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NORA Manufacturing Sector Strategic Goals

9277101 - Noise Sampling Strategies and Exposure-Response Models

Start Date: 6/1/2001
End Date: 9/30/2009

Principal Investigator (PI)
Name: Cheryl Estill
Phone: 513-841-4476
Organization: NIOSH
Sub-Unit: DSHEFS
Funded By: NIOSH

Primary Goal Addressed

Secondary Goal Addressed


Attributed to Manufacturing


Project Description

Short Summary

Very loud peak noises (like gunshots, stamping presses, drop hammers) may have more of an effect on hearing loss than continuous noise exposure. This project will improve on existing noise and hearing loss methods by determining the most accurate way of estimating the time-weighted average (TWA) and incorporating the combined effect of impulsive and continuous noise. Two approaches to estimating the TWA noise exposure will be compared: task-based assessment (noise levels associated with each task in a given job, combined with time-at-task) and dosimetry (full-shift personal monitoring). Repeated measures of noise over several points in time on individuals and jobs will permit an evaluation of how the precision of the exposure assessment approach affects exposure-response analysis. Results can be used to develop intervention strategies to reduce hazards through better quantification of NIHL risk from mixed exposure environments.


The objectives of the project are to evaluate workplace exposures to impact noise and to evaluate the measurement errors present in daily time weighted average (TWA) noise exposure assessments by conducting paired, side-by-side dosimetry and task-based sampling (TBS) methods.

The study include three manufacturing plants in Montreal, Quebec, Canada having different exposure environments: continuous noise with background impact noise, intermittent noise, and high peak noise with low background noise levels less than 80 dBA. For each plant, full shift noise exposure measurements and hearing tests, conducted pre- and post-shift were collected. The pre-and post-shift hearing tests evaluated the extent of temporary hearing loss assumed to be due to poor fit of hearing protection devices (HPD). Representative samples of impact noise were collected along with general demographic data, work practices, exposure determinants, and detailed task-based information on noise and HPD use during the shift. Noise exposure metrics for impact noise will be identified that best predict hearing hazard using both statistical modeling approaches and biologically-based models of the ear.

During Phase I, noise data were collected on 38 representative jobs with at least seven workers per job to evaluate the validity and cost-effectiveness of each sampling method for different job characteristics. Using the full-shift dosimetry with direct worker observation as the gold standard, simultaneous measures were taken using task based methods of worker diary and supervisor assessment of typical (average) time-at-task. During Phase II, two additional repeated measures were collected on the same workers in several jobs across the three plants to estimate the variability in exposures across jobs, persons and days. The repeat noise measures were analyzed to evaluate the relative contribution of variability in time-at-task and in noise level of the task to within-job exposure variability.

All data collection has been completed at the three plants in Montreal; field data have been coded, entered into a Microsoft Access database, quality control cleanup completed, and several tables of time at task completed; a contract report on impact noise evaluation has been completed; and the analysis of noise measurements at all plants has been completed through contract report. The first paper of this study, which compared the three time-at-tasks methods, was presented in FY08 and has been submitted to peer-reviewed journals. Noise exposure and audiometry employee notification was conducted during FY08. During FY09, impact noise data will be evaluated to determine the best analysis approach.


The methods and results of this study will be relevant to OSHA and MSHA noise regulations for developing efficient, effective noise exposure assessment strategies and in updating models of NIHL risk to include impulsive, intermittent and mixed noise exposure environments.

Mission Relevance

There are more than 30 million U.S. workers exposed to noise levels in excess of 85 dBA, a level that is associated with a significant risk of noise induced hearing loss (NIHL). A significant portion of these workers are employed by the manufacturing sector. Workers exposed to high noise levels need to be identified by companies so that they can be enrolled in a hearing conservation program. Current exposure assessment of high risk workers is accomplished through either individual dosimetry monitoring or area surveys focusing on measurement of noise levels for specific tasks or processes. These methods are outdated and imprecise in capturing impact noise (or impulse noise). Impact noise exposure may be a greater risk factor for noise induced hearing loss than continuous noise of the same magnitude. This study will measure impact noise and continuous noise in three manufacturing workplaces and also capture employee's audiometric results. To evaluate methods of exposure assessment, this study will compare employee exposures using direct observation, employee reports, and supervisor reports. This study will be conducted at an equipment manufacturing plant and will add to the understanding of risk and protective factors of noise-induced hearing loss in that subsector and other manufacturing sectors. The impact noise evaluation directly addresses the hearing loss goal of identifying hearing loss risk factors. The methods compared in this study will address several exposure assessment goals one of which is developing new methods to measure occupational hazards.

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