Journal of Health and Safety at Work

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Introduction: previous studies have shown approximately 90% of accidents in the workplace are due to unsafe behavior and human errors. Identifying predictors of unsafe behaviors would be unsafe in accidents prevention. The purpose of this study was to investigate personality characteristics, cognitive and organizational variables of line workers in an industrial company in bojnurd.

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Material and Method: The sample, in the main stage, consisted of 300 employees and in the validation stage 100 They were selected thought stratified random sampling. Firstly, participants were divided into two groups (safe and unsafe) using safety behavior scale. Next, each group was evaluated using the five-factor personality questionnaire, safety efficiency questionnaire, regulatory focus at work, safety climate, safety motivation and safety competency scales and also perceived work pressure questionnaire. In order to analyze the data, the discriminate analysis, the confirmatory factor analysis and the Pearson’s correlation coefficient were applied.

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Result: According to the result of the present study, unsafe behaviors of employees can be predicted by neuroticism, extroversion, agreeableness, consciousness, safety efficiency, regulatory focus and its dimensions, safety climate and its dimensions, safety motivation, safety competency and role overload variables.

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Conclusion: The results of this study showed the importance of safety competency, prevention focus, safety rules and procedures, safety efficiency and consciousness as predictors of unsafe work behaviors. Therefore, it is recommended to rely on these variables in the safety training courses and also in selecting people for high risk environments.

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Introduction: The acoustic performance of natural fiber adsorbents has been investigated in numerous studies. A part of these materials show a poor adsorption within the frequency range of less than 1000 Hz. In the present study, attempts were made to investigate the effect of layout sequence of double-layered composites consisting of natural and synthetic fibers on improving the acoustic adsorption coefficient of natural fiber in the low-frequency range (63 to 1000 Hz) using the numerical finite element method.
Material and Methods: In this study, the finite element method and the Johnson-Champoux-Allard model in COMSOL software version 5.3a were used to investigate the acoustic performance of the double-layered composites consisting of natural and synthetic adsorbents. The acoustic absorbers under study included date palm fiber, polyurethane foam and cellular rubber. Each double-layered composite included a date palm fiber with 10mm in thickness and a synthetic adsorbent (polyurethane foam or cellular rubber) with 10mm in thickness. In sum, four double-layered composite structures with different layouts of adsorbents in each structure were studied.
Results: The location of natural fiber can play a critical role in the acoustic performance of the double-layered composite structures such that comparing the studied double-layered composites revealed that when the natural fiber was the first layer exposed to the normal sound in the double-layered composites with 20mm in thickness, the trend of acoustic performance was approximately the same as the single-layered composite of natural fiber with 20mm in thickness; but in the composite structures, when the synthetic adsorbent was the first layer exposed to the sound, the trend of acoustic absorption was improved.
Conclusion: On the basis of the results, the double-layered composite structure with a higher-density and lower-porosity upper layer showed a better acoustic absorption trend than the single-layered composite including the natural adsorbent.

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Introduction: Micro-perforated absorbents are one of the structures that are widely used nowadays. The sound absorption mechanism is performed by viscous energy losses in the cavities on the plate. In this study, the acoustic properties of non-flat perforated panels in oblique angle was investigated in numerical method.
Material and Methods: This paper examined the effect of the surface shape on the micro perforated absorber performance at low frequencies (less than 500 Hz). The three-dimensional finite element method was used to predict the absorption coefficient of this group of adsorbents. Also, the results obtained from the shaped absorbents were compared with the flat micro perforated ones. After validating the numerical results, six different designs were defined as the surface shape of the micro perforated plates in the COMSOL Multiphasic, Ver. 5.3a software
Results:  The results reflected the fact that the factor of the surface shape can be used as a contributing factor in lower frequencies. In general, the dented or concave shapes provide better outcomes than other flat designs and shapes and the convex or outward shapes bring the weakest results.
Conclusion: To explain this function, shaping creates a phase difference and angling the sound wave and creates a variable depth behind the micro-perforated plate. It also influences the reflection process which affect the absorption coefficient.

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Introduction: Natural materials are more efficient and attractive than synthetic materials. In this study, the sound absorption behavior by natural kenaf composite and Micro-Perforated Panel (MPP) at low and medium frequency region was investigated.
Material and Methods: Initially, the results of kenaf fibers with a thickness of 10 mm were validated by the Finite Element Method (FEM) based on COMSOL Multiphysics 5.3a. The studied combined panel is consisting kenaf fibers with micro-perforated plates and an air layer. This study examined the varying arrangement of the behind layers of the MPP, the different thickness of the layers, and the structural parameters of MPP. The structure with the best absorption coefficient was chosen for the following stage and was considered constant at each stage.
Results: The arrangement of composite layers indicated a strong direct effect on the sound absorption performance; as we discovered that kenaf fibers behind MPP led to better performance in frequencies below 2500 Hz. In addition to the chamber depth behind the MPP, the material and macroscopic properties of the layers, at the same depth, are also important determinants of the exact point of the resonant frequency. Furthermore, configurations in which air layer depth is more than the absorption layer, with the same diameter (hole) and depth (chamber), maximum resonant absorption peak is achieved.
Conclusion: Low-frequency sounds can be successfully dissipated by combining MP plates with kenaf fibers as reinforcing absorber in combined panel. In general, choosing the optimum structural parameters (Composite panel according to structure A with 0.5 mm hole diameter and 2% perforation percentage) allows a significant absorption at a specific frequency range. In this context, the use of numerical estimation to assess the sound absorption behavior can be meticulously substituted the difficult methods and laboratory costs.

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Introduction: The aim of this study was to investigate the effect of particle size (mesh) on the sound absorption coefficient of the absorbers made from Arundo Donax reed and to determine the optimal mesh for sound absorption.
Material and Methods: After crushing the reed stems in 10, 30, 20, 16, and 40 mesh sizes, they were washed with 5% NaOH. To make the samples 3 and 10 cm in diameter, 10% PVA was used as a binder, and the impedance of the two-channel tube was used according to ISO 10534-2 standard to determine the absorption coefficient. 22 samples of meshes 16 and 20 were made to achieve the optimal mesh based on the optimized RSM method, and the SAA index was used to compare the samples and determine the optimal mesh.
Results: The highest absorption peak was related to meshes 16 and 20 at the frequency of 2500 Hz, which is 0.94 and 0.98 ,respectively. The effect of increasing the thickness and density on the absorption coefficient is evident. The results have shown the effect of increasing the thickness and density on the absorption coefficient in mesh 20 in such a way that by increasing the density from 150 to 250 and the thickness from 10 to 30 mm, the absorption coefficient has increased from 35 to 63.5%. The optimal sample was mesh 20 with a thickness of 30 and a density of 250 kg/m3, which had the highest average absorption (SAA=0.57). The greater distance between the real and imaginary parts of the impedance shows the reactivity of the sample. In mesh 16 this distance is greater, as a result, mesh 16 has more reactivity and correspondingly less absorption.
Conclusion: The role of particle mesh as one of the important and influencing parameters on absorption coefficient has been investigated in this study.

 

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Introduction: Microperforated panels (MPPs), often considered as potential replacements for fiber absorbers, have a significant limitation in their absorption bandwidth, particularly around the natural frequency. This study aims to address this challenge by focusing on the optimization and modeling of sound absorption in a manufactured MPP.
Material and Methods: The study employed Response Surface Methodology (RSM) with a Central Composite Design (CCD) approach using Design Expert software to determine the average normal absorption coefficient within the frequency range of 125 to 2500 Hz. Numerical simulations using the Finite Element Method (FEM) were conducted to validate the RSM findings. An MPP absorber was then designed, manufactured, and evaluated for its normal absorption coefficient using an impedance tube. Additionally, a theoretical Equivalent Circuit Model (ECM) was utilized to predict the normal absorption coefficient for the manufactured MPP.
Results: The optimization process revealed that setting the hole diameter to 0.3 mm, the percentage of perforation to 2.5%, and the air cavity depth behind the panel to 25 mm resulted in maximum absorption within the specified frequency range. Under these optimized conditions, the average absorption coefficient closely aligned with the predictions generated by RSM across numerical, theoretical, and laboratory assessments, demonstrating a 13.8% improvement compared to non-optimized MPPs.
Conclusion: This study demonstrates the effectiveness of using RSM to optimize the parameters affecting MPP performance. The substantial correlation between the FEM numerical model, ECM theory model, and impedance tube results positions these models as both cost-effective and reliable alternatives to conventional laboratory methods. The consistency of these models with the experimental outcomes validates their potential for practical applications.

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Introduction: Micro-perforated panel (MPP) absorbers are emerging as next-generation absorbers due to their considerable advantages. However, their main drawback compared to other absorbers is their limited bandwidth. This study aims to investigate methods for enhancing the bandwidth of an MPP in the frequency range of 1 to 1500 Hz through simulation using the Finite Element Analysis (FEA) in COMSOL software.
Material and Methods: The modeling was conducted using FEA in COMSOL version 5.3a. To increase the bandwidth, techniques such as series-parallel configurations, symmetrical and asymmetrical air gap depths, and the incorporation of two porous absorbing materials in symmetric and asymmetric air gap layers were employed. In the initial phase, the best configuration was selected and retained for the subsequent stages.
Results: The optimal arrangement involved two upper MPPs having larger holes and a lower perforation percentage compared to the two lower MPPs. It was also found that increasing the depth difference between the air layers of the upper and lower MPPs led to a greater increase in bandwidth than when they were closer together. Furthermore, the use of fibrous porous materials in one of the layers resulted in a reduction of resonance peak while enhancing the bandwidth.
Conclusion: MPP absorbers exhibit diverse behaviors due to their Helmholtz structure and parametric design. If their constituent parameters are tailored to match the acoustic characteristics of the target sound, they achieve optimal efficiency. Additionally, employing numerical methods such as FEA serves as a suitable alternative to more costly laboratory methods.