Chapter x. Industrial Noise Control. 1. Summary

Transcription

1 Chapter x Industrial Noise Control 1. Summary. 2. Introduction. 3. Hierarchy of Control. 4. New Workplaces or New Equipment. Buy Quiet Company Policy. Case Studies. Buy Quiet Manufacturing Standards 5. New Workplaces Layout. Case Studies. 6. Existing Workplaces. 7. Elimination. Case Studies. 8. Substitution. 9. Isolation. 10. Tests and Exercises. 11. References. 1. Summary Noise is one of the most common occupational hazards and results in many workers being affected by noise induced hearing loss. As with any other occupational hazard, the risk due to exposure to high noise levels should be reduced by applying the following hierarchy of control: Elimination Substitution Isolation Engineering control at source and in the transmission path This chapter covers the basics of the noise reduction methods, with more emphasis on physical means of noise reduction rather than administrative controls or protective hearing devices. Industrial Noise Control 1

2 2. Introduction. This lecture describes basic principles of noise control and explains how to apply the hierarchy of control of exposure to high noise levels. It outlines the methods, equipment and materials for engineering control of noise and gives many examples that illustrate their use. 3. Hierarchy of Control. Noise is one of the most common health hazards found in the workplace. Exposure to excessive noise can cause noise induced hearing loss, which has been the most prevalent occupational disease for the past decades. Many countries have introduced legal obligations and guidelines requiring employers to protect their employees and others from exposure to excessive noise. These legal aspects set up the desired steps of a comprehensive prevention management system to achieve reduction in risk due to exposure to noise. The hierarchy of control requires that risk is reduced by noise control measures in the first instance and then, if the achieved reduction is not sufficient, by administrative controls and personal hearing protectors. Noise control measures are physical means that reduce noise levels and can be divided into the following categories: Elimination Substitution Isolation Engineering Control at the source and in the transmission path. Administrative control is any arrangement that significantly reduces the worker's exposure time to noise hazards, for example, job rotation, production scheduling, job redesign and introducing appropriate training on noise. The next step in a prevention management system is the provision of personal protective equipment such as earplugs or earmuffs. It should be treated as the last line of defence against noise when noise and administrative control measures are unable to keep the noise levels below the criteria set for the workplace. 2 The Almond Tree Effect

3 Health surveillance also plays an important part because it helps to identify hearing problems so they can be prevented from developing further. All these steps should be considered when developing a noise control program for the workplace. There will be some differences in the categories of noise control measures selected depending on whether the workplace is already established or a new one is under consideration. 4. New Workplaces or New Equipment. It is very important to incorporate noise aspects in the early design process for new workplaces, so the decisions made about what equipment to purchase and how to layout this equipment lead to the quietest practicable workplace. 4.1 "Buy Quiet" Is the Most Effective Means of Noise Control "Buy quiet" is the most effective means of noise control because it prevents sources of noise from entering the workplace. So the first step in the noise control program for a new workplace should be to establish the acceptable noise criteria for new equipment and include them in the purchase specifications. Plate x: Example of possible noise control measures Industrial Noise Control 3

4 4.2 Company Policy Requires Equipment with Lowest Practicable Noise Emission Levels LAeq,8h (eight-hour equivalent continuous A- weighted sound pressure level in db(a) referenced to 20 micropascals) means that steady noise level which would, in the course of an eight-hour period, cause the same A- weighted sound energy as that due to the actual noise over an actual working day. LAeq,8h is determined in accordance with Australian Standard AS/NZS Occupational Noise Management. 4.3 Case Study. Baulderstone Clough Joint Venture is a construction company involved in the construction of an underground road-tunnel citybypass in Perth, Western Australia. Their noise policy requires the company to use equipment with the lowest practicable noise emission levels. This requirement applies to both purchasing and hiring policies, with the aim of achieving employee daily noise exposures of or below an LAeq,8h of 85 db(a). The policy was exercised during the purchasing of new excavators. Several machines were taken into consideration and finally one of the quietest types available was chosen. The purchased excavators are Yanmar Diesel Vio50 with noise levels at 7 m distance of 65 db(a). When purchasing a new portable generator, the company researched what was available on the market and finally decided to buy a 5 KVa FNG Peacekeeper set with a noise level at 7 m distance of 64 db(a). 4.4 Case Study. Macmahon Contractors (WA) Pty Ltd is a large construction company involved mainly in mining and sewage operations. The company is working towards a 'buy quiet' policy that requires all future equipment bought for construction sites to have the lowest practicable noise emission levels. For example, all earth moving equipment is fitted with operator cabins that have noise levels of 75 db(a) or below. Another example is that all future generators and compressors bought will have noise levels below 85 db(a) at 1 m. Plate x: Yanmar Vio50 excavator with a rock breaker attachment Plate x: Earth Moving equipment fitted with acoustically treated cabin 4 The Almond Tree Effect

5 When purchasing new pneumatic hand tools for their workshop, Macmahon requires them to be fitted with exhaust silencers, as these reduce noise levels of an idling tool by around 10 db(a). A silenced pencil grinder emits a noise level of 85 db(a) at 0.5 m away when idling, whereas an unsilenced version has a noise level of 95 db(a) under the same conditions. 4.3 Manufacturers Follow Standards on Design of Low Noise Equipment To help designers, various countries have developed specific standards dealing with noise specifications for new machinery. The European Union (EU) has produced directives addressing groups of machinery which cover noise control as an essential part of machine safety. The basic aim of these directives is that for a machine to be sold within the EU, it must satisfy the essential requirements regarding noise. In the United States, the relevant standard is ANSI S12.16: Guidelines for the Specification of Noise of New Machinery (1992). The standard contains guidelines on how to set up internal company noise specifications and gives directions for obtaining sound level data from machinery manufacturers. In Australia the law requires designers, manufacturers, producers, suppliers, importers and installers of plant to be used in workplaces to provide information about any hazard associated with the plant. These standards and directives have already led to manufacturers placing greater emphasis on the design of low noise equipment. Plate x: Typical generator set used by Macmahon on their construction sites Plate x: Typical generator set used by Macmahon on their construction sites The buy quiet process. Industrial Noise Control 5

6 5. New Workplaces - Layout. Another aspect of noise control is the layout of the purchased machinery. Evaluating the location of machinery on paper is much cheaper and easier than physically moving the equipment later. Simple rules to follow are: keep machines, processes and work areas of approximately equal noise levels together; and separate noisy and quiet areas by buffer zones with intermediate noise levels. 5.1 Company Incorporates Layout Principles in New Workshop Design John's Engineering and Cranes is a heavy engineering workshop manufacturing and repairing mining equipment. The premises consist of fitting, machining and fabrication sections and a spray booth. The fabrication section is further divided into preparation, cutting and boiler making areas. In their previous building, the boiler making section, which is the noisiest, was placed in the middle of the workshop, thus affecting other areas that didn't generate high noise levels. About a year ago the company built new premises. Before building the new workshop they decided to address the noise problems at the planning stage. The decision was made to use all the space available to separate noisy sections from quiet ones and provide some buffer zones between. In the new premises, the office building separates the fabrication section from the fitting and machining section. In the fabrication section, the noisy area - boiler making - is placed away from the rest. The spray booth is also separated and situated in an adjacent building, away from noise. The administration building is separated from the workshop building. The lunchroom, workshop offices and stores are specially designed, fully enclosed with well sealed doors and windows, to reduce background noise levels as far as possible. In the new workshop, noise levels are reduced for operators in the spray booth, and in the fitting Plate x: Boiler making section situated away from other sections. Plate x: Spray booth situated in a separated building. Plate x: Administration building (left) separated from the workshop (to the right). 6 The Almond Tree Effect

7 /machining and profile cutting areas, so their daily noise exposures are at or below an LAeq,8h of 85 db(a). 6. Existing Workplaces. A noise control program in established workplaces should encompass identification, assessment and ranking of the noise sources. Once the noise sources have been identified and assessed, a decision can be made on the best ways to control them, in accordance with the hierarchy of control. The hierarchy of control can be divided into: Elimination Substitution Isolation Engineering Control Noise is a by-product produced during a transfer of energy, when some of the energy is not directly converted into useful work or into waste heat. The ways to control noise are: reduce the amount of sound energy released; divert the flow of the energy away from the receiver; or protect the receiver from this energy. In other words, engineering noise controls are concerned with the noise source, the noise transmission path, or the receiver. The rest of the lecture details the hierarchy of control and ways to control noise. Plate x: Quiet lunchroom. Plate x: Fitting/machining placed away from noisy sections. Industrial Noise Control 7

8 7. Elimination. Elimination is the first step that should be considered when addressing exposure to noise at a workplace. After a critical examination of all existing processes it may be possible to eliminate the exposure entirely by changing one or more operations. For example, high quality welding eliminates or significantly reduces the need for grinding. Companies Adopt Procedures to Eliminate Extremely Noisy Processes 7.1. Case Study. John's Engineering and Cranes changed their metal cutting method to a low noise one, using an oxy-acetylene profile cutter. Oxy-acetylene cutting gives a cleaner finish and helps to eliminate any need for further finishing with noisy angle grinders. The use of the oxyacetylene profile cutter minimises the use of arcair gouging, another very noisy process. Arc-air gouging is now used only occasionally for cutting large pieces when oxy-acetylene cannot be utilised because of the amount of heat produced Case Study. Macmahon Contractors eliminated the use of hammers when installing or removing bearings. Before, bearings were knocked into position with hammers. Since the change, the bearings are either heated or cooled which allows them to easily slip into position. A pie warmer is used for heating the bearings and liquid nitrogen for cooling the bearings. Plate x: Hammering bearings into their position - a noisy process. Plate x: Bearings cooled in liquid nitrogen fit easily and silently into casing. Oxy-acetylene cutting produces a cleaner finish and eliminates need for grinding Plate x: Heating bearings in a pie warmer to fit them in their place without hammering. 8 The Almond Tree Effect

9 8. Substitution. 8.1 When Purchasing "Buy Quiet" In many areas it is possible to substitute quieter processes for noisy ones. A properly designed purchasing policy that incorporates the "buy quiet" concept is often the best and most cost-effective way of controlling noise exposure. It also minimises the need for noise control later, which often can be very costly. A decision on the maximum acceptable noise emission levels from new equipment should be made before purchasing. This decision should take into account the organisation's noise policy and the existing noise levels in the area where equipment is to be placed. When purchasing new plant: specify acceptable maximum noise levels during the tendering process, or obtain noise emission data before purchasing to choose the quietest available and affordable plant. Noise emission values obtained from various suppliers can be compared with each other, and can be used for prediction of the likely noise levels in the workplace. 8.2 Examples of Alternative Low-Noise Processes The following table from AS/NZS , 1998 lists a few examples of possible substitutions for high-noise processes. Key Point: "Buy Quiet" is the most effective way of controlling noise exposure. Examples of alternative low-noise processes. High-Noise Processes Low-Noise Processes Percussion riveting Compression and roll riveting Drive by compressed air or Electrical drive internal combustion engine Heading in the die Tapering/full forward extrusion Push cutting Pull cutting Flow drying Radiation drying Plasma oxygen cutting Plasma cutting under water Cutting shock, punching Laser-beam cutting Conventional TIG/TAG welding TIG/TAG shielded arc welding Cutting with saw blade Water-jet cutting Flame-hardening Laser-beam hardening Fastening with rivets Pressure fixing Stroke forming Hydraulic pressing Industrial Noise Control 9

10 Contractors Used Substitution to Reduce Noise Levels 8.3 Case Study. Macmahon Contractors use both 4" and 9" angle grinders. Supervisors and employees are instructed in when each type is best used, as the 4" achieves a reduction in noise level at the operator's position of 6 db(a), from 108 db(a) down to 102 db(a). The company decided to substitute its Makita 2414 cut-off saw with a Flexovit F16 saw, reducing noise levels from 97 db(a) when cutting a 1" hollow tube to 92 db(a) Case Study. Baulderstone Clough Joint Venture, in the early stages of its operation, used an impact sheet pile driver with noise levels of 105 db(a) at 5 m and 96 db(a) at the crane operator's position. This method was soon replaced by a Franki Pile drilling rig emitting noise levels of 95 db(a) at 5 m and 94 db(a) at the operator's position. To further improve the operation and reduce noise levels the company decided to use a bore piling rig, the Bauer BG22. This technique further reduced noise levels to 90 db(a) at 5 m. Additionally the company replaced most of their Honda 9 HP portable generators with low noise Yanmar units, reducing noise levels from 96 to 78 db(a) at 1 m distance. By using middle range instead of large jackhammers the company achieved a reduction in noise levels of about 10 db(a). Plate x: 9" grinder (top) is noisier than 4" one (bottom). Plate x: 9" grinder (top) is noisier than 4" one (bottom). 9. Isolation. Isolation means separating noise sources from people involved in the work or others standing near by. It could mean relocating the noise source or relocating the operators or others to positions away from the noise source. For example, by doubling the distance from the source inside a workshop the noise level decreases by about 2-4 db(a), or in the open the noise level decreases by 6 db(a) Isolating a Compressor from Workers Reduced Noise Levels. By placing a compressor outside a workshop, a significant reduction of the background noise levels in that workshop is achieved. Plate x: Flexovit saw. 10 The Almond Tree Effect

11 Plate x: Portable Yanmar generator Plate x: Middle range Plate x: Bauer BG22 bore pile. Plate x: Compressor placed outside a factory workshop. Industrial Noise Control 11

12 9.2. Operators' Noise Exposure Reduced By Isolating Spray Booth. At John's Engineering and Cranes old premises, a spray booth was situated inside the workshop next to a boiler making/welding section. Operators were exposed to noise levels varying from 83 to 86 db(a) with a possibility of being exposed to LAeq,8h above 85 db(a). Since the relocation, the spray booth is situated in a separate adjacent building, isolated from the main workshop. The operators are currently exposed to noise levels of around 78 db(a), which gives a reduction of 5-8 db(a). Spray booth away from noisy areas. 12 The Almond Tree Effect