). Wilcoxon test also represented a significant change in errors after gripping a grinder vibratory handle (P ≤ 0.003). The differences at all of the knuckles were significant with a confidence interval percentage of 99%. There was a significant reduction in finger skin temperature before and after exposure to vibration (mean = 0.45°C, based on paired sample test). The obtained results considerably demonstrated the relation between hand performance and vibrations due to gripping a grinder. It can be concluded that an injury or accident may happen after exposure to vibrations for the fine duties, in fast actions.

In addition to the adverse effects of noise in the auditory system, non-auditory effects can be regarded as factors which cause physiological harassment, discomfort and also disorder in cognitive functions. The present study aimed at determining cognitive function after exposuring to different levels of sound pressure level in a clinical trial study.
This study was clinical trial type (before and after clinical trial). In order to evaluate the effects of noise (65, 75 and 85 dB) on cognitive function, 12 students (6 males and 6 females) of Isfahan Medical Science University students between the ages 22 and 27 with BMI 20-25kg/m were studied. To analyze data, the statistical pair-T test was used and ANOVA (P=0.05) was run.
Applying sound pressure level of 65 dB in comparison with prior applying of 65 dB sound pressure level led to average increase in chosen reaction times colors (P=0.041) and sounds (P=0.038) were significant. Also, by increasing the sound pressure level of 65 dB to 75 and then 85 dB reaction time average increase was significant (001/0> P).
Accordingly, the 75 and 85 dB sound pressure level of 65 dB sound pressure range cannot be considered within safe limits for non-auditory effects according to its impact on cognitive function. Besides, this issue in jobs that expose people to high sound leads to disorder in cognitive function (reaction time, attention, etc.) causing the risk which must be taken into consideration.