Occupational Soundscapes – Part 8: Effects of Exposure

     Some effects of exposure to sound with certain characteristics have been mentioned in previous installments of this series.  Given the importance of understanding the potential consequences of failing to manage soundscapes effectively, compiling these in one place is advantageous.  The effects of exposure to challenging soundscapes provide the “why” that motivates efforts to manage them.
     In this installment, both auditory and extra-auditory effects are explored.  Auditory effects may be more intuitive, as direct impacts to hearing are highly relatable.  Extra-auditory effects, in contrast, often lack an obvious link between sound and the effects experienced by those exposed.  Recognizing this link is key to effective facility and workforce management.

     The term “auditory effect” is used herein to refer to physiological changes that directly impact an individual’s ability to perceive (“hear”), identify, differentiate, locate, or interpret various sounds.  These changes take place within the auditory system, anywhere from the outer ear to the brain.
     Extra-auditory effects are those that occur outside the auditory system; they can be physiological or psychological in nature.  The term “nonauditory effect” is also commonly used; the two are used interchangeably in this discussion.

Auditory Effects
     Several references to auditory effects have been made as the primary focus of this series.  However, this should not lead readers to conclude that it is only these that are important.  It is their relevance to previous discussions, prevalence in occupational settings, and relatability that encourage frequent mention.
     In this section, brief descriptions of the most common auditory effects are provided.  Those previously mentioned are included here to provide a single resource for this type of information.
Noise-Induced Hearing Loss (NIHL):  results from damage to the inner ear, specifically, “over-bending” the hair cells in the cochlea.  Trauma suffered by the tympanic membrane (i.e. “ruptured eardrum”) can also cause hearing loss.  NIHL refers to both temporary and permanent threshold shifts (TTS, PTS).  Refer to Part 2 for a presentation of the parts of the ear and Part 5 for a discussion of threshold shifts.  Experiencing a TTS is sometimes called “auditory fatigue,” but the term’s ambiguity limits its acceptance and value as a descriptor.  The greatest NIHL typically occurs in the first 10 – 15 years of exposure.  After this, its impact declines as other forms of hearing loss become more influential to overall auditory health.
Tinnitus:  ringing in the ear(s); the perception, usually, of a high-pitched sound that is not externally generated (i.e. not “received” by the “listener”).  Typically, tinnitus accompanies hearing loss and is often the warning sign that prompts individuals out of their complacency about sound exposures.
Hyperacusis:  extreme sensitivity to sound, often occurring in the aftermath of a traumatic “noise event.”  Hyperacusis can be difficult to diagnose and manage, as those that suffer from it often generate “normal” audiograms.  That is, the increased sensitivity to sound exposure is not detected by standard audiometric testing.
Recruitment:  narrowing of the audible range of SPLs that may accompany hearing loss.  A person with recruitment has a raised hearing threshold and increased sensitivity to higher-intensity sound.
Diplacusis:  asymmetrical hearing loss, typically caused by differential exposure.  For example, a machine operator whose task posture causes his/her left ear to “face” the noise source is susceptible to greater NIHL in the left ear than in the right.  As this condition worsens, localization of a sound source (see Part 6) becomes increasingly difficult.
Acoustic trauma:  sudden damage to the auditory system caused by an explosion or similarly-extreme release of energy in excess of 130 dBC.  Acoustic trauma is associated with transient sounds, whereas NIHL is associated with continuous and intermittent sounds (see Part 6 for descriptions of sound types).
Speech discrimination:  the ability to differentiate speech sounds is effected by total hearing loss and the nature of one’s soundscape.  Consonant sounds (e.g. “b” vs. “d;” see Part 5) are effected most and background noise is particularly problematic.
     There are two types of auditory system damage to consider in relation to auditory effects:  mechanical injury and metabolic injury.  Mechanical injury correlates with peak pressure levels (SPLs); the most severe conditions exist with transient sounds.  Metabolic injury correlates with the duration of exposures and corresponding recovery periods.  Both types must be considered to effectively manage a soundscape.
     The preceding presentation is merely an overview of the most-commonly cited auditory effects of sound exposure.  Sound level measurements, exposure indices (e.g. 8-hr TWA), and frequency weighting (see Part 6) are used to quantify the potential for NIHL.  Individual sensitivities will always differ, however; this variability must not be ignored.

Extra-Auditory (Nonauditory) Effects
     Previous references to extra-auditory effects have been made without clarifying this distinction; for example, annoyance was discussed in Part 7.  Annoyance is a subjective experience and a psychological response to sound that may occur at relatively low intensity levels.  This exemplifies an important characteristic of nonauditory effects of sound:  they are not correlated with auditory system damage and often occur at energy levels much lower than required to cause a threshold shift.
     Several physiological and psychological effects of sound exposure are introduced in this section.  Thorough analysis of these effects requires medical and/or psychological expertise far beyond the scope of this series.  Fortunately, for most practitioners, awareness and superficial knowledge of these effects suffice; detailed research is left to those with the interest and capacity to conduct it independently.
     Sound exposure has been identified as a significant stressor.  Readers are likely aware of health concerns related to excessive stress, such as hypertension and other cardiovascular conditions.  It has also been linked to issues in the digestive system, such as ulcers, and sleep disturbance, which can lead to a further decline in health.
     A natural response to sound exposure – namely, shouting to communicate – can also cause an indirect health effect.  Throat pain, lesions, and hoarseness can result from exerting the vocal energy required to be heard in a noisy environment.
     Behavioral changes have also been linked to sound exposure.  Absenteeism and disciplinary action have been correlated to levels of sound exposure in workplaces.  Depression and social isolation are experienced within the work environment and outside it, particularly when substantial permanent threshold shifts (PTS) have occurred.  Cognitive decline and dementia can also be accelerated.
     Productivity, quality, and safety performance also suffer in noisy environments.  Increases in falls and other mishaps, including traffic accidents, have been correlated with sound exposure.  The combined effect of distraction by sound and difficulty hearing warning signals or other auditory feedback contribute to the occurrence of various types of accidents and errors.  Vigilance tasks, where changes in conditions are to be closely monitored, exhibit significant declines in performance in this type of environment.  Learning, typically used to improve performance on various metrics, can also be impaired by the soundscape.
     Although the nonauditory effects have not been explored in great detail, the presentation should, nonetheless, make clear that a multitude of negative impacts can result from an uncontrolled or poorly-managed soundscape.  The connections between sound exposure and nonauditory effects are not as intuitive as those to auditory effects and could, therefore, easily be overlooked.  Mere awareness of the potential to cause or contribute to these ailments could be the key to successful management.

Interactions and Synergies
     Sound exposures and NIHL do not occur independently of other conditions.  Other characteristics of the surrounding environment and of the exposed individual can amplify, accelerate, or otherwise modify the effects of sound exposure.  Individual sensitivity to any single factor, or combination of factors, is highly variable and extremely difficult to quantify or predict.  For this reason, awareness, rather than deep knowledge, remains the goal of this presentation.
     Environmental factors to be considered in conjunction with the soundscape include:
·     Ototoxic substances (solvents, heavy metals, etc.) affect the cochlea.
·     Neurotoxic substances affect the central nervous system.
·     Vibration.
·     Thermal conditions (see Thermal Work Environments series).
·     Verbal and nonverbal communication requirements.
     Individual factors to be considered in conjunction with the soundscape and environmental factors include:
·     All types of hearing loss (NIHL, presbycusis, sociocusis, etc.).
·     Overall health and fitness (cardiovascular health, for example, seems to exhibit a circular influence – that is, a decline in CV health increases sensitivity to sound exposures and sound exposures increase CV risk).
·     Illness, infection, or chronic disease (e.g. diabetes).
·     Diet and exercise.
·     Smoking or other tobacco use.
·     Alcohol consumption.
·     Use of OTC or other medications, drugs.
Specific concerns about any of these factors should be referred to medical professionals.  Professional medical advice may be needed to provide appropriate protections for individuals working in challenging soundscapes.

      Thus far, the focus has been on implications of a “noisy” environment.  The effects of a “quiet” environment should also be considered.  Very low levels of continuous sound could exacerbate startle reactions (see Part 7), as changes in sound are more noticeable.
      A very quiet environment can be relaxing, causing drowsiness, increasing error rates, and reducing productivity.  To offset this, some introduce random noise or music to the environment.  Either of these can be problematic and, in general, are not recommended.  If either is used, careful evaluation of the task, environment, communication requirements, and effect on others must be conducted to ensure that problems are not created unnecessarily.  Expending the analysis effort on other aspects of job design will typically yield more favorable results.  For example, adaptive workstations, such as those that accommodate both standing and seated postures, assignment rotations, or task modification to reduce monotony may yield better results than the introduction of an artificial soundscape.

Summary and Conclusion
     There are many potential effects of sound exposure.  Some are physiological and quantifiable, while others are psychological and sometimes perplexing.  These effects are often interconnected, exhibiting complex relationships that inhibit thorough comprehension.  This in no way diminishes their applicability to workforce and facility management, as superficial knowledge is often sufficient to implement appropriate protections.
     Examples of the effects of sound exposure at various intensity levels are summarized in the concluding exhibits.  In Exhibit 1, effects on conversation and perception are presented, while Exhibit 2 presents additional physiological and psychological responses to sounds throughout the audible range.  The levels at which the onset of certain health effects typically occur are provided in Exhibit 3.  Finally, conditions affecting the relationship between signal presence and human perception of sound are explored in Exhibit 4.

     For additional guidance or assistance with Safety, Health, and Environmental (SHE) issues, or other Operations challenges, feel free to leave a comment, contact JayWink Solutions, or schedule an appointment.

     For a directory of “Occupational Soundscapes” volumes on “The Third Degree,” see Part 1: An Introduction to Noise-Induced Hearing Loss (26Jul2023).

References
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[Link] “Hearing Protection.”  Laborers-AGC Education and Training Fund; July 2000.
[Link] Noise Control in Industry – A Practical Guide.  Nicholas P. Cheremisinoff.  Noyes Publications; 1996.
[Link] The Effects of Noise on Man.  Karl D. Kryter.  Academic Press; 1970.
[Link] “Protection and Enhancement of Hearing in Noise.”  John G. Casali and Samir N. Y. Gerges.  Reviews of Human Factors and Ergonomics; April 2006.
[Link] Kodak's Ergonomic Design for People at Work.  The Eastman Kodak Company (ed).  John Wiley & Sons, Inc.; 2004.
[Link] Fundamentals of Industrial Ergonomics, 2ed.  B. Mustafa Pulat.  Waveland Press; 1997.
[Link] “Risk Observatory Thematic Report - Noise in Figures.”  Elke Schneider, Pascal Paoli, and Emmanuelle Brun.  Luxembourg Office for Official Publications of the European Communities; December 2005.
[Link] “Noise exposure as related to productivity, disciplinary actions, absenteeism, and accidents among textile workers.”  Madbuli H. Noweir.  Journal of Safety Research; Winter 1984.
[Link] “Extra-Auditory Effects of Noise as a Health Hazard.”  Joseph R. Anticaglia and Alexander Cohen.  American Industrial Hygiene Association Journal; May-June 1970.
[Link] “Noise Exposures:  Effects on Hearing and Prevention of Noise Induced Hearing Loss.”  Sally L. Lusk.  American Association of Occupational Health Nurses Journal; August 1997.
[Link] “Hazardous Exposure to Intermittent and Steady-State Noise.”  K.D. Kryter, W. Dixon Ward, James D. Miller, and Donald H. Elderedge.  Journal of the Acoustical Society of America; March 1966.
[Link] “Occupational Noise-Induced Hearing Loss.”  Raul Mirza, Bruce Kirchner, Robert A. Dobie, and James Crawford.  Journal of Occupational and Environmental Medicine; September 2018.
 
Jody W. Phelps, MSc, PMP®, MBA
Principal Consultant
JayWink Solutions, LLC
[email protected]