William W. Clark

Exchange rates for intermittent and fluctuating occupational noise: a systematic review of studies of human permanent threshold shift.

Objective: The aim of this study was to review the literature regarding human noise-induced permanent threshold shift and to determine whether the observed data agreed with the predictions of two different exchange rates (ERs). Design: An initial list of possibly relevant studies included those cited by authors who endorsed the 3 dB ER, as well as studies in personal files, studies retrieved by a MEDLINE search, and the reference lists of all of these. Criteria for relevance were designed to ensure that exposures were sufficiently intermittent or fluctuating that effective exposure levels based on the 3 dB (LAeq8h) and 5 dB (time-weighted average [TWA]) ERs would differ by at least 1 dB, that at least one of these metrics could be estimated, and that audiometric data were available for groups of defined age, sex, and exposure. Relevant studies were reviewed in detail, and their audiometric data were compared with the predictions of the ISO-1999/ANSI S3.44 model. Results: Nine relevant studies were identified. For six articles, the reported hearing levels were substantially less than would have been predicted from LAeq8h. In each of these cases, TWA would have predicted lower hearing levels than LAeq8h and would have better fit the observed data. In three cases it was not possible to say which ER would have better fit the observed data. Conclusions: The 3 dB ER systematically overestimates the risk of noise-induced hearing loss for intermittent or fluctuating noise. The 5 dB ER appears to be more accurate, but also overestimates risk, particularly for exposures above 100 dBA.

Corrected values for Annex B of ISO 1999

A recalculation of the values contained in Annex B of the new ISO standard R1999: ‘‘Determination of occupational noise exposure and the estimation of noise‐induced hearing impairment,’’ utilizing procedures specified in the standard and in its supporting documentation was conducted. Three calculation errors, which occurred in the supporting document and were perseverated into the standard, were identified. These errors are explained and a corrected version of Annex B is presented.

Response to suter and NIOSH

492 We thank Suter and Morata et al. for their letters. The authors of Morata et al. are all employees of the National Institute for Occupational Safety and Health (NIOSH); it is our understanding that their letter, lacking the disclaimer usually attached to public comments of federal employees, represents the official position of that agency, and thus, we will refer to it as the NIOSH letter. We will address each of the comments in the Suter and NIOSH letters, followed by a brief discussion on important issues that they omitted. Although we would have preferred a brief response, the extent, nature, and scientific foundation of the arguments brought forward require a thorough rebuttal. Suter and NIOSH are longtime collaborators and proponents of the 3-dB exchange rate (ER), so their disagreement with our article is not unexpected. What was unexpected was NIOSH’s assertion that a “re-examination of the exchange rate” requires adherence to a long list of criteria, including the use of two raters of study quality, with a third to adjudicate conflicts; a formal assessment of quality across multiple domains; attempting to contact authors; presenting study findings grouped by “certainty of exposure level estimates”; an evaluation of the risk of bias; and others. We disagree and note that neither NIOSH (1998) nor Suter’s (1992) report to NIOSH considered any of these elements when they re-examined the 5-dB ER, which NIOSH (1972) had previously recommended, and decided to instead advocate for the 3-dB ER. For those who have not read our article, we reviewed all the literature we could find that could shed light on the issue of the appropriate ER, based on human noise-induced permanent threshold shift (NIPTS). We included every study that had been cited by Suter (1992) and NIOSH (1998), as well as other studies from the reference lists of those articles, and additional studies discovered by a literature search. We applied clear inclusion criteria, analyzed included studies in comparison with the predictions of an international standard (International Organization for Standardization [ISO]-1999, 1990) using fully transparent methodology that others can replicate, and submitted our work to a peer-reviewed journal. We believe that our contribution was unique in this literature. We could not replicate the findings of a frequently cited previous review (Passchier-Vermeer 1973) that despite its unclear methodology and lack of peer review has been very influential (as we note later). Although we reviewed 19 studies in detail and included nine in our summary table, it is notable that neither Suter nor NIOSH question any of our exclusions, nor do they suggest alternative interpretations for any of the included studies. Suter notes that we “excluded most of the studies used by Passchier-Vermeer from their analysis.” That is misleading: we read, analyzed, and commented on all the studies Passchier-Vermeer relied on and explained why most of them had to be excluded from our final summary table. Some studies that NIOSH now considers of questionable quality (Holmgren et al. 1971; Johansson et al. 1973; Thierry et al. 1978) were explicitly cited by NIOSH (1998) and Suter (1992) without any critique of study quality. For these three and a fourth (NIOSH 1982), NIOSH argues that we did not adhere to our own inclusion criteria because both exposure metrics (time-weighted average, and the equal-energy average or LAeq8h) could not be estimated. A careful reading of our article would have shown that the relevant criterion was not that both could be estimated but rather that one could be estimated and the other would be expected to differ by at least 1 dB. In all these cases, this criterion was met. Regarding Martin et al. (1975), we reported that their electric furnace subgroup had a timeweighted average/L Aeq8h difference of 2 dB, thus meeting our inclusion criteria. For Sataloff et al. (1969), we clearly indicated our assumption that the miners had begun their work at age 20 years. Stephenson et al. (2010) made the identical assumption in their analysis of data from a U.S. Army hearing conservation program (HCP). To summarize, we applied our inclusion criteria uniformly and made our assumptions explicit. Suter claims that 82% of Sataloff’s miners used hearing protection devices (HPDs) regularly, but the cited article does not say that. As we acknowledged, Sataloff et al. stated that the miners had had some use of HPDs, after many years of unprotected exposure. In addition, Sataloff et al. found no difference in hearing thresholds between (occasional) users and nonusers of HPDs. NIOSH states (and we agree) that searching Medline alone is not “sufficient for a systematic review,” implying that we did only that. However, a careful reading of our article would have shown that we went far beyond a Medline search. For example, we asked multiple other colleagues, including Suter and one of the NIOSH authors (Murphy), to point us to publications other than the ones we had already found. NIOSH’s comment that we ignored “gray literature” and examined only peer-reviewed literature is surprising because our analysis included two reports by their own agency (NIOSH 1976, 1982) that were not published in peer-reviewed journals and would be considered “gray literature.” NIOSH objects to our use of the binomial sign test because the six different studies might not have been statistically independent. However, these studies were reported by different and nonoverlapping author groups, in different sites and different years, with nonoverlapping subject groups. Thus, it is difficult to see how their independence can be doubted. The six studies were not, of course, randomly selected (they were the entire known population of such studies); random selection is appropriate only when the entire population is too large to conveniently study. Their third objection is of course valid: if one of the six studies had favored the 3-dB rather than the 5-dB ER, the sign test would not have been statistically significant. That Response to Suter and NIOSH

Assessment of noise exposures for pre-term infants during air transport to neonatal intensive care units using iPhone sound meter apps

A significant number of infants born prematurely or with life-threatening conditions in local hospitals require transport to a regional tertiary care center. St. Louis Children’s Hospital’s (SLCH) neonatal intensive care unit (NICU) serves southern Missouri and Illinois, and 3000 pre-term neonates are transported to the hospital annually, most by helicopter or fixed wing aircraft. This initial study evaluates the accuracy and efficacy of using an iPhone app (SoundMeterPro,Faber Acoustics) for routine collection of infants’ noise exposures inside the isolette during air transport. The app was downloaded onto iPhones (4,6S) calibrated in a sound field using a Larson-Davis type I sound level meter (831). The meter and the iPhones were placed inside an unoccupied isolette and recorded in-flight noise levels during the outbound portion of trips from the NICU to the local hospital. Sound levels were high (85–90 dBA) and higher during take-off and landings or when the isolette lid was opened, and level and OBN m...

Evaluation of a hearing conservation program at a large industrial company

The hearing conservation program (HCP) of a large industrial company was evaluated by comparing the audiometric data of two groups of workers from three geographically separate plants. Group 1 was selected from individuals employed in areas where the time‐weighted average (TWA) sound level exceeded 90 dBA and group 2 from individuals with TWAs of less than 85 dBA. Differences between mean STS values for groups and plants were the main criteria used in making judgments on the HCP effectiveness. In addition, age, sex, years of service, and nonoccupational noise exposure were evaluated. A significant difference in mean STS was found between the two groups; however, the “nonoccupationally exposed” group had more STS than expected. The male‐female distribution, previous hearing loss, and nonoccupational exposure were judged to be contributing factors in the differences that existed between plants and groups. [Work supported by Grant OH 02128 from NIOSH.]

Noise in the neonatal intensive care unit: a new approach to examining acoustic events

Introduction: Environmental noise is associated with negative developmental outcomes for infants treated in the neonatal intensive care unit (NICU). The existing noise level recommendations are outdated, with current studies showing that these standards are universally unattainable in the modern NICU environment. Study Aim: This study sought to identify the types, rate, and levels of acoustic events that occur in the NICU and their potential effects on infant physiologic state. Materials and Methods: Dosimeters were used to record the acoustic environment in open and private room settings of a large hospital NICU. Heart and respiratory rate data of three infants located near the dosimeters were obtained. Infant physiologic data measured at time points when there was a marked increase in sound levels were compared to data measured at time points when the acoustic levels were steady. Results: All recorded sound levels exceeded the recommended noise level of 45 decibels, A-weighted (dBA). The 4-h Leq of the open-pod environment was 58.1 dBA, while the private room was 54.7 dBA. The average level of acoustic events was 11–14 dB higher than the background noise. The occurrence of transient events was 600% greater in the open room when compared to the private room. While correlations between acoustic events and infant physiologic state could not be established due to the extreme variability of infant state, a few trends were visible. Increasing the number of data points to overcome the extreme physiologic variability of medically fragile neonates would not be feasible or cost-effective in this environment. Conclusion: NICU noise level recommendations need to be modified with an emphasis placed on reducing acoustic events that disrupt infant state. The goal of all future standards should be to optimize infant neurodevelopmental outcomes.

Authors' response to editorial note.

In accordance with the Uniform Requirements for Manuscripts Submitted to Biomedical Journals (2007) and the Council of Science Editors (2006), the Editors of Ear and Hearing wish to set forth their concerns regarding the sufficiency of the authors’ disclosure of potential conflicts of interest in this article. Questions regarding the sufficiency of the disclosure were initially raised in July 2006 and became widely publicized in a front-page article in the June 22, 2007 issue of the Wall Street Journal. Ear and Hearing has conducted an examination of the facts underlying the questions that have been raised, including a review of court documents in the litigation discussed further below. Based on that review, we have concluded that the disclosures made in the Acknowledgments section of the article insufficiently informed readers of potential conflicts of interest and that, in part, that disclosure could be construed as misleading. The Editors asked the authors of the article to amend the Acknowledgments section to reflect the first author’s consultancy with Federal Signal Corporation (FSC) and to reflect the support provided by FSC for the study. The authors declined this request stating that they felt the disclosure sufficiently met Ear and Hearing Instructions to Authors. We respectfully disagree and provide the following information in an effort to provide full disclosure of potential conflicts of interest relevant to this article. FSC is a manufacturer of firefighting equipment, including sirens, and is a company for which the first author has provided consulting services. In 1999, approximately 33 separate lawsuits on behalf of thousands of firefighters were commenced against FSC in Illinois, and then consolidated for pretrial discovery. The lawsuits contend that FSC’s sirens cause hearing loss. Available information (publicly available court documents including depositions and invoices) clearly shows that the first author has provided consulting services to FSC since 1999 and that during the time the data for this article were analyzed and the manuscript was prepared, the first author provided consulting services to FSC. The Acknowledgments section of this article stated “The first author has provided consulting services for manufacturers of emergency firefighting equipment.” We believe that the first author’s specific consulting relationship with FSC should have been included in the Acknowledgments section. FSC is certainly a manufacturer of firefighting equipment but because it had a direct interest in the outcome of this study, we feel that the authors should have specifically named FSC. In our opinion the authors did not provide full and transparent disclosure of potential conflict of interest when the article was submitted for publication and in the Acknowledgments section of the article. Every author who publishes an article in Ear and Hearing is required to sign a “Copyright Transfer” form. In its “Financial Disclosures” section, the form states that “All funding sources supporting the Work and all institutional or corporate affiliations of the authors are acknowledged in a footnote in the Work.” The authors of the article in question signed the form. In the Acknowledgments section of the article the authors stated “No external funding was received for this study.” No footnote was provided. Publicly available court documents show that Thomas Jayne, a lawyer for FSC in the litigation, helped gather the data for this publication. Invoices show that from 2000 to at least 2004, Mr. Jayne and the first author discussed the hearing study. The first author has stated in a deposition that he welcomed the company’s “assistance” because he did not have “the time, or the energy, or the resources” to obtain the data from individual fire departments. Invoices, along with statements by the first author in a deposition and by Mr. Jayne in a sworn affidavit in the case, indicate that FSC asked Mr. Jayne to contact fire departments to obtain the data that the first author used in his study, and that FSC paid Mr. Jayne for this work. We believe the money paid by FSC to Mr. Jayne for these services, which supported the research underlying the preparation of the article, constitutes a source of “external funding” that should have been disclosed, even if the money was not paid to the authors, since it represents funds that “supported” the “work.” We are sympathetic to the first author’s expressed desire for help in obtaining the data necessary for the study, and he may well be right when he stated in a deposition that he “really couldn’t see any other way to do it.” In the same deposition, the first author said he did not know how the data were selected. He also indicated he did not know what other sources of data FSC considered before providing him the data to be used in the study. To the extent the data were obtained by a party with a direct interest in the outcome of the study, we believe our Editorial Board, our reviewers, and our readers needed to know this. This information was not disclosed in any form when the article was submitted for publication. Based on our own extensive review we have concluded that the disclosures provided by the authors were incomplete and misleading. More specifically, we believe the authors should have disclosed the support provided by FSC, its role in obtaining the data, and the specific on-going consultancy relationship of the first author with FSC. It may be useful here to remind our readership and potential authors that the disclosures currently required by Ear and Hearing are contained in at least two documents. These are the “Instructions for Authors” and the *Note: Copies of unreferenced documents cited or mentioned in this Editorial Note can be obtained by contacting the Editorial Office of Ear and Hearing at eheditor@cisat.jmu.edu.

Real‐time switching of piezoelectric shunts for structural vibration control

The use of piezoelectric actuators to passively add damping to vibrating structures has been investigated for over a decade. Simple resonant shunt circuits consisting of resistors and inductors are connected to the piezoelectric actuators to add damping to one of the structural modes [Hagood and Crawley, J. Guid. Control Dyn. 14]. Modifications to the method have been proposed to enable a multi‐modal damping technique, but at the cost of performance to any one mode [e.g., Wu, Proc. of 1998 SPIE Smart Structures and Materials Conference, Vol. 3327, pp. 159–168]. The objective of this talk is to discuss recent research into methods that help eliminate the disadvantages of passive resonant shunt damping. The methods to be discussed involve real‐time switching of piezoelectric shunt circuits, and are based on the foundations laid by Larson [Ph.D. Dissertation, Georgia Institute of Technology, 1996], Clark [J. Intell. Mater. Syst. Struct. 11, 263–271], and Richard et al. [Proc. of 1999 SPIE Smart Structures an...

Designing and building for quiet in a school for deaf children

Central Institute for the Deaf (CID) recently completed construction of a new 42 000‐sq. ft. school for deaf children. High priority was placed upon designing and building a facility that would provide ideal acoustic environments that fostered learning and auditory/oral communication for students wearing powerful hearing aids or cochlear implants and teachers. A team composed of scientists, architects, and acoustical engineers was assigned the task of designing and building a school that would provide classroom environmental levels at or below the NC 20 contour, interclassroom attenuation exceeding 50 dB, reverberation times on the order of 0.4 s, and sound reinforcement for teachers’ voices when facing the blackboard. In group spaces and in the hallways, higher noise levels and longer reverberation times were sought to provide students with experiences more like those faced in the real world. Challenges included a site bounded by a busy interstate highway and a medical center heliport. The team developed and implemented numerous unique acoustic treatments for the facility which are reviewed in the presentation. Although designed as a school for the deaf, the approaches are useful for designing any educational classroom environment. The school opened on 10 January 2000 and met all acoustic criteria.

Risk assessment for occupational noise induced hearing loss: W. Dixon Ward and the ‘‘Anti‐Chicken Little Movement.’’

One of the hallmarks of W. Dixon Ward’s illustrious career was his proclivity to criticize effectively the efforts of his colleagues. Depending upon the topic and the victim, this ability led him to be characterized as an outstanding editor, a thoughtful reviewer, an overzealous critic, or an impediment to consensus. Despite the variety of responses, Dix’s critiques shared one characteristic: They were almost always correct. One of his favorite targets was the international standard, ‘‘Acoustics—Determination of occupational noise exposure and estimation of noise‐induced hearing impairment’’ (ISO 1999, 1990). Throughout the two decades of its development Dix took to task the framers of the standard, challenging the assumptions which underly it. Dix was particularly vexed by ISO’s use of the 3‐dB exchange rate, the presumption of 0% risk of noise induced hearing loss for those nonoccupationally exposed, and the estimation that normal 18‐year‐olds have perfect hearing. In this tribute, Dix’s criticisms of the ISO standard will be articulated and supported with recent data, and his role as the leader of the ‘‘Anti‐Chicken Little Movement’’ justified.