Monitoring Hearing Hazards

As with any health hazard, it is of utmost importance to accurately determine the nature of the hearing hazard and to identify the affected employees. Those responsible for this aspect of the program must ensure that the exposures of all employees have been properly evaluated and that reevaluations are conducted when changes in equipment or operations significantly alter working conditions. Readers are encouraged to consult items no. 1-11, 49, and 56 in Appendix A to ensure compliance with the noise monitoring requirements in the OSHA standard. Also, the checklist entitled Noise Measurement in Appendix B should be helpful in designing and evaluating a noise monitoring program.

Recent evidence has indicated that aromatic solvents, metals, and petrochemicals may be associated with occupational hearing loss. Although studies are exploring the relationship between hearing loss and chemical exposures, there is insufficient information about this relationship to speculate on potential risk factors. Therefore, this section will focus on monitoring noise exposure, certainly the major factor associated with occupational hearing losses.

2. To determine whether noise presents a safety hazard by interfering with speech communication or the recognition of audible warning signals.

4. To classify employees' noise exposures for prioritizing noise control efforts and defining and establishing hearing protection practices.

Various kinds of instrumentation and measurement methods may be used, depending on the type of measurements being conducted. The most common measurements are area surveys, dosimetry, and engineering surveys.

In an area survey, environmental noise levels are measured, using a sound level meter to identify work areas where employees' exposures are above or below hazardous levels, and where more thorough exposure monitoring may be needed. The result is often plotted in the form of a "noise map," showing noise level measurements for the different areas of the workplace.

Dosimetry involves the use of body-worn instruments (dosimeters) to monitor an employee's noise exposure over the work-shift. Monitoring results for one employee can also represent the exposures of other workers in the area whose noise exposures are similar. It may also be possible to use task-based exposure methods to represent the exposures of other workers in different areas whose exposures result from having performed the same task(s).

Engineering surveys typically employ more sophisticated acoustical equipment in addition to sound level meters. These may include octave-band analyzers and sound level recorders which furnish information on the frequency/intensity composition of the noise being emitted by machinery or other sound sources in various modes of operation. These measurements are used to assess options for applying engineering controls.

Management must decide whether to contract with an external service provider or to purchase the necessary equipment and have the on-site staff trained to perform the sound survey. Because sound surveys should be performed periodically, it may be cost-effective to develop in-house expertise with the ability to schedule sound level checks (i.e., annually, whenever production machinery is added or changed, or when work processes are changed and have the potential for affecting noise levels).

Management should make sure that the individuals who monitor the noise are properly qualified to perform noise measurements, whether in-house personnel or contractors. A certified industrial hygienist can conduct most noise monitoring activities, although audiologists or technicians can do so if they have the necessary training and experience. Sound surveys for the purpose of selecting or evaluating engineering controls should involve an acoustical engineer.

Management should also ensure that operating procedures for conducting and evaluating noise measurements are available, well defined, carefully documented, and closely followed. These procedures should specify the scheduling of surveys, the type of measurements to be made, instrument calibration procedures, sampling criteria, methods for recording data, and procedures for reporting results. Management can also support the monitoring process by ensuring personnel who are familiar with equipment and operations are available to assist in characterizing the samples as representative of "normal" operations.

Results of the noise measurements must be reported to the program implementor and to employees in an understandable, uniform format. Results of area measurements or noise exposure dosimetry should be placed in each employee's hearing loss prevention record. In addition, a summary of the survey results should be presented during education programs for management and employees.

Maintenance of noise control systems is critical to their success. If a drive unit is fitted with an enclosure to reduce the noise radiated into the immediate area, the enclosure will be effective only as long as it is kept closed and its seals are in good condition. Most seals deteriorate over time and need replacement. If bad seals are left in place, much of the noise reduction will be lost. The same applies to a belt driven system because the noise level will increase as the belts wear. Maintenance of the belts should be maintained so that the noise levels stay as low as possible. A punch press that is isolated from the floor by vibration dampers will become a contributor to the plant noise as the dampers compress with age. A schedule should be established for replacing such dampers.

The program implementer should be involved with the sound survey activities from the planning stages to the completion of the survey. During the planning stage, the program implementer should coordinate activities between management and the sound surveyors with respect to agreeing upon the fundamental strategies to be used in conducting the sound surveys. The implementor should work closely with management to address the reason(s) for obtaining the measurements, such as: to define hazardous noise areas, to identify employees to be included in a hearing loss prevention program, or to evaluate specific machinery for noise control purposes. To ensure the noise measurement program answers relevant questions, implementors must have an awareness of the major factors that will influence the noise exposure monitoring results. For example, will area sampling, personnel sampling, or a combination of both be employed? What types of measurement equipment will be beneficial in characterizing the noise environment? Which areas or machines will be evaluated? Which workers and/or how many workers will need to be monitored? Will full shift or partial shifts be studied? Who will ensure measurements are made with equipment that has been suitably calibrated and that there is a suitable record of the calibration? What parameters will be used in obtaining measurements (e.g., exchange rate, weighting, dynamic range, criterion levels, and threshold levels, etc.) How will "borderline" results be handled?

The implementor should be actively involved in overseeing survey activities. In most cases, it will be important that noise measurements be representative of typical production cycles. Hence, the implementor should ensure the work processes are appropriately surveyed.

It is important that noise measurements are representative of typical production cycles. Hence, noise surveys should ensure adequate sampling of all work processes. When dosimetry is performed, make sure that employees wearing dosimeters are engaged in typical activities. Because employee cooperation and know-how is needed to obtain valid results, sound surveyors (those who measure the noise) must establish rapport with employees to benefit from their familiarity with the work environment and production process. By explaining the purpose of the measurements to employees and soliciting their help, surveyors can avoid errors, oversights, and possible mishandling of noise dosimeters by employees. Employees need to understand that realistic noise measurements are essential to plan noise control efforts and select appropriate hearing protection devices, and that they are helping themselves by helping the surveyors.

Program implementors must ensure that sound surveyors consistently follow the policies and procedures established by management with regard to the selection, maintenance, and calibration of instruments, measurement techniques, data analysis, and reporting. A good rule of thumb is to make the procedural description detailed enough so another person could reproduce the results. Comprehensive sound surveys may require additional instrumentation and greater detail than is necessary for basic surveys.

The report must present the results clearly. Results lead to recommendations, which are transformed into actions. The emphasis of the report may vary depending on the purpose of the survey (for example, OSHA compliance, documentation for worker compensation, or internal company hearing loss prevention program decision), so the writer should state the objectives and present the data relevant to these objectives. Because few report users will need or read every detail of the survey, it is critical to write a concise abstract for higher level management. A slightly longer summary should also be included for employees in the hearing loss prevention program. The body of the report should explain the calibration and measurement procedures, as well as the results, and detailed documentation (including the original data sheets) must be kept with the report in case it is needed for research, inspection by government representatives, or legal purposes.

A summary of the results of the survey should be available in the shop area hazards folder or in another convenient location. Copies of the noise maps should be readily available to the program implementor. The noise maps should be explained to the employees during their educational programs and posted for reference. Dosimeter wearers should be given the readings from the dosimeter they wore along with a short explanation of what the readings mean. If an area is labeled as requiring the use of hearing protection for all who enter, warning signs should be posted and appropriate hearing protectors should be available near the perimeter of the restricted area. Likewise, if a survey documents that a specific piece of equipment produces a hearing hazard, personal protection devices should be available both to those who operate the equipment as well as to those who may have to work in the immediate vicinity of the equipment.

Employees should assist those who make the measurements by sharing their knowledge about the work environment, the machinery in operation, and specific jobs. Employee assistance is especially critical to the success of 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. Employees also need to cooperate by maintaining their normal work routine when asked to wear dosimeters, so that the results will be representative of their actual exposures.

Sound levels often increase when equipment begins to wear or fails to receive appropriate maintenance. Also, changes in equipment placement may cause unintended effects on sound levels. When employees notice such changes, they need to inform the supervisory personnel or the program implementor that a change has occurred. A re-survey will be needed to evaluate the new sound levels and employee exposures whenever equipment or production changes occur.

Code of Federal Regulations, Title 29, Chapter XVII, Part 1910, Subpart G, 1910.95: sections (a), (b), (c), (d), (e), (f), Appendix A, and Appendix G.

See Checklist in Appendix A of this guidebook,
items no. 1-11, 50, and 56.
See checklist in Appendix B of this guidebook,
section entitled "Noise Measurement."

Earshen JJ [1986] Sound measurement: Instrumentation and noise descriptors. In: Berger EH, . Ward WD, Morrill JC, Royster LH eds. Noise and Hearing Conservation Manual 4^th ed. Akron, OH: American Industrial Hygiene Assoc. Chapter 3.

Harris CM ed. [1991] Handbook of Acoustical Measurements and Noise Control 3^rd ed. New York: McGraw-Hill, Inc.

Royster LH, Berger EH, Royster JD [1986]. Noise surveys and data analysis. In: Berger EH, Ward WD, Morrill JC, Royster LH, eds. Noise and Hearing Conservation Manual 4^th ed. Akron, OH: American Industrial Hygiene Assoc. Chapter 4.