Kurtosis: A New Tool for Noise Analysis

Details

• Personal Author:
  Murphy, William J. ; Qiu W ; Suter A
• Description:
  Hearing loss due to high-level noise exposure remains a significant occupational health hazard that continues to increase in prevalence in industrial and military work environments despite government-mandated hearing conservation programs. The underlying assumption in current noise standards is that hearing loss over an 8-hour A-weighted equivalent continuous exposure level (often abbreviated as LAeq,8h) can be predicted by the equal energy hypothesis. This method assumes equivalent effects on hearing for a 3 dB increase or decrease in exposure intensity with a halving or doubling of exposure duration, respectively. In other words, equal amounts of hearing loss are expected regardless of how the noise exposure levels have occurred over time. The equal energy hypothesis is the basis of most noise standards and guidelines in the United States and internationally. Although this approach is generally considered appropriate for steady-state noise, it is not adequate for complex noise (Hamernik and Qiu, 2001). Some Background: Consensus has been lacking on the use of simple energy averaging to predict the effects of noise on hearing. In the United States, some government agencies use a modification consisting of a 5 dB trading relationship, whereas others use the internationally accepted 3 dB rule. Use of the 3 dB rule has been recommended by the National Institute of Occupational Safety and Health (NIOSH) since 1998, which recommendation has been validated based on additional, more recent research (Suter, 2017). Another issue with using a simple energy metric is the inability of sound energy averaging to account for the increased hazard of noise with impulsive components. Although intermittences in noise exposures may have been considered helpful to hearing in the past, this no longer seems to be the case with complex noise exposures, which are found frequently in manufacturing industries. Because the additional hazards from impulsive noise were already recognized, the earliest version of the International Standards Organization (ISO) 1999 standard (1971) suggested a 10 dB adjustment to the average exposure level when impulsive noise is superimposed on a background of continuous noise. At a 1981 meeting of noise experts in Southampton, UK, some participants proposed keeping the 10 dB adjustment, with others wanting to change it to 5 dB, and a third group proposing just using simple energy averaging (Personal Observation, Suter, 1981). The resulting report concluded that hearing conservation programs should be initiated at a 5 dB lower level as a precautionary measure whenever there are impulsive noise conditions (von Gierke et al., 1981). Consequently, the 1990 version of the standard contained a note suggesting a 5 dB correction but even that disappeared without explanation in later iterations of the ISO 1999 standard (2013). Since then, more evidence has emerged regarding the hazard to hearing from complex noise environments relative to continuous noise environments. Complex or Non-Gaussian Noise: A steady-state, continuous noise exposure typically has a normal or Gaussian amplitude distribution (see background in Figure 1). However, the temporal pattern of noise exposures often varies significantly in work environments. A complex noise environment may be described as Gaussian background noise punctuated by a series of high-level transient noises resulting in a non-Gaussian distribution (as shown in Figure 1). These transients can be brief, high-level noise bursts, impulses, or impacts with varying interpeak intervals, peak levels, and peak durations. Industrial workers are often exposed to complex noise environments. Examples include jobs involving maintenance work, metalworking, and power tools, such as impact wrenches and nail guns. Over the past several decades, a number of studies using animal models have shown that exposure to complex noise produces more hearing damage than an equivalent energy exposure to continuous Gaussian noise, in terms of both behavioral hearing loss and sensory cell loss (e.g., Lei et al., 1994). These results, along with similar findings from human data in industrial settings, have demonstrated that although acoustic energy and exposure duration are necessary metrics, they are not sufficient to evaluate the hearing loss from complex non-Gaussian noise exposure. Because many noise environments can be characterized by the same equivalent energy and spectra, a metric that describes the temporal structure of an exposure would be a useful adjunct to the equivalent sound pressure level metric. The kurtosis of a sample distribution is such a metric. [Description provided by NIOSH]
• Subjects:
  Hearing Loss Hearing Loss, Noise-Induced Noise Noise, Occupational Occupational Exposure Occupational Health Safety
• Keywords:
  Hearing Loss Impulse Noise Noise Analysis Noise Exposure Noise Induced Hearing Loss Noise Levels Occupational Exposure
• ISSN:
  1557-0215
• Document Type:
  Text
• Genre:
  Journal Article
• Place as Subject:
  New York ; Ohio ; Oregon ; OSHA Region 10 ; OSHA Region 2 ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  DFSE - Division of Field Studies and Engineering
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  39-47
• Volume:
  16
• Issue:
  4
• NIOSHTIC Number:
  nn:20062066
• Citation:
  Acoustics Today 2020 Winter; 16(4):39-47
• Contact Point Address:
  Wei Qiu, Auditory Research Laboratorym State University of New York at Plattsburgh, 101 Broad Street, Plattsburgh, New York, NY 12901, USA
• Email:
  qiuw@plattsburgh.edu
• Federal Fiscal Year:
  2021
• Peer Reviewed:
  False
• Source Full Name:
  Acoustics Today
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:e6a67a851c22f531d8019ec2d83b027c6919579612a979e8c3207429f2803e8c957ee0779cbe327c819ea9008184082e163268b002b4ccbe1e4b7d1adfef924d
• Download URL:
  https://stacks.cdc.gov/view/cdc/225384/cdc_225384_DS1.pdf
• File Type:
  [PDF - 330.74 KB ]