کنترل صدا

A significant contributor to noise pollution in urban areas is automobile exhaust systems, wherein mufflers, as passive devices, are designed to mitigate the noise produced. The dimensions, shape, and configuration of the muffler, along with its associated components and pipes, influence its effectiveness in sound transmission loss. This study investigates the impact of varying the length of the muffler’s connecting pipes and their associated holes on sound transmission loss in reactive mufflers, utilizing software simulation for analysis.

The research utilized COMSOL 5.5 to simulate the effects of different geometric factors on sound transmission loss in mufflers. Modifying factors such as the length of connecting pipes and the existence of holes led to the development of various designs. Analysis of the results was conducted to assess the impact of each parameter on sound attenuation, enabling a straightforward comparison of acoustic efficiency.

Studies demonstrate that changing the form of pipes at different frequencies produces diverse outcomes. Introducing a perforation prior to the tube and utilizing elongated connecting tubes with expansion chambers can enhance transmission attenuation. On the other hand, transmission loss decreases with longer pipes that lack holes. Lower pitches experience minimal attenuation, whereas higher pitches undergo more loss. Reactive mufflers work best at certain frequencies, where the length of the connecting pipe affects both the acoustic mass and the effectiveness of the muffler.

The results obtained from this study can inform the optimal design of mufflers aimed at enhancing their efficacy in sound transmission loss. Furthermore, it is essential to consider the synergistic impact of the geometrical configurations of the internal pipes within the muffler to minimize sound emissions from the exhaust outlet.

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.

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.

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.

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.

Punch press is contributed as one of the major industrial machines to produce metal objects, which typically propagates hazardous noise. Acoustic enclosure is the most common method to mitigate noise transmitted from industrial equipment. This study aimed to assess the role of opening dimension and location in a partial acoustic enclosure on occupational noise exposure of punch press’s operator.

A punch press with the capacity of 60 tons in an automotive manufacturing company was considered as a real noise source. Equivalent noise exposure level was measured with reference to ISO 9612 using Cassella Cell-450 sound meter, before and after noise control intervention. Rubber sheet and mineral wool as insulation and absorption acoustical material with the thickness of 2 and 50 mm, respectively, applied to build acoustic enclosure. Rubber sheet sound transmission loss was measured using BSAW SW 477 acoustic impedance tube to predict acoustic performance of enclosure. In addition, Partial acoustic enclosure with the dimensions of 1.4 by 1.2 by 3 meter was constructed and opening areas which was equal to 2, 3, 5 and 7 percentage of total area of enclosure was created in front of punch press operator. Finally, an opening equals to 2 percentage of total area of enclosure was created on the left sidewall of enclosure to assess the location of opening on noise level.

Punch press operator noise exposure level was measured to be 89 and 67 dBA before and after using full acoustic enclosure respectively.  After using partial acoustic enclosure with open area percentage of 2, 3.5 and 7 on the front side of press, operator noise exposure level was measured 78, 79, 78 dBA, respectively which was a little bit more than predicted noise. As the opening position was relocated from the front wall to the sidewall of the enclosure, operator noise exposure was reduced from 78 to 69 dBA respectively. Although, there was not significant differences between mean sound level of the punch press after relocation of opening. 

Utilizing full acoustic enclosure constructed from insulation material recommended in this study, reduced punch press operator noise exposure remarkably. Although, opening area of partial acoustic enclosure was increased to some general extent to feed punch press, there was a slight change in noise exposure of press operator. On the other hand, press operator noise exposure was plummeted with the relocation of opening. Therefore, front opening dimension could be chosen fairly wide to access and feed operation zone of punch press without exposing operator with more noise level. Furthermore, repositioning the opening from the front wall to the side wall of the enclosure and automatically feeding the press through side opening could substantially reduce the operator noise exposure.

Noise is a kind of mechanical energy that is sensed by the human hearing system. It can cause physiological and psychological disturbances, therefore controlling the exposure to this harmful factor is highly important in industrial and non-industrial workplaces. The purpose of this study is to determine the effectiveness of acoustic barriers on noise reduction in one generator building.

 This case study carried out four stages in January 2020, which including: determining the purpose of the measurement, gathering information from the location, selecting the proper material, designing, installing the noise barrier, and evaluating its effectiveness. The environment noise level was measured according to ISO 9612-2009 [E] by the Casella CEL Model 450 sound level meter.

The average noise reduction, 1 m from the noise barrier was 19.5 dB, the highest transmission loss recorded was 22.4 dB.at 8000 Hz.

Due to the simplicity of the design, the ease of implementation, and the efficiency of the sound barrier introduced in this project is recommended for similar conditions with an effectiveness of 19±0.5 dB.

Consideration to time constraints, implementation and funding in each industry, one of the essential strategies for managing noise control and selection the best method is to prioritize noise control methods. The aim of this study was to Prioritizing of Noise Control Methods in the battery making industry by the Analytical Hierarchy Process (AHP).

The present study was a descriptive-analytical cross-sectional study.After measurement of sound pressure level and identifying the main sources of noise pollution, Content validity index (CVI) and content validity ratio (CVR) were used to sieve the criteria and methods of noise control. Prioritization of noise control methods based on the study criteria was done by calculating the relative weight of each of them by two factors of Eigenvalue and eigenvector.

The results of the study showed that the inconsistency ratio(IR) in pairwise comparisons was less than )10%( in all cases and the consistency of the answers was confirmed. Based on the results, among the study criteria, the acoustic efficiency criterion of method with weight(0.1810), and Among the proposed methods of noise control, the method of controlling the exposure time to noise and training of workers with weight(0.1732) had the highest priority.

Findings showed that in the studied battery making industry, the best criterion in noise control is the safety of the noise control device. Also based on the results, controlling the duration of exposure time to noise and training workers in conditions of high noise exposure was the best method to noise control in the battery making.

Abstract Introduction:

This study was aimed to prioritize noise control in different units of an oil refinery using noise control priority index (NCPI) and technique for order of preference by similarity to ideal solution (TOPSIS)
 
 

This cross-sectional-descriptive and analytical study was conducted in the oil storage tanks and transportation unit of an oil refinery, in 2019. In the first stage, environmental sound was measured based on the standard of ISO 91612. In the second stage, the values of NCPI index in different units was calculated by three variables, including the exposed people number, the exposure duration, and the weighting factor related to the sound pressure level. In the third stage, noise control strategies were prioritized using TOPSIS method.
 

The highest sound emission was observed in NTA unit (98 dB) and the lowest sound emission was related to spherical tanks (84 dB). Among the 10 units studied, the NTA unit with 12 workers had the highest priority of noise control (NCPI = 1.25). The results of TOPSIS method showed that the solution of time exposure control with the final weight of 0.722 is the most ideal method to decrease noise exposure in NTA unit.
 

via the two method of NCPI and TOPSIS, it is possible to determine the appropriate prioritization in different units and implement the solutions of technical and managerial noise control in order of priority. The model used in this study can also be applied in other similar industries with noise pollution

Noise pollution is the most widespread physical harmful factor in industrial environments. Noise control is intended to control its effects and comfort of work, including general management and engineering control techniques. Harmful noise is considered as an important occupational hazard in the iron and steel, textile and process industries. In addition, noise pollution is a potentially harmful component of the plant industrials. Metal Industry have been identified as one of the environments with higher noise than permissible and for many countries, implemented Hearing protection programs for workers protection in these industrials. Occupational exposure to the noise caused by Devices and Processes productive processes is often described as a form of self-harm. Noise control is intended to control its effects and Convenience of work, including general management control and engineering control. In most industries there is at least one process unit in which the noise pressure level is higher than the permitted level and oil industry is also subject to this. Therefore, the present study aimed to evaluate the noise pressure level in some units of the oil industry and to evaluate the effectiveness of the implementation of engineering control methods including sub-seismic installation, modification of control room doors and windows, floating floor implementation, construction and installation of acoustic chamber.

This descriptive, analytical and interventional study was conducted at an oil factory in Khuzestan province. This study was carried out in four phases, including Phase I; measuring and evaluating noise and identifying important bands and sources of noise production, Phase II designing technical control methods at the resource location, and location of workers, Phase III, Implementation of engineering interventions and Phase IV Reassessment and effectiveness of the interventions were performed. In the first phase, the noise pressure level in the pressing, assembly, installation and bottling sections was measured peripherally and locally. In addition, at some peripheral stations and all local stations, was performed the frequency analysis of one octave of noise by the advanced digital level meter AWA 5688 in accordance with ISO 9612. In addition to for Local Stations the equilibrium, was determined the received dose to determine its reduction after interventions. Then, according to the type and level of noise pressure level as well as the environmental characteristics of the hall, were performed appropriate engineering control measures. Then in the second and third phases in this research in the high noise pressure level units Was performed Interventional actions Includes sub-seismic installation, installation of acoustic panel on the ceiling and absorbent panel on the common wall with assembly hall, installation of absorbent panel on the adjacent walls of press operators, installation of polymer plates on the desks, modification of doors and windows of control room and floating floor installation, installation Metal cab with foam elastomeric inner surface, galvanized steel ceiling and elastomeric adsorbent in cabin cab, acoustic chamber fabrication and installation.  In the fourth phase of this study was performed a reassessment of the noise pressure level in the intervention units and at the workstation to determine the effectiveness of the interventions. For this purpose, was compared the noise pressure level of each indicator station and compared before and after the intervention. also In evaluating the effectiveness of the interventions performed was recorded, the approximate cost per unit separately and was presented their effectiveness in reducing the noise pressure level as a cost-effectiveness index as well as a cost-benefit index to determine each cost reduction How much does it cost to decibel.  

The results of noise pressure level measurement in different units showed that the equivalent noise pressure level was Above than Exposure limit before the intervention in all stations so that The highest level of noise pressure in the vicinity of one of the 63 tone presses was equal to 92/63 dB (A). After the interventions, the noise pressure level was reduced at all stations and was lower than the limit at all points except one press also. The results showed that the largest reduction in noise was in the correction of the tetra pack chambers. Frequency analysis of noise was performed at most of the indicator stations and presented at two sample stations. The results showed that the noise pressure level was effectively reduced. In addition to technical efficiency and scientific justification, noise control techniques must be applied with economic considerations in mind. Due to the cost of technical methods of noise control, it is essential that the designer assess the economic aspects including cost-effectiveness and even cost-benefit before executing the plan until the employer can estimate the cost of the project with economic considerations In addition to the technical results. If so with noise levels are lowered to the permissible level using less expensive methods, there is no need for high costs. In this study, the economic aspects of technical control plans in different units and their total in the company were estimated. In this paper, the cost-benefit index was calculated, which showed that the total direct cost of the project in the press unit was about 502 million Rails and given that the number of people who were disqualified was 13 in three shifts, the average cost-benefit index was 0.70 million Rails per person over a one-year period.

In this study, were used interventional methods of modification and fabrication of chambers for tetra pack and bottle-filling machines in the bottling hall After examining the unit, it was found that environmental control was not a priority in this unit And the problems with this unit were due to technical glitches and the incompleteness of the tetra-pockets cab room and the lack of a queuing bottle chamber. Completing walls reduced the noise pressure level to 9.5 dB and reduced workerschr('39') exposure to below 82 dB by steel sheets and technical modifications to control noise in Tetra pack chambers. Also, the noise of the Bottle Row Unit reduced by Construction and  installation of a simple chamber with steel wall and UPVC door and window  about 10 dB and reduced the exposure to below 79 dB Another intervention in this unit was the use of silicone sealant and Silicone Glue to block all leakage pores. According to the guidelines outlined in the Volume Control Guide, acoustic chamber installation can be a good way of controlling the noise of industrial sources, and the use of steel sheet as the main approved layer of ISO 15667 has been well used in this study. One of the interventions that was effective was the installation of an elastomeric sealant at the base of the presses to reduce vibration, which reduced the noise pressure level in the low frequency range. In addition, the use of rock wool insulation has a significant effect on reducing the noise pressure level. In this study, it was found that enclosure can reduce the noise level in the unit production pump, but should be considered the limitations of the enclosure method. In the industry under review there were two staff control rooms in the liquid production unit and facilities, which had major drawbacks in the number, dimensions, and gender of the windows. In this plan equivalent noise pressure level decreased more than 16 dB in the listenerchr('39')s room with reduced the size and number of windows and replaced them with UPVC double-glazed windows, as well as replacing doors of the same type with a low cost. Eventually the investigations showed that all the control measures performed in different units in this study resulted in a significant reduction in the noise pressure equivalent level. Units taken these indices are within the acceptable range.

Noise exposure, risk exposure in a wide range of work station, especially oil and gas industry and related companies is considered. This study was carried out to evaluate the noise before and after corrective action in 11 operational units of tanks and transportation in Abadan oil refining company.

First, the basic information including the location of noise sources and operating conditions of the equipment was collected. noise measurements was performed based on ISO 9612 standard before and after implementation of corrective actions, including repair or replacement of defective and worn out Parts or lubrication of moving parts  and using SLM CEL 490 mode calibrated with CEL-110/1  of casella  company was performed.

According to the results, the NTA has the highest amount of noise (97 dB) and spherical tanks with the lowest noise (82 dB). In this study, measured total 523 stations, 115 stations with noise levels over 85 dB, 373 stations between 65 and 85 dB sound pressure level and sound pressure level less than 65 dB in 30 stations. After carrying out corrective measures to reduce noise measurements, result showed that reduction of average sound pressure level of unit 1 of oil pumping with the 2/39 dB, 1.7 dB with a unit of Control Center, pus oil pumping unit with 0.98 dB and NTA unit with 0.08 dB, carried out respectively.

Noise measurements showed that the NTA unit was one of the severest conditions from the viewpoint of noise pollution among the other units. This study confirms the need to identify the main sources of sound and prioritize different parts of the industrial unit in order to implement control schemes engineering.

Undoubtedly, noise and vibration are major problems of industrial world and lot of people are very exposed to these phenomena in their workplace or residential areas. Researchers have shown that exposure to noise may increase the risks related to personal health, like nervous frailty, extreme irritability, muscle cramps, stress and anxiety, dizziness, headache and migraine, anger, loss of body balance, vomiting, pain, hypertension, high blood pressure, cardiovascular problems, deterioration of sleep quality, mental stress, etc. However, the purpose of this study was to assess and control and reduce the risks resulting from noise in the reduction unit 2 of a steel industry. This study was conducted in two steps. 1) Evaluation of noise pollution in the compressor room and its surrounding: For this purpose, total sound pressure level (SPL) and SPLpeak were measured in the places where workers worked or were traveled. The parameters were measured in the mentioned places according to a grid pattern in both the compressor turn on/off. Because the workers exposed to a noise fluctuating, in addition to SPL analysis on the octave-band frequencies to determine critical frequency when the compressor was switched on, the value of Leq was also measured. The critical frequency is very important in noise control issues. The measurements were performed by using sound level meter, model of “B&K 2231.” The apparatus was calibrated before and after measurements by using “B&K 4230 calibrator.” 2) Noise control measurements: After identifying noise leakage paths to outside of the compressor room, noise was controlled in door, wall-fans and roof window area through installing a silencer on the wall-fans and redesigning the door and the roof window using the previous step data. Inside the compressor room, the total sound pressure level and the critical frequency was estimated 106.2 dB (A) and of 250 Hz in the Lin network, respectively. The total sound pressure level in the area around the compressor and the critical frequency were also estimated 94.3 dB (A) and 2000 Hz respectively. Moreover, the value of Leq was more than the threshold value (<85 dB) at all measured stations. In order to control the noise in the area of ​​the fans, considering the noise assessment and the critical frequency, there was used an absorption silencer with glass wool as adsorbent material. To control noise at the door and roof window, there was designed and installed a steel door with dimensions of 3.9 * 2.13 meter and thickness of 1.5 mm which was filled by a noise-adsorbent 40 mm of glass wool and attached to a metal grid. Moreover, to control noise in the roof window was applied a structure with the same specifications, but with the different dimensions (4.2 * 4.2 m and 7 mm mesh diameter). However, the results related to before and after implementation of the control measurements showed an acceptable attenuation in the SPL (91.8%). The average SPL before and after implementation of the control measurements was 95 and 87.2 dBA, respectively which this value was an acceptable level in comparison with background noise, i.e., 86.4 dBA. On the other hand, The slight difference between the mean value of the background sound pressure level and the average of controlled sound pressure level (0.8 dB) is due to factors such as temperature, variations in sound at different positions, generated noise sources (off or on and so no) and the movement of fluids in the pipes and so on.  

The results of the field study indicated that door, window and roof window were identified as the main paths of noise leakage to outside of the compressor room. Therefore, the implementation of the control measurements could be reduced to an acceptable level, but due to high background noise level even after the implementation of the control measurements, the noise level was less higher than the maximum permissible level (85 dB). Therefore, there were presented a few recommendations such as controlling the other sources of noise (e.g. moving fluid through pipes), utilizing the hearing protection devices and how to choose them properly to reduce background noise and the protection of workers against noise.

Noise reduction in the source is always in priority. For acoustic engineers, taking a systematic approach and considering small details of designing an enclosure can be one of the most effective ways of noise reduction. This study was carried out to detect major noise generator sources in a screw manufacturing company. In this interventional study, primarily information were collected, including machines' specifications, number of workers exposed to noise, time of exposure, and their deployment location. Then environmental assessment was carried out to assess the noise level around the sound source and dosimetry devices. Finally, a design of an enclosure was developed to control noise level in machines producing noise. Results indicated that BV2 and BR3 machines, with total sound pressure level of 95.7 and 94.4 dB, were major sources of noise, which exceeded the noise limit. To control the generated noise of the mentioned machines, an enclosure was designed with minimum damping of 19 dB. The designed enclosure consisted of a compact layer of 3 mm steel, a layer of 20 mm self-stick foam, a layer of 40 mm mineral wool and a 1 mm layer of punched aluminum plate with open mouth of 60%. the designed enclosure for BV2 and BR3 machines can empirically reduce sound pressure level by 19.3 and 19.7 dB respectively and the exposure of operators was reduced to 76.4 and 74.7 dB, which provides safety for workers of the factory.

Hospital acoustics, noisy equipment and people have adversely impacts on patient’s physical and mental health. This paper aims to identify the major sources of noise and noise control techniques in hospitals of Behbahan
Noise measurement was done according to ISO9612 at designated stations. Equivalent sound pressure levels were measured at 243 measuring stations in 30 minute intervals. The validated questionnaire was completed for the evaluation of major sources noise among 158 staffs. The Data with SPSS and EXCEL were analyzed. Finally were provided practical suggestions for noise control
The results showed that the maximum equivalent sound levels were 65.8 dB (A), 61.65 dB (A), and 71.1 dB (A) at the Shahid zade, Faride behbahani and Tamin Ejtemaee hospitals respectively. In this paper we shall consider the main source of noise pollution in hospitals were staff and clients, sound of doors, and air conditioning, medical equipment and furniture and beds
This work try to put forward some possible solutions including: Indoor planning, selection of suitable materials, noise control both inside and outside buildings.

Using water pump in residential buildings to provide the required water pressure is accompanied by noise pollution and the annoyance of residents. So, the purpose of this study is to reduce water pump noise pollution with designed acoustic curtains in a residential building of Qazvin city.
The mean sound pressure level was measured before and after control intervention around the sound source based on ISO 9612, using the sound level meter (Casella-Cell.450). The sound level meter was calibrated using a calibrator(Cell-110/2). The frequency analysis was done in 1.1 octave band and the weighting frequency of A. Acoustical features of acoustic curtains (thickness, material and dimensions)were determined on the base of required sound transmission loss in predominant frequency. The volumetric flow of air required to decrease the temperature inside the enclosure up to 40°C to maintain a reasonable air temperature for pump performance was calculated using the energy-mass conservation law. Temperature inside the enclosure was measured with a mercuric thermometer.
The mean sound pressure level before and after control around the pump was measured 67 dBA and 46 dBA respectively. The required insertion loss in predominant frequency(2000 Hz) to accommodate noise limit in residential buildings was considered to be 26 dB and based on which acoustic curtain surface density was calculated between. The average sound pressure level measured after control(46dBA) with predicted sound pressure level by mathematical calculation after control(47dBA) was not significantly different. The volumetric flow rate required to maintain a temperature of 40°C inside the enclosure was calculated to be 1.2 cubic meters per minute. The temperature was measured inside the enclosure of 38° C.
Control of noise pollution using acoustic curtains with a lower cost and weight, higher installation speed and higher sealing can be considered as one of the proper methods for enclosing noise resources.

Introduction; controlling noise pollution in an indoor environment has always been faced with administrative and financial constraints. Prioritizing in a scientific manner is a useful approach in dealing with such problems. The aim of the present study was to determine the noise control prioritizing index (NCPI) in various units from a tire manufacturing company.
Methods; the sound pressure levels in various units were determined in accordance with ISO 9612 standard. The index was a function of three parameters; the number of people exposed of the noise, exposure time, and a weighting factor corresponding to the sound pressure level. The distribution of noise levels on the unit with the highest priority was depicted using Surfer ver.10.
Results; according to the environmental measurements, 22.9% of the investigated stations had a noise level in the danger zone and other 77.1% was in the caution zone. No station was in the safe zone. The sound pressure level had a range between 69.9-104.7 dB(A). Among the investigated units, the curing unit with 20 employees had the highest priority of noise control (NCPI=1.369).
Conclusion; the results of the present study indicated that using an index resulted from a combination of various parameters affecting the noise pollution, we would be able to prioritize units for implementing noise pollution control confidently. The results of the present study are applicable to all similar industrial settings.

The power plants, including important industry of the country in which a large number of noise sources which workers are exposed with harmful levels occupational noise. The aim of this study was designing enclosures to noise control in the feed water pumps in a power plant.
This cross-sectional study and their Interventional plants were done on the ground floor of the turbine unit of a thermal power plant on 2014. The feed water pumps in the preliminary stage of study, in the ground floor was determined the major noise sources. The Sound power level of the main sources were estimated according to the ISO 3746. To determine the distribution of the sound pressure level measuring and frequency analysis on the vertical axis for the study sources we used the SLM model TES 1358 and the measuring technique was small scale mesh networking and using the SURFER software for interpolation calculation and noise map drawing. Eventually, in order to control the noise we designed a multilayer enclosure for this pump and the effectiveness of this layer was estimated.
The results of the noise analysis of this pumps showed that the dominant frequency of the noise were 2000 Hz. The results of the noise separation in the vertical axis of the sources confirms that the main pump and gearbox has the largest share in the noise distribution. The results also showed that the sound power level of the main pump is 107dB and of the gearbox is 108 dB. The design of the enclosure contains a primary layer made of steel and the inner layer made of rubber foam.In this design, including a percentage of noise leakage, the sound pressure level of the main parts of the pump will be reduced by 20 dB.
Enclosing technique can be reduced of noise levels for boiler feed water pumps. This result could protect the workers against harmful noise to the permissible limits.

In the steel industry, air blowers used to supply compressed air are considered as sources of annoying noise. This study aims to design acoustic room chamber in order to noise control of air blower. Measuring of the noise level along with frequency analysis were performed by using sound level meter model of CASELLA-Cell.450. Dosimetery in order to worker exposure was performed using the dosimeter model TES-1345. Linear sound power level of machine was calculated based on ISO 3746. Distribution of noise emission of the source was shown in form of workroom noise maps using Surfer software. Acoustic analysis of workroom was performed based on sound absorption characteristic of internal surfaces. In order to noise control, an enclosure along with condensed sandwich panels for blower was designed and finally, the effect of this intervention was estimated. The results showed the total sound pressure level of the air blower was 95.4dB (Lin) in which the dominant frequency was 2000 Hz. Moreover, sound power level of the air blower in the dominant frequency was 102.94dB (Lin). The effective absorption surface of workroom was estimated equal to 0.082 and the average occupational noise exposure level based on noise dose was equal to 230%. The designed enclosure along with the steel and fiberglass as a primary insulation layer and punched sheet by steel layer as absorption sound on internal surfaces, actual transmission loss in the dominant frequency, by taking 0.001 opening, was estimated 30dB. gearbox and compressor was the main cause air blower noise that is created Because of the Spiral gearing wheels spinning rotor gearbox parts and the interaction between the rotary and fixed blades move air through the compressor is caused. Enclosure design noise dose received by worker reduced to less than 20 percent. Keywords: module design, air blower, noise control, acrostic analysis, steel industry.

In the steel industry, coke-fueled furnaces are used for smelting iron ore to produce cast iron are considered as sources of annoying noise.This study aims to evaluate the noise pollution blast furnace and sound source characteristics in order to present noise control measures in the steel industry.

Measurement of noise level and its frequency analysis was performed using sound level meter model of CASELLA-Cell.450. Dosimetery in order to worker exposure was performed using the dosimeter model TES-1345.Distribution of noise level in the furnace area in form of noise map was provided using Surfer software. In addition, acoustic analysis of control and furnace workers rest rooms was performed in view point of and insulation.Redesign of door and window of control room and reform of worker's rest room were proposed and the efficiency of these interventions was estimated.

The total sound pressure level in the furnace workroom was 90.3dB(L) and the dominant frequency was 2000Hz. Sound transmission loss of the wall dividing the control room and rest room workers furnace 10.3 and 4.23dB, respectively. The average of noise dose in furnace worker was 240%. And sound transmission loss of the new The performance of the proposed control schemes based on sound insulation of rooms was estimated equal to 30dB.

The main cause of noise pollution caused by turbulent air flow in the air ducts furnace. The acoustic Shelter was designed for standard control room and rest as the most effective method of controlling worker's exposure to noise. Accordingly, the workers received a noise dose of less than 100% can reduce.

In the steel industry،air blowers used to supply compressed air are considered as sources of annoying noise. This study aims to acoustics analysis of theairblower workroomand sound source characteristics in order to present noise controlmeasuresinthe steel industry. Measurement of noiselevel and its frequency analysis was performed usingsound levelmetermodelof CASELLA-Cell. 450. Distribution of noise level in the investigated workroom in form of noise map was provided using Surfer software. In addition، acoustic analysis of workroom and control room was performed in view point of soundabsorption andinsulation. Redesignofdoor and window of controlroom and installation of soundabsorbing materialson theceiling of the workroom were proposed and the efficiency of these interventionswasestimated. The totalsound pressurelevelin the blower workroom was 95. 4 dB (L) and the dominant frequency was 2000Hz. Sound pressure level inside the room control was 80. 1dB (A). The average absorption coefficient and reverberation time in the blower workroom was estimated equal to 0. 082 Sab. m2 and 3. 9 seconds respectively. These value in control room was 0. 04 Sab. m2 and 3/4 seconds respectively. In control room، sound transmission loss between the two parts of the wall dividing was 13. 7 dB (A). The average of noise dose in blower operators was 230%. With the installation of sound absorber on ceiling of workroom، average of absorption coefficient can increase to 0. 33 Sab. m2 and sound transmission loss of the new designed door and window was estimated equal to 20dB. The main cause of noise leakage in the control room was insufficient insulation properties of door and windows. By replacing the door and window and installation of sound absorbing on ceiling of workroom، the noise dose can reduce to 49. 6%. New Improved door and window of control room can reduce noise dose to 69. 65% solely.

The purpose of this study was prioritizing the noise control methods using Analytic Hierarchy Process (AHP) technique in Hamadan glass industry. This is a cross-sectional – descriptive - analytical study. According to a survey of experts by questionnaire and Delphi method four criteria were selected including cost, efficiency, executive capability and not to interfere in the process and eleven alternatives for control options. Prioritizing of the items was conducted based on the study criteria as well as the importance ranking determined in this study. The results showed all that consistently Ratios were less than 10 % and compatibility of answers has been confirmed. According to expert’s views, the criteria of executive capability (0.277) and using the barrier between the two main sections (0.111) have achieved the highest priority among the criteria and control methods, respectively. In this study a pattern of decision-making structure was introduced based on Analytic Hierarchy Process for determining the method noise control. This method can improve the decision making process and prioritizing noise control methods as an efficient and effective approach.