Reducing Noise-Related Hazards

Introduction

Decibels are measured on a logarithmic scale which means that a small change in the number of decibels results in a large change in the level of noise employees hear.

With the reduction of even a few decibels, the hazard to hearing is reduced, communication is improved, and noise-related annoyance is reduced.

There are various ways to reduce or eliminate exposure to unwanted noise using the "Hierarchy of Controls." We'll discuss some of these controls in this module.

Use the Hierarchy of Controls to reduce exposure to noise hazards.

The Hierarchy of Control Strategies

Occupational safety and health professionals use the "Hierarchy of Controls" to determine how to implement feasible and effective controls. This approach groups actions by their likely effectiveness in reducing or removing the noise hazard. The first three control strategies attempt to change the source of the hazard to reduce noise levels. The last three strategies do not change the source of the noise, but rather, they try to reduce employee exposure to the noise.

Hazard Controls - These controls change the source of the noise hazard:

1. Elimination - remove the source of the hazard.
2. Substitution - replace the source of the hazard with a quieter source.
3. Engineering - design/redesign equipment to isolate the source of the noise.

Exposure Controls - These controls manage employee exposure to the source of the noise hazard:

4. Warnings - signs, signals, alarms, etc., to increase awareness.
5. Administration - information and training, scheduling, work practices, rules, etc.
6. Personal protective equipment (PPE) - ear plugs and muffs, etc.

The use of these controls should reduce exposure to the point where the risk to hearing is eliminated or at least more manageable. Warnings, Administrative Controls, and PPE are less reliable because they only work when employees use or otherwise comply with the strategies.

Elimination and Substitution

In most cases, the preferred approach is to eliminate the source of hazardous noise. When elimination is not possible, substitution of the loud equipment for quieter equipment may be the next best alternative to protect workers from hazardous noise.

Changing a hard bend to a soft bend in a steam line an reduce noise levels.

Engineering Controls

Engineering controls that can reduce the noise level at the worker's location include: 

• design or modification of equipment, or
• physical changes to the noise source or transmission path.

Simple engineering noise control solutions can reduce the noise hazard to the extent that audiometric testing, a hearing conservation program, and the use of hearing protectors, are not necessary. Examples of inexpensive, effective engineering controls that can be applied include:

• Choosing low-noise tools and machinery (e.g., compressors, grinders, etc.).
• Maintaining and lubricating machinery and equipment (e.g., oil bearings).
• Placing a barrier between the noise source and employee (e.g., sound walls or curtains).
• Enclosing or isolating the noise source.

Selecting Engineering Controls

Assessing the applicability of engineering controls is a sophisticated process.

• First, the noise problem must be thoroughly defined. This necessitates measuring the noise levels and developing complete information on employee noise exposure and the need for noise reduction.
• Next, an approach to engineering control must be developed, requiring the identification of individual noise sources and assessment of their contributions to the overall noise levels.

Employees who work with the equipment on a daily basis will be able to provide valuable guidance. In situations where employees will be working on or around equipment fitted with engineering controls, it is important to explain why the controls should not be modified, removed, or otherwise defeated.

Examples of engineering controls.

Examples of Engineering Controls

For hearing loss prevention purposes, engineering controls are defined as any modification or replacement of equipment, or related physical change at the noise source or along the transmission path (with the exception of hearing protectors) that reduces the noise level at the employee's ear.

Typical engineering controls involve:

1. Reducing noise at the source - providing proper lubrication.
2. Interrupting the noise path - erecting enclosures.
3. Reducing reverberation - installing sound absorption material.
4. Reducing structure-borne vibration - installing vibration mounts.

Warnings

Signs can be used to warn people of potential hazards.

With the release of ANSI Z10-2012, "warnings" have been promoted to their own hierarchy level. Previously they were considered part of administrative controls. Warnings do not prevent exposure to a hazard, but they do provide a visual or audible indicator to warn people of potential danger.

Warnings can be either visual, audible, or both. They may also be tactile. Some examples of warnings are:

• Visual. Signs, labels, tags, and flashing/strobe lights.
• Audible. Alarms, bells, beepers, sirens, announcement system and horns.
• Tactile. Vibration devices or air fans.

For instance, a door could have both a sign warning of a hazard as well as an alarm if opened. Warnings can be effective deterrents, but are not as effective as elimination, substitution, or engineering controls.

Warnings may lose their effectiveness when constantly posted because employees may begin to ignore them.

Administrative Controls

Administrative controls are changes in policies, procedures, rules, and practices that reduce or eliminate worker exposure to noise. Examples include:

Controlling noise exposure through distance can be effective and inexpensive.

• Operating noisy machines during shifts when fewer people are exposed.
• Limiting the amount of time a person spends at a noise source.
• Providing quiet areas where workers can gain relief from hazardous noise sources (e.g., construct a soundproof room where workers' hearing can recover – depending upon their individual noise level and duration of exposure, and time spent in the quiet area).

• Restricting worker presence to a suitable distance away from noisy equipment. Controlling noise exposure through distance is often an effective, yet simple and inexpensive administrative control. This control may be applicable when workers are present but are not actually working with a noise source or equipment. Increasing the distance between the noise source and the worker, reduces their exposure. In open space, for every doubling of the distance between the source of noise and the worker, the sound level of the noise is decreased by 6.02 dB. No matter what the scale of measurement, you will get a 6.02 dB sound level drop for every doubling of distance. You can see how this works by entering values in the table below.

  Calculate Decrease in Sound Level as Distance Increases
  Enter the initial distance from sound source: meters or feet, and...	Enter the initial sound level at the initial distance: dB
  Enter another distance farther away from sound source meters or feet	The sound level at this farther distance will be: dB	The sound level decreases by: dB

Personal Protective Equipment

Types of Hearing Protective Devices (HPDs)

If other hazard and exposure control strategies to reduce noise levels can't be used or fail to reduce noise levels below OSHA's permissible exposure limits (PELs), the employer should make sure all exposed employees wear hearing protective devices. As you are probably well aware, there are basically four types of hearing protectors.

Each type is designed for certain noise conditions. But remember - unless employees wear hearing protection properly and wear them all the time in high noise areas, the devices will not be effective. Proper use of hearing protection is one of the major challenges inherent in this exposure control strategy.

Convenience and comfort are important for frequent use of hearing protective devices. Earmuffs and foam earplugs in most cases offer the most noise reduction. However, preformed plugs or canal caps may be more convenient where construction work generates moderate daily average noise levels. There is no one device that is the best type for all situations. You can see the various types by enlarging the image to the right.

We'll discuss the OSHA requirements for hearing protective devices as part of the employer's Hearing Conservation Program (HCP) later in the course.

Management Responsibilities

Managers may need to commit resources for in-house development of technology to control exposure problems specific to their companies and processes.

Management's primary responsibilities are to make sure that potentially controllable noise sources are identified and that priorities for controls are set and accomplished. It is also management's responsibility to see that any changes in equipment or process are done only after evaluation of their impact on employee noise exposure.

Purchasing more quiet equipment can be very helpful, but sometimes the company must be willing to pay more for quieter equipment, but these investments should be cost-effective in the long run.

Implementing a "buy-quiet" program can significantly reduce the amount of time it takes for workplace noise to no longer be hazardous.

Often a noise-control effort may seem to be overwhelming. As a result, the company may decide that noise control is not feasible and instead rely on hearing loss prevention measures to prevent hearing loss. However, if noise sources are taken on one at a time, dealing with the noisiest or easiest to quiet sources first, the problem can become manageable over time so that hearing loss prevention measures will be needed only until the noise is reduced to a safe level. Many times two hazards can be reduced or eliminated at once such as in the case of enclosing a noisy machine that generates high heat levels as well. The enclosure can trap the noise and the heat can be vented off to the outside.

Managers may need to commit resources for in-house development of technology to control exposure problems specific to their companies and processes. In some cases, they may need to budget for maintenance of exposure control devices to prevent their deterioration over time. Finally, they should make sure that lunch and break areas are as free from noise hazards as reasonably possible.

Employee Responsibilities

Employees should assist those who make the measurements by sharing their knowledge about the work environment.

Employees who operate or maintain and repair the equipment are often the ones who know most about the processes involved. Employees need to:

• learn to operate their machines with the noise controls in place;
• maintain the controls properly;
• notify appropriate personnel when additional maintenance is needed;
• notify supervisors when they notice changes in equipment sound levels;
• express their concerns and ideas to management, the program implementer, or the noise-control engineer so that the noise-control devices will be as practical and effective as possible;
• assist with engineering noise surveys where sound sources within a work process or a piece of equipment need to be evaluated and only the employee knows the proper operation of the equipment; and
• cooperate by maintaining their normal work routine when asked to wear dosimeters, so that the results will be representative of their actual exposures.

Check your Work

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