E. Berger, E-A-R/Aearo Company, Indianapolis, IN.
For nearly 25 years the legally mandated specification of hearing protector effectiveness has been the Environmental Protection Agency’s (EPA) Noise Reduction Rating (NRR). In March 2003, the EPA convened a workshop to examine the labeling regulation and the concerns that have been expressed as to its appropriateness and validity. Numerous suggestions were proffered, including ones concerning ratings that might better predict real-world performance. However, besides EPA’s avowed intention to revise the regulation, its details and the future are still uncertain. In terms of a scientifically valid approach to predicting protection, one must specify a method of measuring attenuation, define the noise exposure of the population or individual in question, and decide upon a computational method for use of those data (i.e., a rating scheme). The focus of this research is on the latter question, namely computation of a rating for hearing protector attenuation and application of that rating to noise measurements. A variety of ratings are possible, from the nominal “gold standard,” namely an octave-band calculation, to simplified ratings that can be applied to more readily available noise measures such as A-weighted sound levels or exposures. The conclusion is that a single number computed in a manner similar to the current EPA-mandated NRR, but with suitable adjustments for use with A weighting, provides sufficient precision. Justification for this recommendation stems from consideration of the inter-wearer variation in fitting, variation in noise spectra, and the accuracy of the basic measurements of hearing protector attenuation and noise-exposure values. Furthermore, to provide additional guidance to the purchaser, two such numbers ought to be provided on the primary package label—a smaller one to indicate expected protection by most users in practice, and a larger one to indicate the protection that is possible to achieve by individual highly-motivated expert users.
E. Stevenson, P. Teare, Liberty Mutual, Hopkinton, MA.
Actual real world noise attenuation is difficult to predict using NRR values, or even using octave band attenuation data from manufacturers. Real world variables include various noise sources with different dominant frequencies than the attenuation test frequencies, use of safety glasses and hard-hats which can affect the seal of the ear muff against the side of the face, different head shapes, variable headband tension over time, and a seemingly infinite variety of “field modifications” done to ear muffs, many of which may reduce their effectiveness. Added complications are the use of communication headsets—which add their own noise source under the ear muff—and use of equipment like sandblasting helmets that may not have advertised noise attenuation data. Using two miniature matched microphones and a two-channel field portable instrument, we have made simultaneous measurements of noise levels inside and outside various ear muffs and calculated the difference between them. The instrument has a 60 dB dynamic range, centered between 60 dBA and 120 dBA. It can also calculate exposure dose for the two microphones over the survey time. Software is used to plot the two microphone levels over time as well as the difference between the two. This is a measure of the actual real world attenuation achieved, which can be used to confirm the adequacy of the selected ear muff, as a training tool for workers which show the effect of modifications on the actual noise attenuation achieved, and to measure difficult exposure assessments, such as the exposure level inside communication headsets.
J. Smith, ExxonMobil Corporation, Houston, TX.
The implementation of robust Hearing Conservation Programs (HCPs) is key to preventing noise-induced hearing loss. This case study describes one company’s efforts to measure and evaluate the effectiveness of HCPs at two large petrochemical facilities.
A three tiered approach was utilized to gain a better understanding of:
The results of the HCP evaluations were utilized to develop global HCP guidelines to drive continuous improvement. Key learnings are discussed along with recommendations for improving HCPs.
S. Henry, Anniston Army Depot, Anniston, AL.
“Representative” time-weighted average (TWA) noise exposures as well as basic sound level meter readings are commonly used as criteria for inclusion of personnel in a hearing conservation program. Derivations for a representative TWA vary, but they often fail to truly characterize long-term noise exposures unless the noise exposures in an environment don’t tend to vary significantly from day to day. This presentation reviews 18 years of noise data using statistical methods to characterize long-term exposures of similar exposure groups (SEGs) at a heavily industrialized military site where the noise environments do vary significantly from day to day. The effectiveness and sensitivity of the method to demonstrate a reasonably accurate depiction of long-term noise exposure of SEGs will be reviewed along with potential usefulness of the data.
R. Neitzel, N. Seixas, W. Daniell, University of Washington, Seattle, WA.
Although a number of studies have examined noise exposures resulting from infrequent, episodic non-occupational events (e.g., concerts), few have assessed noise levels resulting from routine daily activities (e.g., commuting), and no published studies have assessed the total noise exposure resulting from both routine and episodic non-occupational activities. In the current study, estimated routine and episodic exposure levels and activity frequencies were integrated to evaluate the typical range of non-occupational exposures and compare these to construction work exposures.
Exposures associated with routine activities were estimated from activity logs collected on 148 construction apprentices and noise exposure data collected on 31 apprentices monitored for 96 hours each. Exposures associated with episodic activities were estimated from questionnaires on 266 apprentices and noise levels for these activities taken from 20 peer-reviewed papers. In each case, low, medium, and high values for the range of non-occupational exposure frequencies and noise levels were combined using the 10th, 50th, and 90th percentiles of the observed distributions. Routine and episodic exposures were combined to estimate total non-occupational noise exposure, and this exposure was then transformed into the equivalent level for a 2000-hr exposure period (Leq(2000)) for comparison to occupational exposure standards.
Mean total non-occupational Leq(2000) levels ranged from 61.7 to 92.5 dBA. For the mid-range of routine and episodic activity exposure, the mean Leq(2000) was 77.9 dBA, and 19% of exposures exceeded 85 dBA. Conversely, 81% of mid-range Leq(2000) non-occupational exposures were below 85 dBA, indicating that work exposure (which frequently exceeds 85 dBA) represents the majority of risk for noise-induced hearing loss for most construction workers. Firearms exposure could not be included in the exposure estimates due to the difficulty of integrating impulse noise into standard exposure metrics. However, the apprentices who reported shooting (22%) had higher estimated non-occupational noise levels even without inclusion of firearms exposure.
T. Morata, NIOSH, Cincinnati, OH.
The occupational health community is giving increasing attention to the combined effects of occupational exposure to noise and other factors on hearing. In particular, the interaction between noise and chemicals such as toluene, styrene, and carbon monoxide, poses a new challenge to industrial hygienists and hearing conservationists. NIOSH has conducted epidemiological studies on the effects of solvents on hearing, alone or in combination with noise. In all of the investigations, solvents were found to affect the hearing of workers. In light of the many chemicals that are used in the work place and evidence that they may affect hearing, numerous populations are being underserved with regard to the prevention of hearing loss. Permissible exposure levels for chemicals do not account for the chemicals’ effects on hearing loss. Thus, workers who are exposed to noise levels below 85-dBA time-weighted average who are not required to be in included hearing conservation programs may still be at risk of hearing loss due to exposure to these chemicals. Furthermore, methods currently used in hearing conservation (e.g., hearing protectors and noise control) may be ineffective, or even inappropriate, for workers exposed to both chemicals and noise. This presentation will review the current knowledge of chemical ototoxicity and the NIOSH strategy for partnering with industry, academia, and professional organizations interested in preventing occupational hearing loss. Key issues to be addressed in this strategy include: rationale and proposal of consensus list for priority chemicals, methods for evaluating exposures of concern for workers and appropriate biomarkers, methods for assessing auditory effects of chemicals, inclusion criteria in prevention programs and appropriate components of such programs, and finally, the need for information dissemination.
B. Pathak, Canadian Centre for Occupational Health and Safety, Hamilton, ON, Canada; S. Bly, Health Canada, Ottawa, ON, Canada.
This paper presents the results of a pilot survey on the availability of noise emission data to Canadian purchasers from 100 manufacturers and distributors of machinery and equipment used in Canadian workplaces. The survey included manufacturers or distributors of specific types of machines such as compressors and fans. Also included was a variety of equipment categorized by use in a number of industries such as: auto repair, construction, food processing and packaging, furniture making, logging, metal manufacturing, mining, pulp and paper, saw mills, and shingle mills. The survey was done by means of telephone interviews using a questionnaire. Information was obtained on whether noise emission data is provided and, if so, the method used. The survey data revealed that 54 of the manufacturers/suppliers responded that they provided noise emission data either voluntarily or on request by the buyer. Twenty-nine of these 54 responses indicated that the data was provided in conformance with a standard.
F. Akbar-Khanzadeh, S. Spino, Medical College of Ohio, Toledo, OH.
Skateboard ramps constructed of metal (steel) act similarly to drums and are perceived to be noisier than ramps constructed of wood or concrete. This study was performed to examine the extent of noise levels in a skateboard park with metallic ramps. A real-time sound level meter (Quest Technologies, Model 400) was located 1 m from the ramp. Noise sources included 1–4 individuals using skateboards, rollerblades, and/or bikes on or around the ramp. The highest peak noise level (dBA), ranging from 88.5–146.7 with a mean (SD) of 100.1 (13.1) and median of 101.7, was recorded when two rollerbladers played at the same time. In 604 measurements of 10-s intervals, the maximum noise levels ranged from 46.7–107.9 dBA with a SD of 70.9 (14.1) and median 69.6. The results of this study indicate there is real potential for hearing damage from noise in skateboard parks with metallic ramps.
J. Thomas, U.S. Air Force, Brooks-City Base, TX; K. Blehm, D. Sandfort, S. Reynolds, M. Andersen, R. Ackley, Colorado State University, Fort Collins, CO.
Recent United States Air Force (USAF) studies hypothesized current measurement techniques are not adequately measuring welder noise exposures, and that welders are losing their hearing at a higher rate than expected based on attributable risk. The objective of this study was to assess noise measurement sampling rates and averaging times to determine potential differences in the amount of total energy characterized during routine exposure assessments.
Seven types of welding (shielded metal arc welding, gas metal arc welding, gas tungsten arc welding, flux core arc welding, oxy-fuel gas cutting, plasma arc cutting, and air carbon arc gouging) were evaluated. Data were collected via a two-channel system using a microphone, pre-amplifier, and front-end unit for each channel. The signals were saved to digital audiotape or a digital oscilloscope and then analyzed with a real time analyzer and the digital oscilloscope. Sampling rates up to 25 MHz were used to collect exposure data.
Increasing sampling rate did not increase the amount of energy measured and hence the dose did not increase. The results of this study point to investigating additional avenues to explain the hearing loss of the welders. Other possible explanations include: ototoxins, non-occupational exposure, other noise sources, inadequate use of hearing protection, or data anomalies in the audiograms.
N. Barone, ExxonMobil Biomedical Sciences, Clinton, NJ.
Real world field tests of hearing protector (HP) attenuation have shown discrepancies with the mandatory experimenter-fit laboratory noise reduction rating testing performed by manufacturers for the purposes of labeling. Based on these findings, OSHA inspectors normally derate HP attenuation by 50% to determine their adequacy of protection. This study describes field testing of HP attenuation conducted to determine the actual adequacy of protection provided at two petrochemical facilities. Workers wearing HP were approached in the field and asked to participate in the study. The hearing threshold levels with HP and without HP was the real-ear-attenuation-at-threshold (REAT). REAT measurements were collected using circumaural headphones and a Compaq Ipaq Pocket PC running Pocket Hearo software. The results of this field testing suggest that this method offers an opportunity to match hearing protectors with individual variability (e.g., size, shape of ear canal) so that the best protector can be selected, fitted, and verified for each worker participating in a hearing conservation program.
Posted May 30, 2004