Noise: Exposure Assessment and Control

Noise: Exposure Assessment and Control

Monday, June 1, 2015, 2:00 PM - 5:00 PM

CS-109-01 2015 Safe-in-Sound Excellence in Hearing Loss Prevention Awards™

S. Schneider, Laborers’ Health & Safety Fund, Washington, D.C.

Situation/Problem: In 2007, NIOSH partnered with the National Hearing Conservation Association (NHCA) to create the Safe-in-Sound Award™ for Excellence and Innovation in Hearing Loss Prevention ( The objectives of this initiative are to recognize organizations that document measurable achievements and to share leading edge information to a broader community.

Resolution: Hearing health practices are evaluated against key performance indicators in a rigorous review process designed to capture and evaluate the successes.

Results: The 2015 Safe‐in‐Sound Excellence in Hearing Loss Prevention Awards™ will be presented. Each of the award recipients will accept their awards and briefly present their success stories.

Lessons Learned: These success stories can hopefully show others how to succeed at hearing loss prevention.

CS-109-02 How Can We Conduct Better Quality Personal Noise Dosimetry Measurements in the Workplace?

B. Selwyn, Sensidyne LP, Merrimack, NH

Situation/Problem: Making noise exposure measurements on individuals is a common task for many industrial hygienists. However, the fact that the majority of these measurements are made with an instrument that is not always supervised can lead to the presence of unknown errors in the results. Deliberate or accidental tampering with the readings has been experienced by many users of noise dosimeters leading to uncertainty in the overall conclusion when the time weighted average value is close to the daily limit. Unexpected spikes in the time history do not always have an adequate explanation or true cause unless the supervisor was present at the time to accurately document what happened. This is not always possible.

Resolution: A new personal noise dosimeter has been developed to assist the industrial hygienist in the correct interpretation of unforeseen spikes in noise levels. The provision of two methods of identification virtually guarantees that the supervisor can be certain of what happened during the study and can make an informed decision about whether to include or exclude any high levels seen in the time history data. The inclusion of a self-vibration monitor in the new dosimeter detects if the instrument itself has been roughly handled by the wearer and tags the time history samples with a high vibration marker. High level spikes in the measurement can also be recorded as an audio signal allowing the supervisor to listen to the event and determine the cause as if they had actually been there.

Results: Downloaded results from the new dosimeter are saved at intervals as short as 10 times per second if needed for rapidly varying noise levels. The tags associated with high self-vibration or the audio markers are visible when the run information is downloaded to the software package supplied with the instruments. The user can choose to reject the samples that are contaminated with the high vibration marker and recalculate the overall noise dose. The audio signal can be listened to in order to determine the true source of the high noise levels for each event and those events determined to be not characteristic of the typically expected noise sources can be eliminated.

Lessons Learned: The errors and uncertainties about valid time history data can now be correctly identified using the new noise dosimeter. High self-vibration and unrepresentative sounds can be identified and removed if required leading to better quality conclusions for personal noise dosimetry measurements.

SR-109-03 Daily Noise Exposure of Patrol Officers

D. Vosburgh, L. Gilbertson, UW-Whitewater, Whitewater, WI

Objective: Previous research shows that police officers are at a higher risk for noise induced hearing loss (NIHL). Little data exists on the occupational tasks, outside of the firing range, that might lead to the increased risk of NIHL. This study measured the noise exposure of patrol officers (police officers who conduct routine patrol in response to calls and traffic enforcement) as they conducted their daily tasks.

Methods: The current study collected noise dosimetry from patrol officers in a smaller agency (n=5) and a larger agency (n=11) in southern Wisconsin, United States. The noise dosimeters simultaneously measured noise in three configurations that had different thresholds, criterion levels and exchange rates. The configurations were: the Occupational Safety and Health Administration hearing conservation criteria (OSHA-HC), the OSHA permissible exposure level criteria (OSHA-PEL), and the American Conference of Governmental Industrial Hygienists (ACGIH). In addition to wearing a noise dosimeter during their respective shifts, officers completed a log form documenting the type of task performed, the duration of that task, if the task involved the use of a siren, and officer characteristics that influenced their noise exposure, such as the type of dispatch radio unit worn.

Results: Analysis revealed that the normalized 8-hour time weighted averages (TWA) for all officers fell below the recommended Occupational Safety and Health Administration (OSHA) and American Conference of Governmental Industrial Hygienists (ACGIH) exposure limits. For the OSHA-HC and ACGIH configurations the tasks involving the use of siren had significantly higher levels than the tasks without (p=0.049 and 0.008). The highest noise exposure levels were encountered when patrol officers were assisting other public safety agencies such as a fire department or emergency medical services (OSHA-HC = 71.4 dBA, OSHA-PEL = 65.5 dBA, ACGIH = 76.4 dBA). Canine officers had higher normalized 8-hour TWA than regular patrol officers for all three configurations (p=0.008, <0.0001, 0.003). There were no significant differences in exposure levels between the two agencies (p=0.28, 0.14, 0.13).

Conclusions: Results suggest that this study population is unlikely to experience NIHL as established by the OSHA standard and ACGIH recommendations from the daily occupational tasks that were monitored.

SR-109-04 Effects of Data Sparsity and Spatiotemporal Variability on Hazard Maps of Workplace Noise

K. Koehler, Johns Hopkins University, Baltimore, MD; J. Volckens, K. Lake, H. Wang, Colorado State University, Fort Collins, CO; J. Zhu, University of Wisconsin, Madison, WI

Objective: Personal sampling, a state-of-the-art technique to assess worker exposures to hazards, provides little information on the spatial variability of exposures. Hazard maps have gained popularity as a way to locate sources and to visualize spatial variability of hazards within a facility. However, these maps are often generated from short duration measures and have little ability to assess temporal variability. The objective of this study was to assess the potential bias that results from the use of short-duration measurements to represent the TWA in a hazard map.

Methods: We measured noise intensity with personal dosimeters at two facilities. A combination of static (i.e., monitors that remained stationary and captured a time series of noise intensity) and roving noise monitors (i.e., monitors that were moved through the facility to capture noise intensity at many locations) were employed to estimate spatial and temporal variability in noise intensity. Ordinary Kriging was utilized to produce hazard maps.

Results: At facilities with low temporal variability, hazard maps produced from roving monitor data were in good agreement with the TWA hazard maps and estimated values were within 5 dB of the TWA over approximately 90% of the facility. However, at the facility with higher temporal variability, large differences between hazard maps were observed for different traverses through the facility, and estimates were at least 5 dB different than the TWA over more than half of the facility. The temporal variability was found to have a greater influence on map accuracy than the spatial sampling resolution.

Conclusions: At facilities with homogeneous noise intensities over time, the similarity between hazard maps produced from static and roving monitoring methods was high. With higher levels of spatial and temporal variability, hazard maps produced with data from static and roving monitoring methods were substantially different. Future studies using roving monitoring to assess the spatial extent of hazards should consider the temporal variability of the hazard. At facilities with higher temporal variability, hazard maps will be useful to capture transient, high-level exposures that are missed by standard TWA methods. However, these maps may be biased compared to the TWA value and replicate measures should be taken to improve map accuracy.

CS-109-05 Ball Mill Noise: An Innovated Approach for Control

G. Graham, Freeport McMoRan, Inc., Morenci, AZ


CS-109-06 Reducing Noise Levels in Hydroelectric Power Plants

J. Komrower, Noise Control Engineering LLC, Billerica, MA; T. Gallagher, Bureau of Reclamation, Denver, CO

Situation/Problem: The US Department of Interior Bureau of Reclamation (Reclamation) and the US Army Corps of Engineers (USACE) oversee a number of hydroelectric power plants across the U.S. Noise induced hearing loss (NIHL) has become the number one workers compensation safety issue in Reclamation. Most of reclamation’s power plants are over 40 years old and were constructed before many modern noise control technologies were developed. The Occupational Safety and Health Administration (OSHA) requires the reduction or elimination of a hazard, such as exposure to prolonged high noise levels, to be addressed through the implementation of engineering controls prior to implementing administrative and personal protective equipment strategies. The objectives of this program were to identify and implement feasible engineering controls in hydroelectric power plants in areas where the overall noise levels exceeded 85 dBA.

Resolution: Measurements were conducted in a number of power plants and three of these plants were chosen in which to install engineering controls. The measurement methodology included conducting complete acoustic and vibration surveys to identify not only airborne paths, but structureborne paths as well. In addition, unique technology which features a 3D solid sphere acoustic “camera” to capture sound pressure levels and specialized software algorithms to localize the sources of noise was employed. Engineering controls were then designed and installed in the selected plants. These controls included silencers for specific noise sources, acoustic absorption panels on hard surfaces to reduce reverberation, high transmission loss acoustic barriers and damping material on vibrating ducts.

Results: As a result of this effort, noise levels were significantly reduced (by as much as 15 dB). The program is a joint cooperation between The Office of Naval Research (ONR) and Reclamation where insights that have been developed as part of ONR’s NIHL program will continue to be applied and leveraged to reduce noise in power plants.

Lessons Learned: Engineering noise control techniques can be successfully designed and implemented to significantly reduce noise levels in power plants which not only will decrease the potential for NIHL disability claims but will also result in a better work environment.

CS-109-07 The Critical First Step in a Noise Control Program

D. Driscoll, Associates in Acoustics, Inc., Evergreen, CO

Situation/Problem: Based on 35 years of experience in noise control, some of the most common causes of elevated noise levels are improper equipment setup and/or the need for maintenance. These issues lead to unnecessary expenditures, such as purchasing acoustical materials to treat the symptoms of noise rather than addressing the root-cause, excessive wear and tear on machinery, and potentially unnecessary inclusion of workers in a hearing conservation program. Equipment motivated by compressed air and programmable-logic controllers (PLCs) will often generate excessive impact forces and/or exhaust noise as the air regulators and PLCs are adjusted or the production has changed. The byproduct of non-optimal settings is almost always an increase in noise. Plus, from a noise exposure standpoint, when equipment is not maintained or setup properly it increases the time workers need to spend in the direct sound field of the machine while performing any service requirements.

Resolution: Before time and money are invested in implementation of noise controls, the first step should be to ensure the noise concern is not due to improper equipment setup and/or maintenance. Carry out the described acoustical maintenance checklist, and meet with engineering and maintenance representatives to ascertain their opinions on the matter as it relates to elevated noise levels. The described checklist includes procedures to be followed by machine operators and mechanics. In most facilities a measurable noise reduction can be achieved simply and inexpensively by paying attention to the details for maintaining equipment in optimal condition.

Results: Optimizing the air pressure driving at a can-manufacturing machine resulted in an attenuation of 20 dBA. Next, changing the PLC timing on a box-forming machine reduced the noise level by 10 dBA. These and other case histories are used to demonstrate the benefits and techniques of proper machine setup and maintenance for noise control.

Lessons Learned: Noise control can often be achieved simply and inexpensively, often producing dramatic results, by adhering to a formal acoustical maintenance program. This process alone will yield significant benefits in both the long-term life of the equipment and minimizing the noise exposure risk to employees. Only after the equipment of concern has been properly setup and maintained, should an advanced noise control assessment be undertaken to mitigate the remaining sources of noise.

SR-109-08 Evaluation of Active Noise Cancelling Headsets during Jackleg Drilling in an Underground Mine Setting

W. DuBose, V. Lee, R. Reed, E. Lutz, University of Arizona, Tucson, AZ

Objective: Overexposure to noise continues to be a prevalent occupational health concern in underground mining. Although the usage of hearing protection can prevent occupational noise induced hearing loss, the personal protective equipment inhibits verbal communication while being worn. This presents a potential hazard to miners working with heavy equipment, such as the jackleg drill. This study evaluated the effectiveness of various active noise cancelling headsets in attenuating occupational noise, as an alternative to traditional muffs that are currently being used by underground miners.

Methods: A total of five participants were recruited for this study: two mining students and three research team members. The jackleg drill was operated by the mining students while the research team members observed. The noise exposures were monitored and collected from each participant during five drilling shifts, averaging 30 minutes per shift. The noise dosage levels were measured and recorded using in-ear dosimeters and shoulder dosimeters. One traditional ear muff and four active noise cancelling headsets were used for testing. Dosage levels were compared between the shoulder and the in-ear measurements using a Kruskal-Wallis test for statistically significant differences. An alpha error threshold of 0.05 was used.

Results: Collectively, the median relative percent difference (RPD) between the shoulder and the in-ear noise dose for all of the active noise cancelling (ANC) headsets combined was 152.3% (n=14; interquartile range (IQR): 115.1-189.1%). The traditional ear muff median RPD was 183.2% (n=4; IQR: 176.4-188.6%). Of all the ANC headsets tested, only one design fared better than the traditional ear muff with a median RPD of 190.7% (n=4; IQR: 185.1-193.9%), but this difference was not statistically significant. The ANC headset that performed the worst had a RPD of 123.6% (n=3; IQR: 55.4-125.8%), which was significantly lower than the best performing headset (p=0.0339).

Conclusions: Results show that there may be a slight advantage to wearing ANC headsets when operating a jackleg drill in an underground mine. Although the difference in noise reduction is small between ANC headsets and traditional ear muffs, their implementation and usage would not only provide workers in the mine protection from noise induced hearing loss, but would also create safer work environment, allowing verbal communication for miners while on shift.

SR-109-09 Photopolymerization 3-D Printing: Preliminary Assessment of Material Hazards

T. Ryan, D. Hubbard, Ohio University, Athens, OH; 

Objective: Printing in 3 dimensions (3-D printing) constitutes a revolutionary new technology for the production of objects made of metals, biologicals, and polymers. The process holds promise for larger scale commercialization and therefore, elevated worker exposures to process hazards. This work was performed as a preliminary hazard assessment of the process and chemicals associated with a commercial grade photopolymerization 3-D printing process. Exposures to organic polymers, a corrosive cleaning agent (sodium hydroxide), and minor physical hazards (UV, noise) were assessed.

Methods: Using Safety Data Sheets to rank order of hazardous resins and support materials toxicologically, specific printing constituents such as polyethylene glycol, toluene, carbon monoxide, Isobornyl acrylate and trace amounts of benzene were targeted for quantification of area airborne concentrations. Strategies for the materials in question were adapted to collect in-printer and ambient facility samples. Post-printing support material removal and solid waste handling was also evaluated.

Results: Results indicated only low concentrations of the targeted compounds within the printer, and non-quantifiable ambient levels, with noise and UV exposures being minimal. Cleaning of polymeric products was found to result in the highest worker potential for exposure.

Conclusions: For the materials utilized in the specific process evaluated here, even large printing jobs will likely pose negligible inhalation hazards but potentially serious corrosives exposures. Since metals and biologicals were not evaluated it is recommended that similar assessments be conducted for those processes.​