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In reviewing IMIS data, note that the exposure levels are not necessarily typical of all worksites and occupations within an industry. Typically, OSHA identified those jobs as having some potential for noise exposure. A number of epidemiological studies have investigated the noise-solvent relationship in humans. Overall, the evidence strongly suggests that combined exposure to noise and organic solvents can have interactive effects either additive or synergistic , in which solvents exacerbate noise-induced impairments even though the noise intensity is below the permissible limit value. In addition to the synergistic effects with solvents, noise may also have additive, potentiating, or synergistic ototoxicity with asphyxiants such as carbon monoxide and metals such as lead.

See Appendix D for additional information and additional sources of information on this topic. Workplace noise exposure is widespread. Although this time span covers many years, the recent decade is well represented: 58, 27 of the personal noise exposure levels in IMIS were measured in or later. These tables also present the median noise levels and the percentage of noise measurements over either the action level AL , 85 dBA, or the permissible exposure limit PEL , 90 dBA 2.

In addition, 47 of the samples taken in the construction industry exceeded the PEL. In addition to median decibels and percent over the PEL, Table II-5 shows the distribution of manufacturing industry dosimetry measurements at the PEL and higher by decibel level. Noise is a potential hazard for most jobs that involve abrasive or high-power machinery, impact of rapidly moving parts product or machinery , or power tools.

According to IMIS noise measurements, workers in certain occupations within specific industries are exposed to excessive noise more frequently than others. While many jobs have noise exposure, historically, some of the occupations with the most extreme exposures listed by Standard Industrial Classification, or SIC have included:.

Source: Adapted from Seixas and Neitzel, This effort to reduce occupational noise hazards was not far-reaching but was a first attempt to regulate noise hazards. Even though noise energy exposure doubles every 3 dB, OSHA thought it important to account for the time during the workday that a worker was not exposed to noise hazards. At the time, using a 5-dB exchange rate was viewed as a sufficient way to account for this.

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In , OSHA published a proposed occupational noise standard, which included a requirement for employers to provide a hearing conservation program for workers exposed to an 8-hour TWA of 85 dBA or more. This provision was adopted as part of the amendments of and While OSHA provided requirements for hearing conservation programs in general industry, the construction industry standard remained less specific in that regard. More recently, in the recordkeeping standard 29 CFR Part , OSHA clarified the criteria for reporting cases involving occupational hearing loss.

In , the U. Environmental Protection Agency EPA developed labeling requirements for hearing protectors, which required hearing protector manufacturers to measure the ability of their products to reduce noise exposure--called the noise reduction rating NRR. OSHA adopted the NRR but later recognized that the NRR listed on hearing protectors often did not reflect the actual level of protection, which likely was lower than indicated on the label because most workers were not provided with fit-testing, and donning methods in a controlled laboratory setting were not representative of the donning methods that workers used in the field.

EPA is considering options for updating this rule. In special cases, noise exposure originates from noise-generating headsets.


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See Appendix F for a discussion of the techniques used to evaluate the noise exposure levels of these workers. General Industry: 29 CFR The General Industry standard establishes permissible noise exposures, requires the use of engineering and administrative controls, and sets out the requirements of a hearing conservation program.


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Paragraphs c through n of the General Industry standard do not apply to the oil and gas well-drilling and servicing operations; however, paragraphs a and b do apply. The general industry noise standard contains two noise exposure limit tables. Each table serves a different purpose:. The requirements for permissible noise exposures and controls under the Construction standard are the same as those under the general industry standard Continuing effective hearing conservation programs are required in all cases where the sound levels exceed the values shown in Table D-2 Agricultural Worksites: Although there is no standard for occupational noise exposure in agriculture, the evaluation and control methods discussed in this chapter are still valid.

Maritime Worksites: Marine terminals and longshoring operations fall under the requirements of the general industry noise standard; therefore, employers in such operations must meet the elements of the general industry Hearing Conservation Amendment, 29 CFR Noise controls should minimize or eliminate sources of noise; prevent the propagation, amplification, and reverberation of noise; and protect workers from excessive noise exposure. Ideally, the use of engineering controls should reduce noise exposure to the point where the risk to hearing is significantly reduced or eliminated.

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Engineering and administrative controls are essential to an effective hearing loss prevention program. They are technologically feasible for most noise sources, but their economic feasibility must be determined on an individual basis. In some instances the application of a relatively simple noise-control solution reduces the hazard to the extent that the other elements of the program, such as audiometric testing and the use of hearing protection devices, are no longer necessary. In other cases, the noise reduction process may be more complex and must be accomplished in stages over a period of time.

Even so, with each reduction of a few decibels, the risk of hearing loss is reduced, communication is improved, and noise-related annoyance is reduced. The first step in noise control is to identify the noise sources and their relative importance. This can be difficult in an industrial setting with many noise sources. It can be accomplished through several methods used together: obtain a frequency spectrum from an octave band analyzer, turn various components in the factory on and off or use temporary mufflers or enclosures to isolate noise sources, and probe areas close to equipment with a sound level meter to pinpoint areas where sound is dominant.

These measures will aid in identifying the sound sources that affect workers the most and should be prioritized when implementing noise controls. Once the noise sources have been identified, it is possible to proceed in choosing an engineering control, administrative control, or a form of personal protective equipment to reduce the noise level if noise exposure is too high Driscoll, Principles of Noise Control. The hierarchy of controls for noise can be summarized as: 1 prevent or contain the escape of the hazardous workplace agent at its source engineering controls , 2 control exposure by changing work schedules to reduce the amount of time any one worker spends in the hazard area administrative controls , and 3 control the exposure with barriers between the worker and the hazard personal protective equipment.

This hierarchy highlights the principle that the best prevention strategy is to eliminate exposure to hazards that can lead to hearing loss. Corporations that have started buy-quiet programs are moving toward workplaces where no harmful noise will exist. Many companies are automating equipment or setting up procedures that can be managed by workers from a quiet control room free from harmful noise.

When it is not possible to eliminate the noise hazard or relocate the worker to a safe area, the worker must be protected with personal protective equipment. The rest of this section, until the discussion of administrative controls, presents information adapted from material developed under contract for the Noise eTool by Dennis Driscoll in Much industrial noise can be controlled through simple solutions.

It is important, however, that all individuals administering abatement projects have a good understanding of the principles of noise control and proper use of acoustical materials. Reducing excessive equipment noise can be accomplished by treating the source, the sound transmission path, the receiver, or any combination of these options. Descriptions of these control measures follow.

The best long-term solution to noise control is to treat the root cause of the noise problem. For source treatment to be effective, however, a comprehensive noise-control survey usually needs to be conducted to clearly identify the source and determine its relative contribution to the area noise level and worker noise exposure. At least four methods exist for treating the source: modification, retrofit, substitution, and relocation.

For the most part, industrial noise is caused by mechanical impacts, high-velocity fluid flow, high-velocity air flow, vibrating surface areas of a machine, and vibrations of the product being manufactured. To reduce noise caused by mechanical impacts, the modifications outlined below should be considered. For any of these options to be practical, however, they must not adversely affect production:. High-velocity fluid flow can often create excessive noise as the transported medium passes through control valves or simply passes through the piping.

A comprehensive acoustical survey can isolate the actual noise source so that the appropriate noise-control measures can be identified. When deemed practical, some effective modifications for high-velocity fluid-flow noise include:. One of the most common noise sources within manufacturing equipment is pneumatic- or compressed-air-driven devices such as air valves, cylinders, and solenoid valves.

High-velocity air is also a major contributor to worker noise exposure where hand-held air wands or guns are used to remove debris from work areas. Finally, compressed air nozzles are often used to eject parts from a machine or conveyor line. All these forms of pneumatic systems generate undesirable noise as the high-velocity air mixes with the atmospheric air, creating excessive turbulence and particle separation. It is important to note that the intensity of sound is proportional to the air flow velocity raised to the 8th power. Therefore, as a source modification, it is recommended that the air-pressure setting for all pneumatic devices be reduced or optimized to as low a value as practical.

As a general guideline, the sound level can be reduced by approximately 6 dBA for each 30 reduction in air velocity. Additional noise controls for high-velocity air are presented in the retrofit and relocation sections below. Machine casings or panels can be a source of noise when sufficient vibratory energy is transferred into the metal structure and the panel is an efficient radiator of sound.

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Typically, machine casings or large metal surface areas have the potential to radiate sound when at least one dimension of the panel is longer than one-quarter of the sound's wavelength. Conducting a thorough noise-control survey will help in identifying the source of vibration and in determining the existence of any surface-radiated sound. When a machine casing or panel is a primary noise source, the most effective modification is to reduce its radiation efficiency.

The following noise-control measures should be considered:. A variety of commercially available acoustical products and applications can be applied on or relatively close to noise sources to minimize noise. The Noise and Vibration Control Product Manufacturer Guide should be consulted for a partial list of the manufacturers of these products and applications. Vibration damping materials are an effective retrofit for controlling resonant tones radiated by vibrating metal panels or surface areas. In addition, this application can minimize the transfer of high-frequency sound energy through a panel.

The two basic damping applications are free-layer and constrained-layer damping. Free-layer damping, also known as extensional damping, consists of attaching an energy-dissipating material on one or both sides of a relatively thin metal panel.

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For thicker machine casings or structures, the best application is constrained-layer damping, which consists of damping material bonded to the metal surface covered by an outer metal constraining layer, forming a laminated construction. Each application can provide up to 30 dB of noise reduction. It is important to note that the noise reduction capabilities of the damping application are essentially equal, regardless of which side it is applied to on a panel or structure.

Also, for practical purposes, it is not necessary to cover of a panel to achieve a significant noise reduction. For example, 50 coverage of a surface area will provide a noise reduction that is roughly 3 dB less than coverage. In other words, assuming that coverage results in 26 dB of attenuation, 50 coverage would provide approximately 23 dB of reduction, 25 coverage would produce a dB decrease, and so on.

Next, for free-layer damping treatments, it is recommended that the application material be at least as thick as the panel or base layer to which it is applied. For constrained-layer damping, the damping material again should be the same thickness as the panel; however, the outer metal constraining layer may be half the thickness of the base layer.

Finally, just because a surface area vibrates, it is not safe to assume it is radiating significant noise. If fact, probably less than 5 of all vibrating panels produce sufficient airborne noise to be of concern in an occupational setting. For damping materials to be successful, at a minimum, the two following conditions must be satisfied determine by a comprehensive noise-control survey :. When selecting the right type of damping material, it is recommended that the person making the decision refer to the expertise of the product manufacturer or their designated representative s.

Typically, the supplier will need to obtain specific information from the buyer, such as the temperature and size of the surface area to be treated and the substrate thickness. The supplier will then use the input data to select the most effective product for the particular application.

The vendor can also provide the buyer with estimates of noise reduction and costs for procuring the material. Most industrial equipment vibrates to some extent. As machines operate, they produce either harmonic forces associated with unbalanced rotating components or impulsive forces attributed to impacts such as punch presses, forging hammers, and shearing actions.