Industrial Noise Control and Acoustics (Dekker Mechanical Engineering)

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It can lead to hearing loss, mental stress and irritation. The industrial limit of sound in the industries must be 75 dB according to the World Health Organization [ 6 ]. Noises are generated by operational activities of a diversity of machine tools and equipment. Noise nuisance from wood processing is generated from circular saws, planers, routers and other equipment.

In many countries, noise-induced hearing loss is one of the most prevalent occupational diseases. The industry provides a series of noise problems which are not always easily resolved, due to the different types of noise [ 7 ]. Noise levels generated by sawmill saws in operation vary from 80dB up to dB. Moreover, not only can the cutting noise be extreme, there is also the additional factor that, even when idling, saws can produce noise levels up to 95dB.

The main sources of noise associated with the sawmill operation include: Transportation, unloading and loading of logs; Chain saw use for off-cuts, and damaged or out of specification timber; Milling and planing operations including headrig, edger, resaw and planer ; Wood By-Product Chipper; Desticking, stacking, and loading for dispatch of boards; Fans in the reconditioner tonal noise ; Heat plant boiler forced air and induced draft fans ; Chipping; Reversing alarms on vehicles; and Kiln associated noises such as fans [ 8 ].

Also, the effect on workers could be injurious if allowable noise exposure level is exceeded Table 2. Table 1. Factors Affecting Machinery Noise Emissions. Table 2. Allowable Noise Exposures Limits. Source: OSHA [ 10 ]. Woodworking Machines. The woodworking industry has experienced noise level increase as a result of modern, higher speed, and more compact machines [ 11 ]. The basic noise elements in woodworking machines are cutter heads and circular saws.

Equivalent sound pressure levels LAeq in the furniture manufacturing industry can reach dB. Three basic noise sources associated with woodworking machinery include:. Structure vibration and noise radiation of the work piece or cutting tool such as a circular saw blade and machine frame, especially at the mechanical resonance frequencies. Aerodynamic noise caused by turbulence, generated by tool rotation and the workplace in the air flow field. Fan dust and chip removal air carrying systems.

Band re-saws are widely used in the wood industry. Without any measures to reduce noise at source, they can produce noise levels of over 85 dB typically dB at the operator position. The Band saw noise is usually from the machine bearings, the cutting teeth, etc. When a band re-saw is idling, vibration of the blade is usually the main source of noise.

When cutting, high vibration levels in the blade caused by sawdust trapped between the pulleys and blade, and vibration of the timber being sawn are the main noise sources. According to Tak et al. The condition of the saw blade, and the smoothness of the pulley faces, has been found to affect idling noise levels by as much as 10dB. Poorly adjusted saw guides can push noise levels up by 3 dB and using an unnecessarily heavy-gauge sawblade produces a wider kerf cut can also produce more noise.

A new 19 gauge mm blade running on mm diameter pulleys has been found to produce levels 5 dB higher than a new 20 gauge blade on the same machine. The three basic sources involved in the noise generated by electric motors include;. The cooling fan is usually the dominant noise source. Discrete frequency components caused by the blade passing frequencies of the fan. Thus careful attention should be given to the vibration isolation, mounting and maintenance. Portable machine tools are also sources of noise in the wood industries and noise level varies from one machine to the other Table 3.

Table 3. Source: OSHA, [ 10 ]. Effects of Industrial Noise Pollution.

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Health Issues. Noise is an important factor that affects work environment. It has direct and indirect effects on workers' health and efficiency. Direct effects include hearing impairments that may lead to complete hearing loss [ 13 ], while indirect effects are backache, nervousness, annoyance, nausea, carelessness, and increased risk of accidents [ 14 , 15 ]. Several field of investigations for industry workers have established the strong association between high levels of exposure to noise and the risk of occupational accidents and injuries [ 14 , 16 - 18 ].

The World Health Organization WHO has highlighted several categories of adverse health and social effects of noise pollution, ranging from hearing impairment, interference with spoken communication, cardiovascular disturbances, mental health problems, impaired cognition, negative social behaviours and sleep disturbances [ 19 ]. The following are some of the major effects of noise on health:.

Hearing Impairment. Noise-induced hearing loss, which occurs due to chronic exposure to high level of noise is caused by the damage of the hair cells of the cochlea in the inner ear [ 20 ]. It has been found that exposure to continuous noise of more than 85 to 90 dB, particularly over a life time in industrial settings, can lead to hearing impairment and ultimately hearing loss [ 21 ].


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Tharr, 22 in a survey in United States sawmill, revealed that Sleep Disturbances. Sleep disturbances is considered as the most deleterious non-auditory effect because of its impact on quality of life and daytime performance, people who have sleep problems are prone to other health problems. Experimental studies demonstrated that both sleep restriction and poor quality sleep affect glucose metabolism by reducing glucose tolerance and insulin sensitivity.

Sleep restrictions has also been shown to increase blood pressure and affect immune processes [ 23 ]. Cardio-Metabolic Disorders. Short-term laboratory studies carried out on humans have shown that exposure to noise affects the sympathetic and endocrine systems, resulting in acute unspecific physiological responses e. There are evidences that implicate noise in higher incidence of diabetes, hypertension and stoke, as well mortality from coronary heart disease [ 23 ].

Many occupational studies have suggested that individuals chronically exposed to continuous noise at levels of at least 85dB have higher blood pressure than those not exposed to noise [ 25 - 26 ]. This is also similar to findings in a study [ 27 ] that hypertension was associated with duration of exposure among continuously noise exposed workers to high levels of occupational noise 98 to dB.

Concentration and Performance Impairment. It has been noted that concentration on task and reading are affected in noisy work places, chronic exposures to noise has been implicated in problems with cognitive function and comprehension [ 28 ]. Noise is a psycho-social stressor that can affect physiological functioning [ 29 ]. People working in noisy environments have been noted to have higher stress levels than those exposed to less noise [ 30 ], and it appears that the longer the exposure, the greater the effects [ 31 ].

Noise Control in the Wood Processing Industry. Noise control is a set of strategies aimed at reducing noise pollution or impact, whether outdoors or indoors. The first step generally involves an assessment of any existing or planned noise sources and their relative contribution to ambient levels.

This facilitates the establishment of target noise levels for the particular source and where necessary the degree of noise attenuation can be estimated. Having established the required reduction, the next stage is the application of noise control engineering principles. However, effective planning and management frequently involves the use of common sense and good practice as opposed to high tech engineering solutions Figures 1 and 2.

Source: Hearing Conservation Programme [ 32 ]. Figure 1. Noise Management Programme. Hearing Conservation Programme [ 31 ]. Figure 2.

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Hearing Conservation Programme. Noise control techniques according to Benz and Colin, [ 33 ] include;.


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  • Sound insulation: prevent the transmission of noise by the introduction of a mass barrier. Common materials have high-density properties such as brick, thick glass, concrete, metal etc. Common sound absorption materials include decoupled lead-based tiles, open cell foams and fiberglass. Vibration damping: applicable for large vibrating surfaces.

    The damping mechanism works by extracting the vibration energy from the thin sheet and dissipating it as heat. A common material is sound deadened steel. Vibration isolation: prevents transmission of vibration energy from a source to a receiver by introducing a flexible element or a physical break. Common vibration isolators are springs, rubber mounts, cork etc. Noise and Vibration Reducing Techniques.

    Depending on the source, noise can be reduced in several ways according to Vaishali, et al. Buying quiet machinery and equipment or the use a machine that emits a low noise level. Maintaining machinery and equipment routinely. Reducing machinery and equipment vibration. Isolating the noise source in an insulated room or enclosure. Placing a barrier between the noise source and the employee. Isolating the employee from the source in an insulated booth or room. Modification of equipment and technologies. Decoupling technical equipment of the physical medium of work. Treat the room: When noise is reverberating around a room, the only way to reduce it is through absorption.

    Panels and baffles absorb a high percentage of sound energy and dissipate it as kinetic heat energy. Maximum noise reduction potential is from 4 to 6 decibels, resulting in a noise level reduction of 20 to 30 percent. Treat the wall nearest the noise source: Another option is to cover the wall closest to the noise source with acoustic foam panels. Maximum sound reduction will vary from 2 to 6 decibels. This solution reduces noise levels from 10 to 30 percent at low cost. Build a barrier or shield: Barriers can be used to create "instant walls" that isolate noisy machinery.

    Composite combines the sound absorption of foam and the containment of barrier material to isolate noise effectively Fig. The most effective way to prevent single-source noise from reverberating around the room is to create an acoustic barrier around the machine to physically block the sound energy. Figure 3. Build a barrier or shield. Build an enclosure: An acoustic enclosure around the machine also contains noise at the source. The Curtain Enclosure System provides maximum noise reduction of at least 20 to 30 decibel.

    At most basic level, correction of room acoustics involves using sound-absorbing materials on three non-parallel surfaces Fig. This technique suppresses unwanted reverberation by keeping sound waves from bouncing back and forth between parallel surfaces.

    Industrial Noise Control and Acoustics

    It also reduces the overall noise level by preventing noise from building up [ 37 ]. In , the flight paths in all of Scandinavia were changed as the new Oslo-Gardermoen Airport was opened. These new paths were straighter, reducing fuel use, and disturbing fewer people, however, vociferous protests came from people near the new paths who had not been disturbed before, and they took legal action NIMBY effect.

    Architectural acoustics noise control practices include interior sound reverberation reduction, inter-room noise transfer mitigation, and exterior building skin augmentation. In the case of construction of new or remodeled apartments , condominiums , hospitals , and hotels , many states and cities have stringent building codes with requirements of acoustical analysis, in order to protect building occupants. With regard to exterior noise, the codes usually require measurement of the exterior acoustic environment in order to determine the performance standard required for exterior building skin design.

    The architect can work with the acoustical scientist to arrive at the best cost-effective means of creating a quiet interior normally 45 dBA. The most important elements of design of the building skin are usually: glazing glass thickness, double pane design etc. Regarding sound generated inside the building, there are two principal types of transmission. Firstly, airborne sound travels through walls or floor and ceiling assemblies and can emanate from either human activities in adjacent living spaces or from mechanical noise within the building systems.

    Human activities might include voice, noise from amplified sound systems, or animal noise. Mechanical systems are elevator systems, boilers , refrigeration or air conditioning systems, generators and trash compactors. Aerodynamic sources include fans, pneumatics, and combustion.

    Noise control for aerodynamic sources include quiet air nozzles , pneumatic silencers and quiet fan technology. Since many mechanical sounds are inherently loud, the principal design element is to require the wall or ceiling assembly to meet certain performance standards, [18] typically Sound transmission class of 50 , which allows considerable attenuation of the sound level reaching occupants.

    This effect arises not from airborne transmission , but rather from the transmission of sound through the building itself. The most common perception of IIC noise is from the footfall of occupants in living spaces above. Low-frequency noise is transferred easily through the ground and buildings. This type of noise is more difficult to abate, but consideration must be given to isolating the floor assembly above or hanging the lower ceiling on resilient channel. Both of the transmission effects noted above may emanate either from building occupants or from building mechanical systems such as elevators, plumbing systems or heating, ventilating and air conditioning units.

    In some cases, it is merely necessary to specify the best available quieting technology in selecting such building hardware. In other cases, shock mounting of systems to control vibration may be in order.

    Industrial Noise Control and Acoustics : Randall F. Barron :

    In the case of plumbing systems, there are specific protocols developed, especially for water supply lines, to create isolation clamping of pipes within building walls. In the case of central air systems, it is important to baffle any ducts that could transmit sound between different building areas. Designing special-purpose rooms has more exotic challenges, since these rooms may have requirements for unusual features such as concert performance, sound studio recording , lecture halls.

    In these cases reverberation and reflection must be analyzed in order to not only quiet the rooms, but to prevent echo effects from occurring. In these situations special sound baffles and sound absorptive lining materials may be specified to dampen unwanted effects. Acoustical wall and ceiling panels are a common commercial and residential solution for noise control in already-constructed buildings. Acoustic panels may be constructed of a variety of materials, though commercial acoustic applications will frequently be composed of fiberglass or mineral wool-based acoustic substrates.

    For example, Mineral fiberboard is a commonly used acoustical substrate, and commercial thermal insulations, such as those used in the insulation of boiler tanks, are frequently repurposed for noise-controlling acoustic use based on their effectiveness at minimizing reverberations. The ideal acoustical panels are those without a face or finish material that could interfere with the performance of the acoustical infill, but aesthetic and safety concerns typically lead to fabric coverings or other finishing materials to minimize impedance.

    Panel finishings are occasionally made of a porous configuration of wood or metal. The effectiveness of post-construction acoustic treatment is limited by the about of space able to be allocated to acoustic treatment, and so on-site acoustical wall panels are frequently made to conform to the shape of the preexisting space. This is done by "framing" the perimeter track into shape, infilling the acoustical substrate and then stretching and tucking the fabric into the perimeter frame system.

    On-site wall panels can be constructed to work around door frames, baseboard, or any other intrusion. Large panels generally greater than 50 feet can be created on walls and ceilings with this method. Industrial noise is traditionally associated with manufacturing settings where industrial machinery produces intense sound levels, [19] often upwards of 85 decibels. While this circumstance is the most dramatic, there are many other work environments where sound levels may lie in the range of 70 to 75 decibels, entirely composed of office equipment, music, public address systems, and even exterior noise intrusion.

    Either type of environment may result in noise health effects if the sound intensity and exposure time is too great. In the case of industrial equipment, the most common techniques for noise protection of workers consist of shock mounting source equipment, creation of acrylic glass or other solid barriers, and provision of ear protection equipment. In certain cases the machinery itself can be re-designed to operate in a manner less prone to produce grating, grinding, frictional, or other motions that induce sound emissions.

    In recent years, Buy Quiet programs and initiatives have arisen in an effort to combat occupational noise exposures. These programs promote the purchase of quieter tools and equipment and encourage manufacturers to design quieter equipment. In the case of more conventional office environments, the techniques in architectural acoustics discussed above may apply.

    Other solutions may involve researching the quietest models of office equipment, particularly printers and photocopy machines. Impact printers and other equipment were often fitted with "acoustic hoods", enclosures to reduce emitted noise. One source of annoying, if not loud, sound level emissions are lighting fixtures notably older fluorescent globes.

    These fixtures can be retrofitted or analyzed to see whether over-illumination is present, a common office environment issue.

    Acoustics and Industrial Noise Control - 16/05/2017 2nd Half

    If over-illumination is occurring, de-lamping or reduced light bank usage may apply. Photographers can quieten noisy still cameras on a film set using sound blimps. Reductions in cost of technology have allowed noise control technology to be used not only in performance facilities and recording studios, but also in noise-sensitive small businesses such as restaurants.

    Using a combination of sound absorption materials, arrays of microphones and speakers, and a digital processor, a restaurant operator can use a tablet computer to selectively control noise levels at different places in the restaurant: the microphone arrays pick up sound and send it to the digital processor, which controls the speakers to output sound signals on command. Post-construction residential acoustic treatment throughout the 20th century was only commonly the practice of music-listening enthusiasts.

    However, developments in home recording technology and fidelity have led to a drastic increase in the spread and popularity of residential acoustic treatment in the pursuit of home recording fidelity and accuracy. A large secondary market of homemade and home use acoustic panels, bass trap, and similar constructed products has developed resulting from this demand, with many small companies and individuals wrapping industrial and commercial-grade insulations in fabric for use in home recording studios, theatre rooms, and music practice spaces.

    Communities may use zoning codes to isolate noisy urban activities from areas that should be protected from such unhealthy exposures and to establish noise standards in areas that may not be conducive to such isolation strategies. Because low-income neighborhoods are often at greater risk of noise pollution, the establishment of such zoning codes is often an environmental justice issue. Noise is generally one consideration in an environmental impact statement , if applicable such as transportation system construction.

    From Wikipedia, the free encyclopedia. See also: Acoustic quieting. Main article: Noise barrier. Main article: Aircraft noise. Main article: Architectural acoustics. Main article: Industrial noise. Federal Register. Part Occupational Noise Exposure. Department of Defense. Instruction DoD Hearing Conservation Program.